title: Fluoxetine (Prozac) binding to serotonin transporter is modulated by chloride and conformational changes.
abstract: Serotonin transporter (SERT) is the main target for widely used antidepressant agents. Several of these drugs, including imipramine, citalopram, sertraline, and fluoxetine (Prozac), bound more avidly to SERT in the presence of Cl(-). In contrast, Cl(-) did not enhance cocaine or paroxetine binding. A Cl(-) binding site recently identified in SERT, and shown to be important for Cl(-) dependent transport, was also critical for the Cl(-) dependence of antidepressant affinity. Mutation of the residues contributing to this site eliminated the Cl(-)-mediated affinity increase for imipramine and fluoxetine. Analysis of ligand docking to a single state of SERT indicated only small differences in the energy of interaction between bound ligands and Cl(-). These differences in interaction energy cannot account for the affinity differences observed for Cl(-) dependence. However, fluoxetine binding led to a conformational change, detected by cysteine accessibility experiments, that was qualitatively different from that induced by cocaine or other ligands. Given the known Cl(-) requirement for serotonin-induced conformational changes, we propose that Cl(-) binding facilitates conformational changes required for optimal binding of fluoxetine and other antidepressant drugs.
authors.affiliation: Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06520-8066, USA.
authors.forename: Sotiria
authors.initials: S
authors.lastname: Tavoulari
authors.forename: Lucy R
authors.initials: LR
authors.lastname: Forrest
authors.forename: Gary
authors.initials: G
authors.lastname: Rudnick
mesh_terms: D000818:Animals; D018687:Antidepressive Agents, Second-Generation / Q000494:pharmacology*; D000929:Antidepressive Agents, Tricyclic / Q000494:pharmacology; D001665:Binding Sites / Q000235:genetics; D002712:Chlorides / Q000378:metabolism*; D003042:Cocaine / Q000494:pharmacology; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005473:Fluoxetine / Q000494:pharmacology*; D007050:Ibogaine / Q000494:pharmacology; D007099:Imipramine / Q000494:pharmacology; D008956:Models, Chemical; D009154:Mutation; D011487:Protein Conformation / Q000187:drug effects; D055550:Protein Stability; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D051381:Rats
chemical_list: D018687:Antidepressive Agents, Second-Generation; D000929:Antidepressive Agents, Tricyclic; D002712:Chlorides; D018765:Dopamine Uptake Inhibitors; D018691:Excitatory Amino Acid Antagonists; D016601:RNA-Binding Proteins; C482440:Sert1 protein, rat; D005473:Fluoxetine; D007050:Ibogaine; D003042:Cocaine; D007099:Imipramine