2q6h
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Crystal Structure Analysis of LeuT complexed with L-leucine, sodium, and clomipramine
OverviewOverview
Sodium-coupled transporters are ubiquitous pumps that harness pre-existing, sodium gradients to catalyse the thermodynamically unfavourable uptake of, essential nutrients, neurotransmitters and inorganic ions across the lipid, bilayer. Dysfunction of these integral membrane proteins has been, implicated in glucose/galactose malabsorption, congenital hypothyroidism, Bartter's syndrome, epilepsy, depression, autism and obsessive-compulsive, disorder. Sodium-coupled transporters are blocked by a number of, therapeutically important compounds, including diuretics, anticonvulsants, and antidepressants, many of which have also become indispensable tools in, biochemical experiments designed to probe antagonist binding sites and to, elucidate transport mechanisms. Steady-state kinetic data have revealed, that both competitive and noncompetitive modes of inhibition exist., Antagonist dissociation experiments on a serotonin transporter tricyclic, antidepressant have also unveiled the existence of a low-affinity, allosteric site that slows the dissociation of inhibitors from a separate, high-affinity site. Despite these strides, atomic-level insights into, inhibitor action have remained elusive. Here we screen a panel of, molecules for their ability to inhibit LeuT, a prokaryotic homologue of, mammalian neurotransmitter sodium symporters, and show that the tricyclic, antidepressant clomipramine noncompetitively inhibits substrate uptake., Cocrystal structures show that clomipramine binds in an, extracellular-facing vestibule about 11 A above the substrate and two, sodium ions, apparently stabilizing the extracellular gate in a closed, conformation. Off-rate assays establish that clomipramine reduces the rate, at which leucine dissociates from LeuT and reinforce our contention that, this inhibits LeuT by slowing substrate release. Our results represent a, molecular view into noncompetitive inhibition of a sodium-coupled, transporter and define principles for the rational design of new, inhibitors.
About this StructureAbout this Structure
2Q6H is a Single protein structure of sequence from Aquifex aeolicus with , , and as ligands. Full crystallographic information is available from OCA.
ReferenceReference
Antidepressant binding site in a bacterial homologue of neurotransmitter transporters., Singh SK, Yamashita A, Gouaux E, Nature. 2007 Aug 8;. PMID:17687333
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