The mechanism and regulation of vesicular glutamate transport: Coordination with the synaptic vesicle cycle.
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ABSTRACT:
SUBMITTER: Eriksen J
PROVIDER: S-EPMC7483692 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Synaptic vesicles accumulate neurotransmitters, enabling the quantal release by exocytosis that underlies synaptic transmission. Specific neurotransmitter transporters are responsible for this activity and therefore are essential for brain function. The vesicular glutamate transporters (VGLUTs) concentrate the principal excitatory neurotransmitter glutamate into synaptic vesicles, driven by membrane potential. However, the mechanism by which they do so remains poorly understood owing to a lack of structural information. We report the cryo-electron microscopy structure of rat VGLUT2 at 3.8-angstrom resolution and propose structure-based mechanisms for substrate recognition and allosteric activation by low pH and chloride. A potential permeation pathway for chloride intersects with the glutamate binding site. These results demonstrate how the activity of VGLUTs can be coordinated with large shifts in proton and chloride concentrations during the synaptic vesicle cycle to ensure normal synaptic transmission.
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Project description:The transport of glutamate into synaptic vesicles exhibits an unusual form of regulation by Cl- as well as an associated Cl- conductance. To distinguish direct effects of Cl- on the transporter from indirect effects via the driving force Δψ, we used whole endosome recording and report the first currents due to glutamate flux by the vesicular glutamate transporters (VGLUTs). Chloride allosterically activates the VGLUTs from both sides of the membrane, and we find that neutralization of an arginine in transmembrane domain four suffices for the lumenal activation. The dose dependence suggests that Cl- permeates through a channel and glutamate through a transporter. Competition between the anions nonetheless indicates that they use a similar permeation pathway. By controlling both ionic gradients and Δψ, endosome recording isolates different steps in the process of synaptic vesicle filling, suggesting distinct roles for Cl- in both allosteric activation and permeation.
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Project description:The amount of neurotransmitter stored in synaptic vesicles determines postsynaptic quantal size and thus the strength of synaptic transmission. However, little is known about regulation of vesicular neurotransmitter uptake. In recordings from the calyx of Held, a giant mammalian glutamatergic synapse, we found that changes in presynaptic Na(+) concentration above and below a resting value of 13 mM regulated vesicular glutamate uptake, consistent with activation of a vesicular monovalent cation Na(+)(K(+))/H(+) exchanger. Na(+) flux through presynaptic plasma membrane hyperpolarization-activated cyclic nucleotide-gated (HCN) channels enhanced presynaptic Na(+) concentration and thus controlled postsynaptic quantal size. Our results indicate that a plasma membrane ion channel controls synaptic strength by modulating vesicular neurotransmitter uptake through a Na(+)-dependent process.
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Project description:Monoamine neurotransmitters such as serotonin and dopamine are loaded by vesicular monoamine transporter 2 (VMAT2) into synaptic vesicles for storage and subsequent release in neurons. Impaired VMAT2 function underlies various neuropsychiatric diseases. VMAT2 inhibitors reserpine and tetrabenazine are used to treat hypertension, movement disorders associated with Huntington's Disease and Tardive Dyskinesia. Despite its physiological and pharmacological significance, the structural basis underlying VMAT2 substrate recognition and its inhibition by various inhibitors remains unknown. Here we present cryo-EM structures of human apo VMAT2 in addition to states bound to serotonin, tetrabenazine, and reserpine. These structures collectively capture three states, namely the lumen-facing, occluded, and cytosol-facing conformations. Notably, tetrabenazine induces a substantial rearrangement of TM2 and TM7, extending beyond the typical rocker-switch movement. These functionally dynamic snapshots, complemented by biochemical analysis, unveil the essential components responsible for ligand recognition, elucidate the proton-driven exchange cycle, and provide a framework to design improved pharmaceutics targeting VMAT2.
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Project description:Schizophrenia (SCZ) is a common, disabling mental illness with high heritability but complex, poorly understood genetic etiology. As the first phase of a genomic convergence analysis of SCZ, we generated 16.7 billion nucleotides of short read, shotgun sequences of cDNA from post-mortem cerebellar cortices of 14 patients and six matched controls. A rigorous analysis pipeline was developed for analysis of digital gene expression studies. Sequences aligned to approximately 33,200 transcripts in each sample, with average coverage of 450 reads per gene. Following adjustments for confounding clinical, sample and experimental sources of variation, 215 genes differed significantly in expression between cases and controls. Golgi apparatus, vesicular transport, membrane association, Zinc binding and regulation of transcription were over-represented among differentially expressed genes. Twenty three genes with altered expression and involvement in presynaptic vesicular transport, Golgi function and GABAergic neurotransmission define a unifying molecular hypothesis for dysfunction in cerebellar cortex in SCZ. Experiment Overall Design: 16.7 billion nucleotides of shotgun, full length cDNA sequence data were generated using Illumina Genome Analyzer platforms with sequencing-by-synthesis (SBS) chemistry from 20 mRNA samples (Lister et al., 2008; Morin et al., 2008)(Mortazvi et al., 2008). mRNA samples were isolated post-mortem from the lateral hemispheres of the cerebellar cortices of 14 patients with SCZ and 6 control individuals (Paz et al., 2006; Bullock et al., In Press)(Table 1). Unrelated subjects were chosen to facilitate sampling of genetic heterogeneity (Freimer and Sabatti, 2004; McClellan et al., 2007). Cases and controls were approximately matched for age (cases, 45.2 + 11.8 years; controls 41.3 + 9.2 years), sex (all male), race, post-mortem interval (cases, 12.2 + 5.0 hours; controls 17.7 + 3.3 hours), cause of death, autopsy brain pH (cases, 6.54 + 0.19; controls 6.46 + 0.10) and RNA integrity number (cases, 8.06 + 0.53; controls, 7.87 + 0.41) (Table 1). 12.5 – 38.7 million, high quality sequences of length 32 – 36 bp were generated per sample (Table 2). Sequences were aligned to the human genome and RefSeq transcript databases using the algorithm GMAP, which allowed < 2 (< 6%) mismatches (Wu and Watanabe, 2005). There was little intra-sample variability in the number of sequences aligned to each locus from run-to-run or instrument-to-instrument (Fig. 1A; all source coefficient of variation 3.4%). 43.5 + 6.7% of sequences aligned to a transcript and 69.4 + 9.6% to the genome, evidence that annotation of mRNA isoforms in Homo sapiens is incomplete (Birney et al., 2007) (Table 2). 91% of alignments were unique (Table 2). Reads aligning to more than one location contained repetitive, paralogous, polymorphic or low complexity sequences and primarily mapped to untranslated regions or highly polymorphic gene families, such as major histocompatibility genes (Sugarbaker et al., 2008). Unmapped sequences did not align to mitochondrial or 1879 viral genomes, offering negative evidence of chronic viral etiology for SCZ in these patients.
2009-08-29 | E-GEOD-12297 | biostudies-arrayexpress
Project description:Dopamine neurons in the ventral tegmental area (VTA) play an important role in the motivational systems underlying drug addiction, and recent work has suggested that they also release the excitatory neurotransmitter glutamate. To assess a physiological role for glutamate corelease, we disrupted the expression of vesicular glutamate transporter 2 selectively in dopamine neurons. The conditional knockout abolishes glutamate release from midbrain dopamine neurons in culture and severely reduces their excitatory synaptic output in mesoaccumbens slices. Baseline motor behavior is not affected, but stimulation of locomotor activity by cocaine is impaired, apparently through a selective reduction of dopamine stores in the projection of VTA neurons to ventral striatum. Glutamate co-entry promotes monoamine storage by increasing the pH gradient that drives vesicular monoamine transport. Remarkably, low concentrations of glutamate acidify synaptic vesicles more slowly but to a greater extent than equimolar Cl(-), indicating a distinct, presynaptic mechanism to regulate quantal size.
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