Interaction of the catch-loop tyrosine beta Y317 with the metal at catalytic site 3 of Chlamydomonas chloroplast F1-ATPase.
Site-directed mutants Y317C, Y317E, Y317F, Y317G, and Y317K were made to the catch-loop tyrosine on the beta subunit of the chloroplast F(1)-ATPase in Chlamydomonas. EPR spectra of VO(2+)-ATP bound to site 3 of CF(1) from wild type and mutants were obtained. Every mutant changed the (51)V hyperfine parameters of the VO(2+) bound at this site in the catalytically active conformation of the enzyme but had no effect on these parameters in the form that predominates when the enzyme activity is latent. These results indicate that this residue is a ligand to the metal of the Mg(2+)-nucleotide complex that binds to the empty catalytic site. The mutations also decreased the k(cat) of the ATPase activity to a much greater extent than k(cat)/K(M). Thus, these mutations limit the rate of product (Mg(2+)-ADP and phosphate) release in the ATPase direction or, conversely, the initial binding of substrates in the ATP synthesis direction. On the basis of these observations, coordination of betaY317 by Mg(2+)-ADP that binds to the empty catalytic site provides a means by which substrate binding could trigger gamma subunit rotation and consequent conformation changes of beta subunits during ATP synthesis.
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The Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, Arizona 85287-1601, USA.
Frasch
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D000255:Adenosine Triphosphate / Q000096:biosynthesis; D000818:Animals; D002384:Catalysis; D020134:Catalytic Domain / Q000235:genetics; D016825:Chlamydomonas reinhardtii / Q000201:enzymology* / Q000235:genetics; D002736:Chloroplasts / Q000201:enzymology / Q000235:genetics; D004578:Electron Spin Resonance Spectroscopy; D007700:Kinetics; D008024:Ligands; D008274:Magnesium / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D006180:Proton-Translocating ATPases / Q000235:genetics / Q000378:metabolism*; D014443:Tyrosine / Q000235:genetics / Q000378:metabolism*; D014638:Vanadates / Q000378:metabolism; D014639:Vanadium / Q000378:metabolism*
D008024:Ligands; D014639:Vanadium; D014638:Vanadates; D014443:Tyrosine; D000255:Adenosine Triphosphate; D006180:Proton-Translocating ATPases; D008274:Magnesium