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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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Resolution of the desensitized GluK2 density mapa, GluK2 desensitized state map shown at increasing contour levels from left to right, to better highlight selected secondary structural features. b, Validation of density map using tilt-pair parameter plot. The spread in orientational assignments around the known goniometer settings is within ~ 25° for > 60 % of the selected particle pairs, with clear clustering observed at the expected location, centered at a distance of 10° from the origin. c, Distal (left) and proximal (right) ATD subunits fit with the corresponding X-ray coordinates (PDB ID: 3H6G). d, Proximal (left) and distal (right) LBD subunits fit with the corresponding X-ray coordinates for glutamate-bound GluK2 LBD monomers (PDB ID: 3G3F). The close similarity in density maps for the individual ATD and LBD monomers of distal and proximal domains that are unrelated by computationally imposed C2 symmetry shows that the LBD monomers move largely as rigid bodies and that the structural changes that occur with desensitization can be described adequately by rigid body movements of the ATD and LBD monomers.
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Figure 13: Resolution of the desensitized GluK2 density mapa, GluK2 desensitized state map shown at increasing contour levels from left to right, to better highlight selected secondary structural features. b, Validation of density map using tilt-pair parameter plot. The spread in orientational assignments around the known goniometer settings is within ~ 25° for > 60 % of the selected particle pairs, with clear clustering observed at the expected location, centered at a distance of 10° from the origin. c, Distal (left) and proximal (right) ATD subunits fit with the corresponding X-ray coordinates (PDB ID: 3H6G). d, Proximal (left) and distal (right) LBD subunits fit with the corresponding X-ray coordinates for glutamate-bound GluK2 LBD monomers (PDB ID: 3G3F). The close similarity in density maps for the individual ATD and LBD monomers of distal and proximal domains that are unrelated by computationally imposed C2 symmetry shows that the LBD monomers move largely as rigid bodies and that the structural changes that occur with desensitization can be described adequately by rigid body movements of the ATD and LBD monomers.

Mentions: In the structure of the GluK2 desensitized state, determined at ~ 7.6 Å resolution (Fig. 4a, Extended Data Fig. 7 and 8), density was resolved for all α-helices in the ATD and LBD assemblies, and also for the M3 helix bundle, the upper segment of M1 and the pre-M1 cuff helix in the ion channel (Fig. 4b). The density map reveals preservation of 2-fold symmetry in the ATD layer while the LBD layer adopts a quasi 4-fold symmetric arrangement (Fig. 4c). To obtain a molecular model for the desensitized state, we fitted two copies of GluK2 ATD dimer assemblies (PDB ID: 3H6G) and four copies of a GluK2 subunit LBD glutamate complex (PDB ID: 3G3F). The resolution of our map is adequate to unambiguously show that in the desensitized state the ion channel adopts a closed conformation (Fig. 4b, panel vii) in which the M3 helices form a crossed bundle assembly with the pre-M1 helices wrapped around the outside of the channel, similar to that seen for GluA2cryst in its antagonist-bound closed state.


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)

Resolution of the desensitized GluK2 density mapa, GluK2 desensitized state map shown at increasing contour levels from left to right, to better highlight selected secondary structural features. b, Validation of density map using tilt-pair parameter plot. The spread in orientational assignments around the known goniometer settings is within ~ 25° for > 60 % of the selected particle pairs, with clear clustering observed at the expected location, centered at a distance of 10° from the origin. c, Distal (left) and proximal (right) ATD subunits fit with the corresponding X-ray coordinates (PDB ID: 3H6G). d, Proximal (left) and distal (right) LBD subunits fit with the corresponding X-ray coordinates for glutamate-bound GluK2 LBD monomers (PDB ID: 3G3F). The close similarity in density maps for the individual ATD and LBD monomers of distal and proximal domains that are unrelated by computationally imposed C2 symmetry shows that the LBD monomers move largely as rigid bodies and that the structural changes that occur with desensitization can be described adequately by rigid body movements of the ATD and LBD monomers.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 13: Resolution of the desensitized GluK2 density mapa, GluK2 desensitized state map shown at increasing contour levels from left to right, to better highlight selected secondary structural features. b, Validation of density map using tilt-pair parameter plot. The spread in orientational assignments around the known goniometer settings is within ~ 25° for > 60 % of the selected particle pairs, with clear clustering observed at the expected location, centered at a distance of 10° from the origin. c, Distal (left) and proximal (right) ATD subunits fit with the corresponding X-ray coordinates (PDB ID: 3H6G). d, Proximal (left) and distal (right) LBD subunits fit with the corresponding X-ray coordinates for glutamate-bound GluK2 LBD monomers (PDB ID: 3G3F). The close similarity in density maps for the individual ATD and LBD monomers of distal and proximal domains that are unrelated by computationally imposed C2 symmetry shows that the LBD monomers move largely as rigid bodies and that the structural changes that occur with desensitization can be described adequately by rigid body movements of the ATD and LBD monomers.
Mentions: In the structure of the GluK2 desensitized state, determined at ~ 7.6 Å resolution (Fig. 4a, Extended Data Fig. 7 and 8), density was resolved for all α-helices in the ATD and LBD assemblies, and also for the M3 helix bundle, the upper segment of M1 and the pre-M1 cuff helix in the ion channel (Fig. 4b). The density map reveals preservation of 2-fold symmetry in the ATD layer while the LBD layer adopts a quasi 4-fold symmetric arrangement (Fig. 4c). To obtain a molecular model for the desensitized state, we fitted two copies of GluK2 ATD dimer assemblies (PDB ID: 3H6G) and four copies of a GluK2 subunit LBD glutamate complex (PDB ID: 3G3F). The resolution of our map is adequate to unambiguously show that in the desensitized state the ion channel adopts a closed conformation (Fig. 4b, panel vii) in which the M3 helices form a crossed bundle assembly with the pre-M1 helices wrapped around the outside of the channel, similar to that seen for GluA2cryst in its antagonist-bound closed state.

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