A model for the structure of subunit a of the Escherichia coli ATP synthase and its role in proton translocation.

Most of what is known about the structure and function of subunit a, of the ATP synthase, has come from the construction and isolation of mutations, and their analysis in the context of the ATP synthase complex. Three classes of mutants will be considered in this review. (1) Cys substitutions have been used for structural analysis of subunit a, and its interactions with subunit c. (2) Functional residues have been identified by extensive mutagenesis. These studies have included the identification of second-site suppressors within subunit a. (3) Disruptive mutations include deletions at both termini, internal deletions, and single amino acid insertions. The results of these studies, in conjunction with information about subunits b and c, can be incorporated into a model for the mechanism of proton translocation in the Escherichia coli ATP synthase.