Modulation at a distance of proton conductance through the Saccharomyces cerevisiae mitochondrial F1F0-ATP synthase by variants of the oligomycin sensitivity-conferring protein containing substitutions near the C-terminus

We have sought to elucidate how the oligomycin sensitivity-conferring prote in (OSCP) of the mitochondrial F1F0-ATP synthase (mtATPase) can influence p roton channel function. Variants of OSCP, from the yeast Saccharomyces cere visiae, having amino acid substitutions at a strictly conserved residue (Gl y166) were expressed in place of normal OSCP. Cells expressing the OSCP var iants were able to grow on nonfermentable substrates, albeit with some incr ease in generation time. Moreover, these strains exhibited increased sensit ivity to oligomycin, suggestive of modification in functional interactions between the F-1 and F-0 sectors mediated by OSCP. Bioenergetic analysis of mitochondria from cells expressing OSCP variants indicated an increased res piratory rate under conditions of no net ATP synthesis. Using specific inhi bitors of mtATPase, in conjunction with measurement of changes in mitochond rial transmembrane potential, it was revealed that this increased respirato ry rate was a result of increased proton flux through the F-0 sector. This proton conductance, which is not coupled to phosphorylation, is exquisitely sensitive to inhibition by oligomycin. Nevertheless, the oxidative phospho rylation capacity of these mitochondria from cells expressing OSCP variants was no different to that of the control. These results suggest that the in corporation of OSCP variants into functional ATP synthase complexes can dis play effects in the control of proton flux through the F-0 sector, most lik ely mediated through altered protein-protein contacts within the enzyme com plex. This conclusion is supported by data indicating impaired stability of solubilized mtATPase complexes that is not, however, reflected in the asse mbly of functional enzyme complexes in vivo. Given a location for OSCP atop the F-1-alpha (3)beta (3) hexamer that is distant from the proton channel, then the modulation of proton flux by OSCP must occur "at a distance." We consider how subtle conformational changes in OSCP may be transmitted to F- 0.