A FULLY ACTIVE NONGLYCOSYLATED V2 VASOPRESSIN RECEPTOR

The human V2 vasopressin receptor belongs to the superfamily of G prot ein-coupled receptors believed to be anchored to the plasma membrane b y seven transmembrane regions. The extracellular portion of the human V2 vasopressin receptor contains one site susceptible to N-linked glyc osylation. Metabolic labeling and immunoprecipitation of the receptor expressed in transfected cells were applied to examine whether the pro tein was indeed glycosylated. The V2 vasopressin receptor expressed tr ansiently was glycosylated, but glycosidase treatment to test the comp lexity of the sugar moiety linked to asparagine revealed that the majo rity of the receptor protein lacked complex carbohydrates, an indicati on of an improperly processed protein. This immature protein displayed a tendency to form aggregates. In contrast with these data, testing o f the sugar complexity of the receptor protein synthesized in stably t ransfected cells identified the predominant form as an appropriately p rocessed receptor protein. Mutagenesis of asparagine 22 to glutamine p roduced on expression in transfected cells a nonglycosylated receptor with ligand binding affinity and coupling characteristics almost ident ical to those of the wild-type form. After exposure to elevated concen trations of AVP (100 nM), the nonglycosylated form desensitized to the same extent as the wild-type receptor.