Desensitization of glutamate dehydrogenase by reaction of tyrosne residues.
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ABSTRACT:
SUBMITTER: Price NC
PROVIDER: S-EPMC1184869 | biostudies-other | 1969 Sep
REPOSITORIES: biostudies-other
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Project description:The glutamate receptor (GluR) agonist-binding site consists of amino acid residues in the extracellular S1 and S2 segments in the N-terminal and M3-M4 loop regions, respectively. Molecular and atomic level structural analyses have identified specific S1 and S2 residues that interact directly with ligands, interact with one another in a dimeric configuration, and influence channel gating and desensitization properties of AMPA receptors. Other studies suggest that KA receptor gating and desensitization may differ mechanistically. In particular, a leucine (L) to tyrosine (Y) mutation in the S1 segment of AMPA receptors is sufficient to block desensitization, whereas KA receptors naturally contain a tyrosine residue at the equivalent position (Y751 in GluR6) but retain the fast-desensitizing phenotype. We hypothesized that KA receptor desensitization is preserved by a compensatory substitution in the S2 segment. We generated a series of GluR6 mutants that converted individual S2 domain residues to their AMPA receptor equivalents. Various S2 mutations had effects on the kinetics of desensitization and recovery from desensitization, but no single amino acid substitution was found to block desensitization, as in the L/Y mutant AMPA receptors, or to prevent desensitization to KA. Other mutations designed to neutralize residues thought to interact across the dimer interface had dramatic effects on channel gating and desensitization. These results are consistent with a close but imperfect structural homology between AMPA and KA receptors and support the role of conserved S1S2 domain interactions at the dimer interface in GluR channel function.
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Project description:1. Glutamate dehydrogenase was subject to rapid inactivation when irradiated in the presence of Rose Bengal or incubated in the presence of ethoxyformic anhydride. 2. Inactivation in the presence of Rose Bengal led to the photo-oxidation of four histidine residues. Oxidation of three histidine residues had little effect on enzyme activity, but oxidation of the fourth residue led to the almost total loss of activity. 3. Acylation of glutamate dehydrogenase with ethoxyformic anhydride at pH6.1 led to the modification of three histidine residues with a corresponding loss of half the original activity. Acylation at pH7.5 led to the modification of two histidine residues and a total loss of enzyme activity. 4. One of the histidine residues undergoing reaction at pH6.1 also undergoes reaction at pH7.5. 5. The presence of either glutamate or NAD(+) in the reaction mixtures at pH6.1 had no appreciable effect. At pH7.5 glutamate caused a marked decrease in both the degree of alkylation and degree of inactivation. NAD(+) had no effect on the degree of inactivation at pH7.5 but did modify the extent of acylation. 6. The normal response of the enzyme towards ADP was unaffected by acylation at pH6.1 or 7.5. 7. The normal response of the enzyme towards GTP was altered by treatment at both pH6.1 and 7.5.
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Project description:1. Kinetic aspects of the reaction between crystalline bovine liver glutamate dehydrogenase and formiminoglutamate were investigated to establish the conditions under which the latter may interfere with the assay of glutamate by using glutamate dehydrogenase and to explain why formiminoglutamate accumulates in vivo after histidine loading, although it can react with glutamate dehydrogenase. The Km and Vmax. values were compared with those of the enzyme reacting with glutamate. At pH 7.4 Km for formiminoglutamate was much higher and Vmax. much lower than the values for glutamate. 2. The equilibrium constant at pH 7.0 was 0.017 micrometer with formiminoglutamate, i.e. about one two-hundredths that with glutamate. 3. In vivo the interaction between glutamate dehydrogenase and formiminoglutamate is minimal even when the concentration of the latter in the liver is greatly raised, as in cobalamine or folate deficiency after histidine loading. 4. At pH 9.3, i.e. under the conditions for the assay of glutamate by glutamate dehydrogenase, formiminoglutamate reacts readily with the enzyme.
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Project description:Glutamate receptors are ligand-gated tetrameric ion channels that mediate synaptic transmission in the central nervous system. They are instrumental in vertebrate cognition and their dysfunction underlies diverse diseases. In both the resting and desensitized states of AMPA and kainate receptor subtypes, the ion channels are closed, whereas the ligand-binding domains, which are physically coupled to the channels, adopt markedly different conformations. Without an atomic model for the desensitized state, it is not possible to address a central problem in receptor gating: how the resting and desensitized receptor states both display closed ion channels, although they have major differences in the quaternary structure of the ligand-binding domain. Here, by determining the structure of the kainate receptor GluK2 subtype in its desensitized state by cryo-electron microscopy (cryo-EM) at 3.8?Å resolution, we show that desensitization is characterized by the establishment of a ring-like structure in the ligand-binding domain layer of the receptor. Formation of this 'desensitization ring' is mediated by staggered helix contacts between adjacent subunits, which leads to a pseudo-four-fold symmetric arrangement of the ligand-binding domains, illustrating subtle changes in symmetry that are important for the gating mechanism. Disruption of the desensitization ring is probably the key switch that enables restoration of the receptor to its resting state, thereby completing the gating cycle.
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Project description:Ionotropic glutamate receptors are ligand-gated ion channels that mediate excitatory synaptic transmission in the vertebrate brain. To gain a better understanding of how structural changes gate ion flux across the membrane, we trapped rat AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) and kainate receptor subtypes in their major functional states and analysed the resulting structures using cryo-electron microscopy. We show that transition to the active state involves a 'corkscrew' motion of the receptor assembly, driven by closure of the ligand-binding domain. Desensitization is accompanied by disruption of the amino-terminal domain tetramer in AMPA, but not kainate, receptors with a two-fold to four-fold symmetry transition in the ligand-binding domains in both subtypes. The 7.6 Å structure of a desensitized kainate receptor shows how these changes accommodate channel closing. These findings integrate previous physiological, biochemical and structural analyses of glutamate receptors and provide a molecular explanation for key steps in receptor gating.
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Project description:The neurotransmitter glutamate mediates excitatory synaptic transmission by activating ionotropic glutamate receptors (iGluRs). In Caenorhabditis elegans, the GLR-1 receptor subunit is required for glutamate-gated current in a subset of interneurons that control avoidance behaviors. Current mediated by GLR-1-containing iGluRs depends on SOL-1, a transmembrane CUB-domain protein that immunoprecipitates with GLR-1. We have found that reconstitution of glutamate-gated current in heterologous cells depends on three proteins, STG-1 (a C. elegans stargazin-like protein), SOL-1, and GLR-1. Here, we use genetic and pharmacological perturbations along with rapid perfusion electrophysiological techniques to demonstrate that SOL-1 functions to slow the rate and limit the extent of receptor desensitization as well as to enhance the recovery from desensitization. We have also identified a SOL-1 homologue from Drosophila and show that Dro SOL1 has a conserved function in promoting C. elegans glutamate-gated currents. SOL-1 homologues may play critical roles in regulating glutamatergic neurotransmission in more complex nervous systems.
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Project description:Cell signaling is often mediated by the binding of multiple ligands to multisubunit receptors. The probabilistic nature and sometimes slow rate of binding encountered with diffusible ligands can impede attempts to determine how the ligand occupancy controls signaling in such protein complexes. We describe a solution to this problem that uses a photoswitched tethered ligand as a 'ligand clamp' to induce rapid and stable binding and unbinding at defined subsets of subunits. We applied the approach to study gating in ionotropic glutamate receptors (iGluRs), ligand-gated ion channels that mediate excitatory neurotransmission and plasticity at glutamatergic synapses in the brain. We probed gating in two kainate-type iGluRs, GluK2 homotetramers and GluK2-GluK5 heterotetramers. Ultrafast (submillisecond) photoswitching of an azobenzene-based ligand on specific subunits provided a real-time measure of gating and revealed that partially occupied receptors can activate without desensitizing. The findings have implications for signaling by locally released and spillover glutamate.
| S-EPMC4041372 | biostudies-literature
Project description:Glud1 (glutamate dehydrogenase 1) transgenic mice release more excitatory neurotransmitter glutamate to synaptic cleft throughout lifespan and show signs of accelerated aging. Here we compared transcriptomic profiles of these animals to their wild-type counterparts. The hippocampus was used for the analysis. Keywords: transgenic analysis Three Glud1 transgenic mice vs. three age-matched wide-type mice. Age: 9-month-old. Tissue: hippocampus.
2010-07-12 | E-GEOD-11419 | biostudies-arrayexpress
Project description:1. One mol of diethyl pyrocarbonate will react with one mol of glutamate dehydrogenase polypeptide chains to form one mol of N(1)-carbethoxyhistidine. Reaction is prevented by NADH. 2. The 1:1 complex has an increased specific activity (1.4-2.0-fold). 3. The reason for the activation is discussed. The results are not consistent with NADH dissociation from the enzyme-glutamate-NADH complex being rate-limiting in the steady state measured. 4. The effects of modification on the properties of the enzyme were investigated. The effects of GTP and NAD(+) on the enzyme activity are unaltered by activation. NADH binding is unaltered and there is no apparent change in the molecular weight. However, the activated enzyme can still be further activated by ADP. K(s) for ADP is decreased fivefold.
| S-EPMC1177682 | biostudies-other
Project description:Glud1 (glutamate dehydrogenase 1) transgenic mice release more excitatory neurotransmitter glutamate to synaptic cleft throughout lifespan and show signs of accelerated aging. Here we compared transcriptomic profiles of these animals to their wild-type counterparts. The hippocampus was used for the analysis. Keywords: transgenic analysis
2010-07-12 | GSE11419 | GEO