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Structural Mobility of the Extracellular Ligand-Binding Core of an Ionotropic Glutamate Receptor. Analysis of NMR Relaxation Dynamics†
journal contribution
posted on 2002-07-26, 00:00 authored by Robert L. McFeeters, Robert E. OswaldIonotropic glutamate receptors play important roles in a variety of neuronal processes and
have been implicated in multiple neurodegenerative diseases. The extracellular ligand-binding (S1S2)
core of the GluR2 subtype can be expressed in bacteria as a soluble, monomeric protein with binding
properties essentially identical to those of the intact receptor. The crystal structure of this protein has
been determined in the presence and absence of various agonists and antagonists [Armstrong, N., Sun,
Y., Chen, G. Q., and Gouaux, E. (1998) Nature 395, 913−917; Armstrong, N., and Gouaux, E. (2000)
Neuron 28, 165−181]. The protein consists of two lobes, with the S1 segment composing the majority of
lobe 1 and the S2 segment composing most of lobe 2. A domain closure upon ligand binding has been
postulated, but details of intradomain motions have not been investigated. In this paper, the backbone
motions of the ligand-binding core of GluR2 bound to glutamate were studied using 15N longitudinal (T1)
and transverse (T2) relaxation measurements as well as {1H}−15N nuclear Overhauser effects at 500 and
600 MHz. Residues in the agonist-binding pocket exhibited two main classes of motion. Those contacting
the α-substituents of the ligand glutamate exhibited minimal internal motion, while those contacting the
γ-constituents exhibited exchange dynamics, indicating two dynamically distinct portions of the binding
pocket. Also, two residues in transdomain linkers between lobes 1 and 2 show exchange, lending new
insight into the previously proposed domain closure hypothesis. Finally, concerted motion of helix F
suggests a pathway for ligand dissociation without the necessity of domain reopening.
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transdomain linkersbackbone motionsligand dissociationrelaxation measurementsGouauxNMRArmstrongdomain closure600 MHzlobe 1S 1 segmentdomain closure hypothesisOverhauser effectsligand bindingT 2T 1ligand glutamatelobe 2.binding properties2 show exchangereceptorneurodegenerative diseaseslobes 1GluR 2S 2 segmentS 1S corebinding pocketexchange dynamicsintradomain motions15 Ncrystal structureGluR 2 subtypeIonotropic Glutamate Receptormonomeric proteinStructural Mobilityhelix F
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