Proteolytic regulation of mitochondrial magnesium channel by m-AAA protease and prohibitin complex

Mitochondrial membrane phospholipid cardiolipin is essential for the stability of several inner mitochondrial membrane protein complexes. We recently showed that the abundance of mitochondrial magnesium channel MRS2 is reduced in models of Barth syndrome, an X-linked genetic disorder caused by a remodeling defect in cardiolipin. However, the mechanism underlying the reduced abundance of MRS2 in cardiolipin-depleted mitochondria remained unknown. In this study, we utilized yeast mutants of mitochondrial proteases to identify an evolutionarily conserved m-AAA protease, Yta10/Yta12, responsible for degrading Mrs2. The activity of m-AAA protease is regulated by the inner mitochondrial membrane scaffolding complex prohibitin, and consistent with this role, we find that Mrs2 turnover is increased in yeast prohibitin mutants. Importantly, we find that deleting Yta10 in cardiolipin-deficient yeast cells restores the steady-state levels of Mrs2 to the wild-type cells, and the knockdown of AFG3L2, a mammalian homolog of Yta12, increases the abundance of MRS2 in a murine muscle cell line. Thus, our work has identified the m-AAA protease/prohibitin complex as an evolutionarily conserved regulator of Mrs2 that can be targeted to restore Mrs2 abundance in cardiolipin-depleted cells.