Cardiolipin remodeling enables protein crowding in the inner mitochondrial membrane

Abstract

Mitochondrial cristae are extraordinarily crowded with proteins, which puts stress on the bilayer organization of lipids. We tested the hypothesis that the high concentration of proteins drives the tafazzin‐catalyzed remodeling of fatty acids in cardiolipin, thereby reducing bilayer stress in the membrane. Specifically, we tested whether protein crowding induces cardiolipin remodeling and whether the lack of cardiolipin remodeling prevents the membrane from accumulating proteins. In vitro , the incorporation of large amounts of proteins into liposomes altered the outcome of the remodeling reaction. In yeast, the concentration of proteins involved in oxidative phosphorylation (OXPHOS) correlated with the cardiolipin composition. Genetic ablation of either remodeling or biosynthesis of cardiolipin caused a substantial drop in the surface density of OXPHOS proteins in the inner membrane of the mouse heart and Drosophila flight muscle mitochondria. Our data suggest that OXPHOS protein crowding induces cardiolipin remodelling and that remodeled cardiolipin supports the high concentration of these proteins in the inner mitochondrial membrane. image In mitochondrial cristae, proteins are packaged at uniquely high density, imposing stress on the membrane lipid composition. This work uncovers acyl group remodeling of the membrane phospholipid cardiolipin as a precondition for concentrating oxidative phosphorylation (OXPHOS) proteins in the inner mitochondrial membrane. Protein crowding affects fatty acid remodeling of cardiolipin in vitro . The surface concentration of OXPHOS proteins correlates with the molecular species composition of cardiolipin. Ablation of cardiolipin remodeling or biosynthesis decreases surface concentration of OXPHOS proteins in mice and flies.