PT - JOURNAL ARTICLE AU - Scheer, Alexander AU - Costa, Tommaso AU - Fanelli, Francesca AU - De Benedetti, Pier G. AU - Mhaouty-Kodja, Sakina AU - Abuin, Liliane AU - Nenniger-Tosato, Monique AU - Cotecchia, Susanna TI - Mutational Analysis of the Highly Conserved Arginine within the Glu/Asp-Arg-Tyr Motif of the α<sub>1b</sub>-Adrenergic Receptor: Effects on Receptor Isomerization and Activation DP - 2000 Feb 01 TA - Molecular Pharmacology PG - 219--231 VI - 57 IP - 2 4099 - http://molpharm.aspetjournals.org/content/57/2/219.short 4100 - http://molpharm.aspetjournals.org/content/57/2/219.full SO - Mol Pharmacol2000 Feb 01; 57 AB - We have suggested previously that both the negatively and positively charged residues of the highly conserved Glu/Asp-Arg-Tyr (E/DRY) motif play an important role in the activation process of the α1b-adreneric receptor (AR). In this study, R143 of the E/DRY sequence in the α1b-AR was mutated into several amino acids (Lys, His, Glu, Asp, Ala, Asn, and Ile). The charge-conserving mutation of R143 into lysine not only preserved the maximal agonist-induced response of the α1b-AR, but it also conferred high degree of constitutive activity to the receptor. Both basal and agonist-induced phosphorylation levels were significantly increased for the R143K mutant compared with those of the wild-type receptor. Other substitutions of R143 resulted in receptor mutants with either a small increase in constitutive activity (R143H and R143D), impairment (R143H, R143D), or complete loss of receptor-mediated response (R143E, R143A, R143N, R143I). The R413E mutant displayed a small, but significant increase in basal phosphorylation despite being severely impaired in receptor-mediated response. Interestingly, all the arginine mutants displayed increased affinity for agonist binding compared with the wild-type α1b-AR. A correlation was found between the extent of the affinity shift and the intrinsic activity of the agonists. The analysis of the receptor mutants using the allosteric ternary complex model in conjunction with the results of molecular dynamics simulations on the receptor models support the hypothesis that mutations of R143 can drive the isomerization of the α1b-AR into different states, highlighting the crucial role of this residue in the activation process of the receptor. The American Society for Pharmacology and Experimental Therapeutics