Purified secB protein of Escherichia coli retards folding and promotes membrane translocation of the maltose-binding protein in vitro.

AUTOR(ES)

Weiss, J B

RESUMO

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.

Documentos Relacionados

• The folding properties of the Escherichia coli maltose-binding protein influence its interaction with SecB in vitro.
• prlA suppression of defective export of maltose-binding protein in secB mutants of Escherichia coli.
• Expression of Escherichia coli SecB in Bacillus subtilis facilitates secretion of the SecB-dependent maltose-binding protein of E. coli.
• Mutations that improve export of maltose-binding protein in SecB- cells of Escherichia coli.
• The mature portion of Escherichia coli maltose-binding protein (MBP) determines the dependence of MBP on SecB for export.