Structure of the Escherichia coli ATP synthase and role of the gamma and epsilon subunits in coupling catalytic site and proton channeling functions.

The structure of the Escherichia coli ATP synthase has been studied by electron microscopy and a model developed in which the alpha and beta subunits of the F1 part are arranged hexagonally (in top view) alternating with one another and surrounding a central cavity of around 35 A at its widest point. The alpha and beta subunits are interdigitated in side view for around 60 A of the 90 A length of the molecule. The F1 narrows and has three-fold symmetry at the end furthest from the F0 part. The F1 is linked to F0 by a stalk approximately 45 A long and 25-30 A in diameter. The F0 part is mostly buried in the lipid bilayer. The gamma subunit provides a domain that extends into the central cavity of the F1 part. The gamma and epsilon subunits are in a different conformation when ATP + Mg2+ are present in catalytic sites than when ATP + EDTA are present. This is consistent with these two small subunits switching conformations as a function of whether or not phosphate is bound to the enzyme at the position of the gamma phosphate of ATP. We suggest that this switching is the key to the coupling of catalytic site events with proton translocation in the F0 part of the complex.