Spin-label electron paramagnetic resonance studies on the interaction of avidin with dimyristoyl-phosphatidylglycerol membranes

The interaction of avidin - a basic protein from hen egg-white - with dimyr istoyl-phosphatidylglycerol membranes was investigated by spin-label electr on paramagnetic resonance spectroscopy. Phosphatidylcholines. bearing the n itroxide spin label at different positions along the sn-2 acyl chain of the lipid were used to investigate the effect of protein binding on the lipid chain-melting phase transition and acyl chain dynamics. Binding of the prot ein at saturating levels results in abolition of the chain-melting phase tr ansition of the lipid and accompanying perturbation of the lipid acyl chain mobility. In the fluid phase region, the outer hyperfine splitting increas es for all phosphatidylcholine spin-label positional isomers, indicating th at the chain mobility is decreased by binding avidin. However, there was no evidence for direct interaction of the protein with the lipid acyl chains, clearly indicating that the protein does not penetrate the hydrophobic int erior of the membrane. Selectivity experiments with different spin-labelled lipid probes indicate that avidin exhibits a preference for negatively cha rged lipid species, although all spin-labelled lipid species indirectly sen se the protein binding. The interaction with negatively charged lipids is r elevant to the use of avidin in applications such as the ultrastructural lo calization of biotinylated lipids in histochemical studies. (C) 2001 Elsevi er Science B.V. All rights reserved.