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Title: Characterisation of OmcA From Shewanella oneidensis MR-1 : biophysical and mineral reduction properties
Author: Baiden, Nanakow A.
ISNI:       0000 0004 5346 7560
Awarding Body: University of East Anglia
Current Institution: University of East Anglia
Date of Award: 2014
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Several Shewanella spp. are versatile in the respiratory substrates they use. A novel set of respiratory substrates implicated are insoluble Fe(III) and Mn(III,IV) oxides. OmcA from Shewanella oneidensis MR-1 plays a role in the terminal electron transfer during respiratory mineral reduction, but has minimal or contrasting properties in the literature. A suite of biophysical techniques confirmed the bis-histidine axial ligation of all OmcA’s haem content in the crystal structure and in solution. The paramagnetic resonance feature designated “LS3” was identified to be unique to OmcA. However this resonance signal is modelled to be produced spin-coupling and not unique haem ligation. OmcA’s electroactive coverage is comparable to UndA and the other major outer membrane multihaem cytochrome (OMMC) clades MtrC and MtrF (i.e. +0.08 V to -0.47 V vs S.H.E.). The crystal structure of OmcA shows domain fold, domain organisation and haem orientation conservation with MtrF and UndA. Comprehensive solution?structure studies of OmcA provided contrasting experimental data on the oligomeric state of OmcA, such that it is unresolved whether OmcA forms an ion-sensitive dimer. The crystal structure shows a predicted mineral interaction peptide (i.e. T725P726S727) is solvent exposed and would putatively bind substrate within electron tunneling distance of a terminal haem. Site-directed mutagenesis indicates Thr725 is significant to maintenance of the molecular environment of haem 10. Although T725G mutation produces a ≈80% decrease in whole cell reduction of synthesised hematite over 120 hours; secondary effects of change in haem reduction potentials or widespread conformational effects were ruled out. OmcA has thus been shown to share a common OMMC-fold and exist in S. oneidensis MR-1 outer membranes as a functioning mineral reductase cytochrome with unique paramagnetic resonance properties in this set of studies.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available