Role of a Polar c‐Ring Residue in the Fo Motor of E. coli ATP Synthase

Abstract

ATP Synthase is a molecular motor that utilizes a rotary mechanism to synthesize adenosine triphosphate (ATP), the fundamental energy currency of life. The torque for this mechanism is generated in the membrane‐embedded FO motor by harnessing the proton motive force, where protons flow down the electrochemical gradient through two half channels in the motor. The exit half channel on the cytoplasmic side is found at the interface of subunit a (stator) and the subunit c ring (rotor). Previous work on the E. coli ATP synthase has suggested that Thr51 in subunit c is involved in the proton translocation process. To investigate the role of this residue and chemical requirements at this position, we generated six substitution mutants and assayed their in vitro ATP synthesis, H+ pumping, and H+ permeability activities as well as the ability of mutants to carry out oxidative phosphorylation in vivo. Polar and hydrophobic mutations were generally tolerated, except for a notable decrease in function when a negative charge is introduced. Unusually, substitution with Cys completely abolished in vitro functions but only mildly inhibited growth on succinate. Overall, our results suggest that cThr51 may play a supporting role in the interaction between the c‐ring and subunit a in the region of the proton exit channel.