Effect of mutations in putative hormone binding sites on V2 vasopressin receptor function.

The vasopressin V2 receptor belongs to the large family of the G-protein coupled receptors and is responsible for the antidiuretic effect of the neurohypophyseal hormone arginine vasopressin (AVP). Based on bioinformatic studies it seems that Ala300 and Asp297 of the V2 vasopressin receptor (V2R) are involved in receptor binding. Ala300Glu mutation resulted in lower energy while Asp297Tyr mutation resulted in higher energy in AVP-V2R docked complex rather than the wild type. Therefore we hypothesized that the Ala300Glu mutation results in stronger and Asp297Tyr mutation leads to weaker ligand-receptor binding. Site directed mutagenesis of Asp297Tyr and Ala300Glu was performed using nested polymerase chain reaction. After restriction enzyme digestion, the inserts were ligated into the pcDNA3 vector and Escherichia coli XL1-Blue competent cells were transformed using commercial kit and electroporation methods. The obtained colonies were analyzed for the presence and orientation of the inserts using proper restriction enzymes. After transient transfection of COS-7 cells using ESCORT™ IV transfection reagent, the adenylyl cyclase activity assay was performed for functional studies. The cell surface expression of V2R was analyzed by indirect ELISA method. Based on the obtained results, the Ala300Glu mutation of V2R led to reduced levels of cAMP production without a marked effect on the receptor expression and the receptor binding. Effect of Asp297Tyr mutation on cell surface expression of V2R was the same as the wild type receptor. Pretreatment with 1 nM vasopressin showed an increased level of Asp297Tyr mutant receptor internalization as compared to the wild type receptor, while the effect of 100 nM vasopressin was similar in the mutant and wild type receptors. These data suggest that alterations in Asp297 but not Ala300 would affect the hormone receptor binding.