Structure of the Membrane Protein FhaC: A Member of the Omp85-TpsB Transporter Superfamily

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Science  17 Aug 2007:
Vol. 317, Issue 5840, pp. 957-961
DOI: 10.1126/science.1143860

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In Gram-negative bacteria and eukaryotic organelles, β-barrel proteins of the outer membrane protein 85–two-partner secretion B (Omp85-TpsB) superfamily are essential components of protein transport machineries. The TpsB transporter FhaC mediates the secretion of Bordetella pertussis filamentous hemagglutinin (FHA). We report the 3.15 Å crystal structure of FhaC. The transporter comprises a 16-stranded β barrel that is occluded by an N-terminal α helix and an extracellular loop and a periplasmic module composed of two aligned polypeptide-transport–associated (POTRA) domains. Functional data reveal that FHA binds to the POTRA 1 domain via its N-terminal domain and likely translocates the adhesin-repeated motifs in an extended hairpin conformation, with folding occurring at the cell surface. General features of the mechanism obtained here are likely to apply throughout the superfamily.

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