Structural and Functional Analysis of Bacterial Formate Channels

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Formate constitutes a major metabolite in bacteria and plays a key role as electron donor in various respiratory pathways. The transport of formate across biological membranes is mediated by the formate channel FocA, a member of the FNT family of membrane transporters. Our three-dimensional structure of the protein from Salmonella typhimurium at low pH showed a concerted and cooperative set of conformational changes of the N-terminus that form the basis for a functional switch from the export of the formate anion by facilitated diffusion at high external pH to secondary active formate/H+ import at a pH below 6.8. This corresponds to a metabolic shift from cytoplasmic formate production by pyruvate:formate lyase (PFL) and periplasmic, respiratory formate oxidation to cytoplasmic formate disproportionation at the formate:hydrogen lyase complex (FHL). We propose to continue and extend our work on FocA to include an electrophysiological characterization of the formate channel and its dependency on the proton motive force in lipid bilayers. We will further analyse the mechanism of pH sensing in FocA by site-directed mutagenesis and investigate the subcellular localization of the protein and its interaction with physiological partners such as PFL or the FHL complex.