How Lipids Mobilise Membrane-Bound Cytochrome C Seen by Solid-State NMR

Abstract

Reactive oxygen species (ROS) in mitochondria are associated with various disease conditions, ranging from cancer to neurodegeneration. ROS-mediated oxidative damage of proteins, DNA and lipids plays an important role in downstream pathogenic processes. Remarkably, the mitochondrial heme protein cytochrome c even specifically catalyzes the reaction between ROS and polyunsaturated anionic lipids, including in particular cardiolipin. The products of this enzymatic reaction act as subsequent triggers of apoptosis. We have employed solid-state NMR spectroscopy as a unique tool to gain insight into the protein-lipid nanocomplex of lipid-bound cytochrome c, in order to understand how lipid binding regulates its pro-apoptotic lipid peroxidase activity. I discuss how our published and unpublished studies reveal new information about the structure and dynamics of the peripheral membrane protein as it interacts with lipid bilayers containing different lipid species. Magic angle spinning NMR is applied to the membrane-bound protein to probe its structure and dynamics, but also its mode of interaction with the lipids and solvent. While the protein retains much of its native fold in its surface-bound state, it also undergoes localised mobilisation. The latter process is essential for the lipid peroxidase activity, with the level of activity (and mobility) regulated by the characteristics of the bound lipid membrane, protein/lipid stoichiometry and other factors.