scholarly journals Cadmium opens GluK2 kainate receptors with cysteine substitutions at the M3 helix bundle crossing

2018 ◽  
Vol 151 (4) ◽  
pp. 435-451 ◽  
Author(s):  
Timothy J. Wilding ◽  
James E. Huettner
Keyword(s):  
Conformational Changes ◽  
Site Occupancy ◽  
Kainate Receptors ◽  
Inhibitory Synapses ◽  
Side Chains ◽  
Glutamatergic Synapses ◽  
Channel Opening ◽  
The Central Nervous System ◽  
Excitatory Neurotransmission ◽  
Ion Pore

Kainate receptors are ligand-gated ion channels that have two major roles in the central nervous system: they mediate a postsynaptic component of excitatory neurotransmission at some glutamatergic synapses and modulate transmitter release at both excitatory and inhibitory synapses. Accumulating evidence implicates kainate receptors in a variety of neuropathologies, including epilepsy, psychiatric disorders, developmental delay, and cognitive impairment. Here, to gain a deeper understanding of the conformational changes associated with agonist binding and channel opening, we generate a series of Cys substitutions in the GluK2 kainate receptor subunit, focusing on the M3 helices that line the ion pore and form the bundle-crossing gate at the extracellular mouth of the channel. Exposure to 50 µM Cd produces direct activation of homomeric mutant channels bearing Cys substitutions in (A657C), or adjacent to (L659C), the conserved SYTANLAAF motif. Activation by Cd is occluded by modification with 2-aminoethyl MTS (MTSEA), indicating that Cd binds directly and specifically to the substituted cysteines. Cd potency for the A657C mutation (EC50 = 10 µM) suggests that binding involves at least two coordinating residues, whereas weaker Cd potency for L659C (EC50 = 2 mM) implies that activation does not require tight coordination by multiple side chains for this substitution. Experiments with heteromeric and chimeric channels indicate that activation by Cd requires Cys substitution at only two of the four subunits within a tetrameric receptor and that activation is similar for substitution within subunits in either the A/C or B/D conformations. We develop simple kinetic models for the A657C substitution that reproduce several features of Cd activation as well as the low-affinity inhibition observed at higher Cd concentrations (5–20 mM). Together, these results demonstrate rapid and reversible channel activation, independent of agonist site occupancy, upon Cd binding to Cys side chains at two specific locations along the GluK2 inner helix.

scholarly journals Cadmium activates AMPA and NMDA receptors with M3 helix cysteine substitutions

2020 ◽  
Vol 152 (7) ◽  
Author(s):  
Timothy J. Wilding ◽  
James E. Huettner
Keyword(s):  
Nmda Receptors ◽  
Conformational Changes ◽  
Neurological Disorders ◽  
Site Occupancy ◽  
Kainate Receptors ◽  
Agonist Binding ◽  
Auxiliary Subunit ◽  
Voltage Dependent ◽  
Ampa And Nmda Receptors ◽  
Mutant Receptors

AMPA and NMDA receptors are ligand-gated ion channels that depolarize postsynaptic neurons when activated by the neurotransmitter L-glutamate. Changes in the distribution and activity of these receptors underlie learning and memory, but excessive change is associated with an array of neurological disorders, including cognitive impairment, developmental delay, and epilepsy. All of the ionotropic glutamate receptors (iGluRs) exhibit similar tetrameric architecture, transmembrane topology, and basic framework for activation; conformational changes induced by extracellular agonist binding deform and splay open the inner helix bundle crossing that occludes ion flux through the channel. NMDA receptors require agonist binding to all four subunits, whereas AMPA and closely related kainate receptors can open with less than complete occupancy. In addition to conventional activation by agonist binding, we recently identified two locations along the inner helix of the GluK2 kainate receptor subunit where cysteine (Cys) substitution yields channels that are opened by exposure to cadmium ions, independent of agonist site occupancy. Here, we generate AMPA and NMDA receptor subunits with homologous Cys substitutions and demonstrate similar activation of the mutant receptors by Cd. Coexpression of the auxiliary subunit stargazin enhanced Cd potency for activation of Cys-substituted GluA1 and altered occlusion upon treatment with sulfhydryl-reactive MTS reagents. Mutant NMDA receptors displayed voltage-dependent Mg block of currents activated by agonist and/or Cd as well as asymmetry between Cd effects on Cys-substituted GluN1 versus GluN2 subunits. In addition, Cd activation of each Cys-substituted iGluR was inhibited by protons. These results, together with our earlier work on GluK2, reveal a novel mechanism shared among the three different iGluR subtypes for prying open the gate that controls ion entry into the pore.

The Cys-loop superfamily of ligand-gated ion channels: the impact of receptor structure on function

2004 ◽  
Vol 32 (3) ◽  
pp. 529-534 ◽  
Author(s):  
C.N. Connolly ◽  
K.A. Wafford
Keyword(s):  
Ion Channels ◽  
Conformational Changes ◽  
Channel Structure ◽  
Channel Function ◽  
Receptor Structure ◽  
Channel Opening ◽  
The Impact ◽  
Ion Pore ◽  
Gated Ion Channels ◽  
Ligand Gated Ion Channels

The Cys-loop receptors constitute an important superfamily of LGICs (ligand-gated ion channels) comprising receptors for acetylcholine, 5-HT3 (5-hydroxytryptamine; 5-HT3 receptors), glycine and GABA (γ-aminobutyric acid; GABAA receptors). A vast knowledge of the structure of the Cys-loop superfamily and its impact on channel function have been accrued over the last few years, leading to exciting new proposals on how ion channels open and close in response to agonist binding. Channel opening is initiated by the extracellular association of agonists to discrete binding pockets, leading to dramatic conformational changes, culminating in the opening of a central ion pore. The importance of channel structure is exemplified in the allosteric modulation of channel function by the binding of other molecules to distinct sites on the channel, which exerts an additional level of control on their function. The subsequent conformational changes (gating) lead to channel opening and ion transport. Following channel pore opening, ion selectivity is determined by receptor structure in, and around, the ion pore. As a final level of control, cytoplasmic determinants control the magnitude (conductance) of ion flow into the cell. Thus the Cys-loop receptors are complex molecular motors, with moving parts, which can transduce extracellular signals across the plasma membrane. Once the full mechanical motions involved are understood, it may be possible to design sophisticated therapeutic agents to modulate their activity, or at least be able to throw a molecular spanner into the works!

scholarly journals Ion Channels and Zinc: Mechanisms of Neurotoxicity and Neurodegeneration

2012 ◽  
Vol 2012 ◽  
pp. 1-6 ◽  
Author(s):  
Deborah R. Morris ◽  
Cathy W. Levenson
Keyword(s):  
Brain Injury ◽  
Ion Channels ◽  
Kainate Receptors ◽  
Zinc Toxicity ◽  
Ischemic Brain Injury ◽  
Ischemic Brain ◽  
The Central Nervous System ◽  
Excitatory Neurotransmission ◽  
The Brain

Ionotropic glutamate receptors, such as NMDA, AMPA and kainate receptors, are ligand-gated ion channels that mediate much of the excitatory neurotransmission in the brain. Not only do these receptors bind glutamate, but they are also regulated by and facilitate the postsynaptic uptake of the trace metal zinc. This paper discusses the role of the excitotoxic influx and accumulation of zinc, the mechanisms responsible for its cytotoxicity, and a number of disorders of the central nervous system that have been linked to these neuronal ion channels and zinc toxicity including ischemic brain injury, traumatic brain injury, and epilepsy.

Infrared spectra of N-acetyl-L-α-amino-acid N'-methylamides with aliphatic side chains in non-polar solvents

1981 ◽  
Vol 46 (3) ◽  
pp. 772-780 ◽  
Author(s):  
Jorga Smolíková ◽  
Jan Pospíšek ◽  
Karel Bláha
Keyword(s):  
Amino Acid ◽  
Conformational Changes ◽  
Infrared Spectra ◽  
Room Temperature ◽  
Side Chains ◽  
Polar Solvents

Infrared spectra of the L-alanine (I), L-leucine (II), L-valine (III) and L-tert-leucine (IV) N-acetyl N'-methylamides were measured. Amides I-IV are not self associated in tetrachlormethane in the concentration 2 . 10-5 mol l-1 at room temperature and in tetrachloroethylene in the concentration 1.5 . 10-4 mol l-1 at temperatures above 65° C. True conformational changes are observable only with the least flexible amide IV which exists at room temperature in a C5 conformation. This conformational type is also highly populated in the valine derivative III, but is less important in the alanine and leucine derivatives I and II in which the intramolecularly bonded C7 and the distorted hydrogen-nonbonded conformations contribute seriously.

Desensitization and resensitization rates of glutamate-activated channels may regulate motoneuron excitability

1991 ◽  
Vol 66 (4) ◽  
pp. 1166-1175 ◽  
Author(s):  
D. O. Smith ◽  
C. Franke ◽  
J. L. Rosenheimer ◽  
F. Zufall ◽  
H. Hatt
Keyword(s):  
Ampa Receptors ◽  
Single Channel ◽  
Kainate Receptors ◽  
Whole Cell ◽  
Solution Exchange ◽  
Channel Opening ◽  
Fast Solution ◽  
Agonist Concentration ◽  
Kinetics Of ◽  
Channel Properties

1. Single-channel properties of desensitizing glutamate-activated channels were analyzed in outside-out patch-clamp recordings from a motoneuron-enriched cell fraction from embryonic chick. A piezo-driven device was used to achieve fast solution exchange at the electrode tip, resulting in maximum activation within 2 ms. 2. Quisqualate/AMPA receptors, with a 13-pS conductance, desensitized rapidly; the desensitization rate depended on agonist concentration but not on membrane potential. When quisqualate was applied slowly, the quisqualate-activated channels desensitized without prior channel opening, indicating desensitization from the closed state. After a 10-ms refractory period, resensitization of all channels required up to 300 ms; resensitization rate did not depend on the duration of the preceding quisqualate application. 3. At agonist concentrations less than or equal to 1 mM, kainate receptors, with a 20-pS conductance, did not desensitize. At kainate concentrations greater than or equal to 1 mM, though, kainate receptors desensitized to a low steady-state conductance within approximately 200 ms. Resensitization of all channels required as long as 3 s, which could render kainate receptors inexcitable during high-frequency activation. 4. Desensitization rates of whole-cell currents were similar to those observed in outside-out mode. Glutamate- and quisqualate-activated responses were similar, suggesting that the rapidly desensitizing quisqualate-sensitive receptor type may dominate the kinetics of whole-cell excitatory postsynaptic currents (EPSCs) in this preparation. 5. It may be concluded that the efficacy of glutamate-mediated synaptic transmission is modulated by differences in the rates of desensitization and resensitization.

Hippocampal glutamine synthetase: insensitivity to glucocorticoids and stress

1990 ◽  
Vol 258 (5) ◽  
pp. E894-E897 ◽  
Author(s):  
G. C. Tombaugh ◽  
R. M. Sapolsky
Keyword(s):  
Skeletal Muscle ◽  
Central Nervous System ◽  
Nervous System ◽  
Glutamine Synthetase ◽  
Glutamate Metabolism ◽  
Glutamatergic Synapses ◽  
Adult Rats ◽  
Glucocorticoid Induction ◽  
The Central Nervous System ◽  
The Brain

Glucocorticoids enhance the neurotoxic potential of several insults to the rat hippocampus that involve overactivation of glutamatergic synapses. These hormones also stimulate the synthesis of glutamine synthetase (GS) in peripheral tissue. Because this enzyme helps regulate glutamate metabolism in the central nervous system, glucocorticoid induction of GS in the brain may underlie the observed synergy. We have measured GS activity in the hippocampus and skeletal muscle (plantaris) of adult rats after bilateral adrenalectomy (ADX), corticosterone (Cort) replacement, or stress. No significant changes in GS were observed in hippocampal tissue, whereas muscle GS was significantly elevated after Cort treatment or stress and was reduced after ADX. These results suggest that Cort-induced shifts in GS activity probably do not explain Cort neurotoxicity, although the stress-induced rise in muscle GS may be relevant to certain types of myopathy.

scholarly journals A scalar Poincaré map for struggling in Xenopus tadpoles

2019 ◽  
Author(s):  
Mark Olenik ◽  
Conor Houghton
Keyword(s):  
Fixed Points ◽  
Activity Patterns ◽  
Synaptic Depression ◽  
The Body ◽  
Synaptic Conductance ◽  
Inhibitory Synapses ◽  
Minimal Network ◽  
Cell Network ◽  
Neuronal Mechanisms ◽  
The Central Nervous System

AbstractSynaptic plasticity is widely found in many areas of the central nervous system. In particular, it is believed that synaptic depression can act as a mechanism to allow simple networks to generate a range of different firing patterns. The simplicity of the locomotor circuit in hatchling Xenopus tadpoles provides an excellent place to understand such basic neuronal mechanisms. Depending on the nature of the external stimulus, tadpoles can generate two types of behaviours: swimming when touched and slower, stronger struggling movements when held. Struggling is associated with rhythmic bends of the body and is accompanied by anti-phase bursts in neurons on each side of the spinal cord. Bursting in struggling is thought to be governed by a short-term synaptic depression of inhibition. To better understand burst generation in struggling, we study a minimal network of two neurons coupled through depressing inhibitory synapses. Depending on the strength of the synaptic conductance between the two neurons, such a network can produce symmetric n - n anti-phase bursts, where neurons fire n spikes in alternation, with the period of such solutions increasing with the strength of the synaptic conductance. Using a fast/slow analysis, we reduce the multidimensional network equations to a scalar Poincaé burst map. This map tracks the state of synaptic depression from one burst to the next, and captures the complex bursting dynamics of the network. Fixed points of this map are associated with stable burst solutions of the full network model, and are created through fold bifurcations of maps. We prove that the map has an infinite number of stable fixed points for a finite coupling strength interval, suggesting that the full two-cell network also can produce n - n bursts for arbitrarily large n. Our findings further support the hypothesis that synaptic depression can enrich the variety of activity patterns a neuronal network generates.

Photoinduced conformational changes of azoaromatic polyaspartates containing octadecyl side chains

1990 ◽  
Vol 28 (5) ◽  
pp. 1161-1170 ◽  
Author(s):  
Akihiko Ueno ◽  
Kayo Adachi ◽  
Junko Nakamura ◽  
Tetsuo Osa
Keyword(s):  
Conformational Changes ◽  
Side Chains

Neuroanatomy and neurophysiology

2021 ◽  
pp. 725-852
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Cervical Vertebrae ◽  
Lymphatic Vessels ◽  
Cell Types ◽  
Cellular Level ◽  
Inhibitory Synapses ◽  
The Central Nervous System ◽  
Emotion Memory ◽  
Different Cell Types

‘Neuroanatomy and neurophysiology’ covers the anatomy and organization of the central nervous system, including the skull and cervical vertebrae, the meninges, the blood and lymphatic vessels, muscles and nerves of the head and neck, and the structures of the eye, ear, and central nervous system. At a cellular level, the different cell types and the mechanism of transmission across synapses are considered, including excitatory and inhibitory synapses. This is followed by a review of the major control and sensory systems (including movement, information processing, locomotion, reflexes, and the main five senses of sight, hearing, touch, taste, and smell). The integration of these processes into higher functions (such as sleep, consciousness and coma, emotion, memory, and ageing) is discussed, along with the causes and treatments of disorders of diseases such as depression, schizophrenia, epilepsy, addiction, and degenerative diseases.

scholarly journals Conformational Changes in the Pore of CLC-0

2003 ◽  
Vol 122 (3) ◽  
pp. 277-294 ◽  
Author(s):  
Alessio Accardi ◽  
Michael Pusch
Keyword(s):  
Conformational Changes ◽  
Single Channel ◽  
General Structure ◽  
Point Mutations ◽  
Clofibric Acid ◽  
Selectivity Filter ◽  
Side Chain ◽  
Closed State ◽  
State Dependent ◽  
Channel Opening

The Torpedo Cl− channel, CLC-0, is inhibited by clofibric acid derivatives from the intracellular side. We used the slow gate-deficient mutant CLC-0C212S to investigate the mechanism of block by the clofibric acid–derivative p-chlorophenoxy-acetic acid (CPA). CPA blocks open channels with low affinity (KDO= 45 mM at 0 mV) and shows fast dissociation (koff = 490 s−1 at −140 mV). In contrast, the blocker binds to closed channels with higher affinity and with much slower kinetics. This state-dependent block coupled with the voltage dependence of the gating transitions results in a highly voltage-dependent inhibition of macroscopic currents (KD ∼1 mM at −140 mV; KD ∼65 mM at 60 mV). The large difference in CPA affinity of the open and closed state suggests that channel opening involves more than just a local conformational rearrangement. On the other hand, in a recent work (Dutzler, R., E.B. Campbell, and R. MacKinnon. 2003. Science. 300:108–112) it was proposed that the conformational change underlying channel opening is limited to a movement of a single side chain. A prediction of this latter model is that mutations that influence CPA binding to the channel should affect the affinities for an open and closed channel in a similar manner since the general structure of the pore remains largely unchanged. To test this hypothesis we introduced point mutations in four residues (S123, T471, Y512, and K519) that lie close to the intracellular pore mouth or to the putative selectivity filter. Mutation T471S alters CPA binding exclusively to closed channels. Pronounced effects on the open channel block are observed in three other mutants, S123T, Y512A, and K519Q. Together, these results collectively suggest that the structure of the CPA binding site is different in the open and closed state. Finally, replacement of Tyr 512, a residue directly coordinating the central Cl− ion in the crystal structure, with Phe or Ala has very little effect on single channel conductance and selectivity. These observations suggest that channel opening in CLC-0 consists in more than a movement of a side chain and that other parts of the channel and of the selectivity filter are probably involved.

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