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Title: Structural and spectroscopic studies on the porin-cytochrome complex from Shewanella oneidensis MR-1
Author: Lawes, Matthew
ISNI:       0000 0004 5371 3362
Awarding Body: University of East Anglia
Current Institution: University of East Anglia
Date of Award: 2015
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The outer membrane, hetero-trimeric multi-heme cytochrome complex MtrCAB, enables the process of dissimilatory metal reduction (DMR) in Shewanella oneidensis. The properties of the decaheme protein MtrA as well as a truncated version of this protein were investigated using analytical ultracentrifugation (AUC), small angle X-ray scattering (SAXS) and spectropotentiometric techniques. MtrA and a truncated N-terminal MtrA construct containing the five N-terminal hemes (MtrA N) were both observed to be prolate and highly extended along one axis. Through aligning MtrA N with MtrA, the N terminus of the MtrA structure was identified. Redox titration experiments were performed on MtrA as well as N and C terminal truncations. From these titrations three distinct groups of hemes were identified; a high, a middle potential and a low potential group of hemes. The five N terminal hemes contained the high and middle potential groups of hemes; whereas the five C terminal hemes contained the middle and low potential groups of hemes. The MtrCAB complex was inserted into liposomes containing either methyl viologen, small tetra heme cytochrome (STC) or cytochrome c. Using these proteoliposomes the rate of electron transfer across MtrCAB was investigated. MtrCAB was seen to enable the reduction and oxidation of methyl viologen and STC, but only the reduction of cytochrome c. STC was reduced during the experiments, implying an electron storage role in the periplasm during respiration. Finally, the structure of MtrCAB was investigated through small angle neutron scattering (SANS). Structures of MtrCAB were highly elongated with a globular head region and a tail region. Through density matching buffers, scattering produced from detergents was removed and a prediction of the relative location of MtrB within the model made. The model produced was found to be long enough to span the periplasm enabling direct contact of MtrA with proteins on the inner membrane.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available