title: The bacterial protein-translocation complex: SecYEG dimers associate with one or two SecA molecules.
abstract: In bacteria, the Sec-protein transport complex facilitates the passage of most secretory and membrane proteins across and into the plasma membrane. The core complex SecYEG forms the protein channel and engages either ribosomes or the ATPase SecA, which drive translocation of unfolded polypeptide chains through the complex and into the periplasmic space. Escherichia coli SecYEG forms dimers in membranes, but in detergent solution the population of these dimers is low. However, we find that stable dimers can be assembled by the addition of a monoclonal antibody. Normally, a stable SecYEG-SecA complex can only form on isolated membranes or on reconstituted proteo-liposomes. The antibody-stabilised SecYEG dimer binds one SecA molecule in detergent solution. In the presence of AMPPNP, a non-hydrolysable analogue of ATP, a complex forms containing one antibody and two each of SecYEG and SecA. SecYEG monomers or tetramers do not associate to a significant degree with SecA. The observed variability in the stoichiometry of SecYEG and SecA association and its nucleotide modulation may be important and necessary for the protein translocation reaction.
authors.affiliation: Institute für Biophysik, JWG-Universität, 60590 Frankfurt am Main, Germany.
authors.forename: Christos
authors.initials: C
authors.lastname: Tziatzios
authors.forename: Dieter
authors.initials: D
authors.lastname: Schubert
authors.forename: Mirko
authors.initials: M
authors.lastname: Lotz
authors.forename: Derya
authors.initials: D
authors.lastname: Gundogan
authors.forename: Heidi
authors.initials: H
authors.lastname: Betz
authors.forename: Hermann
authors.initials: H
authors.lastname: Schägger
authors.forename: Winfried
authors.initials: W
authors.lastname: Haase
authors.forename: Franck
authors.initials: F
authors.lastname: Duong
authors.forename: Ian
authors.initials: I
authors.lastname: Collinson
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000906:Antibodies / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D002850:Chromatography, Gel; D019281:Dimerization; D004591:Electrophoresis, Polyacrylamide Gel; D026901:Membrane Transport Proteins / Q000378:metabolism*; D021381:Protein Transport; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D012996:Solutions; D014461:Ultracentrifugation
chemical_list: D000906:Antibodies; D001426:Bacterial Proteins; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; D012996:Solutions; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins