The Mutation E242K in the Chloroplast ATP Synthase Gamma Subunit Increases the Inhibitory Binding of the Epsilon Subunit without Changing the Apparent Redox Potential of the Regulatory Dithiol

摘要

A single point mutation in the gamma subunit of the ATP synthase, E244K, was recently shown to change the apparent redox potential of a critically placed, regulatory dithiol in the gamma subunit of the photosynthetic ATP synthase in situ in thyolakoid membranes of Arabadopsis thaliana (Wu et al., 2006). The mutation resulted in loss of light-dependent activation of the ATPase activity of the ATP synthase and decreased ATP synthesis. This identified, for the first time, that the redox state of the gamma dithiol is a strong determinant of photosynthetic efficiency in higher plants. To determine how the gamma dithiol modulates ATP synthesis the effect of the E244K mutation on the redox potential of the gamma dithiol was examined in vitro using an assembled recombinant hybrid CF1 enzyme system previously described. The mutation did not significantly alter the redox potential of the gamma dithiol. It did, however, decrease the dilution-dependent activation of the ATP hydrolysis activity of the enzyme that results from release of the inhibitory epsilon subunit. This suggests that the mutation blocks the light-dependent change in epsilon conformation that leads to activation of the latent ATPase activity of CF1 in situ.