title: Bacterial protein translocation requires only one copy of the SecY complex in vivo.
abstract: The transport of proteins across the plasma membrane in bacteria requires a channel formed from the SecY complex, which cooperates with either a translating ribosome in cotranslational translocation or the SecA ATPase in post-translational translocation. Whether translocation requires oligomers of the SecY complex is an important but controversial issue: it determines channel size, how the permeation of small molecules is prevented, and how the channel interacts with the ribosome and SecA. Here, we probe in vivo the oligomeric state of SecY by cross-linking, using defined co- and post-translational translocation intermediates in intact Escherichia coli cells. We show that nontranslocating SecY associated transiently through different interaction surfaces with other SecY molecules inside the membrane. These interactions were significantly reduced when a translocating polypeptide inserted into the SecY channel co- or post-translationally. Mutations that abolish the interaction between SecY molecules still supported viability of E. coli. These results show that a single SecY molecule is sufficient for protein translocation.
authors.affiliation: Howard Hughes Medical Institute and Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Eunyong
authors.initials: E
authors.lastname: Park
authors.forename: Tom A
authors.initials: TA
authors.lastname: Rapoport
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D055503:Protein Multimerization; D011499:Protein Processing, Post-Translational; D021381:Protein Transport; D012270:Ribosomes / Q000235:genetics / Q000378:metabolism; D000069816:SEC Translocation Channels; D000081416:SecA Proteins
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; C057841:SecY protein, E coli; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins