Identification of agonist and antagonist binding sites at the G-Protein Coupled Receptor, GPR18

UNCG Author/Contributor (non-UNCG co-authors, if there are any, appear on document)
Jennifer L. Pyle (Creator)
The University of North Carolina at Greensboro (UNCG )
Web Site:
Patricia Reggio

Abstract: GPR18, a member of the Class A G-Protein Coupled Receptors (GPCRs), is recently a de-orphanized receptor, that upon activation has been found to boost the immune system. Although a GPR18 crystal structure has not been solved, a homology model of the inactive state (R) of GPR18 was built in the Reggio lab based upon the mu-opioid x-ray crystal structure. The present study continues this work by adding loop regions and N- and C-termini to the R state model and by developing a model of GPR18 R* (Active) state, complete with loop regions and N- and C-termini. The complete inactive and active state models were used for docking studies of five known GPR18 antagonists, 1,3-dimethoxy-5-methyl-2-[(1R,6R)-3-methyl-6-prop-1-en-2-ylcyclohex-2-en-1-yl]benzene; 1, (Z)-2-(3((4-chlorobenzyl)oxy)benzylidene)-3-methylene-2,3,6,7-tetrahydro-5H-imidazo[2,1-b][1,3]thiazine; 2, (1R,2R)-2',6'-dimethoxy-4',5-dimethyl-2-(prop-1-en-2-yl)-1,2,3,4-tetrahydro-1,1'-biphenyl; 3, (Z)-2-(3-(4-chlorobenzyloxy)benzylidene)-6,7-dihydro-2H-imidazo[2,1-b][1,3]thiazin-3(5H)-one; 4, and 2-[(1R,6R)-6-isopropenyl-3-methylcyclohex-2-en-1-yl]-5-pentylbenzene-1,3-diol; 5 and the GPR18 endogenous ligand, N-arachidonylglycine (NAGly). Conformational searches were performed on all antagonists using a systematic search using the Hartree-Fock method at the 6-31G* level of theory. Because NAGly is highly flexible, its low energy conformations were determined using the Conformational Memories method. All low energy conformations, less than 3.0 kcal/mol, of each ligand were docked using Glide into their respective bundles based on the state of the receptor each ligand stabilizes. The key interaction site for all antagonists, an ARG in TMH5, R5.42, anchors each antagonist in the TMH bundle such that rotameric changes in key toggle switch residues, F6.48/H6.52, are prevented, thus preventing the activation of the receptor. The extracellular loop 2 (EC2 loop) residue Y160 further stabilizes each antagonist in the binding site. Identified interactions result in Glide scores consistent with experimental EC50 data. The primary interaction site for the agonist, NAGly, was TMH2 residue R2.60. An additional NAGly interaction was identified with the EC2 loop residue K174. Mutation experiments of key residues identified here are underway in a collaborator’s lab. These studies will help confirm the importance of these key residues and further our understanding of the receptor.

Additional Information

Language: English
Date: 2015
Activation, Binding sites, GPCR, GPR18, Models, Receptor
G proteins $x Receptors

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