The two rotor components of yeast mitochondrial ATP synthase are mechanically coupled by subunit δ

The mitochondrial ATP synthase is made of a membrane-integrated F-0 component that forms a proton-permeable pore through the inner membrane and a globular peripheral F-1 domain where ATP is synthesized. The catalytic mechanism is thought to involve the rotation of a 10-12 c subunit ring in the F-0 together with the gamma subunit of F-1. An important and not yet resolved question is to define precisely how the gamma subunit is connected with the c-ring. In this study, using a doxycycline-regulatable expression system, we provide direct evidence that the rest of the enzyme can assemble without the delta subunit of F-1, and we show that delta-less mitochondria are uncoupled because of an F-0-mediated proton leak. Based on these observations, and taking into account high-resolution structural models, we propose that subunit delta plays a key role in the mechanical coupling of the c-ring to subunit gamma.