Abstract
We assessed the relative importance of two serine residues located near the top of transmembrane helix 5 of the human 5-HT2A receptor, comparing the wild type with S5.43(239)A or S5.46(242)A mutations. Using the ergoline lysergic acid diethylamide (LSD), and a series of substituted tryptamine and phenethylamine 5-HT2A receptor agonists, we found that Ser5.43(239) is more critical for agonist binding and function than Ser5.46(242). Ser5.43(239) seems to engage oxygen substituents at either the 4- or 5-position of tryptamine ligands and the 5-position of phenylalkylamine ligands. Even when a direct binding interaction cannot occur, our data suggest that Ser5.43(239) is still important for receptor activation. Polar ring-substituted tryptamine ligands also seem to engage Ser5.46(242), but tryptamines lacking such a substituent may adopt an alternate binding orientation that does not engage this residue. Our results are consistent with the role of Ser5.43(239) as a hydrogen bond donor, whereas Ser5.46(242) seems to serve as a hydrogen bond acceptor. These results are consistent with the functional topography and utility of our in silico-activated homology model of the h5-HT2A receptor. In addition, being more distal from the absolutely conserved Pro5.50, a strong interaction with Ser5.43(239) may be more effective in straightening the kink in helix 5, a feature that is possibly common to all type A GPCRs that have polar residues at position 5.43.
Footnotes
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This research was supported by National Institute on Drug Abuse grant DA02189, a grant from the Heffter Research Institute, and the work was conducted in a facility constructed with support from Research Facilities Improvement Program grant C06–14499 from the National Center for Research Resources of the National Institutes of Health.
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Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
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doi:10.1124/mol.107.039255.
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ABBREVIATIONS: 1-iPr-5-MeO-T, 1-isopropyl-5-methoxytryptamine; 1-Me-5-HT, 1-methyl-5-hydroxytryptamine (1-methylserotonin); 2CH, 2,5-dimethoxyphenethylamine; 2CI, 2,5-dimethoxy-4-iodophenethylamine; 2-Et-DOM, 2-ethyl-5-methoxy-4-methylphenyl-isopropylamine; 5-Et-DOM, 5-ethyl-2-methoxy-4-methylphenylisopropylamine; 5-H-DOM, 2-methoxy-4-methylphenylisopropylamine; 5-HT, 5-hydroxtryptamine (serotonin); 5-Me-T, 5-methyltryptamine; 5-MeO-DMT, 5-methoxy-N,N-dimethyltryptamine; 5-MeO-T, 5-methoxytryptamine; DMT, N,N-dimethyltryptamine; DOH, 2,5-dimethoxyphenyl-isopropylamine; DOI, 4-iodo-2,5-dimethoxyphenylisopropylamine; DOM, 2,5-dimethoxy-4-methylphenylisopropylamine; PI, phosphoinositide; TM, transmembrane; GPCR, G protein-coupled receptor; LSD, lysergic acid diethylamide; ANOVA, analysis of variance; WT, wild type.
- Received June 22, 2007.
- Accepted August 22, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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