ATP syntheses in the year 2000: Evolving views about the structures of these remarkable enzyme complexes

This introductory article briefly summarizes how our views about the struct ural features of ATP synthases (F-0,F-1) have evolved over the past 30 year s and also reviews some of our current views in the year 2000 about the str uctures of these remarkably unique enzyme complexes. Suffice it to say that as we approach the end of the first year of this new millinium, we can be conservatively confident that we have a reasonably good grasp of the overal l "low-resolution" structural features of ATP synthases. Electron microscop y techniques, combined with the tools of biochemistry, molecular biology, a nd immunology, have played the leading role here by identifying the headpie ce, basepiece, central stalk, side stalk, cap, and in the mitochondrial enz yme, the collar around the central stalk. We can be reasonably confident al so that we have a fairly good grasp of much of the "high-resolution" struct ural features of both the F-1 moiety comprised of fives subunit types (alph a, beta, gamma, delta, and epsilon) and parts of the F-o moiety comprised o f either three (E. coli) or at least ten (mitochondria) subunit types. This information acquired in several different laboratories, either by X-ray cr ystallography or NMR spectroscopy, includes details about the active site a nd subunit relationships. Moreover, it is consistent with recently reported data that the F-1 moiety may be an ATP driven motor, which, during ATP syn thesis, is driven in reverse by the electrochemical proton gradient generat ed by the electron transport chain. The real structural challenges of the f uture are to acquire at high resolution "complete" ATP synthase complexes r epresentative of different stages of the catalytic cycle during ATP synthes is and representative also of key regulatory states.