The α/β Interfaces of α1β1, α3β3, and F1: Domain Motions and Elastic Energy Stored during γ Rotation

ATP synthase (FoF1) consists of F1(ATP-driven motor) and Fo(H+-driven motor). F1is a complex of α3β3γδε subunits, and γ is the rotating cam in α3β3. Thermophilic F1(TF1) is exceptional in that it can be crystallized as a β monomer and an α3β3oligomer, and it is sufficiently stable to allow αβ refolding and reassembly of hybrid complexes containing 1, 2, and 3 modified α or β. The nucleotide-dependent open–close conversion of conformation is an inherent property of an isolated β and energy and signals are transferred through α/β interfaces. The catalytic and noncatalytic interfaces of both mitochondrial F1(MF1) and TF1were analyzed by an atom search within the limits of 0.40 nm across the αβ interfaces. Seven (plus thermophilic loop in TF1) contact areas are located at both the catalytic and noncatalytic interfaces on the open β form. The number of contact areas on closed β increased to 11 and 9, respectively, in the catalytic and noncatalytic interfaces. The interfaces in the barrel domain are immobile. The torsional elastic strain applied through the mobile areas is concentrated in hinge residues and the P-loop in β. The notion of elastic energy in FoF1has been revised. X-ray crystallography of F1is a static snap shot of one state and the elastic hypotheses are still inconsistent with the structure, dyamics, and kinetics of FoF1. The domain motion and elastic energy in FoF1will be elucidated by time-resolved crystallography.