Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.3.1.107 (DAT)
 1,471 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The extracellular concentration of the neurotransmitters dopamine, serotonin, norepinephrine, GABA and glycine is tightly controlled by plasma membrane transporters belonging to the SLC6 gene family. A very large number of putative transport proteins with a remarkable homology to the SLC6 transporters has recently been identified in prokaryotes. Here we have probed structural relationships in a 'microdoman' corresponding to the extracellular ends of transmembrane segments (TM) 7 and 8 in one of these homologs, the tryptophan transporter TnaT from Symbiobacterium thermophilum. We found that simultaneous - but not individual - substitution of Ala286 at the top of TM7 and Met311 at the top of TM8 with cysteines conferred sensitivity to submicromolar concentrations of Hg(2+) as assessed in a [(3)H]tryptophan uptake assay. Because Hg(2+) can cross-link pairs of cysteines, this suggests close proximity between TM 7 and 8 in the tertiary structure of TnaT as previously suggested for the mammalian counterparts. Furthermore, the inhibition of uptake upon cross-linking the two cysteines provides indirect support for a conserved conformational role of these transmembrane domains in the transport process. It was not possible, however, to transfer to TnaT binding sites for another metal ion, Zn(2+), that we previously engineered in the dopamine (DAT) and GABA (GAT-1) transporters between TM 7 and 8. This suggests that the structure of the TM7/8 microdomain is not identical with that of DAT and GAT-1. Hence, our data also emphasize possible structural differences that should be taken into account when interpreting future data on bacterial homologs of the SLC6 transporters.
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PMID:Intramolecular cross-linking in a bacterial homolog of mammalian SLC6 neurotransmitter transporters suggests an evolutionary conserved role of transmembrane segments 7 and 8. 1612 57

Neurotransmitter:sodium symporters (NSS) have a critical role in regulating neurotransmission and are targets for psychostimulants, anti-depressants and other drugs. Whereas the non-homologous glutamate transporters mediate chloride conductance, in the eukaryotic NSS chloride is transported together with the neurotransmitter. In contrast, transport by the bacterial NSS family members LeuT, Tyt1 and TnaT is chloride independent. The crystal structure of LeuT reveals an occluded binding pocket containing leucine and two sodium ions, and is highly relevant for the neurotransmitter transporters. However, the precise role of chloride in neurotransmitter transport and the location of its binding site remain elusive. Here we show that introduction of a negatively charged amino acid at or near one of the two putative sodium-binding sites of the GABA (gamma-aminobutyric acid) transporter GAT-1 from rat brain (also called SLC6A1) renders both net flux and exchange of GABA largely chloride independent. In contrast to wild-type GAT-1, a marked stimulation of the rate of net flux, but not of exchange, was observed when the internal pH was lowered. Equivalent mutations introduced in the mouse GABA transporter GAT4 (SLC6A11) and the human dopamine transporter DAT (SLC6A3) also result in chloride-independent transport, whereas the reciprocal mutations in LeuT and Tyt1 render substrate binding and/or uptake by these bacterial NSS chloride dependent. Our data indicate that the negative charge, provided either by chloride or by the transporter itself, is required during binding and translocation of the neurotransmitter, probably to counterbalance the charge of the co-transported sodium ions.
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PMID:Mechanism of chloride interaction with neurotransmitter:sodium symporters. 1770 62

Antidepressant drugs produce therapeutic actions and many of their side effects via blockade of the plasma membrane transporters for serotonin (SERT/SLC6A2), norepinephrine (NET/SLC6A1), and dopamine (DAT/SLC6A3). Many antidepressants block several of these transporters; some are more selective. Mouse gene knockouts of these transporters provide interesting models for possible effects of chronic antidepressant treatments. To examine the role of monoamine transporters in models of depression DAT, NET, and SERT knockout (KO) mice and wild-type littermates were studied in the forced swim test (FST), the tail suspension test, and for sucrose consumption. To dissociate general activity from potential antidepressant effects three types of behavior were assessed in the FST: immobility, climbing, and swimming. In confirmation of earlier reports, both DAT KO and NET KO mice exhibited less immobility than wild-type littermates whereas SERT KO mice did not. Effects of DAT deletion were not simply because of hyperactivity, as decreased immobility was observed in DAT+/- mice that were not hyperactive as well as in DAT-/- mice that displayed profound hyperactivity. Climbing was increased, whereas swimming was almost eliminated in DAT-/- mice, and a modest but similar effect was seen in NET KO mice, which showed a modest decrease in locomotor activity. Combined increases in climbing and decreases in immobility are characteristic of FST results in antidepressant animal models, whereas selective effects on swimming are associated with the effects of stimulant drugs. Therefore, an effect on climbing is thought to more specifically reflect antidepressant effects, as has been observed in several other proposed animal models of reduced depressive phenotypes. A similar profile was observed in the tail suspension test, where DAT, NET, and SERT knockouts were all found to reduce immobility, but much greater effects were observed in DAT KO mice. However, to further determine whether these effects of DAT KO in animal models of depression may be because of the confounding effects of hyperactivity, mice were also assessed in a sucrose consumption test. Sucrose consumption was increased in DAT KO mice consistent with reduced anhedonia, and inconsistent with competitive hyperactivity; no increases were observed in SERT KO or NET KO mice. In summary, the effects of DAT KO in animal models of depression are larger than those produced by NET or SERT KO, and unlikely to be simply the result of the confounding effects of locomotor hyperactivity; thus, these data support reevaluation of the role that DAT expression could play in depression and the potential antidepressant effects of DAT blockade.
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PMID:Animal models of depression in dopamine, serotonin, and norepinephrine transporter knockout mice: prominent effects of dopamine transporter deletions. 1869 Jan 11

Methylone (2-methylamino-1-[3,4-methylenedioxyphenyl]propane-1-one) is a synthetic hallucinogenic amphetamine analog, like MDMA (3,4-methylenedioxy- methamphetamine), considered to act on monoaminergic systems. However, the psychopharmacological profile of its cytotoxicity as a consequence of monoaminergic deficits remains unclear. We examined here the effects of methylone on the transporters for dopamine (DAT), norepinephrine (NET), and serotonin (SERT), using a heterologous expression system in CHO cells, in association with its cytotoxicity. Methylone inhibited the activities of DAT, NET, and SERT, but not GABA transporter-1 (GAT1), in a concentration-dependent fashion with a rank order of NET > DAT > SERT. Methylone was less effective at inhibiting DAT and NET, but more effective against SERT, than was methamphetamine. Methylone alone was not toxic to cells except at high concentrations, but in combination with methamphetamine had a synergistic effect in CHO cells expressing the monoamine transporters but not in control CHO cells or cells expressing GAT1. The ability of methylone to inhibit monoamine transporter function, probably by acting as a transportable substrate, underlies the synergistic effect of methylone and methamphetamine.
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PMID:Methylone and monoamine transporters: correlation with toxicity. 2188 63

The neurotransmitter transporters of the SLC6 family play critical roles in the regulation of neurotransmission and are the primary targets of therapeutic agents used to treat clinical disorders involving compromised neurotransmitter signaling. The dopamine and norepinephrine transporters have been implicated in clinical disorders such as attention deficit hyperactivity disorder (ADHD) and substance abuse. The GABA transporters (GATs) serve as a target for anxiolytic, antidepressant, and antiepileptic therapies. In this work, the interaction with neurotransmitter transporters was characterized for a derivative of the lignan (-)-cubebin (1), namely, (-)-hinokinin (2). Using in vitro pharmacological assays, 2 selectively inhibited the human dopamine and norepinephrine transporters, in a noncompetitive manner possibly mediated by binding to a novel site within the transporters, and displayed low affinity for the serotonin transporter. Compound 2 also specifically inhibited the GAT-1 GABA transporter subtype. Compound 2 is not a substrate of the carriers as it had no effect on the efflux of either of the neurotransmitters investigated. This compound is inactive toward glutamate and glycine transporters. These results suggest that 2 may serve as a tool to develop new therapeutic drugs for ADHD and anxiety that target the DAT, NET, and GAT-1 transporters.
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PMID:The lignan (-)-hinokinin displays modulatory effects on human monoamine and GABA transporter activities. 2411 84

Transporters of the solute carrier 6 (SLC6) family translocate their cognate substrate together with Na+ and Cl- Detailed kinetic models exist for the transporters of GABA (GAT1/SLC6A1) and the monoamines dopamine (DAT/SLC6A3) and serotonin (SERT/SLC6A4). Here, we posited that the transport cycle of individual SLC6 transporters reflects the physiological requirements they operate under. We tested this hypothesis by analyzing the transport cycle of glycine transporter 1 (GlyT1/SLC6A9) and glycine transporter 2 (GlyT2/SLC6A5). GlyT2 is the only SLC6 family member known to translocate glycine, Na+, and Cl- in a 1:3:1 stoichiometry. We analyzed partial reactions in real time by electrophysiological recordings. Contrary to monoamine transporters, both GlyTs were found to have a high transport capacity driven by rapid return of the empty transporter after release of Cl- on the intracellular side. Rapid cycling of both GlyTs was further supported by highly cooperative binding of cosubstrate ions and substrate such that their forward transport mode was maintained even under conditions of elevated intracellular Na+ or Cl- The most important differences in the transport cycle of GlyT1 and GlyT2 arose from the kinetics of charge movement and the resulting voltage-dependent rate-limiting reactions: the kinetics of GlyT1 were governed by transition of the substrate-bound transporter from outward- to inward-facing conformations, whereas the kinetics of GlyT2 were governed by Na+ binding (or a related conformational change). Kinetic modeling showed that the kinetics of GlyT1 are ideally suited for supplying the extracellular glycine levels required for NMDA receptor activation.
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PMID:A comparison of the transport kinetics of glycine transporter 1 and glycine transporter 2. 3127 Jan 29