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Structural mechanism of glutamate receptor activation and desensitization.

Meyerson JR, Kumar J, Chittori S, Rao P, Pierson J, Bartesaghi A, Mayer ML, Subramaniam S - Nature (2014)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Cell Biology, Center for Cancer Research, NCI, NIH, Bethesda, Maryland 20892, USA.

ABSTRACT
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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Related in: MedlinePlus

Unified view of glutamate receptor gating cyclea, Schematic summary of global conformational changes highlighting domain movements with channel opening and closure during the receptor gating cycle. The dashed lines over the open state indicate the shortening as a result of the corkscrew rotation that opens the channel. The differences observed between desensitized states of GluK2 and GluA2 are illustrated as variations of a common theme in which the LBD layer shifts to 4-fold symmetry with or without separation of the ATD dimer pairs.
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Figure 5: Unified view of glutamate receptor gating cyclea, Schematic summary of global conformational changes highlighting domain movements with channel opening and closure during the receptor gating cycle. The dashed lines over the open state indicate the shortening as a result of the corkscrew rotation that opens the channel. The differences observed between desensitized states of GluK2 and GluA2 are illustrated as variations of a common theme in which the LBD layer shifts to 4-fold symmetry with or without separation of the ATD dimer pairs.

Mentions: AMPA and kainate receptors are widely regarded as functionally and structurally related families. Our study exploited the availability of unique AMPA receptor allosteric modulators to trap GluA2 in the active state, while the greater thermodynamic stability of the GluK2 desensitized state yielded a higher resolution structure than could be achieved for GluA2em. Based on the similarity observed in the LBD layer in the desensitized states of both GluA2em and GluK2, we conclude that transition to quasi 4-fold symmetry in the LBD layer is a key structural signature of desensitization in these iGluR families. Based on these similarities, we propose a unified description of the structural changes that occur during the gating cycle of receptors in the iGluR family (Fig. 5). Several lines of evidence justify this approach: after genetic removal of the ATD, both GluA2 and GluK2 display gating properties that are similar to those of the parent receptors27–29, with activation and desensitization on the millisecond time scale, indicating that the conformational change underlying activation and desensitization occurs primarily in the LBD and ion channel assemblies, independent of conformational variability in the ATD. Consistent with this observation, numerous crystallographic studies of soluble GluA2 and GluK2 LBDs have established essentially identical sets of structures and extents of movement for complexes with agonists and antagonists30. In the ion channel domain, GluA2 and GluK2 share 73% amino acid sequence similarity, and exhibit common functional properties including prominent sub-conductance states1, similar relative permeability to sodium and calcium ions31, and channel block by cytoplasmic polyamines32.


Structural mechanism of glutamate receptor activation and desensitization.

Meyerson JR, Kumar J, Chittori S, Rao P, Pierson J, Bartesaghi A, Mayer ML, Subramaniam S - Nature (2014)

Unified view of glutamate receptor gating cyclea, Schematic summary of global conformational changes highlighting domain movements with channel opening and closure during the receptor gating cycle. The dashed lines over the open state indicate the shortening as a result of the corkscrew rotation that opens the channel. The differences observed between desensitized states of GluK2 and GluA2 are illustrated as variations of a common theme in which the LBD layer shifts to 4-fold symmetry with or without separation of the ATD dimer pairs.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4199900&req=5

Figure 5: Unified view of glutamate receptor gating cyclea, Schematic summary of global conformational changes highlighting domain movements with channel opening and closure during the receptor gating cycle. The dashed lines over the open state indicate the shortening as a result of the corkscrew rotation that opens the channel. The differences observed between desensitized states of GluK2 and GluA2 are illustrated as variations of a common theme in which the LBD layer shifts to 4-fold symmetry with or without separation of the ATD dimer pairs.
Mentions: AMPA and kainate receptors are widely regarded as functionally and structurally related families. Our study exploited the availability of unique AMPA receptor allosteric modulators to trap GluA2 in the active state, while the greater thermodynamic stability of the GluK2 desensitized state yielded a higher resolution structure than could be achieved for GluA2em. Based on the similarity observed in the LBD layer in the desensitized states of both GluA2em and GluK2, we conclude that transition to quasi 4-fold symmetry in the LBD layer is a key structural signature of desensitization in these iGluR families. Based on these similarities, we propose a unified description of the structural changes that occur during the gating cycle of receptors in the iGluR family (Fig. 5). Several lines of evidence justify this approach: after genetic removal of the ATD, both GluA2 and GluK2 display gating properties that are similar to those of the parent receptors27–29, with activation and desensitization on the millisecond time scale, indicating that the conformational change underlying activation and desensitization occurs primarily in the LBD and ion channel assemblies, independent of conformational variability in the ATD. Consistent with this observation, numerous crystallographic studies of soluble GluA2 and GluK2 LBDs have established essentially identical sets of structures and extents of movement for complexes with agonists and antagonists30. In the ion channel domain, GluA2 and GluK2 share 73% amino acid sequence similarity, and exhibit common functional properties including prominent sub-conductance states1, similar relative permeability to sodium and calcium ions31, and channel block by cytoplasmic polyamines32.

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Cell Biology, Center for Cancer Research, NCI, NIH, Bethesda, Maryland 20892, USA.

ABSTRACT
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.

Show MeSH
Related in: MedlinePlus