A unique resting position of the ATP-synthase from chloroplasts.

The chloroplast ATP-synthase catalyzes ATP synthesis coupled to transmembrane proton transport. The enzyme consists of two parts, a membrane-embedded F(0) part and an extrinsic F(1) part, which are linked by two connectors. One of these rotates during catalysis and the other remains static. Although the atomic structures of various sub-complexes and individual subunits have been reported, only limited structural information on the complex, as a whole, is available. In particular, information on the static connector is lacking. We contribute a three-dimensional map at about 20-A resolution, derived from electron cryomicroscopy of enzymes embedded in vitrified buffer followed by single particle image analysis. In the three-dimensional map both connectors, between the F(1) part and the F(0) part, are clearly visible. The static connector is tightly attached to an alpha subunit and faces the side of the neighboring beta subunit. The three-dimensional map provides a scaffold for fitting in the known atomic structures of various subunits and sub-complexes, and suggests that the oxidized, non-activated ATP-synthase from chloroplasts adopts a unique resting position.