title: Purified secB protein of Escherichia coli retards folding and promotes membrane translocation of the maltose-binding protein in vitro.
abstract: The efficient export of a subset of Escherichia coli envelope proteins is dependent upon the product of the secB gene. Previous studies indicated that SecB promotes the export of the periplasmic maltose-binding protein (MBP) by preventing premature folding of the precursor MBP in the cytoplasm into an export-incompetent form. In this study, SecB has been purified to homogeneity and shown to be a soluble, cytoplasmic, multimeric protein composed of identical 17-kDa subunits. SecB was required for efficient in vitro translocation of MBP into inverted membrane vesicles. The addition of purified SecB to an in vitro system prepared from SecB- cells significantly enhanced MBP translocation. The purified protein also quantitatively retarded folding of precursor MBP into a stable, protease-resistant conformation in the absence of membranes. Finally, the inclusion of excess purified SecB in a SecB+ in vitro system significantly prolonged the time in which precursor MBP remained competent for posttranslational import into membrane vesicles.
authors.affiliation: Department of Microbiology and Immunology, School of Medicine, University of North Carolina, Chapel Hill 27514.
authors.forename: J B
authors.initials: JB
authors.lastname: Weiss
authors.forename: P H
authors.initials: PH
authors.lastname: Ray
authors.forename: P J
authors.initials: PJ
authors.lastname: Bassford
mesh_terms: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins / Q000302:isolation & purification / Q000502:physiology*; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D007700:Kinetics; D008320:Maltose / Q000378:metabolism; D058619:Maltose-Binding Proteins; D009004:Monosaccharide Transport Proteins; D033902:Periplasmic Binding Proteins; D010957:Plasmids; D011487:Protein Conformation; D011499:Protein Processing, Post-Translational
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; C461619:MalE protein, E coli; D058619:Maltose-Binding Proteins; D009004:Monosaccharide Transport Proteins; D033902:Periplasmic Binding Proteins; C461599:maltose transport system, E coli; D008320:Maltose