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Biochemistry Underpinning the Biogeochemical Fe, S and N Cycles.


Reduction of oxygen is fundamental to the life of higher animals and plants. However, many species of bacteria are able to survive in the absence of oxygen. Furthermore, many of these species display respiratory versatility because they are able to utilise a diverse range of electron acceptors and electron donors in their energy conserving metabolisms that result in ATP synthesis. Our research aims to resolve structures and properties of proteins catalysing these energy conserving reactions. This knowledge helps elucidate the cellular roles of these enzymes and assist in the annotation of sequenced genomes.     

We have particular interest in multiheme cytochromes that support dissimilatory metal oxide reduction in the model electrogenic bacterium Shewanella oneidensis. We are studying how these proteins move electrons from the bacterial inner membrane, across the periplasm and outer membrane to reach the Fe(III) and Mn(IV) oxide nanoparticles and terminate the anaerobic respiratory chain. This research provides insight into processes underpinning biogeochemical cycling of transition metals and also technologies that use the same proteins to exchange electrons between electrodes and cellular enzymes, microbial electrosynthesis and microbial fuel cells. 

Microbes exploit redox transformations of inorganic nitrogen species to support aerobic and anaerobic respiration, to allow nitrogen assimilation into amino acids and nucleotides and to defend against cytotoxins such as nitric oxide. Protein film voltammetry has resolved the windows of electrochemical potential over which enzymes reducing nitrate, nitrite, nitric oxide and/or hydroxylamine are active. Present research aims to understand the origin of these properties at the molecular level and their contribution to cellular function by site specific protein engineering, spectroscopy and cellular studies. These same approaches are applied to understand enzymes that catalyse thiosulfate oxidation in bacteria including Campylobacter jejuni.

Selected Publications

1. Reaction of Thiosulfate Dehydrogenase with a Substrate Mimic Induces Dissociation of the Cysteine Heme Ligand Giving Insights into the Mechanism of Oxidative Catalysis

J. Am. Chem. Soc. 2022

2. Nanosecond Heme-to-Heme Electron Transfer Rates in a Multiheme Cytochrome Nanowire Reported by a Spectrally Unique His/Met-Ligated Heme.

Proc. Natl. Acad. Sci. USA 2021


3. The Crystal Structure of a Biological Insulated Transmembrane Molecular Wire.

Cell 2020

4. His/Met Heme Ligation in the PioA Outer Membrane Cytochrome Enabling Light-Driven Extracellular Electron Transfer by Rhodopseudomonas palustris TIE-1

Nanotechnology 2020

5. Structural Modeling of an Outer Membrane Electron Conduit from a Metal-Reducing Bacterium Suggests Electron Transfer via Periplasmic Redox Partners. 

J. Biol. Chem. 2018

6. Electron Accepting Units of the Diheme Cytochrome c TsdA, a Bifunctional Thiosulfate Dehydrogenase/Tetrathionate Reductase

J. Biol. Chem. 2016

7. Catalytic Protein Film Electrochemistry Provides a Direct Measure of the Tetrathionate/Thiosulfate Reduction Potential.

J. Am. Chem. Soc. 2015

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