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How subunit coupling produces the γ-subunit rotary motion in F₁-ATPase

Pu, Jingzhi, Karplus, Martin
Proceedings of the National Academy of Sciences of the United States of America 2008 v.105 no.4 pp. 1192-1197
H-transporting ATP synthase, adenosine triphosphate, energy, hydrolysis, manufacturing, models, torque, van der Waals forces
FoF₁-ATP synthase manufactures the energy "currency," ATP, of living cells. The soluble F₁ portion, called F₁-ATPase, can act as a rotary motor, with ATP binding, hydrolysis, and product release, inducing a torque on the γ-subunit. A coarse-grained plastic network model is used to show at a residue level of detail how the conformational changes of the catalytic β-subunits act on the γ-subunit through repulsive van der Waals interactions to generate a torque that drives unidirectional rotation, as observed experimentally. The simulations suggest that the calculated 85° substep rotation is driven primarily by ATP binding and that the subsequent 35° substep rotation is produced by product release from one β-subunit and a concomitant binding pocket expansion of another β-subunit. The results of the simulation agree with single-molecule experiments [see, for example, Adachi K, et al. (2007) Cell 130:309-321] and support a tri-site rotary mechanism for F₁-ATPase under physiological condition.