The participation of metals in the mechanism of the F1-ATPase

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Abstract

The Mg2+ cofactor of the F1F0 ATP synthase is required for the asymmetry of the catalytic sites that leads to the differences in affinity for nucleotides. Vanadyl (V(IV) = O)2+ is a functional surrogate for Mg2+ in the F1-ATPase. The 51V-hyperfine parameters derived from EPR spectra of VO2+ bound to specific sites on the enzyme provide a direct probe of the metal ligands at each site. Site-directed mutations of residues that serve as metal ligands were found to cause measurable changes in the 51V-hyperfine parameters of the bound VO2+, thereby providing a means by which metal ligands were identified in the functional enzyme in several conformations. At the low-affinity catalytic site comparable to β(E) in mitochondrial F1, activation of the chloroplast F1-ATPase activity induces a conformational change that inserts the P-loop threonine and catch-loop tyrosine hydroxyl groups into the metal coordination sphere thereby displacing an amino group and the Walker homology B aspartate. Kinetic evidence suggests that coordination of this tyrosine by the metal when the empty site binds substrate may provide an escapement mechanism that allows the γ subunit to rotate and the conformation of the catalytic sites to change, thereby allowing rotation only when the catalytic sites are filled. In the high-affinity conformation analogous to the β(DP) site of mitochondrial F1, the catch-loop tyrosine has been displaced by carboxyl groups from the Walker homology B aspartate and from βE197 in Chlamydomonas CF1. Coordination of the metal by these carboxyl groups contributes significantly to the ability of the enzyme to bind the nucleotide with high affinity. Copyright (C) 2000 Elsevier Science B.V.

Original languageEnglish (US)
Pages (from-to)310-325
Number of pages16
JournalBiochimica et Biophysica Acta - Bioenergetics
Volume1458
Issue number2-3
DOIs
StatePublished - May 31 2000

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Keywords

  • F ATPase
  • FF ATP synthase
  • Vanadyl

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

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