The mitochondrial cohibitin complex facilitates the biogenesis of inner membrane proteins

The inner membrane of mitochondria contains many membrane-embedded carrier proteins of the SLC25 family to facilitate the exchange of metabolites between the cytosol and mitochondria. These carriers use a specific import route for their biogenesis that relies on the TIM22 complex as an inner membrane translocase. The molecular details of carrier biogenesis are not well understood. Using an improved, desthiobiotin-based proximity labeling approach called Destni in living yeast cells, we identified the mitochondrial protein Aim11 as an interactor of newly imported carrier proteins. Aim11 forms a 160 kDa complex together with Iai11, Gep7 and Mtc1 in the mitochondrial inner membrane that we named the comrade-of-prohibitin (cohibitin) complex owing to its genetic interaction with prohibitins. Deletion of Aim11 impairs the import of carrier proteins into the inner membrane and renders cells hypersensitive to carrier overexpression. Our data suggest that the cohibitin complex plays a quality control function that supports the TIM22-mediated insertion of carrier proteins into the inner membrane of mitochondria. SummaryKizmaz et al. identified Aim11 as a novel quality control factor that facilitates the insertion of carrier proteins into the inner membrane of mitochondria. Aim11 is part of the membrane-embedded cohibitin complex which cooperates with prohibitins in inner membrane protein biogenesis.