1iit
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(New page: 200px<br /><applet load="1iit" size="450" color="white" frame="true" align="right" spinBox="true" caption="1iit, resolution 1.90Å" /> '''GLUR0 LIGAND BINDING...)
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Revision as of 15:18, 20 November 2007
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GLUR0 LIGAND BINDING CORE COMPLEX WITH L-SERINE
Overview
High-resolution structures of the ligand binding core of GluR0, a, glutamate receptor ion channel from Synechocystis PCC 6803, have been, solved by X-ray diffraction. The GluR0 structures reveal homology with, bacterial periplasmic binding proteins and the rat GluR2 AMPA subtype, neurotransmitter receptor. The ligand binding site is formed by a cleft, between two globular alpha/beta domains. L-Glutamate binds in an extended, conformation, similar to that observed for glutamine binding protein, (GlnBP). However, the L-glutamate gamma-carboxyl group interacts, exclusively with Asn51 in domain 1, different from the interactions of, ligand with domain 2 residues observed for GluR2 and GlnBP. To address how, neutral amino acids activate GluR0 gating we solved the structure of the, binding site complex with L-serine. This revealed solvent molecules acting, as surrogate ligand atoms, such that the serine OH group makes, solvent-mediated hydrogen bonds with Asn51. The structure of a, ligand-free, closed-cleft conformation revealed an extensive hydrogen bond, network mediated by solvent molecules. Equilibrium centrifugation analysis, revealed dimerization of the GluR0 ligand binding core with a dissociation, constant of 0.8 microM. In the crystal, a symmetrical dimer involving, residues in domain 1 occurs along a crystallographic 2-fold axis and, suggests that tetrameric glutamate receptor ion channels are assembled, from dimers of dimers. We propose that ligand-induced conformational, changes cause the ion channel to open as a result of an increase in domain, 2 separation relative to the dimer interface.
About this Structure
1IIT is a Single protein structure of sequence from Synechocystis sp. with SER as ligand. Full crystallographic information is available from OCA.
Reference
Mechanisms for ligand binding to GluR0 ion channels: crystal structures of the glutamate and serine complexes and a closed apo state., Mayer ML, Olson R, Gouaux E, J Mol Biol. 2001 Aug 24;311(4):815-36. PMID:11518533
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