ATP synthase is the primary producer of adenosine triphosphate (ATP), which acts as the chemical energy currency of all known life. This ubiquitous molecular machine consists of two coupled rotary motors. The membrane-embedded Fo motor converts the H+ electrochemical potential into mechanical rotation that then drives the synthesis of ATP in a trio of active sites on the soluble F1 motor. In addition to ATP synthesis, F1Fo of E. coli and other bacteria can operate in reverse to maintain the gradient through ATP-driven H+ pumping. H+ translocation through the Fo sector is facilitated by two aqueous half channels, the entry channel in subunit a (stator) and the exit channel at the interface of subunit a and the c10 ring (rotor). The functional roles of residues at the rotor-stator interface in H+ translocation are not completely resolved. We have investigated the chemical requirements of several positions on the surface of subunit c using site-directed mutagenesis and chemical modification. While residues in this region were remarkably tolerant of most mutations, substitution with cysteine caused a profound defect in permeability that could be partially rescued by chemical modification. Additionally, altering the polarity of threonine 51 affected ATP synthesis and ATP-driven H+ pumping disproportionately, suggesting that the role of this residue differs depending on the direction of H+ movement.

Asymmetric effects of rotor mutations on H+ translocation in E. coli ATP synthase

ACS Spring Meeting 2021

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