Structure of theEscherichia coli ATP synthase and role of the ? and ? subunits in coupling catalytic site and proton channeling functions

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Abstract
The structure of theEscherichia coli ATP synthase has been studied by electron microscopy and a model developed in which the α and β subunits of the F1 part are arranged hexagonally (in top view) alternating with one another and surrounding a central cavity of around 35 Å at its widest point. The α and β subunits are interdigitated in side view for around 60 Å of the 90 Å 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 Å long and 25–30 Å in diameter. The F0 part is mostly buried in the lipid bilayer. The γ subunit provides a domain that extends into the central cavity of the F1 part. The γ and ε 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 γ 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.

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