Carbohydrate moieties of the α1-adrenergic receptor (α1-R): complex type glycosylation of N-linked oligosaccharides

The binding subunit of the α1-R has been identified as a M/sub r/ = 80,000 peptide in several tissues. Adsorption of the α1-R to a WGA lectin-agarose resin suggests that the receptor protein is glycosylated. In this study, they investigated the nature of the carbohydrate linkage to the α1-R peptide. The α1-R in DDT1 MF-2 whole cells was photolabeled with 125I-azido-prazosin, the cells were lysed in the presence of DNAase, and cell membranes were treated with exo- and endoglycohydrolases prior to SDS-PAGE and autoradiography. Removal of terminal sialic acid residues by neuraminidase decreased the receptor M/sub r/ by 4000; however α-mannosidase was without effect indicating complex type glycosylation of the receptor-protein. Similar results were observed for the rat hepatic membrane α1-R. After deglycosylation of N-linked carbohydrates at asparagine residues by N-glycanase a specifically labeled peptide at a M/sub r/ = 50,000 was observed in DDT1 MF-2 cells. Treatment of photolabeled α1-R with endo-β-N-acetylglucosaminidase F or H had no effect. These results indicate that the α1-R is heavily glycosylated, the major oligosaccharide moiety being of the complex type, N-linked to asparagine residues and that the peptide backbone has a M/sub r/ < 50,000. By contrast, the α2-R has a peptide backbone of M/sub r/ = 38,000 and N-linked oligosaccharides of the hybrid type