title: The mammalian beta-adrenergic receptor: structural and functional characterization of the carbohydrate moiety.
abstract: Mammalian beta-adrenergic receptors are glycoproteins consisting of a single polypeptide chain of Mr approximately 64,000. Treatment of purified [125I]-labeled hamster lung beta-adrenergic receptor with alpha-mannosidase reveals two discrete populations of receptor consistent with previous studies using membrane bound photoaffinity-labeled receptor. Treatment of the [125I]-labeled receptor with endoglycosidase F results initially in the formation of a Mr approximately 57,000 peptide which is further converted to Mr approximately 49,000 suggesting that there are two N-linked carbohydrate chains per receptor polypeptide. Exoglycosidase treatments and lectin chromatography of the [125I]-labeled receptor reveals the presence of two complex type carbohydrate chains (approximately 10% of which are fucosylated) on approximately 45% of the receptors. The remaining approximately 55% of the receptors appear to contain a mixture of carbohydrate chains (possibly high mannose, hybrid and complex type chains). Deglycosylation of the receptor by endoglycosidase F does not appear to alter the binding affinity of the receptor for a variety of beta-adrenergic agonists and antagonists. Moreover, the ability of control, alpha-mannosidase sensitive or insensitive (fractionated on immobilized wheat germ agglutinin) and neuraminidase, alpha-mannosidase or endoglycosidase F treated receptors to interact with the stimulatory guanine nucleotide regulatory protein in a reconstituted system were virtually identical. The deglycosylated receptor was also unaltered in its heat lability as well as its susceptibility to a variety of proteases. These findings demonstrate that the carbohydrate portion of the beta-receptor does not contribute to determining either its specificity of ligand binding or coupling to the adenylate cyclase system.
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D002241:Carbohydrates / Q000032:analysis*; D002846:Chromatography, Affinity; D006224:Cricetinae; D020558:GTP Phosphohydrolases / Q000378:metabolism; D006023:Glycoproteins / Q000032:analysis*; D006026:Glycoside Hydrolases; D037102:Lectins; D008168:Lung / Q000032:analysis; D008565:Membrane Proteins / Q000032:analysis; D010447:Peptide Hydrolases; D011485:Protein Binding; D011943:Receptors, Adrenergic, beta / Q000032:analysis* / Q000187:drug effects; D013696:Temperature
chemical_list: D000318:Adrenergic beta-Agonists; D002241:Carbohydrates; D006023:Glycoproteins; D037102:Lectins; D008565:Membrane Proteins; D011943:Receptors, Adrenergic, beta; D006026:Glycoside Hydrolases; D010447:Peptide Hydrolases; D020558:GTP Phosphohydrolases