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The mature portion of Escherichia coli maltose-binding protein (MBP) determines the dependence of MBP on SecB for

P M Gannon1, P Li, C A Kumamoto

  • 1Department of Physiology, Tufts University School of Medicine, Boston, Massachusetts 02111.

Journal of Bacteriology
|February 1, 1989
PubMed

Insights

The secB gene product is crucial for exporting certain proteins in E. coli. Just the initial part of maltose-binding protein (MBP) can make other proteins require SecB for export.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Protein Transport

Background:

  • The secB gene in Escherichia coli encodes a protein essential for the secretion of specific proteins.
  • Mutations in secB lead to the accumulation of precursor maltose-binding protein (MBP) in the cytoplasm.
  • While MBP export is significantly affected, alkaline phosphatase export is less dependent on SecB.

Purpose of the Study:

  • To investigate the role of specific protein domains in SecB-dependent protein export.
  • To identify the region of maltose-binding protein (MBP) responsible for conferring SecB dependency.

Main Methods:

  • Construction and analysis of MBP-alkaline phosphatase hybrid proteins in wild-type and secB mutant Escherichia coli strains.
  • Assessment of protein export efficiency by monitoring protein localization (cytoplasm, periplasm, outer membrane).
  • Substitution of signal sequences to determine their effect on SecB dependency.

Main Results:

  • The first third of mature maltose-binding protein (MBP) was found to be sufficient to render hybrid proteins dependent on SecB for export.
  • Export of hybrid proteins containing the initial MBP segment was impaired in secB mutants.
  • Replacing the MBP signal sequence with one from a SecB-independent protein did not alter the hybrid's SecB dependency.

Conclusions:

  • The initial portion of maltose-binding protein contains critical information that dictates its requirement for SecB-mediated export.
  • This finding highlights the domain-specific nature of protein targeting and secretion pathways in bacteria.
  • The SecB pathway's specificity is determined by features within the N-terminal region of certain secreted proteins.

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