Thiol modulation of the chimeric ATP synthase complex of bacterial F1 containing the regulatory region of the gamma subunit of chloroplast ATP synthase

The ATP synthase of chloroplasts (CFoCF1) is activated by the proton gradient across the thylakoid membrane and modulated by the reduction of a disulfide bridge in the g subunit (thiol modulation). The cysteines involved in this regulation are located in an additional amino acid stretch (the regulatory region) of CF1-g subunit. In the solubilized CF1 reduction of the disulfide bond in g causes elicitation of the latent ATP hydrolyzing activity. We identified the important sequences for the regulation from the study of the reconstituted complex, which contains the mutant g subunit with a partial deletion of this regulatory region. In addition, we constructed a mutant F1-ATPase a3b3g sub-complex from a thermophilic bacterium in which the central region of the g subunit was replaced by the homologous region from spinach CF1 g subunit including the regulatory region. ATP hydrolysis activity of this mutant showed that thiol modulation and was inhibited by the e subunit from CF1, but not by TF1-e. Using a single-molecule observation technique, we investigated ATP hydrolysis-coupled rotation of the g subunit and the redox regulation of this rotation. The e subunit of ATP synthase is a well-known intrinsic inhibitor subunit. We recently elucidated the relationship between the conformational change of this subunit and the function. The results showed that the interaction between the C-terminal a-helix of e and the DELSEED region of b is very important for the inhibition. Based on these findings, I will discuss on the regulation system for ATP synthase.