The fifth transmembrane domain of angiotensin II Type 1 receptor participates in the formation of the ligand-binding pocket and undergoes a counterclockwise rotation upon receptor activation.
The octapeptide hormone angiotensin II exerts a wide variety of cardiovascular effects through the activation of the angiotensin II Type 1 (AT(1)) receptor, which belongs to the G protein-coupled receptor superfamily. Like other G protein- coupled receptors, the AT(1) receptor possesses seven transmembrane domains that provide structural support for the formation of the ligand-binding pocket. The role of the fifth transmembrane domain (TMD5) was investigated using the substituted cysteine accessibility method. All of the residues within Thr-190 to Leu-217 region were mutated one at a time to cysteine, and after expression in COS-7 cells, the mutant receptors were treated with the sulfhydryl-specific alkylating agent methanethiosulfonate-ethylammonium (MTSEA). MTSEA reacts selectively with water-accessible, free sulfhydryl groups of endogenous or introduced point mutation cysteines. If a cysteine is found in the binding pocket, the covalent modification will affect the binding kinetics of the ligand. MTSEA substantially decreased the binding affinity of L197C-AT(1), N200C-AT(1), I201C-AT(1), G203C-AT(1), and F204C-AT(1) mutant receptors, which suggests that these residues orient themselves within the water-accessible binding pocket of the AT(1) receptor. Interestingly, this pattern of acquired MTSEA sensitivity was altered for TMD5 reporter cysteines engineered in a constitutively active N111G-AT(1) receptor background. Indeed, mutant I201C-N111G-AT(1) became more sensitive to MTSEA, whereas mutant G203C-N111G-AT(1) lost some sensitivity. Our results suggest that constitutive activation of AT(1) receptor causes an apparent counterclockwise rotation of TMD5 as viewed from the extracellular side.
Department of Pharmacology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Quebec J1H 5N4, Canada.
Ivana
I
Domazet
Stéphane S
SS
Martin
Brian J
BJ
Holleran
Marie-Eve
ME
Morin
Patrick
P
Lacasse
Pierre
P
Lavigne
Emanuel
E
Escher
Richard
R
Leduc
Gaétan
G
Guillemette
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002522:Chlorocebus aethiops; D005020:Ethyl Methanesulfonate / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D007202:Indicators and Reagents / Q000494:pharmacology; D007700:Kinetics; D008024:Ligands; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D011487:Protein Conformation; D044140:Receptor, Angiotensin, Type 1 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D010738:Type C Phospholipases / Q000378:metabolism; D014662:Vasoconstrictor Agents / Q000494:pharmacology*
D007202:Indicators and Reagents; D008024:Ligands; D044140:Receptor, Angiotensin, Type 1; D014662:Vasoconstrictor Agents; C093171:methanethiosulfonate ethylammonium; D000804:Angiotensin II; D005020:Ethyl Methanesulfonate; D010738:Type C Phospholipases