RT Journal Article SR Electronic T1 Constitutively Active Mutants of the Histamine H1 Receptor Suggest a Conserved Hydrophobic Asparagine-Cage That Constrains the Activation of Class A G Protein-Coupled Receptors JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 94 OP 103 DO 10.1124/mol.107.038547 VO 73 IS 1 A1 Remko A. Bakker A1 Aldo Jongejan A1 Kamonchanok Sansuk A1 Uli Hacksell A1 Henk Timmerman A1 Mark R. Brann A1 Dave M. Weiner A1 Leonardo Pardo A1 Rob Leurs YR 2008 UL http://molpharm.aspetjournals.org/content/73/1/94.abstract AB The aim of this study was to create and characterize constitutively active mutant (CAM) histamine H1 receptors (H1R) using random mutagenesis methods to further investigate the activation process of the rhodopsin-like family of G protein-coupled receptors (GPCRs). This approach identified position 6.40 in TM 6 as a “hot spot” because mutation of Ile6.40420 either to Glu, Gly, Ala, Arg, Lys, or Ser resulted in highly active CAM H1Rs, for which almost no histamine-induced receptor activation response could be detected. The highly conserved hydrophobic amino acid at position 6.40 defines, in a computational model of the H1R, the asparagine cage motif that restrains the side chain of Asn7.49 of the NPxxY motif toward transmembrane domain (TM 6) in the inactive state of the receptor. Mutation of the asparagine cage into Ala or Gly, removing the interfering bulky constraints, increases the constitutive activity of the receptor. The fact that the Ile6.40420Arg/Lys/Glu mutant receptors are highly active CAM H1Rs leads us to suggest that a positively charged residue, presumably the highly conserved Arg3.50 from the DRY motif, interacts in a direct or an indirect (through other side chains or/and internal water molecules) manner with the acidic Asp2.50··Asn7.49 pair for receptor activation. The American Society for Pharmacology and Experimental Therapeutics