| Structural highlights
Function
[CA1A_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 PubMed
The 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
- ↑ Sharpe IA, Gehrmann J, Loughnan ML, Thomas L, Adams DA, Atkins A, Palant E, Craik DJ, Adams DJ, Alewood PF, Lewis RJ. Two new classes of conopeptides inhibit the alpha1-adrenoceptor and noradrenaline transporter. Nat Neurosci. 2001 Sep;4(9):902-7. PMID:11528421 doi:http://dx.doi.org/10.1038/nn0901-902
- ↑ Sharpe IA, Thomas L, Loughnan M, Motin L, Palant E, Croker DE, Alewood D, Chen S, Graham RM, Alewood PF, Adams DJ, Lewis RJ. Allosteric alpha 1-adrenoreceptor antagonism by the conopeptide rho-TIA. J Biol Chem. 2003 Sep 5;278(36):34451-7. Epub 2003 Jun 24. PMID:12824165 doi:http://dx.doi.org/10.1074/jbc.M305410200
- ↑ Chen Z, Rogge G, Hague C, Alewood D, Colless B, Lewis RJ, Minneman KP. Subtype-selective noncompetitive or competitive inhibition of human alpha1-adrenergic receptors by rho-TIA. J Biol Chem. 2004 Aug 20;279(34):35326-33. Epub 2004 Jun 11. PMID:15194691 doi:http://dx.doi.org/10.1074/jbc.M403703200
- ↑ Lima V, Mueller A, Kamikihara SY, Raymundi V, Alewood D, Lewis RJ, Chen Z, Minneman KP, Pupo AS. Differential antagonism by conotoxin rho-TIA of contractions mediated by distinct alpha1-adrenoceptor subtypes in rat vas deferens, spleen and aorta. Eur J Pharmacol. 2005 Jan 31;508(1-3):183-92. Epub 2005 Jan 12. PMID:15680270 doi:http://dx.doi.org/10.1016/j.ejphar.2004.12.011
- ↑ Ragnarsson L, Wang CI, Andersson A, Fajarningsih D, Monks T, Brust A, Rosengren KJ, Lewis RJ. Conopeptide rho-TIA defines a new allosteric site on the extracellular surface of the alpha1B-adrenoceptor. J Biol Chem. 2013 Jan 18;288(3):1814-27. doi: 10.1074/jbc.M112.430785. Epub 2012 , Nov 26. PMID:23184947 doi:http://dx.doi.org/10.1074/jbc.M112.430785
- ↑ Ragnarsson L, Wang CI, Andersson A, Fajarningsih D, Monks T, Brust A, Rosengren KJ, Lewis RJ. Conopeptide rho-TIA defines a new allosteric site on the extracellular surface of the alpha1B-adrenoceptor. J Biol Chem. 2013 Jan 18;288(3):1814-27. doi: 10.1074/jbc.M112.430785. Epub 2012 , Nov 26. PMID:23184947 doi:http://dx.doi.org/10.1074/jbc.M112.430785
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