Angiotensin IV is a potent agonist for constitutive active human AT1 receptors. Distinct roles of the N-and C-terminal residues of angiotensin II during AT1 receptor activation.
The octapeptide hormone, angiotensin II (Ang II), exerts its major physiological effects by activating AT(1) receptors. In vivo Ang II is degraded to bioactive peptides, including Ang III (angiotensin-(2-8)) and Ang IV (angiotensin-(3-8)). These peptides stimulate inositol phosphate generation in human AT(1) receptor expressing CHO-K1 cells, but the potency of Ang IV is very low. Substitution of Asn(111) with glycine, which is known to cause constitutive receptor activation by disrupting its interaction with the seventh transmembrane helix (TM VII), selectively increased the potency of Ang IV (900-fold) and angiotensin-(4-8), and leads to partial agonism of angiotensin-(5-8). Consistent with the need for the interaction between Arg(2) of Ang II and Ang III with Asp(281), substitution of this residue with alanine (D281A) decreased the peptide's potency without affecting that of Ang IV. All effects of the D281A mutation were superseded by the N111G mutation. The increased affinity of Ang IV to the N111G mutant was also demonstrated by binding studies. A model is proposed in which the Arg(2)-Asp(281) interaction causes a conformational change in TM VII of the receptor, which, similar to the N111G mutation, eliminates the constraining intramolecular interaction between Asn(111) and TM VII. The receptor adopts a more relaxed conformation, allowing the binding of the C-terminal five residues of Ang II that switches this "preactivated" receptor into the fully active conformation.
Le
Minh Tam
MT
Department of Molecular and Biochemical Pharmacology, Institute of Molecular Biology and Biotechnology, Vrije Universiteit Brussel, B-1640 Sint-Genesius Rode, Belgium.
Vanderheyden
Patrick M L
PM
Szaszák
Márta
M
Hunyady
László
L
Vauquelin
Georges
G
D000804:Angiotensin II / Q000031:analogs & derivatives* / Q000737:chemistry* / Q000494:pharmacology* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D006801:Humans; D011487:Protein Conformation; D044140:Receptor, Angiotensin, Type 1; D011945:Receptors, Angiotensin / Q000819:agonists* / Q000737:chemistry / Q000378:metabolism; D013329:Structure-Activity Relationship
D044140:Receptor, Angiotensin, Type 1; D011945:Receptors, Angiotensin; D000804:Angiotensin II; C012877:angiotensin II, des-Asp(1)-des-Arg(2)-Ile(5)-