title: Two electrical potential-dependent steps are required for transport by the Escherichia coli Tat machinery.
abstract: The twin-arginine translocation (Tat) pathway in Escherichia coli transports fully folded and assembled proteins across the energy-transducing periplasmic membrane. In chloroplasts, Tat transport requires energy input only from the proton motive force. To elucidate the mechanism and energetics of bacterial Tat protein transport, we developed an efficient in vitro transport assay using TatABC-enriched inverted membrane vesicles and the physiological precursor pre-SufI. We report transport efficiencies of 60-80% for nanomolar pre-SufI concentrations. Dissipation of the pH gradient does not reduce pre-SufI transport efficiency. Instead, pre-SufI transport requires at least two electrical potential (Deltapsi)-dependent steps that differ in both the duration and minimum magnitude of the required Deltapsi. The data are consistent with a model in which a substantial Deltapsi of short duration is required for an early transport step, and in which a small Deltapsi of long duration is necessary to drive a later transport step.
authors.affiliation: Department of Molecular and Cellular Medicine, College of Medicine, Texas A&M Health Science Center, College Station, TX 77843, USA.
authors.forename: Umesh K
authors.initials: UK
authors.lastname: Bageshwar
authors.forename: Siegfried M
authors.initials: SM
authors.lastname: Musser
mesh_terms: D000200:Action Potentials; D000595:Amino Acid Sequence; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism / Q000502:physiology*; D049452:Green Fluorescent Proteins / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D026901:Membrane Transport Proteins / Q000502:physiology*; D008969:Molecular Sequence Data; D021381:Protein Transport / Q000502:physiology; D018892:Proton-Motive Force
chemical_list: D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; C473632:SufI protein, E coli; C408585:twin-arginine translocase complex, E coli; D049452:Green Fluorescent Proteins