title: A mutation in secY that causes enhanced SecA insertion and impaired late functions in protein translocation.
abstract: A cold-sensitive secY mutant (secY125) with an amino acid substitution in the first periplasmic domain causes in vivo retardation of protein export. Inverted membrane vesicles prepared from this mutant were as active as the wild-type membrane vesicles in translocation of a minute amount of radioactive preprotein. The mutant membrane also allowed enhanced insertion of SecA, and this SecA insertion was dependent on the SecD and SecF functions. These and other observations suggested that the early events in translocation, such as SecA-dependent insertion of the signal sequence region, is actually enhanced by the SecY125 alteration. In contrast, since the mutant membrane vesicles had decreased capacity to translocate chemical quantity of pro-OmpA and since they were readily inactivated by pretreatment of the vesicles under the conditions in which a pro-OmpA translocation intermediate once accumulated, the late translocation functions appear to be impaired. We conclude that this periplasmic secY mutation causes unbalanced early and late functions in translocation, compromising the translocase's ability to catalyze multiple rounds of reactions.
authors.affiliation: Institute for Virus Research, Kyoto University, Japan.
authors.forename: G
authors.initials: G
authors.lastname: Matsumoto
authors.forename: T
authors.initials: T
authors.lastname: Homma
authors.forename: H
authors.initials: H
authors.lastname: Mori
authors.forename: K
authors.initials: K
authors.lastname: Ito
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D019943:Amino Acid Substitution; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D009154:Mutation; D010641:Phenotype; D011498:Protein Precursors / Q000378:metabolism; D000069816:SEC Translocation Channels; D000081416:SecA Proteins
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D011498:Protein Precursors; D000069816:SEC Translocation Channels; C057841:SecY protein, E coli; C078167:OMPA outer membrane proteins; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins