Surface-Binding to Cardiolipin Nanodomains Triggers Cytochrome c Pro-apoptotic Peroxidase Activity via Localized Dynamics.

The peroxidation of cardiolipins by reactive oxygen species, which is regulated and enhanced by cytochrome c (cyt c), is a critical signaling event in mitochondrial apoptosis. We probe the molecular underpinnings of this mitochondrial death signal through structural and functional studies of horse heart cyt c binding to mixed-lipid membranes containing cardiolipin with mono- and polyunsaturated acyl chains. Lipidomics reveal the selective oxidation of polyunsaturated fatty acid (PUFA) cardiolipin (CL), while multidimensional solid-state NMR probes the structure and dynamics of the membrane and the peripherally bound protein. The hydrophilic milieu at the membrane interface stabilizes a native-like fold, but also leads to localized flexibility at the membrane-interacting protein face. PUFA CL acts as both a preferred substrate and a dynamic regulator by affecting the dynamics of the cyt c N70-I85 Ω loop, which covers the heme cavity. • Cytochrome c is a cardiolipin-selective lipid peroxidase in intrinsic apoptosis • Lipidomics probe oxygenation products of cardiolipin peroxidation in vitro • Solid-state NMR shows folded, but dynamically perturbed, protein on lipid surface • PUFA lipid-coupled dynamics of 70–85 Ω loop regulate access to heme cavity Li et al. show how cardiolipin acts as both a substrate and a dynamic regulator of cytochrome c 's pro-apoptotic lipid peroxidase functionality. Combining solid-state NMR and mass spectrometry lipidomics, they find that localized motion of the 70–85 Ω loop regulates heme cavity access in the peroxidase-active peripherally membrane-bound protein. [ABSTRACT FROM AUTHOR]