Section 9
Chapter 8,469

Different sec-requirements for signal peptide cleavage and protein translocation in a model Escherichia coli protein

Nilsson, I.; Gafvelin, G.; Von Heijne, G.

FEBS (Federation of European Biochemical Societies) Letters 318(1): 7-10


Accession: 008468629

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We describe a secretory E. coli protein with a novel phenotype: signal peptide cleavage is largely unaffected whereas chain translocation is efficiently blocked under conditions where SecA, a central component of the secretory machinery, is rendered non-functional, and we have traced this phenotype to the presence of a mildly hydrophobic segment located apprx 30 residues downstream of the signal peptide. When this segment is deleted, normal SecA-dependent signal peptide cleavage and chain translocation is observed; when its hydrophobicity is increased, it becomes a permanent membrane anchor with cleavage of the signal peptide and membrane insertion both being SecA-independent. These findings suggest that the initial insertion of the signal peptide across the membrane can be uncoupled from the translocation process proper.

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