Catalytic mechanism of F₁-ATPase

The structure of the core catalytic unit of ATP synthase, α₃β₃γ, has been determined by X-ray crystallography, revealing a roughly symmetrical arrangement of alternating α and β subunits around a central cavity in which helical portions of γ are found. A low-resolution structural model of F₀, based on electron spectroscopic imaging, locates subunit a and the two copies of subunit b outside of a subunit c oligomer. The structures of individual subunits ε and c (largely) have been solved by NMR spectroscopy, but the oligomeric structure of c is still unknown. The structures of subunits a and δ remain undefined, that of b has not yet been defined but biochemical evidence indicates a credible model. Subunits γ, ε, b, and δ are at the interface between F₁ and F₀; γε complex forms one element of the stalk, interacting with c at the base and α and β at the top. The locations of b and δ are less clear. Elucidation of the structure F₀, of the stalk, and of the entire F₁F₀ remains a challenging goal.