Selectivity of interaction of spin-labelled lipids with peripheral proteins bound to dimyristoylphosphatidylglycerol bilayers, as determined by ESR spectroscopy

Abstract

The selectivity of interaction between spin-labelled lipids and the peripheral proteins, apocytochrome c, cytochrome c, lysozyme and polylysine has been studied using ESR spectroscopy. Derivatives of phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), phosphatidylserine (PS), phosphatidylinositol (PI), diphosphatidylglycerol (CL) and diacylglycerol (DG) spin-labelled at the 5-C atom position of the sn-2 chain were used to study the association of these proteins with bilayers of dimyristoylphosphatidylglycero. Binding of the proteins increased the outer hyperfine splitting in the ESR spectra of the lipid spin labees to an extent which depended both on the spin-labelled lipid species involved and on the particular protein. The order of selectivity for apocytochrome c follows the sequence: PI −>CL −≈DG PS −>PC ±>PG −>PE ±. The selectivity pattern for cytochrome c is: PI −>PG −>CL −>DG PS −≈PC ±>PE ±; for lysozyme is: CL −>PG −>DG PE −>PC ±PS −>PI −; and that for polylysine is: CL −>PS −⩾PG −>PI −>PC ±>DG PE +-. The overall strength of interaction is in the order lysozyme>cytochrome c>apcoytochrome c, for equivalent binding, and the spread of the selectivity for the different proteins is in the reverse order. Assuming fast exchange for the ESR spectra of the 5-C atom labelled lipids, the relative association constants of the different labels with the different proteins have been estimated.