Structure of the dimeric ATP synthase from bovine mitochondria

Significance

Adenosine triphosphate (ATP), the fuel of life, is produced in inner membranes of the mitochondria of eukaryotic cells by an embedded molecular machine with a rotary action, called ATP synthase. Single ATP synthases associate into dimers and form long rows, influencing the formation of characteristic cristae which change shape constantly. Our structure of bovine dimers has a wedge made of small proteins and specific lipids in the membrane domain of each monomer that imposes a range of acute angles on the central axes of the monomers, and a pivot between the wedges accommodates rocking motions of the machine accompanying catalysis and other movements that happen independently. It also throws light on how the membrane rotor is made to turn.

Abstract

The structure of the dimeric ATP synthase from bovine mitochondria determined in three rotational states by electron cryo-microscopy provides evidence that the proton uptake from the mitochondrial matrix via the proton inlet half channel proceeds via a Grotthus mechanism, and a similar mechanism may operate in the exit half channel. The structure has given information about the architecture and mechanical constitution and properties of the peripheral stalk, part of the membrane extrinsic region of the stator, and how the action of the peripheral stalk damps the side-to-side rocking motions that occur in the enzyme complex during the catalytic cycle. It also describes wedge structures in the membrane domains of each monomer, where the skeleton of each wedge is provided by three α-helices in the membrane domains of the b-subunit to which the supernumerary subunits e, f, and g and the membrane domain of subunit A6L are bound. Protein voids in the wedge are filled by three specifically bound cardiolipin molecules and two other phospholipids. The external surfaces of the wedges link the monomeric complexes together into the dimeric structures and provide a pivot to allow the monomer–monomer interfaces to change during catalysis and to accommodate other changes not related directly to catalysis in the monomer–monomer interface that occur in mitochondrial cristae. The structure of the bovine dimer also demonstrates that the structures of dimeric ATP synthases in a tetrameric porcine enzyme have been seriously misinterpreted in the membrane domains.