title: Putative drug binding conformations of monoamine transporters.
abstract: Structural information about monoamine transporters and their interactions with psychotropic drugs is important for understanding their molecular mechanisms of action and for drug development. The crystal structure of a Major Facilitator Superfamily (MFS) transporter, the lactose permease symporter (lac permease), has provided insight into the three-dimensional structure and mechanisms of secondary transporters. Based on the hypothesis that the 12 transmembrane alpha-helix (TMH) secondary transporters belong to a common folding class, the lac permease structure was used for molecular modeling of the serotonin transporter (SERT), the dopamine transporter (DAT), and the noradrenaline transporter (NET). The molecular modeling methods used included amino acid sequence alignment, homology modeling, and molecular mechanical energy calculations. The lac permease crystal structure has an inward-facing conformation, and construction of outward-facing SERT, DAT, and NET conformations allowing ligand binding was the most challenging step of the modeling procedure. The psychomotor stimulants cocaine and S-amphetamine, and the selective serotonin reuptake inhibitor (SSRI) S-citalopram, were docked into putative binding sites on the transporters to examine their molecular binding mechanisms. In the inward-facing conformation of SERT the translocation pore was closed towards the extracellular side by hydrophobic interactions between the conserved amino acids Phe105, Pro106, Phe117, and Ala372. An unconserved amino acid, Asp499 in TMH10 in NET, may contribute to the low affinity of S-citalopram to NET.
authors.affiliation: Department of Pharmacology, Institute of Medical Biology, University of Tromsø, N-9037 Tromsø, Norway. aina@fagmed.uit.no
authors.forename: Aina Westrheim
authors.initials: AW
authors.lastname: Ravna
authors.forename: Ingebrigt
authors.initials: I
authors.lastname: Sylte
authors.forename: Kurt
authors.initials: K
authors.lastname: Kristiansen
authors.forename: Svein G
authors.initials: SG
authors.lastname: Dahl
mesh_terms: D000595:Amino Acid Sequence; D000661:Amphetamine / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D015306:Biogenic Monoamines / Q000378:metabolism*; D015283:Citalopram / Q000737:chemistry / Q000378:metabolism; D003042:Cocaine / Q000737:chemistry / Q000378:metabolism; D050483:Dopamine Plasma Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D050484:Norepinephrine Plasma Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D050486:Serotonin Plasma Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017367:Selective Serotonin Reuptake Inhibitors / Q000378:metabolism; D027981:Symporters / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D013816:Thermodynamics
chemical_list: D000661:Amphetamine; D015306:Biogenic Monoamines; D015283:Citalopram; D003042:Cocaine; D050483:Dopamine Plasma Membrane Transport Proteins; D008024:Ligands; D050484:Norepinephrine Plasma Membrane Transport Proteins; D050486:Serotonin Plasma Membrane Transport Proteins; D017367:Selective Serotonin Reuptake Inhibitors; D027981:Symporters