The UK High-End Computing Consortium for Biomolecular Simulation
Lead Research Organisation:
University of Oxford
Department Name: Biochemistry
Abstract
There is tremendous future scope for biomolecular simulation to provide unprecedented insights into biomolecular systems. The level of detail afforded by these methods, along with their ability to rationalise experimental data and their predictive power are already enabling them to make significant contributions in a wide variety of areas that are crucial for healthcare, quality of life and the environment. The UK biomolecular simulation community has a strong international reputation, with world-leading efforts in in drug design and development, biocatalysis, bionano-technology, chemical biology and medicine. HECBioSim has already delivered outstanding research with impact in bionanotechology, drug design and AMR. But we have only just scratched the surface and there is currently huge room for expansion. Having access to the largest, most modern computing facilities is essential for this. Renewal of the Consortium will enable us to continue allocating time ARCHER for cutting-edge biomolecular simulations.
We will place a special emphasis on reaching out to experimentalists and scientists working in industry in order to foster interactions between computational and experimental scientists, and academia and industry to encourage integrated multidisciplinary studies of key problems.
Biomolecular simulation and modelling is an integral part of drug design and development. The pharmaceutical industry needs well-trained scientists in this area, as well as the development of new methods (e.g. for prediction of drug binding affinities, ligand selectivity and metabolism). Members of the consortium have a strong track record of collaboration with industry to deliver trained scientists and new methodologies. For example, PhD students trained by consortium members have recently taken up positions in UCB, Unilever, Oxford Nanoimaging and even Sky Broadcasting as software developer. Many of these academic-industry collaborations have been strengthened by work done through HECBioSim allocations.
The Consortium will continue to welcome new members from across the whole community. We will continue to develop computational tools and training for both experts and non-experts using biomolecular simulation on HEC resources. We propose to develop new tools that will enable inter-conversion between biomolecular systems at different levels of resolution thereby allowing users to tackle more ambitious 'grand challenges' than are currently feasible.
In summary HECBioSim will foster collaborations between computational and experimental scientists between scientists working in industry and academia in all disciplines within biomolecular simulation to maintain the UK as a world-leader in this field.
We will place a special emphasis on reaching out to experimentalists and scientists working in industry in order to foster interactions between computational and experimental scientists, and academia and industry to encourage integrated multidisciplinary studies of key problems.
Biomolecular simulation and modelling is an integral part of drug design and development. The pharmaceutical industry needs well-trained scientists in this area, as well as the development of new methods (e.g. for prediction of drug binding affinities, ligand selectivity and metabolism). Members of the consortium have a strong track record of collaboration with industry to deliver trained scientists and new methodologies. For example, PhD students trained by consortium members have recently taken up positions in UCB, Unilever, Oxford Nanoimaging and even Sky Broadcasting as software developer. Many of these academic-industry collaborations have been strengthened by work done through HECBioSim allocations.
The Consortium will continue to welcome new members from across the whole community. We will continue to develop computational tools and training for both experts and non-experts using biomolecular simulation on HEC resources. We propose to develop new tools that will enable inter-conversion between biomolecular systems at different levels of resolution thereby allowing users to tackle more ambitious 'grand challenges' than are currently feasible.
In summary HECBioSim will foster collaborations between computational and experimental scientists between scientists working in industry and academia in all disciplines within biomolecular simulation to maintain the UK as a world-leader in this field.
Planned Impact
Who might benefit from this research?
The direct beneficiaries of this research include academic and industrial scientists, including experimentalists working across a very wide range of disciplines including X-ray crystallography, NMR, electron microscopy, single molecule biophysics methods, mass spectrometry, hydrodynamics, enzyme kinetics, drug design medicinal chemistry, chemical and synthetic biology and design on biosensors. The two most obvious industrial beneficiaries are the pharmaceutical sector, which is of huge economic importance to the UK; and the biotechnology sector in which the UK is a world leader in e.g. nanopore DNA sequencing. Other industries (such as biocatalysis analysis and processing, IT hardware and software development) will also benefit from the UK High-End Computing Consortium for Biomolecular Simulation (HECBioSim) through our already established excellent links and new ones that will be fostered through the renewal of the Consortium. In the longer term, All of the work will impact on the general public through improvements in health and quality of life.
How will they benefit?
The focus of HECBioSim is to support access and use of high-end computing in the UK, both in terms of increased uptake and awareness by experimental colleagues, but also from experimental groups in both academia and industry. We also engage other interested parties and the general public.
Focused Training workshops and webinars:
We will undertake 3-4 workshops that will have a definitive focus on engaging more strongly with: i) industrial users, ii) experimental groups (mainly in academia but could also be from industry) and iii) emerging technology areas (including cryo-EM, and machine learning). We propose to deliver an annual webinar, showcasing HECBioSim outputs. Webinars offer the distinct advantage that they are virtual and can be accessed by anyone worldwide for zero cost to participants.
Making it easier for industry and academics to adopt.
In industry the use of electronic notebooks is widespread and the capture of metadata for experiments and simulations is absolutely critical. In order to make the use and adoption of HPC simulation data more viable, we plan to develop quality control metrics for simulation data and integrate capturing this information seamlessly into electronic notebooks. These electronic notebooks will be of benefit for industrial and academic scientists and will facilitate multidisciplinary projects.
Engagement to a more general audience.
We propose to put in a proposal for major science festivals including the Summer Science Exhibition at the Royal Society or the Cheltenham Science Festival to reach out to the wider community. Furthermore we will also generate a short promotional video that highlights the role of the HECBioSim and the impact that the work it supports has on UK science and the benefit to the general public. This will be hosted on our main website but we will disseminate via as many other routes as well (for example, youtube). We will highlight key results from the consortium via the website but also via social media, mainly via Twitter.
Maximizing code development potential
We plan to continue to develop our existing codes, which are already freely available Longbow and FESetup in addition to a new project which will focus around providing an easy-to-use interface for running coarse-grain and atomistic simulations and quantum mechanics calculations and interconverting between them, on HEC resources. This will be provided free of charge to the academic community along with training material.
Commitment to Diversity
We are committed to a philosophy of diversity within our science. To ensure this, we have made contact with Women in high Performance Computing ), in order to work closely with them to ensure a fair gender representation across all of our activities.
The direct beneficiaries of this research include academic and industrial scientists, including experimentalists working across a very wide range of disciplines including X-ray crystallography, NMR, electron microscopy, single molecule biophysics methods, mass spectrometry, hydrodynamics, enzyme kinetics, drug design medicinal chemistry, chemical and synthetic biology and design on biosensors. The two most obvious industrial beneficiaries are the pharmaceutical sector, which is of huge economic importance to the UK; and the biotechnology sector in which the UK is a world leader in e.g. nanopore DNA sequencing. Other industries (such as biocatalysis analysis and processing, IT hardware and software development) will also benefit from the UK High-End Computing Consortium for Biomolecular Simulation (HECBioSim) through our already established excellent links and new ones that will be fostered through the renewal of the Consortium. In the longer term, All of the work will impact on the general public through improvements in health and quality of life.
How will they benefit?
The focus of HECBioSim is to support access and use of high-end computing in the UK, both in terms of increased uptake and awareness by experimental colleagues, but also from experimental groups in both academia and industry. We also engage other interested parties and the general public.
Focused Training workshops and webinars:
We will undertake 3-4 workshops that will have a definitive focus on engaging more strongly with: i) industrial users, ii) experimental groups (mainly in academia but could also be from industry) and iii) emerging technology areas (including cryo-EM, and machine learning). We propose to deliver an annual webinar, showcasing HECBioSim outputs. Webinars offer the distinct advantage that they are virtual and can be accessed by anyone worldwide for zero cost to participants.
Making it easier for industry and academics to adopt.
In industry the use of electronic notebooks is widespread and the capture of metadata for experiments and simulations is absolutely critical. In order to make the use and adoption of HPC simulation data more viable, we plan to develop quality control metrics for simulation data and integrate capturing this information seamlessly into electronic notebooks. These electronic notebooks will be of benefit for industrial and academic scientists and will facilitate multidisciplinary projects.
Engagement to a more general audience.
We propose to put in a proposal for major science festivals including the Summer Science Exhibition at the Royal Society or the Cheltenham Science Festival to reach out to the wider community. Furthermore we will also generate a short promotional video that highlights the role of the HECBioSim and the impact that the work it supports has on UK science and the benefit to the general public. This will be hosted on our main website but we will disseminate via as many other routes as well (for example, youtube). We will highlight key results from the consortium via the website but also via social media, mainly via Twitter.
Maximizing code development potential
We plan to continue to develop our existing codes, which are already freely available Longbow and FESetup in addition to a new project which will focus around providing an easy-to-use interface for running coarse-grain and atomistic simulations and quantum mechanics calculations and interconverting between them, on HEC resources. This will be provided free of charge to the academic community along with training material.
Commitment to Diversity
We are committed to a philosophy of diversity within our science. To ensure this, we have made contact with Women in high Performance Computing ), in order to work closely with them to ensure a fair gender representation across all of our activities.
Organisations
Publications
Amos STA
(2021)
Membrane Interactions of a-Synuclein Revealed by Multiscale Molecular Dynamics Simulations, Markov State Models, and NMR.
in The journal of physical chemistry. B
Ansell TB
(2021)
Relative Affinities of Protein-Cholesterol Interactions from Equilibrium Molecular Dynamics Simulations.
in Journal of chemical theory and computation
Antonovic AK
(2023)
Comparative study of binding pocket structure and dynamics in cardiac and skeletal myosin.
in Biophysical journal
Ashraf S
(2021)
Exploration of the structural requirements of Aurora Kinase B inhibitors by a combined QSAR, modelling and molecular simulation approach.
in Scientific reports
Balint-Kurti G
(1991)
The calculation of product quantum state distributions and partial cross-sections in time-dependent molecular collision and photodissociation theory
in Computer Physics Communications
Bennie S
(2016)
A Projector-Embedding Approach for Multiscale Coupled-Cluster Calculations Applied to Citrate Synthase
in Journal of Chemical Theory and Computation
Bunzel H
(2022)
Photovoltaic enzymes by design and evolution
Bunzel H
(2021)
Evolution of dynamical networks enhances catalysis in a designer enzyme
in Nature Chemistry
Bunzel HA
(2021)
Designing better enzymes: Insights from directed evolution.
in Current opinion in structural biology
| Description | A team from of scientists from across the world have found that a hydrogenase enzyme from a common soil bacterium is able to generate an electrical current using the atmosphere as an energy source. The study included structural biology (cryoEM), mutagenesis (experimental and computational), molecular dynamics simulations and a range of microbiology techniques. The findings open up the possibility of clean and safe energy generation from air. This work has made the popular news in Australia and the UK (including Daily Mail, Independent) Simulations of the SARS-Cov2 Spike protein using benzene mapping have revealed a novel, potential druggable pocket. Simulations of the mycobacterial plasma membrane have predicted the arrangement of lipids in the membrane - previously almost completely unexplored . |
| Exploitation Route | 1- Clean energy generation 2- Potential therapeutics against SARS-Cov2 |
| Sectors | Chemicals Digital/Communication/Information Technologies (including Software) Healthcare Manufacturing including Industrial Biotechology Pharmaceuticals and Medical Biotechnology |
| URL | https://www.hecbiosim.ac.uk/ |
| Description | Sansom (Oxford): UCB have supported a number of BBSRC iCASE studentships in the general area of membrane protein/lipid interactions, all of which have benefitted from ARCHER access. These molecular interactions play a key role in modulating the function of membrane proteins implicated in many diseases, and therefore are of importance to pharmaceutical companies such as UCB. Sansom (Oxford) and Stansfeld (Warwick): IBM support an EPSRC iCASE studentship to examine peptide /lipid interactions which also benefits from ARCHER access. This has resulted in a preprint within the funding period: (which is now published, but just after this reporting period): Biggin (Oxford) We have been extending our work on absolute binding free energies to fragment design with Boehringer Ingelheim, via a fully-funded PDRA. New code has been developed as part of this collaboration, which will be made available soon. An iCASE studentship on membrane proteins is funded by Vertex. Both projects have been built on the successful usage of ARCHER via HECBioSim. Khalid (Oxford) A studentship funded through Oxford Nanopore Technologies Ltd (ONT) relies upon access to ARCHER via HECBioSim. We are simulating the protein used in the commercial devices made by the world leading nanopore DNA sequencing company. Much of the work cannot be published due to the highly sensitive nature of the details of the engineered protein being used. However a paper on a model system has been published as well as second on the wildtype protein complex CsgG/F with the Steve Matthews and Sarah Rouse groups at Imperial College (also HECBioSim members). Discussion is ongoing with ONT for future funding. Essex (Southampton) A PhD student has been exploring the conformations of the recognition loops of antibodies to understand how they achieve such high affinity and specificity. This work is supported by UCB Another PhD student is using ARCHER2 to simulate the protein complex apoferritin in very large volumes of water, to provide model data to explore the accuracy of cryo-EM image reconstruction algorithms. This is in collaboration with the Rosalind Franklin Institute. Publications from both of these projects are in the pipeline. Michel (Edinburgh) PhD student funded by Cresset. The Michel group and Cresset are using HPC provided through HECBioSim to develop machine-learned (ML) models of the difficulty of protein ligand binding Free Energy Perturbation (FEP) calculations. The ML models are used to power new automated FEP workflows for high-throughput studies that support industrial drug design R&D efforts. Fraternali (King's College London). A novel antimicrobial nanocapsule construct able of self assembly. The results are presented in the manuscript under revision "Nanocapsule Designs for Antimicrobial Resistance". The project carried on previous work performed in collaboration with the National Physics Laboratory (UK), and prompted a collaboration with Unilever (UK) for the investigation of analogous antimicrobial peptides interactions and self-assembly. Unilever provided funding for a PDRA, access to ARCHER via HECBioSim played a role in securing the funding and setting up the collaboration. Such molecules are of interest for the company, aiming at incorporating antimicrobial elements into its products. Two manuscripts are resulting from this collaboration, one is in second revision and the other is in preparation. Stansfeld (Warwick) PhD studentship funded by OMASS has yielded the paper: Ligand induced conformational dynamics of the LPS translocon LptDE. Francesco Fiorentino, Joshua B. Sauer, Xing Yu Qiu, Robin A. Corey, C. Keith Cassidy, Benjamin Mynors-Wallis, Shahid Mehmood, Jani Reddy Bolla, Phillip J. Stansfeld, Carol V. Robinson (2020) Nature Chemical Biology. The simulations reported here were performed on ARCHER with access provided by HECBioSim Gervasio (UCL) Collaboration with Ben Cossins (UCB, Slough) on developing accurate algorithms for ligand binding free energy calculations Collaboration with Astra Zeneca (who are co-sponsoring an industrial student with EPSRC): understating the effects of cancer-causing mutations on the structure and dynamics of EGFR. |
| First Year Of Impact | 2021 |
| Sector | Agriculture, Food and Drink,Healthcare,Pharmaceuticals and Medical Biotechnology |
| Impact Types | Societal |
| Description | Research data and policy |
| Geographic Reach | National |
| Policy Influence Type | Contribution to new or improved professional practice |
| URL | https://www.chemistryworld.com/news/ukri-finds-itself-in-hot-water-too-over-researchfish-cyberbullyi... |
| Description | UKRI research data capture approaches |
| Geographic Reach | National |
| Policy Influence Type | Contribution to new or improved professional practice |
| URL | https://www.researchprofessionalnews.com/rr-news-uk-research-councils-2023-1-researchfish-tweets-aga... |
| Description | participation at digital research infrastructure meeting |
| Geographic Reach | National |
| Policy Influence Type | Participation in a guidance/advisory committee |
| Description | Oracle for Research Cloud Fellowship |
| Amount | $100,000 (USD) |
| Organisation | Oracle Corporation |
| Sector | Private |
| Country | United States |
| Start | 02/2023 |
| End | 12/2023 |
| Description | PREDACTED Predictive computational models for Enzyme Dynamics, Antimicrobial resistance, Catalysis and Thermoadaptation for Evolution and Desig |
| Amount | € 2,482,332 (EUR) |
| Funding ID | 101021207 |
| Organisation | European Research Council (ERC) |
| Sector | Public |
| Country | Belgium |
| Start | 09/2021 |
| End | 09/2026 |
| Description | https://gtr.ukri.org/person/2A2990B1-E1E1-4888-8848-7C256C3A3B43 |
| Amount | £20,009,000 (GBP) |
| Funding ID | https://gtr.ukri.org/person/2A2990B1-E1E1-4888-8848-7C256C3A3B43 |
| Organisation | United Kingdom Research and Innovation |
| Sector | Public |
| Country | United Kingdom |
| Start | 01/2006 |
| End | 02/2033 |
| Title | COVID is airborne |
| Description | Multscale model of SARS-CoV-2 in respiratory aerosol |
| Type Of Material | Improvements to research infrastructure |
| Year Produced | 2022 |
| Provided To Others? | Yes |
| Impact | HPC2021 Gordon Bell Special Prize Finalist Skip to main content U.S. flagAn official website of the United States government Here's how you know NIH NLM Logo Log in Access keysNCBI HomepageMyNCBI HomepageMain ContentMain Navigation Search PMC Full-Text Archive Search in PMC Run this search in PubMed Advanced Search User Guide Journal List SAGE Choice PMC9527558 Logo of sageopen The International Journal of High Performance Computing Applications Int J High Perform Comput Appl. 2023 Jan; 37(1): 28-44. Published online 2022 Oct 2. doi: 10.1177/10943420221128233 PMCID: PMC9527558 PMID: 36647365 #COVIDisAirborne: AI-enabled multiscale computational microscopy of delta SARS-CoV-2 in a respiratory aerosol Monitoring Editor: Mark Parsons Abigail Dommer,1,† Lorenzo Casalino,1,† Fiona Kearns,1,† Mia Rosenfeld,1 Nicholas Wauer,1 Surl-Hee Ahn,1 John Russo,2 Sofia Oliveira,3 Clare Morris,1 Anthony Bogetti,4 Anda Trifan,5,6 Alexander Brace,5,7 Terra Sztain,1,8 Austin Clyde,5,7 Heng Ma,5 Chakra Chennubhotla,4 Hyungro Lee,9 Matteo Turilli,9 Syma Khalid,10 Teresa Tamayo-Mendoza,11 Matthew Welborn,11 Anders Christensen,11 Daniel GA Smith,11 Zhuoran Qiao,12 Sai K Sirumalla,11 Michael O'Connor,11 Frederick Manby,11 Anima Anandkumar,12,13 David Hardy,6 James Phillips,6 Abraham Stern,13 Josh Romero,13 David Clark,13 Mitchell Dorrell,14 Tom Maiden,14 Lei Huang,15 John McCalpin,15 Christopher Woods,3 Alan Gray,13 Matt Williams,3 Bryan Barker,16 Harinda Rajapaksha,16 Richard Pitts,16 Tom Gibbs,13 John Stone,6,13 Daniel M. Zuckerman,2 Adrian J. Mulholland,3 Thomas Miller, III,11,12 Shantenu Jha,9 Arvind Ramanathan,5 Lillian Chong,4 and Rommie E Amaro1 Author information Copyright and License information Disclaimer Previous version available: This article is based on a previously available preprint: "#COVIDisAirborne: AI-Enabled Multiscale Computational Microscopy of Delta SARS-CoV-2 in a Respiratory Aerosol". Go to: Abstract We seek to completely revise current models of airborne transmission of respiratory viruses by providing never-before-seen atomic-level views of the SARS-CoV-2 virus within a respiratory aerosol. Our work dramatically extends the capabilities of multiscale computational microscopy to address the significant gaps that exist in current experimental methods, which are limited in their ability to interrogate aerosols at the atomic/molecular level and thus obscure our understanding of airborne transmission. We demonstrate how our integrated data-driven platform provides a new way of exploring the composition, structure, and dynamics of aerosols and aerosolized viruses, while driving simulation method development along several important axes. We present a series of initial scientific discoveries for the SARS-CoV-2 Delta variant, noting that the full scientific impact of this work has yet to be realized. Keywords: molecular dynamics, deep learning, multiscale simulation, weighted ensemble, computational virology, SARS-CoV-2, aerosols, COVID-19, HPC, AI, GPU, Delta Go to: Justification We develop a novel HPC-enabled multiscale research framework to study aerosolized viruses and the full complexity of species that comprise them. We present technological and methodological advances that bridge time and length scales from electronic structure through whole aerosol particle morphology and dynamics. Performance attributes Performance attribute Our submission Category of achievement Scalability, Time-to-solution Type of method used Explicit, Deep Learning Results reported on the basis of Whole application including I/O Precision reported Mixed Precision System scale Measured on full system Measurement mechanism Hardware performance counters Application timers Performance Modeling Open in a separate window Overview of the problem Respiratory pathogens, such as SARS-CoV-2 and influenza, are the cause of significant morbidity and mortality worldwide. These respiratory pathogens are spread by virus-laden aerosols and droplets that are produced in an infected person, exhaled, and transported through the environment (Wang et al., 2021) (Figure 1). Medical dogma has long focused on droplets as the main transmission route for respiratory viruses, where either a person has contact with an infected surface (fomites) or direct droplet transmission by close contact with an infected individual. However, as we continue to observe with SARS-CoV-2, airborne transmission also plays a significant role in spreading disease. We know this from various super spreader events, for example, during a choir rehearsal (Miller et al., 2021). Intervention and mitigation decisions, such as the relative importance of surface cleaning or whether and when to wear a mask, have unfortunately hinged on a weak understanding of aerosol transmission, to the detriment of public health. An external file that holds a picture, illustration, etc. Object name is 10.1177_10943420221128233-fig1.jpg Figure 1. Overall schematic depicting the construction and multiscale simulations of Delta SARS-CoV-2 in a respiratory aerosol. (N.B.: The size of di-valent cations has been increased for visibility.) A central challenge to understanding airborne transmission has been the inability of experimental science to reliably probe the structure and dynamics of viruses once they are inside respiratory aerosol particles. Single particle experimental methods have poor resolution for smaller particles (<1 micron) and are prone to sample destruction during collection. Airborne viruses are present in low concentrations in the air and are similarly prone to viral inactivation during sampling. In addition, studies of the initial infection event, for example, in the deep lung, are limited in their ability to provide a detailed understanding of the myriad of molecular interactions and dynamics taking place in situ. Altogether, these knowledge gaps hamper our collective ability to understand mechanisms of infection and develop novel effective antivirals, as well as prevent us from developing concrete, science-driven mitigation measures (e.g., masking and ventilation protocols). Here, we aim to reconceptualize current models of airborne transmission of respiratory viruses by providing never-before-seen views of viruses within aerosols. Our approach relies on the use of all-atom molecular dynamics (MD) simulations as a multiscale "computational microscope." MD simulations can synthesize multiple types of biological data (e.g., multiresolution structural datasets, glycomics, lipidomics, etc.) into cohesive, biologically "accurate" structural models. Once created, we then approximate the model down to its many atoms, creating trajectories of its time dependent dynamics under cell-like (or in this case, aerosol-like) conditions. Critically, MD simulations are more than just "pretty movies." MD equations are solved in a theoretically rigorous manner, allowing us to compute experimentally testable macroscopic observables from time-averaged microscopic properties. What this means is that we can directly connect MD simulations with experiments, each validating and providing testable hypotheses to the other, which is the real power of the approach. An ongoing challenge to the successful application of such methods, however, is the need for technological and methodological advances that make it possible to access length scales relevant to the study of large, biologically complex systems (spanning nanometers to ~one micron in size) and, correspondingly, longer timescales (microseconds to seconds). Such challenges and opportunities manifest in the study of aerosolized viruses. Aerosols are generally defined as being less than 5 microns in diameter, able to float in the air for hours, travel significant distances (i.e., can fill a room, like cigarette smoke), and be inhaled. Fine aerosols < 1 micron in size can stay in the air for over 12 h and are enriched with viral particles (Fennelly 2020; Coleman et al., 2021). Our work focuses on these finer aerosols that travel deeper into the respiratory tract. Several studies provide the molecular recipes necessary to reconstitute respiratory aerosols according to their actual biologically relevant composition (Vejerano and Marr 2018; Walker et al., 2021). These aerosols can contain lipids, cholesterol, albumin (protein), various mono- and di-valent salts, mucins, other surfactants, and water (Figure 1). Simulations of aerosolized viruses embody a novel framework for the study of aerosols: they will allow us and others to tune different species, relative humidity, ion concentrations, etc. to match experiments that can directly and indirectly connect to and inform our simulations, as well as test hypotheses. Some of the species under study here, for example, mucins, have not yet been structurally characterized or explored with simulations and thus the models we generate are expected to have impact beyond their roles in aerosols. In addition to varying aerosol composition and size, the viruses themselves can be modified to reflect new variants of concern, where such mutations may affect interactions with particular species in the aerosol that might affect its structural dynamics and/or viability. The virion developed here is the Delta variant (B.1.617.2 lineage) of SARS-CoV-2 (Figure 2), which presents a careful integration of multiple biological datasets: (1) a complete viral envelope with realistic membrane composition, (2) fully glycosylated full-length spike proteins integrating 3D structural coordinates from multiple cryoelectron microscopy (cryoEM) studies (McCallum et al., 2021; Wrapp et al., 2020; Walls et al., 2020; Bangaru et al., 2020) (3) all biologically known features (post-translational modifications, palmitoylation, etc.), (4) any other known membrane proteins (e.g. the envelope (E) and membrane (M) proteins), and (5) virion size and patterning taken directly from cryoelectron tomography (cryoET). Each of the individual components of the virus are built up before being integrated into the composite virion, and thus represent useful molecular-scale scientific contributions in their own right (Casalino et al., 2020; Sztain et al., 2021). An external file that holds a picture, illustration, etc. Object name is 10.1177_10943420221128233-fig2.jpg Figure 2. Individual protein components of the SARS-CoV-2 Delta virion. The spike is shown with the surface in cyan and with Delta's mutated residues and deletion sites highlighted in pink and yellow, respectively. Glycans attached to the spike are shown in blue. The E protein is shown in yellow and the M-protein is shown in silver and white. Visualized with VMD. Altogether in this work, we dramatically extend the capabilities of data-driven, multiscale computational microscopy to provide a new way of exploring the composition, structure, and dynamics of respiratory aerosols. While a seemingly limitless number of putative hypotheses could result from these investigations, the first set of questions we expect to answer are: How does the virus exist within a droplet of the same order of magnitude in size, without being affected by the air-water interface, which is known to destroy molecular structure (D'Imprima et al. 2019)? How does the biochemical composition of the droplet, including pH, affect the structural dynamics of the virus? Are there species within the aerosols that "buffer" the viral structure from damage, and are there particular conditions under which the impact of those species changes? Our simulations can also provide specific parameters that can be included in physical models of aerosols, which still assume a simple water or water-salt composition even though it is well known that such models, for example, using kappa-Kohler theory, break down significantly as the molecular species diversify (Petters and Kreidenweis 2007). Go to: Current state of the art Current experimental methods are unable to directly interrogate the atomic-level structure and dynamics of viruses and other molecules within aerosols. Here we showcase computational microscopy as a powerful tool capable to overcome these significant experimental limitations. We present the major elements of our multiscale computational microscope and how they come together in an integrated manner to enable the study of aerosols across multiple scales of resolution. We demonstrate the impact such methods can bring to bear on scientific challenges that until now have been intractable, and present a series of new scientific discoveries for SARS-CoV-2. Parallel molecular dynamics All-atom molecular dynamics simulation has emerged as an increasingly powerful tool for understanding the molecular mechanisms underlying biophysical behaviors in complex systems. Leading simulation engines, NAMD (Phillips et al., 2020), AMBER (Case et al. [n. d.]), and GROMACS (Páll et al., 2020), are broadly useful, with each providing unique strengths in terms of specific methods or capabilities as required to address a particular biological question, and in terms of their support for particular HPC hardware platforms. Within the multiscale computational microscopy platform developed here, we show how each of these different codes contributes different elements to the overall framework, oftentimes utilizing different computing modalities/architectures, while simultaneously extending on state-of-the-art for each. Structure building, simulation preparation, visualization, and post hoc trajectory analysis are performed using VMD on both local workstations and remote HPC resources, enabling modeling of the molecular systems studied herein (Humphrey et al., 1996; Stone et al., 2013a,b, 2016b; Sener et al., 2021). We show how further development of each of these codes, considered together within the larger-scale collective framework, enables the study of SARS-CoV-2 in a wholly novel manner, with extension to numerous other complex systems and diseases. AI-enhanced WE simulations Because the virulence of the Delta variant of SARS-CoV-2 may be partly attributable to spike protein (S) opening, it is of pressing interest to characterize the mechanism and kinetics of the process. Although S-opening in principle can be studied via conventional MD simulations, in practice the system complexity and timescales make this wholly intractable. Splitting strategies that periodically replicate promising MD trajectories, among them the weighted ensemble (WE) method (Huber and Kim 1996; Zuckerman and Chong 2017), have enabled simulations of the spike opening of WT SARS-CoV-2 (Sztain et al., 2021; Zimmerman et al., 2021). WE simulations can be orders of magnitude more efficient than conventional MD in generating pathways and rate constants for rare events (e.g. protein folding (Adhikari et al., 2019) and binding (Saglam and Chong 2019)). The WESTPA software for running WE (Zwier et al., 2015) is well-suited for high-performance computing with nearly perfect CPU/GPU scaling. The software is interoperable with any dynamics engine, including the GPU-accelerated AMBER dynamics engine (Salomon-Ferrer et al., 2013) that is used here. As shown below, major upgrades to WESTPA (v. 2.0) have enabled a dramatic demonstration of spike opening in the Delta variant (Figures 5 and and6)6) and exponentially improved analysis of spike-opening kinetics (Russo et al., 2022). An external file that holds a picture, illustration, etc. Object name is 10.1177_10943420221128233-fig5.jpg Figure 5. Delta variant spike opening from WE simulations, and AI/haMSM analysis. A) The integrated workflow. B) Snapshots of the "down," "up," and "open" states for Delta S-opening from a representative pathway generated by WE simulation, which represents ~ 105 speedup compared to conventional MD. C) Rate constant estimation with haMSM analysis of WE data (purple lines) significantly improves direct WE computation (red), by comparison to experimental measurement (black dashed). Varying haMSM estimates result from different featurizations which will be individually cross-validated. D) The first three dimensions of the ANCA-AE embeddings depict a clear separation between the closed (darker purple) and open (yellow) conformations of the Delta spike. A sub-sampled landscape is shown here where each sphere represents a conformation from the WE simulations and colored with the root-mean squared deviations (Å) with respect to the closed state. Visualized with VMD. An external file that holds a picture, illustration, etc. Object name is 10.1177_10943420221128233-fig6.jpg Figure 6. WE simulations reveal a dramatic opening of the Delta S (cyan), compared to WT S (white). While further investigation is needed, this super open state seen in the Delta S may indicate increased capacity for binding to human host-cell receptors. The integration of AI techniques with WE can further enhance the efficiency of sampling rare events (Noe 2020; Brace et al., 2021b; Casalino et al., 2021). One frontier area couples unsupervised linear and non-linear dimensionality reduction methods to identify collective variables/progress coordinates in high-dimensional molecular systems (Bhowmik et al., 2018; Clyde et al., 2021). Such methods may be well suited for analyzing the aerosolized virus. Integrating these approaches with WE simulations is advantageous in sampling the closed ? open transitions in the Delta S landscape (Figure 5) as these unsupervised AI approaches automatically stratify progress coordinates (Figure 5(D)). Dynamical non-equilibrium MD Aerosols rapidly acidify during flight via reactive uptake of atmospheric gases, which is likely to impact the opening/closing of the S protein (Vejerano and Marr 2018; Warwicker 2021). Here, we describe the extension of dynamical non-equilibrium MD (D-NEMD) (Ciccotti and Ferrario 2016) to investigate pH effects on the Delta S. D-NEMD simulations (Ciccotti and Ferrario 2016) are emerging as a useful technique for identifying allosteric effects and communication pathways in proteins (Galdadas et al., 2021; Oliveira et al., 2019), including recently identifying effects of linoleic acid in the WT spike (Oliveira et al., 2021b). This approach complements equilibrium MD simulations, which provide a distribution of configurations as starting points for an ensemble of short non-equilibrium trajectories under the effect of the external perturbation. The response of the protein to the perturbation introduced can then be determined using the Kubo-Onsager relation (Oliveira et al., 2021a; Ciccotti and Ferrario 2016) by directly tracking the change in atomic positions between the equilibrium and non-equilibrium simulations at equivalent points in time (Oliveira et al., 2021a). OrbNet Ca2+ ions are known to play a key role in mucin aggregation in epithelial tissues (Hughes et al., 2019). Our RAV simulations would be an ideal case-study to probe such complex interactions between Ca2+, mucins, and the SARS-CoV-2 virion in aerosols. However, Ca2+ binding energies can be difficult to capture accurately due to electronic dispersion and polarization, terms which are not typically modeled in classical mechanical force fields. Quantum mechanical (QM) methods are uniquely suited to capture these subtle interactions. Thus, we set out to estimate the correlation in Ca2+ binding energies between CHARMM36m and quantum mechanical estimates enabled via AI with OrbNet. Calculation of energies with sufficient accuracy in biological systems can, in many cases, be adequately described with density functional theory (DFT). However, its high cost limits the applicability of DFT in comparison to fixed charge force fields. To capture quantum quality energetics at a fraction of the computational expense, we employ a novel approach (OrbNet) based on the featurization of molecules in terms of symmetry-adapted atomic orbitals and the use of graph neural network methods for deep learning quantum-mechanical properties (Qiao et al., 2020). Our method outperforms existing methods in terms of its training efficiency and transferable accuracy across diverse molecular systems, opening a new pathway for replacing DFT in large-scale scientific applications such as those explored here. (Christensen et al., 2021). Innovations realized Construction and simulation of SARS-CoV-2 in a respiratory aerosol Our approach to simulating the entire aerosol follows a composite framework wherein each of the individual molecular pieces is refined and simulated on its own before it is incorporated into the composite model. Simulations of each of the components are useful in their own right, and often serve as the basis for biochemical and biophysical validation and experiments (Casalino et al., 2020). Throughout, we refer to the original circulating SARS-CoV-2 strain as "WT," whereas all SARS-CoV-2 proteins constructed in this work represent the Delta variant (Figure 2). All simulated membranes reflect mammalian ER-Golgi intermediate compartment (ERGIC) mimetic lipid compositions. VMD (Humphrey et al., 1996; Stone et al., 2016a), psfgen (Phillips et al., 2005), and CHARMM-GUI (Park et al., 2019) were used for construction and parameterization. Topologies and parameters for simulations were taken from CHARMM36m all-atom additive force fields (Guvench et al., 2009; Huang and Mackerell 2013; Huang et al., 2017; Klauda et al., 2010; Beglov and Roux 1994; Han et al., 2018; Venable et al., 2013). NAMD was used to perform MD simulations (Phillips et al., 2020), adopting similar settings and protocols as in (Casalino et al., 2020). All systems underwent solvation, charge neutralization, minimization, heating, and equilibration prior to production runs. Refer to Table 1 for Abbreviations, PBC dimensions, total number of atoms, and total equilibration times for each system of interest. Table 1. Summary of all systems constructed in this work. See Figure 3 for illustration of aerosol construction. asystems bAbb c(Å × Å × Å) dNa e (ns) fM dimers M 125 × 125 × 124 164,741 700 fE pentamers E 123 × 125 × 102 136,775 41 Spikes f (Open) S 206 × 200 × 410 1,692,444 330 f (Closed) S 204 × 202 × 400 1,658,224 330 g (Closed, head) SH 172 × 184 × 206 615,593 73µs Mucins fshort mucin 1 m1 123 × 104 × 72 87,076 25 fshort mucin 2 m2 120 × 101 × 72 82,155 25 flong mucin 1 m3 810 × 104 × 115 931,778 23 flong mucin 2 m4 904 × 106 × 109 997,029 15 flong mucin 3 m5 860 × 111 × 113 1,040,215 18 fS+m1/m2+ALB SMA 227 × 229 × 433 2,156,689 840 fVirion V 1460 × 1460 × 1460 305,326,834 41 fResp.Aero.+Vir RAV 2834 × 2820 × 2828 1,016,813,441 2.42 Total FLOPS 2.4 ZFLOPS Open in a separate window aM, E, S, SH, and V models represent SARS-CoV-2 Delta strain. bAbbreviations used throughout document. cPeriodic boundary dimensions. dTotal number of atoms. eTotal aggregate simulation time, including heating and equilibration runs. fSimulated with NAMD. gSimulated with NAMD, AMBER, and GROMACS. Simulating the SARS-CoV-2 structural proteins Fully glycosylated Delta spike (S) structures in open and closed conformations were built based on WT constructs from Casalino et al. (Casalino et al., 2020) with the following mutations: T19R, T95I, G142D, E156G, ?157-158, L452R, T478K, D614G, P681R, and D950N (McCallum et al., 2021; Kannan et al., 2021). Higher resolved regions were grafted from PDB 7JJI (Bangaru et al., 2020). Additionally, coordinates of residues 128-167-accounting for a drastic conformational change seen in the Delta variant S-graciously made available to us by the Veesler Lab, were similarly grafted onto our constructs (McCallum et al., 2021). Finally, the S proteins were glycosylated following work by Casalino et al. (Casalino et al., 2020). By incorporating the Veesler Lab's bleeding-edge structure (McCallum et al., 2021) and highly resolved regions from 7JJI (Bangaru et al., 2020), our models represent the most complete and accurate structures of the Delta S to date. The S proteins were inserted into membrane patches and equilibrated for 3 × 110 ns. For non-equilibrium and weighted ensemble simulations, a closed S head (SH, residues 13-1140) was constructed by removing the stalk from the full-length closed S structure, then resolvated, neutralized, minimized, and subsequently passed to WE and D-NEMD teams. The M-protein was built from a structure graciously provided by the Feig Lab (paper in prep). The model was inserted into a membrane patch and equilibrated for 700 ns. RMSD-based clustering was used to select a stable starting M-protein conformation. From the equilibrated and clustered M structure, VMD's Mutator plugin (Humphrey et al., 1996) was used to incorporate the I82T mutation onto each M monomer to arrive at the Delta variant M. To construct the most complete E protein model to-date, the structure was patched together by resolving incomplete PDBs 5X29 (Surya et al., 2018), 7K3G (Mandala et al., 2020) and 7M4R (Chai et al., 2021). To do so, the transmembrane domain (residues 8-38) from 7K3G were aligned to the N-terminal domain (residues 1-7) and residues 39 to 68 of 5X29 and residues 69 to 75 of 7M4R by their Ca atoms. E was then inserted into a membrane patch and equilibrated for 40 ns. Constructing the SARS-CoV-2 Delta virion The SARS-CoV-2 Delta virion (V) model was constructed following Casalino et al. (Casalino et al., 2021) using CHARMM-GUI (Lee et al., 2016), LipidWrapper (Durrant and Amaro 2014), and Blender (Blender Online Community 2020), using a 350 Å lipid bilayer with an equilibrium area per lipid of 63 Å2 and a 100 nm diameter Blender icospherical surface mesh (Turonova et al., 2020). The resulting lipid membrane was solvated in a 1100 Å3 waterbox and subjected to four rounds of equilibration and patching (Casalino et al., 2021). 360 m dimers and 4 E pentamers were then tiled onto the surface, followed by random placement of 29 full-length S proteins (9 open, 20 closed) according to experimentally observed S protein density (Ke et al., 2020). M and E proteins were oriented with intravirion C-termini. After solvation in a 1460 Å waterbox, the complete V model tallied >305 million atoms (Table 1). V was equilibrated for 41 ns prior to placement in the respiratory aerosol (RA) model. The equilibrated membrane was 90 nm in diameter and remains in close structural agreement with the experimental studies (Ke et al., 2020). Building and simulating the respiratory aerosol Respiratory aerosols contain a complex mixture of chemical and biological species. We constructed a respiratory aerosol (RA) fluid based on a composition from artificial saliva and surrogate deep lung fluid recipes (Walker et al., 2021). This recipe includes 0.7 mm DPPG, 6.5 mm DPPC, 0.3 mm cholesterol, 1.4 mm Ca2+, 0.8 mm Mg2+, and 142 mm Na+ (Vejerano and Marr 2018; Walker et al., 2021), human serum albumin (ALB) protein, and a composition of mucins (Figure 3). Mucins are long polymer-like structures that are decorated by dense, heterogeneous, and complex regions of O-glycans. This work represents the first of its kind as, due to their complexity, the O-glycosylated regions of mucins have never before been constructed for molecular simulations. Two short (m1, m2, ~5 nm) and three long (m3, m4, m5 ~55 nm) mucin models were constructed following known experimental compositions of protein and glycosylation sequences (Symmes et al., 2018; Hughes et al., 2019; Markovetz et al., 2019; Thomsson et al., 2005; Mariethoz et al., 2018) with ROSETTA (Raveh et al., 2010) and CHARMM-GUI Glycan Modeller (Jo et al., 2011). Mucin models (short and long) were solvated, neutralized by charge matching with Ca2+ ions, minimized, and equilibrated for 15-25 ns each (Table 1). Human serum albumin (ALB), which is also found in respiratory aerosols, was constructed from PDB 1AO6 (Sugio et al., 1999). ALB was solvated, neutralized, minimized, and equilibrated for 7ns. Equilibrated structures of ALB and the three long mucins were used in construction of the RAV with m3+m4+m5 added at 6 g/mol and ALB at 4.4 g/mol. An external file that holds a picture, illustration, etc. Object name is 10.1177_10943420221128233-fig3.jpg Figure 3. Image of RAV with relative mass ratios of RA molecular components represented in the colorbar. Water content is dependent on the relative humidity of the environment and is thus omitted from the molecular ratios. Constructing the respiratory aerosolized virion model A 100 nm cubic box with the RA fluid recipe specified above was built with PACKMOL (Martínez et al., 2009), minimized, equilibrated briefly on TACC Frontera, then replicated to form a 300 nm cube. The RA box was then carved into a 270 nm diameter sphere. To make space for the placement of V within the RA, a spherical selection with volume corresponding to that of the V membrane + S crown (radius 734 Å) was deleted from the center of the RA. The final equilibrated V model, including surrounding equilibrated waters and ions (733 Å radius), was translated into the RA. Atom clashes were resolved using a 1.2 Å cutoff. Hydrogen mass repartitioning (Hopkins et al., 2015) was applied to the structure to improve performance. The simulation box was increased to 2800 Å per side to provide a 100 Å vacuum atmospheric buffer. The RAV simulation was conducted in an NVT ensemble with a 4 fs timestep. After minimizing, the RAV was heated to 298 K with 0.1 kcal/mol Å2 restraints on the viral lipid headgroups, then equilibrated for 1.5 ns. Finally, a cross-section of the RAV model-including and open S, m1/m2, and ALB (called the SMA system)-was constructed with PACKMOL to closely observe atomic scale interactions within the RAV model (Figure 4). An external file that holds a picture, illustration, etc. Object name is 10.1177_10943420221128233-fig4.jpg Figure 4. SMA system captured with multiscale modeling from classical MD to AI-enabled quantum mechanics. For all panels: S protein shown in cyan, S glycans in blue, m1/m2 shown in red, ALB in orange, Ca2+ in yellow spheres, viral membrane in purple. A) Interactions between mucins and S facilitated by glycans and Ca2+. B) Snapshot from SMA simulations. C) Example Ca2+ binding site from SMA simulations (1800 sites, each 1000+ atoms) used for AI-enabled quantum mechanical estimates from OrbNet Sky. D) Quantification of contacts between S and mucin from SMA simulations. E) OrbNet Sky energies versus CHARMM36m energies for each sub-selected system, colored by total number of atoms. Performance of OrbNet Sky versus DFT in subplot (?B97x-D3/def-TZVP, R2=0.99, for 17 systems of peptides chelating Ca2+ (Hu et al., 2021)). Visualized with VMD. Parameter evaluation with OrbNet Comparison to quantum methods reveals significant polarization effects, and shows that there is opportunity to improve the accuracy of fixed charge force fields. For the large system sizes associated with solvated Ca2+-protein interaction motifs (over 1000 atoms, even in aggressively truncated systems), conventional quantum mechanics methods like density functional theory (DFT) are impractical for analyzing a statistically significant ensemble of distinct configurations (see discussion in Performance Results). In contrast, OrbNet allows for DFT accuracy with over 1000-fold speedup, providing a useful method for benchmarking and refining the force field simulation parameters with quantum accuracy (Christensen et al., 2021). To confirm the accuracy of OrbNet versus DFT (?B97X-D/def2-TZVP), the inset of Figure 4(E) correlates the two methods for the Ca2+-binding energy in a benchmark dataset of small Ca2+-peptide complexes (Hu et al., 2021). The excellent correlation of OrbNet and DFT for the present use case is clear from the inset figure; six datapoints were removed from this plot on the basis of a diagnostic applied to the semi-empirical GFN-xTB solution used for feature generation of OrbNet (Christensen et al., 2021). Figure 4 presents a comparison of the validated OrbNet method with the CHARMM36m force field for 1800 snapshots taken from the SMA MD simulations. At each snapshot, a subsystem containing a solvated Ca2+-protein complex was extracted (Figure 4(E)), with protein bonds capped by hydrogens. For both OrbNet and the force field, the Ca2+-binding energy was computed and shown in the correlation plot. Lack of correlation between OrbNet and the force field identifies important polarization effects, absent in a fixed charge description. Similarly, the steep slope of the best-fit line in Figure 4(E) reflects the fact that some of the configurations sampled using MD with the CHARMM36m force field are relatively high in energy according to the more accurate OrbNet potential. This approach allows us to test and quantify limitations of empirical force fields, such as lack of electronic polarization. The practicality of OrbNet for these simulation snapshots with 1000+ atoms offers a straightforward multiscale strategy for refining the accuracy of the CHARMM36m force field. By optimizing the partial charges and other force field parameters, improved correlation with OrbNet for the subtle Ca2+-protein interactions could be achieved, leading to near-quantum accuracy simulations with improved configurational sampling. The calculations presented here present a proof-of-concept of this iterative strategy. AI-WE simulations of delta spike opening While our previous WE simulations of the WT SARS-CoV-2 S-opening (Sztain et al., 2021) were notable in generating pathways for a seconds-timescale process of a massive system, we have made two critical technological advancements in the WESTPA software that greatly enhance the efficiency and analysis of WE simulations. These advances enabled striking observations of Delta variant S opening (Figures 5 and and6).6). First, in contrast to prior manual bins for controlling trajectory replication, we have developed automated and adaptive binning that enables more efficient surmounting of large barriers via early identification of "bottleneck" regions (Torrillo et al., 2021). Second, we have parallelized, memory-optimized, and implemented data streaming for the history-augmented Markov state model (haMSM) analysis scheme (Copperman and Zuckerman 2020) to enable application to the TB-scale S-opening datasets. The haMSM approach estimates rate constants from simulations that have not yet reached a steady state (Suarez et al., 2014). Our WE simulations generated >800 atomically detailed, Delta variant S-opening pathways (Figures 5(B) and and6)6) of the receptor binding domain (RBD) switching from a glycan-shielded "down" to an exposed "up" state using 72 µs of total simulation time within 14 days using 192 NVIDIA V100 GPUs at a time on TACC's Longhorn supercomputer. Among these pathways, 83 reach an "open" state that aligns with the structure of the human ACE2-bound WT S protein (Benton et al., 2020) and 18 reach a dramatically open state (Figure 6). Our haMSM analysis of WT WE simulations successfully provided long-timescale (steady state) rate constants for S-opening based on highly transient information (Figure 5(C)). We also leveraged a simple, yet powerful unsupervised deep learning method called Anharmonic Conformational Analysis enabled Autoencoders (ANCA-AE) Clyde et al. (2021) to extract conformational states from our long-timescale WE simulations of Delta spike opening (Figures 5(A) and (D)). ANCA-AE first minimizes the fourth order correlations in atomistic fluctuations from MD simulation datasets and projects the data onto a low dimensional space where one can visualize the anharmonic conformational fluctuations. These projections are then input to an autoencoder that further minimizes non-linear correlations in the atomistic fluctuations to learn an embedding where conformations are automatically clustered based on their structural and energetic similarity. A visualization of the first three dimensions from the latent space articulates the RBD opening motion from its closed state (Figure 5(D)). It is notable that while other deep learning techniques need special purpose hardware (such as GPUs), the ANCA-AE approach can be run with relatively modest CPU resources and can therefore scale to much larger systems (e.g., the virion within aerosol) when optimized. D-NEMD explores pH effects on delta spike We performed D-NEMD simulations of the SH system with GROMACS (Abraham et al., 2015) using a ?pH=2.0 (from 7.0 to 5.0) as the external perturbation. We ran 3200-ns equilibrium MD simulations of SH to generate 87 configurations (29 configurations per replicate) that were used as the starting points for multiple short (10 ns) D-NEMD trajectories under the effect of the external perturbation (?pH=2.0). The effect of a ?pH was modeled by changing the protonation state of histidines 66, 69, 146, 245, 625, 655, 1064, 1083, 1088, and 1101 (we note that other residues may also become protonated (Lobo and Warwicker 2021); the D-NEMD approach can also be applied to examine those). The structural response of the S to the pH decrease was investigated by measuring the difference in the position for each Ca atom between the equilibrium and corresponding D-NEMD simulation at equivalent points in time (Oliveira et al., 2021a), namely after 0, 0.1, 1, 5, and 10 ns of simulation. The D-NEMD simulations reveal that pH changes, of the type expected in aerosols, affect the dynamics of functionally important regions of the spike, with potential implications for viral behavior (Figure 7). As this approach involves multiple short independent non-equilibrium trajectories, it is well suited for cloud computing. All D-NEMD simulations were performed using Oracle Cloud. An external file that holds a picture, illustration, etc. Object name is 10.1177_10943420221128233-fig7.jpg Figure 7. D-NEMD simulations reveal changes in key functional regions of the S protein, including the receptor binding domain, as the result of a pH decrease. Color scale and ribbon thickness indicate the degree of deviation of Ca atoms from their equilibrium position. Red spheres indicate the location of positively charged histidines. How performance was measured WESTPA For the WE simulations of spike opening using WESTPA, we defined the time-to-solution as the total simulation time required to generate the first spike opening event. Spike opening is essentially impossible to observe via conventional MD. WESTPA simulations were run using the AMBER20 dynamics engine and 192 NVIDIA V100 GPUs at a time on TACC's Longhorn supercomputer. NAMD NAMD performance metrics were collected using hardware performance counters for FLOPs/step measurements, and application-internal timers for overall simulation rates achieved by production runs including all I/O for simulation trajectory and checkpoint output. NAMD FLOPs/step measurements were conducted on TACC Frontera, by querying hardware performance counters with the rdmsr utility from Intel msr-tools1 and the "TACC stats" system programs.2 For each simulation, FLOP counts were measured for NAMD simulation runs of two different step counts. The results of the two simulation lengths were subtracted to eliminate NAMD startup operations, yielding an accurate estimate of the marginal FLOPs per step for a continuing simulation (Phillips et al., 2002). Using the FLOPs/step values computed for each simulation, overall FLOP rates were computed by dividing the FLOPs/step value by seconds/step performance data reported by NAMD internal application timers during production runs. GROMACS GROMACS 2020.4 benchmarking was performed on Oracle Cloud Infrastructure (OCI)3 compute shape BM.GPU4.8 consisting of 8×NVIDIA A100 tensor core GPUs, and 64 AMD Rome CPU cores. The simulation used for benchmarking contained 615,563 atoms and was run for 500,000 steps with 2 fs time steps. The simulations were run on increasing numbers of GPUs, from 1 to 8, using eight CPU cores per GPU, running for both the production (Nose-Hoover) and GPU-accelerated (velocity rescaling) thermostats. Particle-mesh Ewald (PME) calculations were pinned to a single GPU, with additional GPUs for multi-GPU jobs used for particle-particle calculations. Performance data (ns/day and average single-precision TFLOPS, calculated as total number of TFLOPs divided by total job walltime) were reported by GROMACS itself. Each simulation was repeated four times and average performance figures reported. Performance results Table 2. Table 2. MD simulation floating point ops per timestep. MD Simulation Code Atoms aFLOPs/step Spike, head AMBER, GROMACS 0.6 m 62.14 GFLOPs/step Spike NAMD 1.7 m 43.05 GFLOPs/step S+m1/m2+ALB NAMD 2.1 m 54.86 GFLOPs/step Resp. Aero.+Vir NAMD 1B 25.81 TFLOPs/step Open in a separate window aFLOPs/step data were computed by direct FLOP measurements from hardware performance counters for NAMD simulations, or by using the application-reported FLOP rates and ns/day simulation performance in the case of GROMACS. NAMD performance NAMD was used to perform all of the simulations listed in Table 1, except for the closed spike "SH" simulations described further below. With the exception of the aerosol and virion simulation, the other NAMD simulations used conventional protocols and have performance and parallel scaling characteristics that closely match the results reported in our previous SARS-CoV-2 research Casalino et al. (2021). NAMD 2.14 scaling performance for the one billion-atom respiratory aerosol and virion simulation run on ORNL Summit is summarized in Tables 3 and and4.4. A significant performance challenge associated with the aerosol virion simulation relates to the roughly 50% reduction in particle density as compared with a more conventional simulation with a fully populated periodic cell. The reduced particle density results in large regions of empty space that nevertheless incur additional overheads associated with both force calculations and integration, and creates problems for the standard NAMD load balancing scheme that estimates the work associated with the cubic "patches" used for parallel domain decomposition. The PME electrostatics algorithm and associated 3-D FFT and transpose operations encompass the entire simulation unit cell and associated patches, requiring involvement in communication and reduction operations despite the inclusion of empty space. Enabling NAMD diagnostic output on a 512-node 1B-atom aerosol and virion simulation revealed that ranks assigned empty regions of the periodic cell had 66 times the number of fixed-size patches as ranks assigned dense regions. The initial load estimate for an empty patch was changed from a fixed 10 atoms to a runtime parameter with a default of 40 atoms, which reduced the patch ratio from 66 to 19 and doubled performance on 512 nodes. Table 3. NAMD performance: Respiratory Aerosol + Virion, 1B atoms, 4 fs timestep w/HMR, and PME every three steps. Nodes Summit Speedup Efficiency CPU + GPU 256 4.18 ns/day ~1.0× ~100% 512 7.68 ns/day 1.84× 92% 1024 13.64 ns/day 3.27× 81% 2048 23.10 ns/day 5.53× 69% 4096 34.21 ns/day 8.19× 51% Open in a separate window Table 4. Peak NAMD FLOP rates, ORNL Summit. NAMD Simulation Atoms, B Nodes Sim rate Performance Resp. Aero.+Vir 1 4096 34.21 ns/day 2.55 PFLOPS Open in a separate window WESTPA performance Our time to solution for WE simulations of spike opening (to the "up" state) (Figure 5) using the WESTPA software and AMBER20 was 14 µs of total simulation time, which was completed in 4 days using 192 NVIDIA V100 GPUs at a time on TACC's Longhorn supercomputer. For reference, conventional MD would require an expected ~5 orders of magnitude more computing. The WESTPA software is highly scalable, with nearly perfect scaling out to >1000 NVIDIA V100 GPUs and this scaling is expected to continue until the filesystem is saturated. Thus, WESTPA makes optimal use of large supercomputers and is limited by filesystem I/O due to the periodic restarting of trajectories after short time intervals. AI-enhanced WE simulations DeepDriveMD is a framework to coordinate the concurrent execution of ensemble simulations and drive them using AI models Brace et al. (2021a); Lee et al. (2019). DeepDriveMD has been shown to improve the scientific performance of diverse problems: from-protein folding to conformation of protein-ligand complexes. We coupled WESTPA to DeepDriveMD, which is responsible for resource dynamism and concurrent heterogeneous task execution (ML and AMBER). The coupled workflow was executed on 1024 nodes on Summit (OLCF), and, in spite of the spatio-temporal heterogeneity of tasks involved, the resource utilization was in the high 90%. Consistent with earlier studies, the coupling of WESTPA to DeepDriveMD results in a 100x improvement in the exploration of phase space. GROMACS performance Figure 8 shows GROMACS parallelizes well across the eight NVIDIA A100 GPUs available on each BM.GPU4.8 instance used in the Cluster in the Cloud4 running on OCI. There is a performance drop for two GPUs due to inefficient division of the PME and particle-particle tasks. Methods to address this exist for the two GPU case Páll et al. (2020), but were not adopted as we were targeting maximum raw performance across all eight GPUs. Production simulations achieved 27% of the peak TFLOPS available from the GPUs. Multiple simulations were run across 10 such compute nodes, enabling the ensemble to run at an average combined speed of 425 TFLOPS and sampling up to 1µs/day. We note that the calculations will be able to run 20%-40% faster once the Nose-Hoover thermostat that is required for the simulation is ported to run on the GPU. Benchmarking using a velocity rescaling thermostat that has been ported to GPU shows that this would enable the simulation to extract 34% of the peak TFLOPS from the cards, enabling each node to achieve an average speed of 53.4 TFLOPS, and 125 ns/day. A cluster of 10 nodes would enable GROMACS to run at an average combined speed of over 0.5 PFLOPs, simulating over 1.2 µs/day. An external file that holds a picture, illustration, etc. Object name is 10.1177_10943420221128233-fig8.jpg Figure 8. GROMACS performance across 1-8 A100 GPUs in ns/day (thicker, blue lines) and the fraction of maximum theoretical TFLOPS (thinner, green lines); production setup shown with solid line, and runs with the GPU-accelerated thermostat in dashed. A significant innovation is that this power is available on demand: Cluster in the Cloud with GPU-optimized GROMACS was provisioned and benchmarked within 1 day of inception of the project. This was handed to the researcher, who submitted the simulations. Automatically, up to 10 BM.GPU4.8 compute nodes were provisioned on-demand based on requests from the Slurm scheduler. These simulations were performed on OCI, using Cluster in the Cloud Williams (2021) to manage automatic scaling. Cluster in the Cloud was configured to dynamically provision and terminate computing nodes based on the workload. Simulations were conducted using GROMACS 2020.4 compiled with CUDA support. Multiple simultaneous simulations were conducted, with each simulation utilizing a single BM.GPU4.8 node without multinode parallelism. This allowed all production simulations to be completed within 2 days. The actual compute cost of the project was less than $6125 USD (on-demand OCI list price). The huge reduction in "time to science" that low-cost cloud enables changes the way that researchers can access and use HPC facilities. In our opinion, such a setup enables "exclusive on-demand" HPC capabilities for the scientific community for rapid advancement in science. OrbNet performance Prior benchmarking reveals that OrbNet provides over 1000-fold speedup compared to DFT (Christensen et al., 2021). For the calculations presented here, the cost of corresponding high quality range-separated DFT calculations (?B97X-D/def2-TZVP) can be estimated. In Figure 4(E), we consider system sizes which would require 14,000-47,000 atomic orbitals for ?B97X-D/def2-TZVP, exceeding the range of typical DFT evaluations. Estimation of the DFT computational cost of the 1811 configurations studied in Figure 4(E) suggests a total of 115M core-hours on NERSC Cori Haswell nodes; in contrast, the OrbNet calculations for the current study require only 100k core-hours on the same nodes. DFT cost estimates were based on extrapolation from a dataset of over 1M ChEMBL molecules ranging in size from 40 to 107 atom systems considering only the cubic cost component of DFT (Christensen et al., 2021). Go to: Implications Our major scientific achievements are 1. We showcase an extensible AI-enabled multiscale computational framework that bridges time and length scales from electronic structure through whole aerosol particle morphology and dynamics. 2. We develop all-atom simulations of respiratory mucins, and use these to understand the structural basis of interaction with the SARS-CoV-2 spike protein. This has implications for viral binding in the deep lung, which is coated with mucins. We expect the impact of our mucin simulations to be far reaching, as malfunctions in mucin secretion and folding have been implicated in progression of severe diseases such as cancer and cystic fibrosis. 3. We present a significantly enhanced all-atom model and simulation of the SARS-CoV-2 Delta virion, which includes the hundreds of tiled M-protein dimers and the E-protein ion channels. This model can be used as a basis to understand why the Delta virus is so much more infectious than the WT or alpha variants. 4. We develop an ultra-large (1 billion+) all-atom simulation capturing massive chemical and biological complexity within a respiratory aerosol. This simulation provides the first atomic-level views of virus-laden aerosols and is already serving as a basis to develop an untold number of experimentally testable hypotheses. An immediate example suggests a mechanism through which mucins and other species, for example, lipids, which are present in the aerosol, arrange to protect the molecular structure of the virus, which otherwise would be exposed to the air-water interface. This work also opens the door for developing simulations of other aerosols, for example, sea spray aerosols, that are involved in regulating climate. 5. We evidence how changes in pH, which are expected in the aerosol environment, may alter dynamics and allosteric communication pathways in key functional regions of the Delta spike protein. 6. We characterize atomically detailed pathways for the spike-opening process of the Delta variant using WE simulations, revealing a dramatically open state that may facilitate binding to human host cells. 7. We demonstrate how parallelized haMSM analysis of WE data can provide physical rate estimates of spike opening, improving prior estimates by many orders of magnitude. The pipeline can readily be applied to the any variant spike protein or other complex systems of interest. 8. We show how HPC and cloud resources can be used to significantly drive down time-to-solution for major scientific efforts as well as connect researchers and greatly enable complex collaborative interactions. 9. We demonstrate how AI coupled to HPC at multiple levels can result in significantly improved effective performance, for example, with AI-driven WESTPA, and extend the reach and domain of applicability of tools ordinarily restricted to smaller, less complex systems, for example, with OrbNet. 10. While our work provides a successful use case, it also exposes weaknesses in the HPC ecosystem in terms of support for key steps in large/complex computational science campaigns. We find lack of widespread support for high performance remote visualization and interactive graphical sessions for system preparation, debugging, and analysis with diverse science tools to be a limiting factor in such efforts. Go to: Acknowledgements We thank Prof. Kim Prather for inspiring and informative discussions about aerosols and for her commitment to convey the airborne nature of SARS-CoV-2. We thank D. Veesler for sharing the Delta spike NTD coordinates in advance of publication. We thank B. Messer, D. Maxwell, and the Oak Ridge Leadership Computing Facility at Oak Ridge National Laboratory supported by the DOE under Contract DE-AC05-00OR22725. We thank the Texas Advanced Computing Center Frontera team, especially D. Stanzione and T. Cockerill, and for compute time made available through a Director's Discretionary Allocation (NSF OAC-1818253). We thank the Argonne Leadership Computing Facility supported by the DOE under DE-AC02-06CH11357. We thank the Pittsburgh Supercomputer Center for providing priority queues on Bridges-2 through the XSEDE allocation NSF TG-CHE060063. We thank N. Kern and J. Lee of the CHARMM-GUI support team for help converting topologies between NAMD and GROMACS. We thank J. Copperman, G. Simpson, D. Aristoff, and J. Leung for valuable discussions and support from NIH grant GM115805. NAMD and VMD are funded by NIH P41-GM104601. This work was supported by the NSF Center for Aerosol Impacts on Chemistry of the Environment (CAICE), National Science Foundation Center for Chemical Innovation (NSF CHE-1801971), as well as NIH GM132826, NSF RAPID MCB-2032054, an award from the RCSA Research Corp., a UC San Diego Moore's Cancer Center 2020 SARS-CoV-2 seed grant, to R.E.A. This work was also supported by Oracle Cloud credits and related resources provided by the Oracle for Research program. AJM and ASFO receive funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (PREDACTED Advanced Grant, Grant agreement No.: 101021207). Go to: Notes 1. https://github.com/intel/msr-tools 2. https://github.com/TACC/tacc_stats 3. https://www.oracle.com/cloud/ 4. https://cluster-in-the-cloud.readthedocs.io/ Go to: Footnotes The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. Funding: The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by National Science Foundation (CHE- 1801971); National Science Foundation (MCB- 2032054); National Science Foundation (OAC-1818253); National Science Foundation (TG-CHE060063); U.S. Department of Energy (DE-AC02-06CH11357); U.S. Department of Energy (DE-AC05- 00OR22725); National Institutes of Health (P41-GM104601); National Institutes of Health (R01-GM132826). Go to: ORCID iDs Lorenzo Casalino https://orcid.org/0000-0003-3581-1148 Mia Rosenfeld https://orcid.org/0000-0002-8961-8231 Surl-Hee Ahn https://orcid.org/0000-0002-3422-805X John Russo https://orcid.org/0000-0002-2813-6554 Sofia Oliveira https://orcid.org/0000-0001-8753-4950 Clare Morris https://orcid.org/0000-0002-4314-5387 Alexander Brace https://orcid.org/0000-0001-9873-9177 Hyungro Lee https://orcid.org/0000-0002-4221-7094 Zhuoran Qiao https://orcid.org/0000-0002-5704-7331 Anima Anandkumar https://orcid.org/0000-0002-6974-6797 James Phillips https://orcid.org/0000-0002-2296-3591 John McCalpin https://orcid.org/0000-0002-2535-1355 Christopher Woods https://orcid.org/0000-0001-6563-9903 Matt Williams https://orcid.org/0000-0003-2198-1058 Richard Pitts https://orcid.org/0000-0002-2037-3360 Daniel Zuckerman https://orcid.org/0000-0001-7662-2031 Adrian Mulholland https://orcid.org/0000-0003-1015-4567 Arvind Ramanathan https://orcid.org/0000-0002-1622-5488 Lillian Chong https://orcid.org/0000-0002-0590-483X Rommie E Amaro https://orcid.org/0000-0002-9275-9553 Go to: References Abraham MJ, Murtola T, Schulz R, et al. 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