Chemical characterization of ligand binding site fragments from turkey beta-adrenergic receptor

Affinity-labeled beta-adrenergic receptor from turkey erythrocyte membranes was specifically cleaved near cysteine residues after S-cyanylation. Analysis of the labeled polypeptide fragments suggests that iodocyanopindolol diazirine reacted with an amino acid residue which is located in the non-glycosylated region containing the sixth and seventh transmembrane domains of the receptor. However, the possibility cannot be excluded that a second residue, located between the third and fifth transmembrane domains, was also labeled. Since treatment with either hydroxylamine or triethylamine resulted in removal of the affinity label from the protein, the present study suggests that aspartic or glutamic acid residues are present in the adrenergic-binding site which is located in the above-mentioned domains. The procedure for specific chemical cleavage of the affinity-labeled adrenergic receptor should also be useful for future structural and comparative studies of other adrenergic receptors.