Thermophilic ATP synthase has a decamer c-ring:: Indication of noninteger 10:3 H+/ATP ratio and permissive elastic coupling

In a rotary motor FoF1-ATP synthase that couples H+ transport with ATIP synthesis/hydrolysis, it is thought that an F(o)c subunit oligomer ring (c-ring) in the membrane rotates as protons pass through F-o and a 120degrees rotation produces one ATP at F-1. Despite several structural studies, the copy number of F(o)c subunits in the c-ring has not been determined for any functional FoF1. Here, we have generated and isolated thermophilic Bacillus FoF1, each containing genetically fused 2-mer-14-mer c (c(2)-c(14)). Among them, FoF1 containing c(2), c(5), or c(10) showed ATP-synthesis and other activities. When F-1 was removed, F-o containing c(10) worked as an H+ channel but F(o)s containing c(9), c(11) or c(12) did not. Thus, the c-ring of functional FoF1 of this organism is a decamer. The inevitable consequence of this finding is noninteger ratios of rotation step sizes of F-1/F-o (120degrees/36degrees) and of H+/ATP (10:3). This step-mismatch necessitates elastic twisting of the rotor shaft (and/or the side stalk) during rotation and permissive coupling between unit rotations by H+ transport at F-o and elementary events in catalysis at F-1.