Elucidation of principles in the assembly of outer membrane proteins

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Respiratory electron transfer over the outer membrane is a key feature within the bacterial electron transport chains to membrane impermeable electron acceptors like ferric iron or manganese oxides. Breathing metals like Fe(III) or Mn(IV) has a profound impact on the global carbon cycle. In the model organism Shewanella oneidensis an outer membrane complex consisting of a periplasmic cytochrome (MtrA), a β-barrel protein (MtrB) and a surface localized cytochrome (MtrC) is essential for the catalysis of dissimilatory ferric iron and manganese reduction. It was shown that MtrA has to be present in order to allow for the production of MtrB. In this research project we aim at elucidating cellular functions that are important for the formation of the MtrABC complex as well as the structural prerequisites necessary to conduct membrane spanning electron transfer. Our preliminary work suggests a dual function of MtrA, being an electron transferring protein and also a scaffold or chaperone necessary for the transport of nascent MtrB through the periplasm. Using cross-linking and pulse chase experiments we will detect how MtrA and other periplasmic chaperons influence MtrB transport and how the interaction with MtrA is established. We will investigate how the surface localized cytochrome is recruited by this complex using random-mutagenesis and cross-linking. In addition, we will attempt to crystallize the MtrABC complex and determine its molcular structure.