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Antidepressant specificity of serotonin transporter suggested by three LeuT–SSRI structures

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Abstract

Sertraline and fluoxetine are selective serotonin re-uptake inhibitors (SSRIs) that are widely prescribed to treat depression. They exert their effects by inhibiting the presynaptic plasma membrane serotonin transporter (SERT). All SSRIs possess halogen atoms at specific positions, which are key determinants for the drugs' specificity for SERT. For the SERT protein, however, the structural basis of its specificity for SSRIs is poorly understood. Here we report the crystal structures of LeuT, a bacterial SERT homolog, in complex with sertraline, R-fluoxetine or S-fluoxetine. The SSRI halogens all bind to exactly the same pocket within LeuT. Mutation at this halogen-binding pocket (HBP) in SERT markedly reduces the transporter's affinity for SSRIs but not for tricyclic antidepressants. Conversely, when the only nonconserved HBP residue in both norepinephrine and dopamine transporters is mutated into that found in SERT, their affinities for all the three SSRIs increase uniformly. Thus, the specificity of SERT for SSRIs is dependent largely on interaction of the drug halogens with the protein's HBP.

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Figure 1: Interaction of three SSRIs with LeuT and the crystal structures of their complexes.
Figure 2: Comparison of common features of SSRI binding to LeuT and key determinants for specificity for SSRIs.
Figure 3: HBP in SERT and its critical importance in the protein's specificity for antidepressants.

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Change history

  • 18 May 2009

    In the version of this article initially published online, “Cl-“ was incorrectly referred to as “Cl“ on the fifth page in the section entitled “SSRI halogens and HBP”. The error has been corrected for the print, PDF and HTML versions of this article.

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Acknowledgements

We thank the staff of the X12B, X25 and X29 beamlines at the National Synchrotron Light Source in Brookhaven National Laboratory for assistance in X-ray diffraction data collection. We are grateful to L.R. Forrest and B. Honig of Columbia University for providing the coordinates of the human SERT homology model, and to B. Czyzewski, M.R. Li, I. Parrington and J. Wu for assistance and helpful discussions. N.K.K. thanks the American Heart Association and the US National Institutes of Health (NIH) for postdoctoral fellowships. This work was financially supported by the NIH Roadmap (GM075936 to D.N.W.) and NIH grants (MH083840 to D.-N.W. and M.E.A.R., DA019676 and DA013261 to M.E.A.R.).

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Contributions

Z.Z. crystallized the LeuT–SSRI complexes, generated mutants and solved the crystal structures with help from N.K.K; J.Z. measured SSRIs binding to LeuT as well as binding to and uptake by human neurotransmitter transporters; N.K.K. performed docking calculations and prepared structural figures; Z.Z and C.J.L. measured LeuT transport in proteoliposomes. All authors discussed the results and commented on the manuscript.

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Correspondence to Maarten E A Reith or Da-Neng Wang.

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Zhou, Z., Zhen, J., Karpowich, N. et al. Antidepressant specificity of serotonin transporter suggested by three LeuT–SSRI structures. Nat Struct Mol Biol 16, 652–657 (2009). https://doi.org/10.1038/nsmb.1602

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