title: Two SecG molecules present in a single protein translocation machinery are functional even after crosslinking.
abstract: SecG, a membrane component of the protein translocation apparatus of Escherichia coli, undergoes membrane topology inversion, which is coupled to the membrane insertion and deinsertion cycle of SecA. Eighteen SecG derivatives possessing a single cysteine residue at various positions were constructed and expressed in a secG null mutant. All the SecG-Cys derivatives retained the SecG function, and stimulated protein translocation both in vivo and in vitro. Inverted membrane vesicles containing a SecG-Cys derivative were labeled with a membrane-permeable or -impermeable sulfhydryl reagent before or after solubilization with a detergent. The accessibility of these reagents to the cysteine residue of each derivative determined the topological arrangement of SecG in the membrane. Derivatives having the cysteine residue in the periplasmic region each existed as a homodimer crosslinked through disulfide bonds, indicating that two SecG molecules closely co-exist in a single translocation machinery. The crosslinking did not abolish the SecG function and the crosslinked SecG dimer underwent topology inversion upon protein translocation.
authors.affiliation: Institute of Molecular and Cellular Biosciences, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Nagamori
authors.forename: K
authors.initials: K
authors.lastname: Nishiyama
authors.forename: H
authors.initials: H
authors.lastname: Tokuda
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D002463:Cell Membrane Permeability; D003432:Cross-Linking Reagents / Q000737:chemistry; D003545:Cysteine / Q000235:genetics; D019281:Dimerization; D004220:Disulfides; D029968:Escherichia coli Proteins; D005033:Ethylmaleimide / Q000737:chemistry; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D000069816:SEC Translocation Channels; D013267:Stilbenes; D013451:Sulfonic Acids
chemical_list: D001426:Bacterial Proteins; D003432:Cross-Linking Reagents; D004220:Disulfides; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D011994:Recombinant Proteins; D000069816:SEC Translocation Channels; C088616:SecG protein, E coli; D013267:Stilbenes; D013451:Sulfonic Acids; C079532:4-acetamido-4'-maleimidylstilbene-2,2'-disulfonic acid; D003545:Cysteine; D005033:Ethylmaleimide