The oligomeric subunit c rotor in the F-o sector of ATP synthase: Unresolved questions in our understanding of function

We have proposed a model for the oligomeric c-rotor of the F-o sector of AT P synthase and its interaction with subunit a during Hi-transport driven ro tation. The model is based upon the solution structure of monomeric subunit c, determined by NMR, and an extensive series of cross-linking distance co nstraints between c subunits and between subunits c and a. To explain the c omplete set of cross-linking data, we have suggested that the second transm embrane helix rotates during its interaction with subunit a in the course o f the H+-translocation cycle. The H+-transport coupled rotation of this hel ix is proposed to drive the stepwise movement of the c-oligomeric rotor. Th e model is testable and provides a useful framework for addressing question s raised by other experiments.