Characterization of an allosteric citalopram-binding site at the serotonin transporter.
The serotonin transporter (SERT), which belongs to a family of sodium/chloride-dependent transporters, is the major pharmacological target in the treatment of several clinical disorders, including depression and anxiety. In the present study we show that the dissociation rate, of [3H]S-citalopram from human SERT, is retarded by the presence of serotonin, as well as by several antidepressants, when present in the dissociation buffer. Dissociation of [3H]S-citalopram from SERT is most potently inhibited by S-citalopram followed by R-citalopram, sertraline, serotonin and paroxetine. EC50 values for S- and R-citalopram are 3.6 +/- 0.4 microm and 19.4 +/- 2.3 microm, respectively. Fluoxetine, venlafaxine and duloxetine have no significant effect on the dissociation of [3H]S-citalopram. Allosteric modulation of dissociation is independent of temperature, or the presence of Na+ in the dissociation buffer. Dissociation of [3H]S-citalopram from a complex with the SERT double-mutant, N208Q/N217Q, which has been suggested to be unable to self-assemble into oligomeric complexes, is retarded to an extent similar to that found with the wild-type, raising the possibility that the allosteric mechanism is mediated within a single subunit. A species-scanning mutagenesis study comparing human and bovine SERT revealed that Met180, Tyr495 and Ser513 are important residues in mediating the allosteric effect, as well as contributing to high-affinity binding at the primary site.
Chen
Fenghua
F
Laboratory of Molecular Neurobiology, Department of Biological Psychiatry, Aarhus Psychiatric University Hospital, Risskov, Denmark.
Larsen
Mads Breum
MB
Neubauer
Henrik Amtoft
HA
Sánchez
Connie
C
Plenge
Per
P
Wiborg
Ove
O
D000495:Allosteric Site / Q000502:physiology*; D000818:Animals; D002417:Cattle; D002460:Cell Line; D015283:Citalopram / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008562:Membrane Glycoproteins / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D012701:Serotonin / Q000378:metabolism*; D018490:Serotonin Agents / Q000378:metabolism; D050486:Serotonin Plasma Membrane Transport Proteins
D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; C493230:SLC6A4 protein, human; D018490:Serotonin Agents; D050486:Serotonin Plasma Membrane Transport Proteins; D015283:Citalopram; D012701:Serotonin