Modulation of the specific interaction of cardiolipin with cytochrome c by zwitterionic phospholipids in binary mixed bilayers; a 2H and 31P NMR study

Abstract

The interaction of cytochrome c with binary phospholipid mixtures was investigated by solid-state 2H and 31P NMR. To examine the effect of interaction on the glycerol backbones, the glycerol moieties of phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG) and cardiolipin (CL) were specifically deuterated. On binding of cytochrome c to the binary mixed bilayers, no changes in the quadrupole splittings of each component were observed for PC/PG, PE/CL and PE/PG liposomes. In contrast, the splittings of CL decreased on binding of the protein to PC/CL liposomes, although those of PC did not change at all. This showed that cytochrome c specifically interacts with cardiolipin (CL) in phosphatidylcholine (PC)/CL bilayers and penetrates into the lipid bilayer to some extent so as to perturb the dynamic structure of the glycerol backbone. This is distinctly different from the mode of interaction of cytochrome c with other binary mixed bilayers. In 31P NMR spectra, line broadening and a decrease of the chemical shift anisotropy were observed on binding of cytochrome c for all binary mixed bilayers examined. These changes were more significant for PC/CL bilayers. Furthermore, the line broadening is more significant for PC than for CL in PC/CL bilayers. Therefore, it can be concluded that as far as the polar head groups are concerned, not only CL but also PC are involved in the interaction with cytochrome c