SecA interacts with secretory proteins by recognizing the positive charge at the amino terminus of the signal peptide in Escherichia coli.
SecA is an acidic, peripheral membrane protein involved in the translocation of secretory proteins across the cytoplasmic membrane. The direct interaction of SecA with secretory proteins was demonstrated by means of chemical cross-linking with 1-ethyl-3-(3-dimethylaminoprophyl)carbodiimide. OmpF-Lpp, a model secretory protein, carries either an uncleavable or cleavable signal peptide, and mutant secretory proteins derived from uncleavable OmpF-Lpp were used as translocation substrates. The interaction was SecA-specific. None of the control proteins, which are as acidic as SecA, was cross-linked with uncleavable OmpF-Lpp. The interaction was signal peptide-dependent. The interaction was increasingly enhanced as the number of positively charged amino acid residues at the amino-terminal region of the signal peptide was increased, irrespective of the species of amino acid residues donating the charge. Finally, parallelism was observed between the efficiency of interaction and that of translocation among mutant secretory proteins. It is suggested that precursors of secretory proteins interact with SecA to initiate the translocation reaction.
Akita
M
M
Institute of Applied Microbiology, University of Tokyo, Japan.
Sasaki
S
S
Matsuyama
S
S
Mizushima
S
S
D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D003432:Cross-Linking Reagents; D004563:Electrochemistry; D004926:Escherichia coli / Q000378:metabolism*; D005022:Ethyldimethylaminopropyl Carbodiimide; D007526:Isoelectric Point; D008969:Molecular Sequence Data; D009154:Mutation; D011498:Protein Precursors / Q000378:metabolism; D021382:Protein Sorting Signals / Q000378:metabolism*
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D003432:Cross-Linking Reagents; D011498:Protein Precursors; D021382:Protein Sorting Signals; D005022:Ethyldimethylaminopropyl Carbodiimide