The structure and function of extracellular redox enzymes

Nash, Benjamin William (2025) The structure and function of extracellular redox enzymes. Doctoral thesis, University of East Anglia.

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Abstract

Increasing numbers of microorganisms are now understood to conserve energy via the coupling of intracellular oxidation of organic compounds with the reduction of diverse extracellular substrates. Such extracellular electron transfer (EET) processes represent exciting opportunities for biotechnological innovations including bioremediation, biosensing, biomining and microbial electrosynthesis, but poor understanding of the underlying molecular mechanisms limits their application. In this work, the structure and properties of two novel protein systems that participate in EET are described.

The outer membrane c-type cytochrome PgcA from Geobacter sulfurreducens is important for EET in that organism and here is shown to contain two unique functionalities. It’s c-terminus is revealed to be a redox shuttle which contains three heme cofactors separated into discrete domains but tethered together by flexible repeat motifs and likely able to transfer electrons fifteen nanometres. It’s N-terminus is revealed to be a conserved domain that exhibits novel autoproteolytic activity for which comprehensive characterisation is described.

The dmsEFABGH gene cluster has been shown to be essential for the reduction of dimethyl sulfoxide by Shewanella oneidensis but the structural basis for this has not been determined. In this work the structure of the DmsEFAB tetramer, solved by cryogenic electron microscopy, is described. DmsEFAB forms a ~120 Å cofactor chain, insulated from the membrane by the DmsF porin, including ten c-type hemes, four Fe4S4 clusters and a molybdopterin active site that ultimately catalyses the two electron reduction of dimethyl sulfoxide.

These results provide unique and insightful contributions not only to the field of extracellular electron transfer, but also to redox protein structural biology in general.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Biological Sciences
Depositing User:	Chris White
Date Deposited:	10 Nov 2025 10:25
Last Modified:	10 Nov 2025 10:25
URI:	https://ueaeprints.uea.ac.uk/id/eprint/100934
DOI:

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