MUTATION OF ASN(111) IN THE 3RD TRANSMEMBRANE DOMAIN OF THE AT(1A) ANGIOTENSIN-II RECEPTOR INDUCES ITS CONSTITUTIVE ACTIVATION

A preliminary model of the rat AT(1A) angiotensin II (AII) receptor (J oseph, M. P., Maigret, B., Bonnafous J.-C., Marie, J., and Scheraga, H . A. (1995) J. Protein Chem. 14, 381-398) has predicted an interaction between Asn(111) located in transmembrane domain (TM) In: and Tyr(292 ) (TM VII) in the nonactivated receptor; a disruption of this interact ion upon AII activation would allow Tyr(292) to interact with the cons erved Asp(74) (TM II), The previous verification that Ty(292) is essen tial for receptor coupling to phospholipase C (Marie, J., Maigret, B., Joseph, M. P., Larguier, R., Nouet, S., Lombard, C., and Bonnafous, J .-C. (1994) J. Biol. Chem. 269, 20815-20818) prompted us to check the possible alterations in receptor properties upon Asn(111)-->Ala mutati on. The mutated receptor (N111A) displayed: (i) strong constitutive ac tivity, with amplification of the maximal phospholipase C response to AII; (ii) agonist behavior of the AT(2)-specific ligand CGP 42112A, [S ar(1),Ile(8)]AII, and [Sar(1),Ala(8)]AII, antagonists of the wild-type receptor; (iii) inverse agonism behavior of the non-peptide ligands D uP 753, LF 7-0156, and LF 8-0129. The results are discussed in the lig ht of the allosteric ternary complex models and other described exampl es of constitutive activation of G protein-coupled receptors.