The depletion of F1 subunit ε in yeast leads to an uncoupled respiratory phenotype that is rescued by mutations in the proton-translocating subunits of F0

The central stalk of the ATP synthase is an elongated hetero-oligomeric structure providing a physical connection between the catalytic sites in F-1 and the proton translocation channel in F-0 for energy transduction between the two subdomains. The shape of the central stalk and relevance to energy coupling are essentially the same in ATP synthases from all forms of life, yet the protein composition of this domain changed during evolution of the mitochondrial enzyme from a two-to a three-subunit structure (gamma, delta, epsilon). Whereas the mitochondrial. gamma- and delta-subunits are homologues of the bacterial central stalk proteins, the deliberate addition of subunit epsilon is poorly understood. Here we report that down-regulation of the gene (ATP15) encoding the epsilon-subunit rapidly leads to lethal F-0-mediated proton leaks through the membrane because of the loss of stability of the ATP synthase. The epsilon-subunit is thus essential for oxidative phosphorylation. Moreover, mutations in F-0 subunits a and c, which slow the proton translocation rate, are identified that prevent epsilon-deficient ATP synthases from dissipating the electrochemical potential. Cumulatively our data lead us to propose that the epsilon-subunit evolved to permit operation of the central stalk under the torque imposed at the normal speed of proton movement through mitochondrial F-0.