Role of the Cys 18–Cys 274 disulfide bond and of the third extracellular loop in the constitutive activation and internalization of angiotensin II type 1 receptor

• Published in: Regulatory peptides Vol. 134; no. 2; pp. 132 - 140
• Main Authors: Correa, Silvana A.A., Pignatari, Graciela C., Ferro, Emer S., Pacheco, Nelson A.S., Costa-Neto, Claudio M., Pesquero, João B., Oliveira, Laerte, Paiva, Antonio C.M., Shimuta, Suma I.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 2006
• Subjects: AT 1 receptor mutations; Constitutively active receptor; GFP fusion proteins; Internalization; Molecular modeling; AT 1 receptor mutations; Internalization; Molecular modeling; Constitutively active receptor; GFP fusion proteins; Protein amino acid residues are represented by the three letter code and ligand residues are represented by the one letter code
• ISSN: 0167-0115; 1873-1686
• DOI: 10.1016/j.regpep.2006.02.008

An insertion of residues in the third extracellular loop and a disulfide bond linking this loop to the N-terminal domain were identified in a structural model of a G-protein coupled receptor specific to angiotensin II (AT 1 receptor), built in homology to the seven-transmembrane-helix bundle of rhodopsin. Both the insertion and the disulfide bond were located close to an extracellular locus, flanked by the second extracellular loop (EC-2), the third extracellular loop (EC-3) and the N-terminal domain of the receptor; they contained residues identified by mutagenesis studies to bind the angiotensin II N-terminal segment (residues D 1 and R 2). It was postulated that the insertion and the disulfide bond, also found in other receptors such as those for bradykinin, endothelin, purine and other ligands, might play a role in regulating the function of the AT 1 receptor. This possibility was investigated by assaying AT 1 forms devoid of the insertion and with mutations to Ser on both positions of Cys residues forming the disulfide bond. Binding and activation experiments showed that abolition of this bond led to constitutive activation, decay of agonist binding and receptor activation levels. Furthermore, the receptors thus mutated were translocated to cytosolic environments including those in the nucleus. The receptor form with full deletion of the EC-3 loop residue insertion, displayed a wild type receptor behavior.