The carboxyl-terminal region is essential for Sec-A dimerization.
SecA, comprising 901 amino acid residues, exists as a dimer. By means of size exclusion chromatography and chemical cross-linking analysis, five truncated SecA derivatives were examined to identify the region of SecA essential for dimer formation. Among them, only N95 (delta 832-901) retained SecA activity. N95 existed as a dimer, indicating that the carboxyl-terminal three cysteine residues are dispensable for physiological dimerization. Both N76 (delta 675-901) and N66 (delta 583-901) existed as monomers. Monomeric N76 was able to bind to ATP, indicating that the dimerization of SecA is not a prerequisite for ATP binding. However, the rate of ATP hydrolysis by N76 was 25% of that by SecA. C53 (delta 1-437) and C28 (delta 1-661) formed dimers irrespective of the presence or absence of 2-mercaptoethanol. C28, but not C53, also existed as an oligomer in the absence of 2-mercaptoethanol, suggesting that the 438-661 region present in C53 prevents intermolecular disulfide bond formation at the carboxyl-terminal cysteine residue. From these results, the region essential for the physiological dimer formation was concluded to be located in the 662-831 region of SecA.
Hirano
M
M
Institute of Molecular and Cellular Biosciences, University of Tokyo, Japan.
Matsuyama
S
S
Tokuda
H
H
D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D004252:DNA Mutational Analysis; D019281:Dimerization; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D011994:Recombinant Proteins / Q000378:metabolism; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D017384:Sequence Deletion; D013329:Structure-Activity Relationship
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D011994:Recombinant Proteins; D000069816:SEC Translocation Channels; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins