A Conformational Change of the γ Subunit Indirectly Regulates the Activity of Cyanobacterial F1-ATPase

The central shaft of the catalytic core of ATP synthase, the gamma subunit consists of a coiled-coil structure of N- and C-terminal alpha-helices, and a globular domain. The gamma subunit of cyanobacterial and chloroplast ATP synthase has a unique 30 - 40-amino acid insertion within the globular domain. We recently prepared the insertion-removed alpha(3)beta(3)gamma complex of cyanobacterial ATP synthase (Sunamura, E., Konno, H., Imashimizu-Kobayashi, M., and Hisabori, T. (2010) Plant Cell Physiol. 51, 855865). Although the insertion is thought to be located in the periphery of the complex and far from catalytic sites, the mutant complex shows a remarkable increase in ATP hydrolysis activity due to a reduced tendency to lapse into ADP inhibition. We postulated that removal of the insertion affects the activity via a conformational change of two central alpha-helices in gamma. To examine this hypothesis, we prepared a mutant complex that can lock the relative position of two central alpha-helices to each other by way of a disulfide bond formation. The mutant obtained showed a significant change in ATP hydrolysis activity caused by this restriction. The highly active locked complex was insensitive to N-dimethyldodecylamine-N-oxide, suggesting that the complex is resistant to ADP inhibition. In addition, the lock affected is an element of inhibition. In contrast, the change in activity caused by removal of the gamma insertion was independent from the conformational restriction of the central axis component. These results imply that the global conformational change of the gamma subunit indirectly regulates complex activity by changing both ADP inhibition and is an element of inhibition.