The six steps of the F1-ATPase rotary catalytic cycle

Abstract

F1Fo ATP synthase interchanges phosphate transfer energy and proton motive force via a rotary catalysis mechanism. When isolated, its F1-ATPase catalytic core can hydrolyze ATP, rotating its {gamma} rotor subunit. Although previous structural studies have contributed greatly to understanding rotary catalysis in F1, the structure of one major conformational state detected in single-molecule studies, termed the binding dwell state, has not yet been determined. Here, by exploiting a temperature-sensitive F1-ATPase mutant from Bacillus PS3, the structure of this binding dwell state was established together with that of the catalytic dwell state. Each state showed three catalytic {beta} subunits in different conformations, providing the complete set of six {beta} subunit conformational states taken up during catalysis cycle. These structures provide molecular details for the power-stroke conformational change that occurs upon ATP binding and induces a ~80{degrees} {gamma} subunit rotation, as well as a second torque-generating conformational change, triggered by hydrolysis and product release, that produces a ~40{degrees} rotation. This study also identifies a putative phosphate-releasing tunnel that indicates how ADP and phosphate releasing steps are coordinated. Overall these findings provide a structural basis for the entire F1-ATPase rotary catalysis cycle.