The phototroph-specific β-hairpin structure of the γ subunit of FoF1-ATP synthase is important for efficient ATP synthesis of cyanobacteria

The F(o)F(1)synthase produces ATP from ADP and inorganic phosphate. The gamma subunit of FoF1 ATP synthase in photosynthetic organisms, which is the rotor subunit of this enzyme, contains a characteristic beta-hairpin structure. This structure is formed from an insertion sequence that has been conserved only in phototrophs. Using recombinant subcomplexes, we previously demonstrated that this region plays an essential role in the regulation of ATP hydrolysis activity, thereby functioning in controlling intracellular ATP levels in response to changes in the light environment. However, the role of this region in ATP synthesis has long remained an open question because its analysis requires the preparation of the whole FoF1 complex and a transmembrane proton-motive force. In this study, we successfully prepared proteoliposomes containing the entire FoF1 ATP synthase from a cyanobacterium, Synechocystis sp. PCC 6803, and measured ATP synthesis/hydrolysis and proton-translocating activities. The relatively simple genetic manipulation of Synechocystis enabled the biochemical investigation of the role of the beta-hairpin structure of FoF1 ATP synthase and its activities. We further performed physiological analyses of Synechocystis mutant strains lacking the beta-hairpin structure, which provided novel insights into the regulatory mechanisms of FoF1 ATP synthase in cyanobacteria via the phototroph-specific region of the gamma subunit. Our results indicated that this structure critically contributes to ATP synthesis and suppresses ATP hydrolysis.

Automated summary

This study investigated the role of the beta-hairpin structure in the FoF1 ATP synthase of photosynthetic organisms in ATP synthesis and hydrolysis. By experimenting with genetically modified Synechocystis and proteoliposomes containing the ATP synthase complex, it was found that this structure plays a critical role in ATP synthesis and inhibits ATP hydrolysis.