A cysteine pair controls flavin reduction by extracellular cytochromes during anoxic/oxic environmental transitions

Norman, Michael P., Edwards, Marcus J., White, Gaye F., Burton, Joshua A. J., Butt, Julea N. ORCID: https://orcid.org/0000-0002-9624-5226, Richardson, David J. ORCID: https://orcid.org/0000-0002-6847-1832, Louro, Ricardo O., Paquete, Catarina M. and Clarke, Thomas A. ORCID: https://orcid.org/0000-0002-6234-1914 (2023) A cysteine pair controls flavin reduction by extracellular cytochromes during anoxic/oxic environmental transitions. mBIO, 14 (1). ISSN 2150-7511

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Abstract

Many bacteria of the genus Shewanella are facultative anaerobes able to reduce a broad range of soluble and insoluble substrates, including Fe(III) mineral oxides. Under anoxic conditions, the bacterium Shewanella oneidensis MR-1 uses a porin-cytochrome complex (Mtr) to mediate extracellular electron transfer (EET) across the outer membrane to extracellular substrates. However, it is unclear how EET prevents generating harmful reactive oxygen species (ROS) when exposed to oxic environments. The Mtr complex is expressed under anoxic and oxygen-limited conditions and contains an extracellular MtrC subunit. This has a conserved CX8C motif that inhibits aerobic growth when removed. This inhibition is caused by an increase in ROS that kills the majority of S. oneidensis cells in culture. To better understand this effect, soluble MtrC isoforms with modified CX8C were isolated. These isoforms produced increased concentrations of H2O2 in the presence of flavin mononucleotide (FMN) and greatly increased the affinity between MtrC and FMN. X-ray crystallography revealed that the molecular structure of MtrC isoforms was largely unchanged, while small-angle X-ray scattering suggested that a change in flexibility was responsible for controlling FMN binding. Together, these results reveal that FMN reduction in S. oneidensis MR-1 is controlled by the redox-active disulfide on the cytochrome surface. In the presence of oxygen, the disulfide forms, lowering the affinity for FMN and decreasing the rate of peroxide formation. This cysteine pair consequently allows the cell to respond to changes in oxygen level and survive in a rapidly transitioning environment.

Item Type:	Article
Faculty \ School:	Faculty of Science > School of Biological Sciences Faculty of Science > School of Chemistry (former - to 2024)
Depositing User:	LivePure Connector
Date Deposited:	26 Sep 2024 15:30
Last Modified:	01 Nov 2024 12:30
URI:	https://ueaeprints.uea.ac.uk/id/eprint/96818
DOI:	10.1128/mbio.02589-22

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