Biology subjects

Gouaux, E.

Publications and source records attributed to Gouaux, E..

7 recordsLinked to original sources

bioRxiv2018

Divalent cation and chloride ion sites of chicken acid sensing ion channel 1a elucidated by x-ray crystallography

Acid sensing ion channels (ASICs) are proton-gated ion channels that are members of the degenerin/epithelial sodium channel superfamily and are expressed throughout central and peripheral nervous systems. ASICs have been implicated in multiple physiological processes and are subject to numerous forms of endogenous and exogenous regulation that include modulation by Ca2+ and Cl- ions. However, the mapping of ion binding sites as well as a structure-based understanding of the mechanisms underlying ionic modulation of ASICs have remained elusive. Here we present ion binding sites of chicken ASIC1a in resting and desensitized states at high and low pH, respectively, determined by anomalous diffraction x-ray crystallography. The acidic pocket serves as a nexus for divalent cation binding at both low and high pH, while we observe divalent cation binding within the central vestibule on the resting channel at high pH only. Moreover, neutralization of residues positioned to coordinate divalent cations via individual and combined Glu to Gln substitutions reduced, but did not extinguish, modulation of proton-dependent gating by Ca2+. Additionally, we demonstrate that anion binding at the canonical thumb domain site is state-dependent and present a previously undetected anion site at the mouth of the extracellular fenestrations on the resting channel. Our results map anion and cation sites on ASICs across multiple functional states, informing possible mechanisms of modulation and providing a blueprint for the design of therapeutics targeting ASICs.

biophysics↗

bioRxiv2018

Mechanisms for zinc and proton inhibition of the GluN1/GluN2A NMDA receptor

N-Methyl-D-aspartate receptors (NMDARs) play essential roles in memory formation, neuronal plasticity and brain development with their dysfunction linked to a range of disorders from ischemia to schizophrenia. Zinc and pH are physiological allosteric modulators of NMDARs with GluN2A containing receptors inhibited by nanomolar concentrations of divalent zinc and by excursions to low pH. Despite the widespread importance of zinc and proton modulation of NMDARs, the molecular mechanism by which these ions modulate receptor activity has proven elusive. Here, we use cryo-electron microscopy to elucidate the structure of the GluN1/GluN2A NMDAR in a large ensemble of conformations under a range of physiologically relevant zinc and proton concentrations. We show how zinc binding to the amino terminal domain elicits structural changes that are transduced though the ligand-binding domain and result in constriction of the ion channel gate.

biophysics↗

bioRxiv2018

Cryo-EM structure of the benzodiazepine-sensitive α1β1γ2 heterotrimeric GABAA receptor in complex with GABA illuminates mechanism of receptor assembly and agonist binding

Fast inhibitory neurotransmission in the mammalian nervous system is largely mediated by GABAA receptors, chloride-selective members of the superfamily of pentameric Cys-loop receptors. Native GABAA receptors are heteromeric assemblies sensitive to many important drugs, from sedatives to anesthetics and anticonvulsive agents, with mutant forms of GABAA receptors implicated in multiple neurological diseases, including epilepsy. Despite the profound importance of heteromeric GABAA receptors in neuroscience and medicine, they have proven recalcitrant to structure determination. Here we present the structure of the triheteromeric 1{beta}1{gamma}2EM GABAA receptor in complex with GABA, determined by single particle cryo-EM at 3.1-3.8 [A] resolution, elucidating the molecular principles of receptor assembly and agonist binding. Remarkable N-linked glycosylation on the 1 subunit occludes the extracellular vestibule of the ion channel and is poised to modulate receptor assembly and perhaps ion channel gating. Our work provides a pathway to structural studies of heteromeric GABAA receptors and a framework for the rational design of novel therapeutic agents.

biophysics↗

bioRxiv2018

Thermostabilization and purification of the human dopamine transporter (hDAT) in an inhibitor and allosteric ligand bound conformation

The human dopamine transporter(hDAT) plays a major role in dopamine homeostasis and regulation of neurotransmission by clearing dopamine from the extracellular space using secondary active transport. Dopamine is an essential monoamine chemical messenger that regulates reward seeking behavior, motor control, hormonal release, and emotional response in humans. Psychostimulants such as cocaine primarily target the central binding site of hDAT and lock the transporter in an outward-facing conformation, thereby inhibiting dopamine reuptake. The inhibition of dopamine reuptake leads to accumulation of dopamine in the synapse causing heightened signaling. In addition, hDAT is implicated in various neurological disorders and disease-associated neurodegeneration. Despite its significance, the molecular architecture of hDAT and its various conformational states are poorly understood. Instability of hDAT in detergent micelles has been a limiting factor in its successful biochemical, biophysical, and structural characterization. To overcome this hurdle, first we identified ligands that stabilize hDAT in detergent micelles. Then, we screened [~]200 single residue mutants of hDAT using high-throughput scintillation proximity assay, and identified a thermostable variant(I248Y). Here we report a robust strategy to overexpress and successfully purify a thermostable variant of hDAT in an inhibitor and allosteric ligand bound conformation.

biochemistry↗

bioRxiv2018

Expression and purification of a functional heteromeric GABAA receptor for structural studies

The multi-subunit GABA-gated chloride channels of the Cys-loop receptor family, known as GABAA receptors, function as the primary gatekeepers of fast inhibitory neurotransmission in the central nervous system. In addition to their role in controlling synaptic tone, these receptors are the targets of a vast array of therapeutic compounds that potentiate channel gating. Importantly, functional activity and pharmacological efficacy of GABAA receptors is coupled directly to the subunit composition. However, the absence of high resolution structural information precludes an explicit determination of the molecular mechanism of ligand binding to ion channel gating and modulation. Efforts to obtain this data are hindered largely by the lack of heterologous expression and purification protocols for high expressing receptor constructs. To address this issue, we describe a unique approach to identify bona fide functional GABAA receptor subunit combinations by using the Xenopus oocyte as an expression host in combination with fluorescence detection size exclusion chromatography. The results demonstrate that formation of a defined pentameric species is dependent on subunit composition. Furthermore, receptor subunits can tolerate large truncations in non-conserved M3/M4 cytoplasmic loop, although removal of N-linked glycosylation sites is negatively correlated with expression level. Additionally, we report methods to improve GABAA receptor expression in mammalian cell culture that employ recombinant baculovirus transduction. From these methods we have identified a well-behaving minimal functional construct for the 1/{beta}1 GABAA receptor subtype that can be purified in milligram quantities while retaining high affinity agonist binding activity.

biochemistry↗

bioRxiv2017

Structural basis for recognition of diverse antidepressants by the human serotonin transporter

Selective serotonin reuptake inhibitors are clinically prescribed antidepressants that act by increasing the local concentration of neurotransmitter at synapses and in extracellular spaces via blockade of the serotonin transporter. Here we report x-ray structures of engineered thermostable variants of the human serotonin transporter bound to the antidepressants sertraline, fluvoxamine, and paroxetine. The drugs prevent serotonin binding by occupying the central substrate binding site and stabilizing the transporter in an outward-open conformation. These structures explain how residues within the central site orchestrate binding of chemically diverse inhibitors and mediate transporter-drug selectivity.

biophysics↗

bioRxiv2017

Activation and desensitization mechanism of AMPA receptor-TARP complex by cryo-EM

Summary Summary Structure determination Agonists expand LBD gating... Activation by full and... Architecture of the ion... Ion-permeation profile of the... Asymmetric water/ion accessible... TARP modulation of receptor... TARP restricts LBD rearrangement... TARP modulation of AMPA... Materials and methods AUTHOR CONTRIBUTIONS AUTHOR INFORMATION References AMPA receptors mediate the majority of fast excitatory neurotransmission in the mammalian brain and transduce the binding of presynaptically released glutamate to the opening of a transmembrane cation channel. Within the postsynaptic density, however, AMPA receptors coassemble with transmembran ...

biophysics↗