Human Serotonin 5-HT G Protein-Coupled Receptor Homology Model from the Adrenoceptor Structure: Ligand Docking and Mutagenesis Studies.

Activation of the serotonin (5-hydroxytryptamine, 5-HT) 5HT G protein-coupled receptor (GPCR) is proposed as novel pharmacotherapy for obesity and neuropsychiatric disorders. In contrast, activation of the 5-HT and 5-HT GPCRs is associated with untoward hallucinogenic and cardiopulmonary effects, respectively. There is no crystal structure available to guide design of 5-HT receptor-specific ligands. For this reason, a homology model of the 5-HT receptor was built based on the crystal structure of the human adrenoceptor GPCR to delineate molecular determinants of ligand-receptor interactions for drug design purposes. Computational and experimental studies were carried out to validate the model. Binding of N(CH)-PAT [(1, 3)-(-)--1-phenyl-3-,-dimethylamino-1,2,3,4-tetrahydronaphthalene], a novel 5-HT agonist/5-HT inverse agonist, and its secondary [NH(CH)-PAT] and primary (NH-PAT) amine analogs were studied at the 5-HT wild type (WT) and D3.32A, S3.36A, and Y7.43A 5-HT point-mutated receptors. Reference ligands included the tertiary amines lisuride and mesulergine and the primary amine 5-HT. Modeling results indicated that 5-HT residues D3.32, S3.36, and Y7.43 play a role in ligand binding. Experimental ligand binding results with WT and point-mutated receptors confirmed the impact of D3.32, S3.36, and Y7.43 on ligand affinity.