How Does F1-ATPase Generate Torque?: Analysis From Cryo-Electron Microscopy and Rotational Catalysis of Thermophilic F1

The F-1-ATPase is a rotary motor fueled by ATP hydrolysis. Its rotational dynamics have been well characterized using single-molecule rotation assays. While F-1-ATPases from various species have been studied using rotation assays, the standard model for single-molecule studies has been the F-1-ATPase from thermophilic Bacillus sp. PS3, named TF1. Single-molecule studies of TF1 have revealed fundamental features of the F-1-ATPase, such as the principal stoichiometry of chemo-mechanical coupling (hydrolysis of 3 ATP per turn), torque (approximately 40 pN center dot nm), and work per hydrolysis reaction (80 pN center dot nm = 48 kJ/mol), which is nearly equivalent to the free energy of ATP hydrolysis. Rotation assays have also revealed that TF1 exhibits two stable conformational states during turn: a binding dwell state and a catalytic dwell state. Although many structures of F-1 have been reported, most of them represent the catalytic dwell state or its related states, and the structure of the binding dwell state remained unknown. A recent cryo-EM study on TF1 revealed the structure of the binding dwell state, providing insights into how F-1 generates torque coupled to ATP hydrolysis. In this review, we discuss the torque generation mechanism of F-1 based on the structure of the binding dwell state and single-molecule studies.