Differential helical orientations among related G protein-coupled receptors provide a novel mechanism for selectivity. Studies with salvinorin A and the kappa-opioid receptor.
Salvinorin A, the active component of the hallucinogenic sage Salvia divinorum, is an apparently selective and highly potent kappa-opioid receptor (KOR) agonist. Salvinorin A is unique among ligands for peptidergic G protein-coupled receptors in being nonnitrogenous and lipid-like in character. To examine the molecular basis for the subtype-selective binding of salvinorin A, we utilized an integrated approach using chimeric opioid receptors, site-directed mutagenesis, the substituted cysteine accessibility method, and molecular modeling and dynamics studies. We discovered that helix 2 is required for salvinorin A binding to KOR and that two residues (Val-108(2.53) and Val-118(2.63)) confer subtype selectivity. Intriguingly, molecular modeling studies predicted that these loci exhibit an indirect effect on salvinorin A binding, presumably through rotation of helix 2. Significantly, and in agreement with our in silico predictions, substituted cysteine accessibility method analysis of helix 2 comparing KOR and the delta-opioid receptor, which has negligible affinity for salvinorin A, revealed that residues known to be important for salvinorin A binding exhibit a differential pattern of water accessibility. These findings imply that differences in the helical orientation of helix 2 are critical for the selectivity of salvinorin A binding to KOR and provide a structurally novel basis for ligand selectivity.
Vortherms
Timothy A
TA
Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106, USA.
Mosier
Philip D
PD
Westkaemper
Richard B
RB
Roth
Bryan L
BL
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D004224:Diterpenes / Q000378:metabolism*; D045785:Diterpenes, Clerodane; D005822:Genetic Vectors; D006213:Hallucinogens / Q000378:metabolism; D006801:Humans; D007668:Kidney; D007700:Kinetics; D051379:Mice; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D011869:Radioligand Assay; D043562:Receptors, G-Protein-Coupled / Q000737:chemistry*; D017473:Receptors, Opioid, kappa / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism
D004224:Diterpenes; D045785:Diterpenes, Clerodane; D006213:Hallucinogens; D043562:Receptors, G-Protein-Coupled; D017473:Receptors, Opioid, kappa; D011994:Recombinant Proteins; C090499:salvinorin A