Mitochondrial Membranes: Model Lipid Compositions, Material Properties and the Changing Curvature of Cardiolipin

Abstract

Mammalian and Drosophila Melanogaster model mitochondrial membrane compositions are constructed from experimental lipidomics data. Simplified compositions for inner and outer mitochondrial membranes are provided, including an asymmetric inner mitochondrial membrane. We performed atomistic molecular dynamics simulations of these membranes and computed their material properties. When comparing these properties to those obtained by extrapolation from their constituting lipids, we find good overall agreement. Finally, we analyzed the curvature effect of cardiolipin, considering ion concentration effects, oxidation and pH. We draw the conclusion that cardiolipin negative curvature is most likely due to counterion effects, such as cation adsorption, in particular of H3O+. This oft-neglected effect might account for the puzzling behavior of this lipid. SIGNIFICANCEMitochondrial membranes are of fundamental interest to the pathogenesis of neurodegenerative diseases. The biophysics of mitochondrial membranes can be expected to profoundly influence both the electron transport chain and larger-scale mitochondrial morphology. We provide model mitochondrial membrane compositions and examine their mechanic properties. Reconstructing these properties from their constituent lipids, we facilitate the creation of mesoscopic models. Cardiolipin, as the key mitochondrial lipid is given special attention. We find that its mechanical properties, in particular its curvature, are not constant, but highly dependent on specific ion effects, concentration and oxidation state.