The functional G protein-coupled membrane receptors (GPCR) bovine rhodopsin and recombinantly expressed type II cannabinoid receptor, CB2, are reconstituted into lipid bilayers to study the influence of membrane composition on receptor function. Lipid-GPCR interaction is investigated directly on the lipids by a variety of solid-state NMR approaches, while receptor function is followed by ligand binding and G protein-activation studies. Elastic deformation of the lipid matrix from lipid-GPCR interactions is investigated by 2H-NMR on bilayers composed of lipids with perdeuterated hydrocarbon chains. The data show that bilayers adjust elastically to the hydrophobic length of transmembrane helices of GPCR. However, any hydrophobic mismatch between the lipid matrix and GPCR also results in structural changes of the GPCR. Specificity towards interaction with particular lipid species is investigated by magnetization transfer experiments from the GPCR to lipids using 1H, 31P-, and 13C magic-angle spinning NMR experiments. For rhodopsin, they revealed that the protein has some preference for interaction with phosphatidylethanolamines with polyunsaturated, docosahexaenoic acid hydrocarbon chains. Furthermore, 13C-MAS NMR relaxation studies showed that such interactions do not result in significant immobilization of lipid molecules near the protein. Lipids in the first layer surrounding the GPCR remain in rapid exchange with the bulk of the lipid matrix on the timescale of microseconds. The relationship between lipid-GPCR interaction, oligomerization of GPCR, and GPCR activation will be discussed.

Lipid interaction with G protein-coupled membrane receptors studied by NMR

247th National Meeting (2014)

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