Role of Cysteine in MtrC-Flavin Interactions of Shewanella oneidensis

Norman, Michael (2017) Role of Cysteine in MtrC-Flavin Interactions of Shewanella oneidensis. Doctoral thesis, University of East Anglia.

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Many microorganisms can utilise a wide range of terminal electron acceptors, including solid minerals in the environment. Shewanella oneidensis is a well studied model for extracellular electron transfer with many of its biochemical pathways the subject of investigation. S. oneidensis utilises c-type cytochromes embedded in its outer membrane to link the oxidation of carbon sources to the reduction of extracellular terminal electron acceptors. Although the MtrCAB complex is known to be the primary pathway by which electrons, originating in the reduced menaquinol pool, can be conducted across the bacterial outer membrane and to extracellular terminal electron acceptors, the exact mechanism by which electrons are transferred from MtrC to electron acceptors remains unclear. MtrA and MtrC are decaheme cytochromes that form wire-like molecular pathway for electrons to be conducted across the bacterial membrane. MtrB is a porin that allows close contact between the periplasmic MtrA and the extracellular facing MtrC. Flavin molecules, secreted by S. oneidensis, have been shown to interact with MtrC either forming cofactor like associations with the protein (forming a flavocytochrome) or functioning as soluble electron shuttles transiently interacting with the protein. The evidence for each mechanism may be dependant on the redox state of a conserved disulphide bond in domain III of MtrC. Chemical reduction of this bond allows formation of a MtrC-flavin bound flavocytochrome form of MtrC. This form could react better with minerals to dictate the mechanism of electron transfer.
Mutations made to mtrC resulted in the substitution of the cysteine disulphide residues to alanine residues in the MtrC amino acid sequence. Growth studies showed S. oneidensis expressing these MtrC variants experienced extended lag phases when growing under aerobic conditions. This was shown to be caused by cytotoxic levels of hydrogen peroxide, generated from reduction of molecular oxygen, accumulating around the bacterial cells. Protein studies implicated stronger interactions between FMN and MtrC, in disulphide disrupted variants, as the cause of increased reactive oxygen species generation. We hypothesise the disulphide bond in domain III of MtrC functions as a redox switch imparting protein level control over reactivity of MtrC in oxygen variable environments with FMN bound MtrC being the [sic]

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Megan Ruddock
Date Deposited: 19 Dec 2018 12:49
Last Modified: 20 Dec 2021 01:38


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