The electronic mechanism for enzymatic cellulose degradation

Sustainable fuel production is a major technological challenge which is of both environmental and politico-economical importance. An appealing prospect is the conversion of cellulose biomass into ethanol, a hydrocarbon which is compatible with existing transport technology. Using biocatalysis to degrade this otherwise highly recalcitrant carbohydrate material is currently the only energetically feasible way in which waste plant materials such as straw can be harvested and utilized as a feedstock for bioethanol production. Lytic polysaccharide monooxygenase enzymes (LPMOs) are important contributors to this bio-catalysed process because they carry out oxidative bond cleavage reactions of recalcitrant polysaccharides, and this aids in the breakdown of the substrate by generating chain ends that can be readily degraded by further classes of enzymes1. As recognised by the recent Global Energy Award at the Institution of Chemical Engineers’ (IChemE), Paul Walton and Gideon Davies have already carried out pioneering work in this area, identifying and characterizing the novel copper containing active sites of LPMOs2-8. The aim of this project is to probe how the copper centre in the enzyme must be structured in order to degrade cellulose. In particular, the mechanism via which concerted proton-coupled-electron-transfer is controlled so that an O2 molecule can be activated to break apart one of the most stable structures in nature will be investigated using a complementary toolkit of molecular biology, spectroscopy, crystallography and electrochemistry.
UV-vis and EPR spectro-electrochemical experiments will be used to determine the reduction potentials of the substrate activation reactions, and to probe the structural rearrangements at the active site which support this reactivity. The particularly powerful approach of protein film Fourier transformed alternating current voltammetry (PF-FTacV), which is being pioneered in the Parkin lab9-12, will examine the kinetics of electron transfer in the presence of a soluble substrate (Figure). The FTacV technique is uniquely suited to this study since classical electrochemical methods would be unable to distinguish between electrode-O2 reduction and rapid, reversible enzyme electron transfer. Comparison between native and variant enzymes will prove which amino acid centres play a vital role in tuning the redox chemistry under interrogation. This insight into the dynamic changes within the enzyme will be complemented with crystallographic studies designed to use appropriate redox reagents to capture snapshots of different states. Overall, this study will therefore aim to derive a blueprint for the design of a copper site capable of activating cellulose using the sustainable input of oxygen and electrons.

All research students follow our innovative Doctoral Training in Chemistry (iDTC): cohort-based training to support the development of scientific, transferable and employability skills

Walton and Davies have a well-established track record in world leading expertise in the structural characterisation and mechanistic understanding of LPMOs and the successful applicant will be joining a thriving research team. This collaboration is supported by joint group meetings which the student will attend, and this will provide an invaluable introduction to the enzyme system being studied. Broader training in presentation skills and an awareness of other outstanding bio-inorganic and enzymatic research will be provided by the student attending Inorganic and YSBL group meetings and seminars throughout their PhD. External collaboration with Dr Glyn Hemsworth (University of Leeds), and Prof Alan Bond (Monash University, Melbourne) will also provide training in communication and project management. It is expected that the successful applicant will have a desire to attend international conferences and will actively pursue opportunities to present their work.
The interdisciplinary mixture of molecular biology, spectroscopy, structural biology and electrochemical measurements make this a unique project. It will be well supported by the existing expertise within the groups of the three supervisors. Molecular biology training, protein purification and crystallography expertise will be passed on from the Davies group who work in the world leading York Structural Biology Lab (YSBL). Expertise in protein spectroscopy, data analysis and DFT calculations will be provided by the Walton group. Electrochemical training and support will be provided by the Parkin group.

Shortlisting will take place as soon as possible after the closing date and successful applicants will be notified promptly. Shortlisted applicants will be invited for an interview to take place at the University of York on either the 13 or 15 February 2018. Candidates will be asked to give a short presentation prior to their interview by an academic panel.

The Department of Chemistry holds an Athena SWAN Gold Award and is committed to supporting equality and diversity for all staff and students. This PhD project is available to study full-time or part-time (50%).