The C-Subunit of the ATP Synthase Forms the Pore of the PTP

Abstract

Mitochondria maintain tight regulation of inner mitochondrial membrane (IMM) permeability to sustain ATP production. Stressful events cause cell Ca2+ dysregulation followed by rapid loss of IMM potential known as permeability transition (PT), which produces osmotic shifts, metabolic dysfunction and cell death. The molecular identity of the mitochondrial PT pore (mPTP) is still in question. We had described previously that, through protein-protein interaction with the beta subunit of the ATP synthase, the anti-apoptotic protein Bcl-xL decreased an inner membrane leak conductance to increase bioenergetic efficiency during neuronal activity. To identify the source of the leak, we used patch clamp recording of submitochondrial vesicles. We have now shown that the leak channel most likely regulated by interaction with the beta subunit is the c-subunit ring of the F1FO ATP synthase and we further suggest that this channel forms the mPTP. High Ca2+ enlarges the c-subunit ring and uncouples it from Ca2+/ cyclosporine A (CsA) binding sites in the F1 of the ATP synthase. Depletion of the c-subunit prevents PT and attenuates cell death, while increasing the expression or conductance of the c-subunit channel sensitizes cells to death. Physical uncoupling of F1 from FO occurs when PT is induced, and an antibody specific to the c-subunit inhibits c-subunit channel conductance and prevents calcium-induced IMM channel activity. We conclude that a highly regulated c-subunit leak channel is the mPTP.