title: The bacterial ATPase SecA functions as a monomer in protein translocation.
abstract: The ATPase SecA drives the post-translational translocation of proteins through the SecY channel in the bacterial inner membrane. SecA is a dimer that can dissociate into monomers under certain conditions. To address the functional importance of the monomeric state, we generated an Escherichia coli SecA mutant that is almost completely monomeric (>99%), consistent with predictions from the crystal structure of Bacillus subtilis SecA. In vitro, the monomeric derivative retained significant activity in various assays, and in vivo, it sustained 85% of the growth rate of wild type cells and reduced the accumulation of precursor proteins in the cytoplasm. Disulfide cross-linking in intact cells showed that mutant SecA is monomeric and that even its parental dimeric form is dissociated. Our results suggest that SecA functions as a monomer during protein translocation in vivo.
authors.affiliation: Howard Hughes Medical Institute and Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: Eran
authors.initials: E
authors.lastname: Or
authors.forename: Dana
authors.initials: D
authors.lastname: Boyd
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Gon
authors.forename: Jonathan
authors.initials: J
authors.lastname: Beckwith
authors.forename: Tom
authors.initials: T
authors.lastname: Rapoport
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D001412:Bacillus subtilis / Q000201:enzymology / Q000254:growth & development; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology; D007700:Kinetics; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D010957:Plasmids / Q000235:genetics; D017433:Protein Structure, Secondary; D021122:Protein Subunits / Q000737:chemistry; D011510:Proteolipids / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D017384:Sequence Deletion
chemical_list: D001426:Bacterial Proteins; D026901:Membrane Transport Proteins; D021122:Protein Subunits; D011510:Proteolipids; D011994:Recombinant Proteins; D000069816:SEC Translocation Channels; C020485:proteoliposomes; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins