Protein folding and unfolding: proline cis‐trans isomerization at the c subunits of F(1)F(O)‐ATPase might open a high conductance ion channel

The c subunits, which constitute the c‐ring apparatus of the F(1)F(O)‐ATPase, could be the main components of the mitochondrial permeability transition pore (mPTP). The well‐known modulator of the mPTP formation and opening is the cyclophilin D (CyPD), a peptidyl‐prolyl cis‐trans isomerase. On the loop, which connects the two hairpin α‐helix of c subunit, is present the unique proline residue (Pro (40)) that could be a biological target of CyPD. Indeed, the proline cis‐trans isomerization might provide the switch that interconverts the open/closed states of the pore by pulling out the c‐ring lipid plug.