The C terminus of SecA is involved in both lipid binding and SecB binding.
Using C-terminal deletion mutations in secA, we localized the previously proposed (Breukink, E., Keller, R.C. A., and de Kruijff, B. (1993), FEBS Lett. 331, 19-24) second lipid binding site on SecA. Since removal of these residues completely abolished the property of SecA to cause aggregation of negatively charged phosphatidyl-glycerol vesicles, we conclude that the C-terminal 70 amino acid residues of SecA are involved in lipid-binding. The C-terminal 70 amino acid residues of SecA are important for efficient in vitro translocation of the SecB-dependent precursor of PhoE across inverted inner membrane vesicles. Moreover, in vivo studies showed that this region is essential for growth. SecB and a SecB-precursor complex were shown to inhibit the SecA-mediated lipid vesicle aggregation, suggesting that the overall acidic SecB protein binds at or near the second lipid binding site on SecA. This together with the observation that the SecA mutant protein lacking the C-terminal 70 residues had a strongly reduced ability to mediate binding of SecB-precursor complexes to inverted inner membrane vesicles demonstrates that the C terminus of SecA is also involved in SecB binding.
Breukink
E
E
Department of Biochemistry of Membranes, Utrecht University, The Netherlands.
Nouwen
N
N
van Raalte
A
A
Mizushima
S
S
Tommassen
J
J
de Kruijff
B
B
D000251:Adenosine Triphosphatases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D001692:Biological Transport; D029968:Escherichia coli Proteins; D007425:Intracellular Membranes / Q000378:metabolism; D050356:Lipid Metabolism; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D000069816:SEC Translocation Channels; D000081416:SecA Proteins
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; C057842:SecB protein, Bacteria; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins