title: "Network leaning" as a mechanism of insurmountable antagonism of the angiotensin II type 1 receptor by non-peptide antagonists.
abstract: A mechanistic understanding of the insurmountable antagonism of the angiotensin II type 1 (AT(1)) receptor could be fundamental in the quest for discovery and improvement of drugs. Candesartan and EXP3174 are competitive, reversible insurmountable antagonists of the AT(1) receptor. They contain di-acidic substitutions, whereas the surmountable antagonist, losartan, contains only one acidic group. We tested the hypothesis that these two classes of ligands interact with the AT(1) receptor through similar but not identical bonds and that the differences in the acid-base group contacts are critical for insurmountable antagonism. By pharmacological characterization of site-directed AT(1) receptor mutants expressed in COS1 cells we show that specific interactions with Gln(257) in transmembrane 6 distinguishes insurmountable antagonists and that abolishing these interactions transforms insurmountable to surmountable antagonism. In the Q257A mutant, the dissociation rate of [(3)H]candesartan is 2.8-fold more than the rate observed with wild type, and the association rate was reduced 4-fold lower than the wild type. The pattern of antagonism of angiotensin II concentration-response in the Q257A mutant pretreated with EXP3174 and candesartan is surmountable. We propose that leaning ability of insurmountable antagonists on Gln(257) in the wild-type receptor is the basis of an antagonist-mediated conformational transition, which is responsible for both slow dissociation and inhibition of maximal IP response.
authors.affiliation: Department of Molecular Cardiology, Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA.
authors.forename: Takanobu
authors.initials: T
authors.lastname: Takezako
authors.forename: Camelia
authors.initials: C
authors.lastname: Gogonea
authors.forename: Yasser
authors.initials: Y
authors.lastname: Saad
authors.forename: Keita
authors.initials: K
authors.lastname: Noda
authors.forename: Sadashiva S
authors.initials: SS
authors.lastname: Karnik
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001562:Benzimidazoles / Q000494:pharmacology; D001667:Binding, Competitive; D001713:Biphenyl Compounds; D019556:COS Cells; D002462:Cell Membrane / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D007093:Imidazoles / Q000494:pharmacology; D007700:Kinetics; D008024:Ligands; D019808:Losartan / Q000494:pharmacology; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010455:Peptides / Q000737:chemistry; D011487:Protein Conformation; D051381:Rats; D044140:Receptor, Angiotensin, Type 1 / Q000737:chemistry* / Q000378:metabolism; D013696:Temperature; D013777:Tetrazoles / Q000494:pharmacology; D013997:Time Factors
chemical_list: D001562:Benzimidazoles; D001713:Biphenyl Compounds; D007093:Imidazoles; D008024:Ligands; D010455:Peptides; D044140:Receptor, Angiotensin, Type 1; D013777:Tetrazoles; C066026:losartan carboxylic acid; D019808:Losartan; C081643:candesartan