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PDBsum entry 1p1n
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Membrane protein
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PDB id
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1p1n
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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Tuning activation of the ampa-Sensitive glur2 ion channel by genetic adjustment of agonist-Induced conformational changes.
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Authors
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N.Armstrong,
M.Mayer,
E.Gouaux.
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Ref.
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Proc Natl Acad Sci U S A, 2003,
100,
5736-5741.
[DOI no: ]
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PubMed id
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Abstract
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The (S)-2-amino-3-(3-hydroxy-5-methyl-4-isoxazole) propionic acid (AMPA)
receptor discriminates between agonists in terms of binding and channel gating;
AMPA is a high-affinity full agonist, whereas kainate is a low-affinity partial
agonist. Although there is extensive literature on the functional
characterization of partial agonist activity in ion channels, structure-based
mechanisms are scarce. Here we investigate the role of Leu-650, a binding cleft
residue conserved among AMPA receptors, in maintaining agonist specificity and
regulating agonist binding and channel gating by using physiological, x-ray
crystallographic, and biochemical techniques. Changing Leu-650 to Thr yields a
receptor that responds more potently and efficaciously to kainate and less
potently and efficaciously to AMPA relative to the WT receptor. Crystal
structures of the Leu-650 to Thr mutant reveal an increase in domain closure in
the kainate-bound state and a partially closed and a fully closed conformation
in the AMPA-bound form. Our results indicate that agonists can induce a range of
conformations in the GluR2 ligand-binding core and that domain closure is
directly correlated to channel activation. The partially closed, AMPA-bound
conformation of the L650T mutant likely captures the structure of an
agonist-bound, inactive state of the receptor. Together with previously solved
structures, we have determined a mechanism of agonist binding and subsequent
conformational rearrangements.
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Figure 4.
Fig. 4. Comparison of WT and S1S2J L650T/AMPA(AS)
conformations. (A) Superposition of WT S1S2J/AMPA (gray) with
S1S2J L650T/AMPA (AS form) protomer A (blue). (B) Superposition
of WT S1S2J/AMPA (gray) with S1S2J L650T/AMPA(AS) protomer B
(green). The black arrows in A and B indicate the axis of
rotation relating the conformational difference between the WT
and L650T structures. (C) Superimposed WT and mutant AMPA dimers.
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Figure 6.
Fig. 6. Mechanism of agonist binding and domain closure.
(A) The binding site of the open-cleft, closed-channel state
(Apo S1S2J, protomer A). (B) The possible first step in agonist
binding as observed in molecule B of the L650T/AMPA(AS)
structure. We suggest that this semiclosed cleft conformation
represents the agonist-bound, closed-channel state. (C) The
closed-cleft, open-channel conformation as observed in the WT
S1S2J/AMPA binding cleft (protomer A). In B and C, water
molecules are shown as green spheres, AMPA is drawn in magenta,
and hydrogen bonds are depicted by black dashed lines. The
degrees of domain closure relative to the Apo conformation are
indicated below each structure.
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