Curious case of a leaky mitochondria.

Abstract

The mitochondrial permeability transition pore (mPTP) leads to cell death upon its activation. The past several decades have seen many studies regarding the modulation of the mPTP, but little is known about the structure. There has been a growing body of evidence that the ATP synthase c-subunit houses the mPTP leak channel. Experimental evidence has shown that ATP Synthase forms voltage-gated and Ca2+-activated channels, consistent to what is known about mPTP activation. Previous experimental and molecular dynamics simulation studies demonstrate that the ATP synthase c-subunit is occupied by lipid and/or detergent molecules, claiming that a leak channel cannot be formed and that ATP synthase does not play a role in mPTP formation. These studies have sparked much controversy regarding the structural identity of the mPTP leak channel. In this work, we investigated whether the ATP synthase c-subunit forms a leak channel upon introducing voltage. We performed molecular dynamics simulations on the ATP synthase c-subunit under an electric field, ranging from −180 mV to +180 mV. Our results show significant expansion of the c-subunit, and lipids exiting as water leaks into the pore. Additionally, we identified a dipole on the c-subunit monomer that aids in voltage-sensing. We also applied voltage to a c-subunit high and low-conductance mutants, where we observe similar results, except for decreased water leakage in the low-conductance mutant. Initially, we observed a bottleneck at a key glutamic acid residue that is responsible for proton transport in the c-subunit. To overcome this bottleneck, we introduced a series of deprotonations on these glutamic acid residues to promote water accessibility, resulting in a full leak channel formation. With our results, we seek to answer a long-standing question about the gating mechanism of ATP synthase c-subunit leak channel and the structural identity of the mPTP.