Molecular evolution of the modulator of chloroplast ATP synthase: origin of the conformational change dependent regulation

Chloroplast ATP synthase synthesizes ATP by utilizing a proton gradient as an energy supply, which is generated by photosynthetic electron transport. The activity of the chloroplast ATP synthase is regulated in several specific ways to avoid futile hydrolysis of ATP under various physiological conditions. Several regulatory signals such as DeltamuH(+), tight binding of ADP and its release, thiol modulation, and inhibition by the intrinsic inhibitory subunit F are sensed by this complex. In this review, we describe the function of two regulatory subunits, gamma and epsilon, of ATP synthase based on their possible conformational changes and discuss the evolutionary origin of these regulation systems. (C) 2003 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.