title: Characterization of a potential catalytic residue, Asp-133, in the high affinity ATP-binding site of Escherichia coli SecA, translocation ATPase.
abstract: The high affinity ATP-binding site of SecA is located in its amino-terminal domain possessing amino acid sequences, the Walker A (GXXXXGKT) and B (ZZZZD) motifs, that are characteristic of a major class of nucleotide-binding sites (Walker, J. E., Saraste, M., Runswick, M. J., and Gay, N. J. (1982) EMBO J. 1, 945-951). Recently, we proposed that proteins possessing a typical set of Walker A and B motifs contain a conserved Glu or Asp between the two motifs. This Glu or Asp acts as a "catalytic residue" that activates a water molecule for an in-line attack on the gamma-phosphate of ATP (Amano, T., Yoshida, M., Matsuo, Y., and Nishikawa, K.(1995) FEBS Lett. 359, 1-5). In the present study, the aspartate residue at position 133 in Escherichia coli SecA, which could be the "catalytic residue," was mutated to an asparagine. The mutant SecA (SecA D133N) protein was expressed in E. coli CK4706, encoding a duplication of the secA gene, and purified to homogeneity. The in vitro protein translocation activity and membrane vesicle stimulated ATPase activity of SecA D133N were drastically reduced. Proteolytic studies indicated that the conformational changes of the mutant SecA occurring on interaction with ATP, presecretory proteins, phospholipids, and membrane vesicles, were similar to those of wild-type SecA. The mutant SecA allowed the signal peptide cleavage of proOmpA during translocation, indicating that the mutant retains the ability to bind ATP to perform the initial step of the translocation reaction. These data indicate that the carboxyl group of Asp-133 plays a role as a catalytic carboxylate, which activates a water molecule to attack gamma-phosphate of ATP, and the mutant lacking this residue cannot perform the total translocation but can still perform the initial step of the protein translocation.
authors.affiliation: Research Laboratory of Resources Utilization, Tokyo Institute of Technology, Nagatsuta 4259, Yokohama 226, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Sato
authors.forename: H
authors.initials: H
authors.lastname: Mori
authors.forename: M
authors.initials: M
authors.lastname: Yoshida
authors.forename: S
authors.initials: S
authors.lastname: Mizushima
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000595:Amino Acid Sequence; D001224:Aspartic Acid; D001419:Bacteria / Q000201:enzymology; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D001692:Biological Transport; D017931:DNA Primers; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D007700:Kinetics; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010944:Plants / Q000201:enzymology; D017354:Point Mutation; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D017931:DNA Primers; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D011994:Recombinant Proteins; D000069816:SEC Translocation Channels; D001224:Aspartic Acid; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins