Formation and dynamics of interacting electron transport chains

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It is the aim of this proposal to analyze the basis of periplasmic and outer membrane spanning electron transfer in the y-proteobacterium Shewanella oneidensis. S. oneidensis is so far the microorganism that shows the highest flexibility in terms of anaerobic electron acceptors, that can be used for respiration. Interestingly, almost all electron acceptors are reduced either in the periplasm or at the cell surface and the electron transfer to these acceptors is dependent on the activity of c-type cytochromes. A dynamic electron transfer network was evolved by the organism, in which the electron transfer chains are interconnected and produced simultaneously. We would like to understand the detailed mechanism of electron transport within this network via mutant analysis and concomitant measurement of electron transport rates in cell suspension and fast kinetic measurement experiments. Moreover, we would like to elucidate principles in the formation of an outer membrane protein complex that enables membrane spanning electron transport. The complex consists of an integral beta-barrel protein (MtrB) that connects a periplasmic (MtrA) and cell surface localized c-type cytochromes. Interestingly, we could show that MtrB is degraded by the periplasmic protease DegP in the absence of MtrA and it was suggested that MtrA is a specialized periplasmic chaperone that is necessary for transport of the unfolded beta-barrel protein through the periplasm. Furthermore, we could provide evidence that the fold of MtrB in the membrane varies in the presence and absence of MtrA, respectively. Via in vivo and in vitro experiments we aim to understand the detailed function of MtrA in formation and folding of MtrB.