Studies of membrane dynamics using nitroxide spin labels

Abstract

Nitroxide free radicals may be covalently attached either to lipids or to proteins in order to study the mobility of the molecular components of biological membranes using electron spin resonance (ESR) spectroscopy. Simulation of the conventional ESR spectra from spin-labelled dimyristoyl phosphatidylcholine in oriented phospholipid bilayer model membranes allows a complete description of the lipid chain conformation, ordering and dynamics on the nanosecond timescale. Experiments with spin-labelled lipids in natural or reconstituted membranes reveal ESR spectral components from the lipids interacting directly with the intramembranous surface of the integral membrane proteins. This allows quantitation of the lipid stoichiometry and specificity of lipid/protein interaction, and determination of the exchange rates of the lipids at the lipid-protein interface on the submicrosecond timescale. Saturation transfer ESR spectroscopy can be used to study the motions of spin-labelled membrane-bound proteins on the submillisecond timescale. These motions include large-scale segmental mobility and rotational diffusion of integral proteins within the membrane. © 1990 De Gruyter