Mitochondrial F-type ATP synthase: multiple enzyme functions revealed by the membrane-embedded FO structure

Of the two main sectors of the F-type ATP synthase, the membrane-intrinsic F(O)domain is the one which, during evolution, has undergone the highest structural variations and changes in subunit composition. The F(O)complexity in mitochondria is apparently related to additional enzyme functions that lack in bacterial and thylakoid complexes. Indeed, the F-type ATP synthase has the main bioenergetic role to synthesize ATP by exploiting the electrochemical gradient built by respiratory complexes. The F(O)membrane domain, essential in the enzyme machinery, also participates in the bioenergetic cost of synthesizing ATP and in the formation of thecristae, thus contributing to mitochondrial morphology. The recent enzyme involvement in a high-conductance channel, which forms in the inner mitochondrial membrane and promotes the mitochondrial permeability transition, highlights a new F-type ATP synthase role. Point mutations which cause amino acid substitutions in F(O)subunits produce mitochondrial dysfunctions and lead to severe pathologies. The F(O)variability in different species, pointed out by cryo-EM analysis, mirrors the multiple enzyme functions and opens a new scenario in mitochondrial biology.