Expression of human peripheral cannabinoid receptor for structural studies

Human peripheral‐type cannabinoid receptor (CB2) was expressed in Escherichia coli as a fusion with the maltose‐binding protein, thioredoxin, and a deca‐histidine tag. Functional activity and structural integrity of the receptor in bacterial protoplast membranes was confirmed by extensive binding studies with a variety of natural and synthetic cannabinoid ligands. E. coli membranes expressing CB2 also activated cognate G‐proteins in an in vitro coupled assay. Detergent‐solubilized receptor was purified to 80%–90% homogeneity by affinity chromatography followed by ion‐exchange chromatography. By high‐resolution NMR on the receptor in DPC micelles, it was determined that purified CB2 forms 1:1 complexes with the ligands CP‐55,940 and anandamide. The receptor was successfully reconstituted into phosphatidylcholine bilayers and the membranes were deposited into a porous substrate as tubular lipid bilayers for structural studies by NMR and scattering techniques.