Cytochrome c induced lateral phase separation in a diphosphatidylglycerol-steroid spin-label model membrane

The extrinsic membrane protein cytochrome c binds to lipid mixtures containing negatively charged phospholipids such as diphosphatidylglycerol (DPG). In this study the effect of cytochrome c on the lipid distribution in a DPG-steroid spin-label (3-doxyl-5alpha-cholestane) model membrane system is examined. The electron spin resonance (ESR) line-shape changes indicate that cytochrome c induces lateral phase separation at room temperature. The resulting two-dimensional lipid distribution is nonrandom, consisting of clusters of phospholipids bound to cytochrome c and patches of steroid spin-label molecules. Phase separations are also observed in the three-component system: DPG, phosphatidylcholine, and 3-doxyl-5alpha-cholestane.