ATP synthase: A tentative structural model

Adenosine triphosphate (ATP) synthase produces ATP from ADP and inorganic phosphate at the expense of proton- or sodium-motive force across the respective coupling membrane in Archaea, Bacteria and Eucarya, Cation flow through the intrinsic membrane portion of this enzyme (F-0, subunits ab(2)c(9-12)) and substrate turnover in the headpiece (F-1, subunits alpha(3) beta(3) gamma delta epsilon) are mechanically coupled by the rotation of subunit yin the center of the catalytic hexagon of subunits (alpha beta)(3) in F-1. ATP synthase is the smallest rotatory engine in nature, With respect to the headpiece alone, it probably operates with three steps. Partial structures of sis out of its at least eight different subunits have been published and a 3-dimensional structure is available for the assembly (alpha beta)3 gamma. In this article, me review the available structural data and build a tentative topological model of the holoenzyme. The rotor portion is proposed to consist of a wheel of at least nine copies of subunits c, epsilon and a portion of gamma as a spoke, and another portion of gamma as a crankshaft. The stator is made up from a, the transmembrane portion of b(2), delta and the catalytic hexagon of (alpha beta)(3) As an educated guess, the model may be of heuristic value for ongoing studies on this fascinating electrochemical-to-mechanical-to-chemical transducer. (C) 1997 Federation of European Biochemical Societies.