Molecular basis of diseases caused by the mtDNA mutation m.8969G>A in the subunit a of ATP synthase.

The ATP synthase which provides aerobic eukaryotes with ATP, organizes into a membrane-extrinsic catalytic domain, where ATP is generated, and a membrane-embedded F domain that shuttles protons across the membrane. We previously identified a mutation in the mitochondrial MT-ATP6 gene (m.8969G>A) in a 14-year-old Chinese female who developed an isolated nephropathy followed by brain and muscle problems. This mutation replaces a highly conserved serine residue into asparagine at amino acid position 148 of the membrane-embedded subunit a of ATP synthase. We showed that an equivalent of this mutation in yeast (aSN) prevents F-mediated proton translocation. Herein we identified four first-site intragenic suppressors (aND, aNK, aNI, and aNT), which, in light of a recently published atomic structure of yeast F indicates that the detrimental consequences of the original mutation result from the establishment of hydrogen bonds between aN and a nearby glutamate residue (aE) that was proposed to be critical for the exit of protons from the ATP synthase towards the mitochondrial matrix. Interestingly also, we found that the aSN mutation can be suppressed by second-site suppressors (aPS, aIF, aIN, aIF, and aIM), of which some are very distantly located (by 20-30 Å) from the original mutation. The possibility to compensate through long-range effects the aSN mutation is an interesting observation that holds promise for the development of therapeutic molecules.