Characterisation and Engineering of Enzymes for the Conversion of Lignin Biomass

Abstract

The second most abundant biopolymer on the planet, lignin is a potential feed- stock of hydrocarbons to produce valuable chemicals. These chemicals are currently produced from fossil fuels, but using lignin for their production provides a more en- vironmentally friendly alternative. Lignin is predominately produced as a byproduct from paper milling, farming and biofuel production, due to its’ recalcitrant nature it is often burnt as a fuel to power the refineries that produce it. Not only does this release harmful gasses into the atmosphere, it is also a waste of potentially valuable compounds. This thesis characterises a selection of biological systems that have the potential to alleviate current bottlenecks in lignin bioprocessing and up-cycling. By determining the structures of several protein systems and attempting engineering upon them, we have identified routes for improved bioconversion towards valuable products. O -demethylation is one key step in lignin bioconversion and in this the- sis we characterise several systems that are able to perform this reaction. GcoA from Amycolatopsis has been extensively characterised in this thesis with several variants produced and analysed for their effectiveness against a range of substrates produced from lignin depolymerisation. Two more P450s are also in focus in this thesis, PbdA and AgcA, both O -demethylate key compounds from lignin. As well as the P450s, other methods for enzymatic O -demethylation are investigated, this includes characterisation of a novel Rieske non-heme iron monooxygenase, GdmA. Up-stream of O -demethylation, biaryl depolymerisation is also investigated via the LdpA system. The data presented here aims to understand the function of each of these systems with the goal of producing a base platform for improving biological lignin valorisation.

Date of Award	22 May 2023
Original language	English
Awarding Institution	University of Portsmouth
Supervisor	Andrew Pickford (Supervisor), John Edward McGeehan (Supervisor) & Gregg T. Beckham (Supervisor)