2lr9
From Proteopedia
High-resolution solution NMR structure of the rho-conotoxin TIA.
Structural highlights
FunctionCA1A_CONTU Allosteric inhibitor of alpha-1B adrenergic receptors (ADRA1B). Binds to an allosteric modulatory site on transmembrane helix 6 and 7 at the base of extracellular loop 3 of ADRA1B (PubMed:23184947). Also weekly inhibits alpha-1A (ADRA1A) and alpha-1D (ADRA1D) adrenergic receptors in a competive manner (PubMed:15194691). Potently inhibits contractions of vas deferens, spleen and aorta in response to noradrenaline (PubMed:15680270).[1] [2] [3] [4] [5] Publication Abstract from PubMedThe G protein-coupled receptor (GPCR) superfamily is an important drug target that includes over 1000 membrane receptors that functionally couple extracellular stimuli to intracellular effectors. Despite the potential of extracellular surface (ECS) residues in GPCRs to interact with subtype-specific allosteric modulators, few ECS pharmacophores for class A receptors have been identified. Using the turkey beta(1)-adrenergic receptor crystal structure, we modeled the alpha(1B)-adrenoceptor (alpha(1B)-AR) to help identify the allosteric site for rho-conopeptide TIA, an inverse agonist at this receptor. Combining mutational radioligand binding and inositol 1-phosphate signaling studies, together with molecular docking simulations using a refined NMR structure of rho-TIA, we identified 14 residues on the ECS of the alpha(1B)-AR that influenced rho-TIA binding. Double mutant cycle analysis and docking confirmed that rho-TIA binding was dominated by a salt bridge and cation-pi between Arg-4-rho-TIA and Asp-327 and Phe-330, respectively, and a T-stacking-pi interaction between Trp-3-rho-TIA and Phe-330. Water-bridging hydrogen bonds between Asn-2-rho-TIA and Val-197, Trp-3-rho-TIA and Ser-318, and the positively charged N terminus and Glu-186, were also identified. These interactions reveal that peptide binding to the ECS on transmembrane helix 6 (TMH6) and TMH7 at the base of extracellular loop 3 (ECL3) is sufficient to allosterically inhibit agonist signaling at a GPCR. The ligand-accessible ECS residues identified provide the first view of an allosteric inhibitor pharmacophore for alpha(1)-adrenoceptors and mechanistic insight and a new set of structural constraints for the design of allosteric antagonists at related GPCRs. Conopeptide rho-TIA defines a new allosteric site on the extracellular surface of the alpha1B-adrenoceptor.,Ragnarsson L, Wang CI, Andersson A, Fajarningsih D, Monks T, Brust A, Rosengren KJ, Lewis RJ J Biol Chem. 2013 Jan 18;288(3):1814-27. doi: 10.1074/jbc.M112.430785. Epub 2012 , Nov 26. PMID:23184947[6] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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