TY - JOUR

T1 - Location of the antidepressant binding site in the serotonin transporter

T2 - importance of SER-438 in recognition of citalopram and tricyclic antidepressants

AU - Andersen, Jacob

AU - Taboureau, Olivier

AU - Hansen, Kasper Bø

AU - Olsen, Lars

AU - Egebjerg, Jan

AU - Strømgaard, Kristian

AU - Kristensen, Anders Skov

N1 - Kasper Bø Hansen er også tilknyttet: Emory University School of Medicine, Atlanta, USA Keywords: Antidepressive Agents, Tricyclic; Citalopram; Humans; Inhibitory Concentration 50; Kinetics; Models, Chemical; Molecular Conformation; Mutation; Protein Binding; Protein Conformation; Protein Structure, Secondary; Serine; Serotonin; Serotonin Plasma Membrane Transport Proteins; Substrate Specificity

PY - 2009

Y1 - 2009

N2 - The serotonin transporter (SERT) regulates extracellular levels of serotonin (5-hydroxytryptamine, 5HT) in the brain by transporting 5HT into neurons and glial cells. The human SERT (hSERT) is the primary target for drugs used in the treatment of emotional disorders, including depression. hSERT belongs to the solute carrier 6 family that includes a bacterial leucine transporter (LeuT), for which a high resolution crystal structure has become available. LeuT has proved to be an excellent model for human transporters and has advanced the understanding of solute carrier 6 transporter structure-function relationships. However, the precise structural mechanism by which antidepressants inhibit hSERT and the location of their binding pockets are still elusive. We have identified a residue (Ser-438) located within the 5HT-binding pocket in hSERT to be a critical determinant for the potency of several antidepressants, including the selective serotonin reuptake inhibitor citalopram and the tricyclic antidepressants imipramine, clomipramine, and amitriptyline. A conservative mutation of Ser-438 to threonine (S438T) selectively increased the K(i) values for these antidepressants up to 175-fold. The effects of introducing a protein methyl group into the 5HT-binding pocket by S438T were absent or reduced for analogs of these antidepressants lacking a single methyl group. This suggests that these antidepressants interact directly with Ser-438 during binding to hSERT, implying an overlapping localization of substrate- and inhibitor-binding sites in hSERT suggesting that antidepressants function by a mechanism that involves direct occlusion of the 5HT-binding site.

AB - The serotonin transporter (SERT) regulates extracellular levels of serotonin (5-hydroxytryptamine, 5HT) in the brain by transporting 5HT into neurons and glial cells. The human SERT (hSERT) is the primary target for drugs used in the treatment of emotional disorders, including depression. hSERT belongs to the solute carrier 6 family that includes a bacterial leucine transporter (LeuT), for which a high resolution crystal structure has become available. LeuT has proved to be an excellent model for human transporters and has advanced the understanding of solute carrier 6 transporter structure-function relationships. However, the precise structural mechanism by which antidepressants inhibit hSERT and the location of their binding pockets are still elusive. We have identified a residue (Ser-438) located within the 5HT-binding pocket in hSERT to be a critical determinant for the potency of several antidepressants, including the selective serotonin reuptake inhibitor citalopram and the tricyclic antidepressants imipramine, clomipramine, and amitriptyline. A conservative mutation of Ser-438 to threonine (S438T) selectively increased the K(i) values for these antidepressants up to 175-fold. The effects of introducing a protein methyl group into the 5HT-binding pocket by S438T were absent or reduced for analogs of these antidepressants lacking a single methyl group. This suggests that these antidepressants interact directly with Ser-438 during binding to hSERT, implying an overlapping localization of substrate- and inhibitor-binding sites in hSERT suggesting that antidepressants function by a mechanism that involves direct occlusion of the 5HT-binding site.

KW - Former Faculty of Pharmaceutical Sciences

U2 - 10.1074/jbc.M806907200

DO - 10.1074/jbc.M806907200

M3 - Journal article

C2 - 19213730

VL - 284

SP - 10276

EP - 10284

JO - Journal of Biological Chemistry

JF - Journal of Biological Chemistry

SN - 0021-9258

IS - 15

ER -