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Proceedings of the National Academy of Sciences of the United States of America logoLink to Proceedings of the National Academy of Sciences of the United States of America
. 1988 Dec;85(23):8978–8982. doi: 10.1073/pnas.85.23.8978

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

J B Weiss 1, P H Ray 1, P J Bassford Jr 1
PMCID: PMC282643  PMID: 2848249

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.

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Selected References

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