The late-stage site-specific functionalisation of peptides and proteins via polyoxometalate-mediated H-atom abstraction

Lead Research Organisation: University of Nottingham
Department Name: Sch of Chemistry


Problems and importance:

The last two decades have witnessed an increase in the regulatory approval of protein-based therapeutic and diagnostic agents. The unparalleled affinity and selectivity with which proteins bind to their target, ensures that such 'biologics' can be employed efficaciously for medical use. Additionally, the application of native proteins to the treatment of disease enables the development of therapeutics which may exhibit fewer side effects and thus reduced toxicity. Within oncology especially, protein-based biologics have stepped to the forefront of cancer diagnosis and treatment. However, despite advances within this field, safer and more efficacious approaches are actively sought.

Functionalising clinically relevant protein sequences with imaging agents or cytotoxic compounds further enhances their therapeutic application and has led to significant interest in protein modification techniques. The development of efficient, chemoselective and generally applicable bioconjugation chemistry will enable the production of more advanced biologic agents which may ultimately have a substantial impact in the clinic.

Relevance to sustainability:

Despite the development of several site-specific protein modification techniques, the most utilised reactions to-date target cysteine residues, which are integral to protein structure and function, or lysine, the abundance of which causes the production of heterogeneously modified isoforms. Alternative techniques that do not make use of native residues may employ non-standard amino acids, a strategy that involves directed evolution of the relevant biologically machinery. Semi-synthetic techniques involving chemically synthesised peptides have also been widely utilised, however, such methods employ toxic reagents and use large quantities of solvent which limits the sustainability of this approach.

The development of an efficient and mild site-selective bioconjugation reaction that could be broadly applied to any biologically expressed protein sequence, targeting native residues that are not integral to protein structure and function, would be a highly impactful advance.

Proposed solution and methodology

We propose the development of a strategy for the late-stage site-specific functionalisation of peptides and proteins utilising radical chemistry. Polyoxometalate (POM) clusters have previously been reported to enable H-atom abstraction from unactivated aliphatic tertiary centres, facilitating the fluorination of selected amino acids. We wish to further explore this POM-mediated strategy, expanding the scope of the approach to enable the broader functionalisation of peptides and proteins in a site-selective manner.

By combining this H-atom abstraction method with a small library of modified radical traps, we aim to install desired functionality (e.g. radioactive nuclides or cytotoxic compounds) at the site of radical formation on several amino acid residues. Starting with a simple decatungstate cluster, we will explore and utilise the tunable properties of the POM to increase control and site-selectivity. The reaction will be mild, proceeding rapidly in an aqueous solution, requiring only catalytic addition of the POM. Our strategy will be tailored to enable the introduction of a toolbox of functionality which could be applied to any chosen protein. Ultimately, we will seek to employ our technique to functionalise proteins that target receptors expressed by highly invasive triple-negative breast cancer.

Planned Impact

This CDT will have a positive impact in the following areas:

PEOPLE. The primary focus is people and training. Industry needs new approaches to reach their sustainability targets and this is driving an increasing demand for highly qualified PhD graduates to lead innovation and manage change in the area of chemicals production. CDT based cohort training will provide industry ready scientists with the required technical competencies and drive to ensure that the sector retains its lead position in both innovation and productivity. In partnership with leading chemical producers and users, we will provide world class training to satisfy the changing needs of tomorrow's chemistry-using sector. Through integrated links to our Business School we will maximise impact by delivering dynamic PhD graduates who are business aware.

ECONOMY. Sustainability is the major issue facing the global chemical industry. Not only is there concern for our environment, there is also is a strong economic driver. Shareholders place emphasis on the Dow Jones Sustainability Index that tracks the performances of the sector and engenders competition. As a result, major companies have set ambitious targets to lower their carbon footprints, or even become carbon neutral. GSK CEO Sir Andrew Witty states that "we have a goal to reduce our emissions and energy use by 45% compared with 2006 levels on a per unit sales basis... " Our CDT will help companies meet these challenges by producing the new chemistries, processes and people that are the key to making the step changes needed.

SOCIETY. The diverse range of products manufactured by the chemical-using industries is vital to maintain a high quality of life in the UK. Our CDT will have a direct impact by ensuring a supply of people and new knowledge to secure sustainability for the benefit of all. The role of chemistry is often hidden from the public view and our CDT will provide a platform to show chemical sciences in a positive light, and to demonstrate the importance of engineering and applications across biosciences and food science.
The "green and sustainable" agenda is now firmly fixed in the public consciousness, our CDT will be an exemplar of how scientists and engineers are providing solutions to very challenging scientific and technical problems, in an environmentally benign manner, for the benefit of society. We will seek sustainable solutions to a wide range of problems, whilst working in sustainable and energy efficient facilities. This environment will engender a sustainability ethos unique to the UK. The CNL will not only serve as a base for the CDT but also as a hub for science communication.
Public engagement is a crucial component of CDT activities; we will invite input and discussion from the public via lectures, showcases and exhibition days. The CNL will form a hub for University open days and will serve as a soft interface to give school children and young adults the opportunity to view science from the inside. Through Dr Sam Tang, public awareness scientist, we have significant expertise in delivering outreach across the social spectrum, and she will lead our activities and ensure that the CDT cohorts engage to realise the impact of science on society. Martyn Poliakoff, in his role as Royal Society Foreign Secretary, will ensure that our CDT dovetails with UK science policy.

KNOWLEDGE. In addition to increasing the supply of highly trained people, the results of the PhD research performed in our CDT will have a major impact on knowledge. Our student cohorts will tackle "the big problems" in sustainable chemistry, and via our industrial partners we will ensure this knowledge is applied in industry, and publicised through high level academic outputs. Our knowledge-based activities will drive innovation and economic activity, realising impact through creation of new jobs and securing the future.


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