Characterization of dimeric ATP synthase and cristae membrane ultrastructure from Saccharomyces and Polytomella mitochondria

arranged in dimers in the inner mitochondrial membrane of several organisms. The dimers are also considered to be the building blocks of oligomers. It was recently found that the monomers in beef and the alga Polytomella ATP synthase dimer make an angle of similar to 40 degrees and similar to 70 degrees, respectively. This arrangement is considered to induce a strong local bending of the membrane. To further understand the packing of dimers into oligomers we performed an electron microscopy analysis of ATP synthase dimers purified from Saccharomyces cerevisiae. Two types of dimers were found in which the angle between the monomers is either similar to 90 degrees or similar to 35 degrees. According to our interpretation, the wide-angle dimers (70-90 degrees) are true-dimers whereas the small-angle dimers (35-40 degrees) rather are pseudo-dimers, which represent breakdown products of two adjacent true dimers in the oligomer. Ultrathin sectioning of intact Polytomella mitochondria indicates that the inner mitochondrial or cristae membrane is folded into lamellae and tubuli. Oligomers of ATP synthase can arrange in a helical fashion in tubular-shaped cristae membranes. These results strongly support the hypothesized role of ATP synthase oligomers in structural determination of the mitochondrial inner membrane. (c) 2006 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.