Different sec-requirements for signal peptide cleavage and protein translocation in a model E. coli protein.
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 approximately 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.
Nilsson
I M
IM
Department of Molecular Biology, Karolinska Institute Center for Structural Biochemistry, NOVUM, Huddinge, Sweden.
Gafvelin
G
G
von Heijne
G
G
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000378:metabolism*; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D010450:Endopeptidases / Q000737:chemistry / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism*; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D021382:Protein Sorting Signals / Q000378:metabolism*; D012697:Serine Endopeptidases
D001426:Bacterial Proteins; D008565:Membrane Proteins; D021382:Protein Sorting Signals; D010450:Endopeptidases; D012697:Serine Endopeptidases; C026515:type I signal peptidase