title: Biochemical characterization of a mutationally altered protein translocase: proton motive force stimulation of the initiation phase of translocation.
abstract: Protein translocation across the Escherichia coli plasma membrane is facilitated by concerted actions of the SecYEG integral membrane complex and the SecA ATPase. A secY mutation (secY39) affects Arg357, an evolutionarily conserved and functionally important residue, and impairs the translocation function in vivo and in vitro. In this study, we used the "superactive" mutant forms of SecA, which suppress the SecY39 deficiency, to characterize the mutationally altered SecY39EG translocase. It was found that SecY39-mediated preprotein translocation exhibited absolute dependence on the proton motive force. The proton motive force-dependent step proved to lie before signal peptide cleavage. We suggest that the proton motive force assists in the initiation phase of protein translocation.
authors.affiliation: Institute for Virus Research, Kyoto University, Sakyo-ku, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Mori
authors.forename: Koreaki
authors.initials: K
authors.lastname: Ito
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics* / Q000378:metabolism*; D001426:Bacterial Proteins; D001693:Biological Transport, Active; D002462:Cell Membrane / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D009154:Mutation; D018892:Proton-Motive Force / Q000502:physiology*; D000069816:SEC Translocation Channels; D000081416:SecA Proteins
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; C065493:SecE protein, E coli; C088616:SecG protein, E coli; C057841:SecY protein, E coli; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins