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Glutamate transporters have a chloride channel with two hydrophobic gates.

ABSTRACT: Glutamate is the most abundant excitatory neurotransmitter in the central nervous system, and its precise control is vital to maintain normal brain function and to prevent excitotoxicity¹. The removal of extracellular glutamate is achieved by plasma-membrane-bound transporters, which couple glutamate transport to sodium, potassium and pH gradients using an elevator mechanism^2-5. Glutamate transporters also conduct chloride ions by means of a channel-like process that is thermodynamically uncoupled from transport^6-8. However, the molecular mechanisms that enable these dual-function transporters to carry out two seemingly contradictory roles are unknown. Here we report the cryo-electron microscopy structure of a glutamate transporter homologue in an open-channel state, which reveals an aqueous cavity that is formed during the glutamate transport cycle. The functional properties of this cavity, combined with molecular dynamics simulations, reveal it to be an aqueous-accessible chloride permeation pathway that is gated by two hydrophobic regions and is conserved across mammalian and archaeal glutamate transporters. Our findings provide insight into the mechanism by which glutamate transporters support their dual function, and add information that will assist in mapping the complete transport cycle shared by the solute carrier 1A transporter family.

SUBMITTER: Chen I

PROVIDER: S-EPMC7954978 | biostudies-literature | 2021 Mar

REPOSITORIES: biostudies-literature

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Glutamate transporters have a chloride channel with two hydrophobic gates.

Chen Ichia I Pant Shashank S Wu Qianyi Q Cater Rosemary J RJ Sobti Meghna M Vandenberg Robert J RJ Stewart Alastair G AG Tajkhorshid Emad E Font Josep J Ryan Renae M RM

Nature 20210217 7849

Glutamate is the most abundant excitatory neurotransmitter in the central nervous system, and its precise control is vital to maintain normal brain function and to prevent excitotoxicity<sup>1</sup>. The removal of extracellular glutamate is achieved by plasma-membrane-bound transporters, which couple glutamate transport to sodium, potassium and pH gradients using an elevator mechanism<sup>2-5</sup>. Glutamate transporters also conduct chloride ions by means of a channel-like process that is the ...[more]

PMID: 33597752

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Project description:Cys-loop ligand-gated ion channels (LGICs) mediate fast ionotropic neurotransmission. They are proven drug targets in nematodes and arthropods, but are poorly characterized in flatworms. In this study, we characterized the anion-selective, non-acetylcholine-gated Cys-loop LGICs from Schistosoma mansoni. Full-length cDNAs were obtained for SmGluCl-1 (Smp_096480), SmGluCl-2 (Smp_015630) and SmGluCl-3 (Smp_104890). A partial cDNA was retrieved for SmGluCl-4 (Smp_099500/Smp_176730). Phylogenetic analyses suggest that SmGluCl-1, SmGluCl-2, SmGluCl-3 and SmGluCl-4 belong to a novel clade of flatworm glutamate-gated chloride channels (GluCl) that includes putative genes from trematodes and cestodes. The flatworm GluCl clade was distinct from the nematode-arthropod and mollusc GluCl clades, and from all GABA receptors. We found no evidence of GABA receptors in S. mansoni. SmGluCl-1, SmGluCl-2 and SmGluCl-3 subunits were characterized by two-electrode voltage clamp (TEVC) in Xenopus oocytes, and shown to encode Cl⁻-permeable channels gated by glutamate. SmGluCl-2 and SmGluCl-3 produced functional homomers, while SmGluCl-1 formed heteromers with SmGluCl-2. Concentration-response relationships revealed that the sensitivity of SmGluCl receptors to L-glutamate is among the highest reported for GluCl receptors, with EC₅₀ values of 7-26 µM. Chloride selectivity was confirmed by current-voltage (I/V) relationships. SmGluCl receptors are insensitive to 1 µM ivermectin (IVM), indicating that they do not belong to the highly IVM-sensitive GluClα subtype group. SmGluCl receptors are also insensitive to 10 µM meclonazepam, a schistosomicidal benzodiazepine. These results provide the first molecular evidence showing the contribution of GluCl receptors to L-glutamate signaling in S. mansoni, an unprecedented finding in parasitic flatworms. Further work is needed to elucidate the roles of GluCl receptors in schistosomes and to explore their potential as drug targets.

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Glutamate transporters have a chloride channel with two hydrophobic gates.

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Glutamate transporters have a chloride channel with two hydrophobic gates.

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