The use of spin-label ESR spectroscopy to study protein-lipid interactions

Abstract

Protein-lipid interactions play crucial roles in the structure and function of biological membranes. Therefore it is important to investigate these interactions in detail. Electron spin resonance (ESR) spectroscopy of spin labelled lipids is particularly suited for investigating how proteins association affects properties of membrane lipids. Studies employing phospholipid probes bearing the stable nitroxide spin label at different positions on the sn-2 acyl chain revealed that the lipid chain mobility is significantly reduced in the presence of transmembrane proteins and to a lesser extent in the presence of peripheral proteins. The strong immobilization of the lipid acyl chains in the presence of transmembrane proteins can be attributed to direct interaction of the lipid acyl chains with the transmembrane protein. ESR spectra of spin-labelled lipids in reconstituted systems with defined lipid-protein ratios can be analysed to estimate the number of lipid molecules present in the annulus (boundary lipid). Systematic studies employing spin-labelled lipids bearing different phospholipid head groups have shown that different membrane proteins exhibit different lipid specificities.