Effects of mutations of conserved Lys-155 and Thr-156 residues in the phosphate-binding glycine-rich sequence of the F1-ATPase beta subunit of Escherichia coli.
beta Lys-155 in the glycine-rich sequence of the beta subunit of Escherichia coli F1-ATPase has been shown to be near the gamma-phosphate moiety of ATP by affinity labeling (Ida, K., Noumi, T., Maeda, M., Fukui, T., and Futai, M. (1991) J. Biol. Chem. 266, 5424-5429). For examination of the roles of beta Lys-155 and beta Thr-156, mutants (beta Lys-155-->Ala, Ser, or Thr; beta Thr-156-->Ala, Cys, Asp, or Ser; beta Lys-155/beta Thr-156-->beta Thr-155/beta Lys-156; and beta Thr-156/beta Val-157-->beta Ala-156/beta Thr-157) were constructed, and their properties were studied extensively. The beta Ser-156 mutant was active in ATP synthesis and had approximately 1.5-fold higher membrane ATPase activity than the wild type. Other mutants were defective in ATP synthesis, had < 0.1% of the membrane ATPase activity of the wild type, and showed no ATP-dependent formation of an electrochemical proton gradient. The mutants had essentially the same amounts of F1 in their membranes as the wild type. Purified mutant enzymes (beta Ala-155, beta Ser-155, beta Ala-156, and beta Cys-156) showed low rates of multisite (< 0.02% of the wild type) and unisite (< 1.5% of the wild type) catalyses. The k1 values of the mutant enzymes for unisite catalysis were lower than that of the wild type: not detectable with the beta Ala-156 and beta Cys-156 enzymes and 10(2)-fold lower with the beta Ala-155 and beta Ser-155 enzymes. The beta Thr-156-->Ala or Cys enzyme showed an altered response to Mg2+, suggesting that beta Thr-156 may be closely related to Mg2+ binding. These results suggest that beta Lys-155 and beta Thr-156 are essential for catalysis and are possibly located in the catalytic site, although beta Thr-156 could be replaced by a serine residue.
Omote
H
H
Department of Organic Chemistry and Biochemistry, Osaka University, Japan.
Maeda
M
M
Futai
M
M
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D002462:Cell Membrane / Q000201:enzymology; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D005998:Glycine; D007700:Kinetics; D008239:Lysine; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009876:Operon; D010957:Plasmids; D006180:Proton-Translocating ATPases / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D013912:Threonine
D046911:Macromolecular Substances; D011994:Recombinant Proteins; D013912:Threonine; D000255:Adenosine Triphosphate; D006180:Proton-Translocating ATPases; D008239:Lysine; D005998:Glycine