Can the Plasmodium falciparum Nedd8 pathway provide new targets for malaria control?

Ubiquitin and Nedd8 are involved in fundamental cellular processes and are essential to all eukaryotes. As such, enzymes mediating their dynamic attachment and removal from substrates present attractive targets for therapeutic intervention for both chronic and communicable diseases. Despite being evolutionarily conserved, differences in how these pathways are controlled in higher and lower eukaryotes do exist and could potentially be exploited to generate pathogen-specific inhibitors. It is, therefore, necessary to understand the cell biological mechanisms behind how these pathways are regulated. We have evidence to support that removal of Nedd8 from target proteins in the malaria parasite, Plasmodium falciparum, is mediated by different enzymes than those of the human host. We now aim to characterize enzymes involved in Nedd8 attachment. We also aim to assess whether these enzymes are essential to P. falciparum survival and if they can be selectively disrupted in the parasite through peptide inhibitors. Overall, we hope to gain a better understanding of how the Nedd8 pathway has evolved across eukaryotes and identify patterns to predict its function in other parasites more widely.

Ubiquitin and Nedd8 control cell-cycle progression, protein trafficking and degradation in all eukaryotic organisms including the malaria parasite, Plasmodium falciparum. These processes are part of the biology canon and affect both parasite maturation as well as host responses to pathogens. Despite being evolutionarily conserved, human enzymatic components of the ubiquitin and Nedd8 cascades share only moderate identity with their P. falciparum orthologs. Through functional proteomics, we have identified PfUCH37 and PfUCHL3 as the only deNeddylating enzymes in Plasmodium parasites and mapped their specificity to a single aspartic acid residue on the contact surface of the enzyme. Interestingly, Plasmodium seems to lack NedP1, the main Nedd8 hydrolase in higher eukaryotes. Since deNeddylation appears to be differently regulated in Plasmodium versus humans, we hypothesize that there will be further differences in how this post-translational modifier is attached and that, collectively, these differences can be targeted to develop a new class of antimalarial therapeutics.
Through chemical biology approaches and parasite transgenics, we aim to identify components of the P. falciparum Nedd8 cascade, determine their necessity to parasite survival and assess whether their activity can be selectively inhibited.

The more immediate and tangible impact of our work will be on the research community, however in the longer term our research outputs stand to influence drug development and, ultimately, patients.
Malaria has resulted in widespread mortality throughout antiquity and continues to be one of the deadliest diseases to date, particularly in sub-Saharan Africa. The economic repercussions of the disease are also immense, with malaria endemicity associated with poverty and reduced rates of economic growth. Environmental and technological changes across the globe mean that malaria threatens to intrude into new, previously unaffected areas. Vaccine development and drug design are plagued by the parasite's immune evasive abilities and its rapid development of drug resistance. Therefore, new approaches to parasite control are essential.
The proposed research aims to characterize the Nedd8 system in Plasmodium falciparum, to understand how it is controlled on the molecular level and to identify how it differs from the Nedd8 pathway of the mammalian host. Ubiquitin and ubiquitin-like modifiers such as Nedd8 are essential for maintaining cellular functions and homeostasis in all eukaryotic organisms. Although these pathways have been studied and successfully targeted in the context of viral and bacterial infections, they have been largely overlooked in parasites. Understanding how Nedd8 is modulated in P. falciparum will lead to the identification of enzymes essential to parasite survival. By further understanding how these enzymes' functions and specificities differ from host orthologues, the research proposed herein stands to highlight enzymatic components of the Nedd8 pathway that can potentially serve as novel target for therapeutic intervention.
Using a deNeddylating enzyme we have already extensively described, PfUCHL3, we aim to validate the development and utility of stapled peptides in inhibiting protein-protein interactions within the Nedd8 pathway and interfering with parasite growth. If successful, this work promises to not only identify new drug targets but also to validate an entirely new class of antimalarial drugs. In turn, these could lead to novel therapeutics and benefit those at risk of contracting malaria.
Since these post-translational modifiers are dynamically attached and detached by similar enzymatic cascades and are conserved across eukaryotes, the proposed research will have significance for systems beyond Plasmodium both from an evolutionary perspective as well as a biological one. Specifically, we stand to gain novel insights into the biological mechanisms underpinning the Nedd8 pathway of other Plasmodium species and, more widely, other apicomplexan parasites, such as Eimeria and Cryptosporidium that are of both medical and veterinary importance. The research outputs could lead to development of therapeutics for diseases well beyond P. falciparum malaria.

The individuals directly involved in conducting the proposed work will be carefully trained in molecular biology and protein chemistry techniques and supported to ensure their career development and seamless transition to their next position of choice. Services provided by the Cambridge University Personal and Professional Development program and the University Careers Service will be available to both the PDRA and Technician to support development of transferable professional skills (presentation, management and communication skills among others).