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

AUTOR(ES)

Mitome, Noriyo

FONTE

National Academy of Sciences

RESUMO

In a rotary motor FoF1-ATP synthase that couples H+ transport with ATP synthesis/hydrolysis, it is thought that an Foc subunit oligomer ring (c-ring) in the membrane rotates as protons pass through Fo and a 120° rotation produces one ATP at F1. Despite several structural studies, the copy number of Foc 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 (c2–c14). Among them, FoF1 containing c2, c5, or c10 showed ATP-synthesis and other activities. When F1 was removed, Fo containing c10 worked as an H+ channel but Fos containing c9, c11 or c12 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 F1/Fo (120°/36°) 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 Fo and elementary events in catalysis at F1.

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