Modelling of serotonergic receptors and molecular optimization of X-ray crystal structures of serotonin transporter and their interactions with exogenous compounds

Abstract

The serotonin (5-hydroxytryptamine, 5-HT) receptors and transporter are in the serotonergic neurotransmission system, and believed to have a major role in pathology of depression. They are of pharmacological importance, being targeted by many nowadays antidepressants. It is therefore of great interest to understand their structural and functional properties for development of future drugs. There is generally little knowledge today about the effects of environmental toxicants on the human brain. If the exogenous compounds interact with the serotonin receptors and transporter, they may interfere with the serotonergic neurotransmission in the brain and interfere with the effects of the CNS drugs. Homology modelling is an in silico method used for prediction of the 3D structure of structurally unknown proteins. Models of serotonergic receptors (5-HT1A, 5-HT2A, 5-HT2C) were constructed by the homology approach with known structures in the PDB. The newly released X-ray crystal structures of the human serotonin transporter (SERT) were also imported from the PDB and optimized with molecular modelling techniques. Molecular docking was utilized to predict putative harmful effects and drug interactions of the toxicants in the Tox21 database with these protein targets. Many toxic compounds were predicted to interact with serotonergic receptors and the SERT and many of these had physiochemical properties that suggest that they may act in the CNS. Detailed interaction analysis of the selected compounds of serotonergic receptors and the SERT indicated that besides the crucial interaction with an aspartic acid, aromatic interactions with phenylalanine residues are also very important. The obtained high CNS MPO scores and similar Glide scores between the known high affinity binders and toxicants could suggest harmful effects and drug interactions in serotonergic system of the CNS.