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The low binding affinity of D-serine at the ionotropic glutamate receptor GluD2 can be attributed to the hinge region

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ABSTRACT

Ionotropic glutamate receptors (iGluRs) are responsible for most of the fast excitatory communication between neurons in our brain. The GluD2 receptor is a puzzling member of the iGluR family: It is involved in synaptic plasticity, plays a role in human diseases, e.g. ataxia, binds glycine and D-serine with low affinity, yet no ligand has been discovered so far that can activate its ion channel. In this study, we show that the hinge region connecting the two subdomains of the GluD2 ligand-binding domain is responsible for the low affinity of D-serine, by analysing GluD2 mutants with electrophysiology, isothermal titration calorimetry and molecular dynamics calculations. The hinge region is highly variable among iGluRs and fine-tunes gating activity, suggesting that in GluD2 this region has evolved to only respond to micromolar concentrations of D-serine.

No MeSH data available.


Structure of the GluD2-LBD (PDB ID 2V3U13).(a) The D1–D2 hinge region (HS1 and HS2; pink) as well as the positions of point mutations in the binding site generated in this study (Y496F: purple; Y543Q: pink; A686S: blue; Y770F: brown) are indicated. The box on the right shows a magnified view of the D1–D2 hinge region and the D-serine binding site with all residues investigated in this study labelled. (b) Comparison of HS1 and HS2 residues among all 18 iGluR subunits. Residues conserved among all subunits are highlighted in magenta, residues conserved within subfamilies in cyan.
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f1: Structure of the GluD2-LBD (PDB ID 2V3U13).(a) The D1–D2 hinge region (HS1 and HS2; pink) as well as the positions of point mutations in the binding site generated in this study (Y496F: purple; Y543Q: pink; A686S: blue; Y770F: brown) are indicated. The box on the right shows a magnified view of the D1–D2 hinge region and the D-serine binding site with all residues investigated in this study labelled. (b) Comparison of HS1 and HS2 residues among all 18 iGluR subunits. Residues conserved among all subunits are highlighted in magenta, residues conserved within subfamilies in cyan.

Mentions: Comparison of amino acid sequences between the LBDs of GluD2 and the glycine/D-serine-binding NMDA receptor subunit GluN1 showed an even distribution of similar residues across the whole LBD. Thus, no specific region in GluD2 was obvious as being responsible for the low binding affinity of D-serine. Therefore, we applied two strategies to investigate the reasons for the low binding affinity: i) mutation of GluD2 binding site residues to corresponding residues of GluN1 and ii) mutation of the D1–D2 hinge region in the GluD2 LBD to that of GluN1 (Fig. 1).


The low binding affinity of D-serine at the ionotropic glutamate receptor GluD2 can be attributed to the hinge region
Structure of the GluD2-LBD (PDB ID 2V3U13).(a) The D1–D2 hinge region (HS1 and HS2; pink) as well as the positions of point mutations in the binding site generated in this study (Y496F: purple; Y543Q: pink; A686S: blue; Y770F: brown) are indicated. The box on the right shows a magnified view of the D1–D2 hinge region and the D-serine binding site with all residues investigated in this study labelled. (b) Comparison of HS1 and HS2 residues among all 18 iGluR subunits. Residues conserved among all subunits are highlighted in magenta, residues conserved within subfamilies in cyan.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384001&req=5

f1: Structure of the GluD2-LBD (PDB ID 2V3U13).(a) The D1–D2 hinge region (HS1 and HS2; pink) as well as the positions of point mutations in the binding site generated in this study (Y496F: purple; Y543Q: pink; A686S: blue; Y770F: brown) are indicated. The box on the right shows a magnified view of the D1–D2 hinge region and the D-serine binding site with all residues investigated in this study labelled. (b) Comparison of HS1 and HS2 residues among all 18 iGluR subunits. Residues conserved among all subunits are highlighted in magenta, residues conserved within subfamilies in cyan.
Mentions: Comparison of amino acid sequences between the LBDs of GluD2 and the glycine/D-serine-binding NMDA receptor subunit GluN1 showed an even distribution of similar residues across the whole LBD. Thus, no specific region in GluD2 was obvious as being responsible for the low binding affinity of D-serine. Therefore, we applied two strategies to investigate the reasons for the low binding affinity: i) mutation of GluD2 binding site residues to corresponding residues of GluN1 and ii) mutation of the D1–D2 hinge region in the GluD2 LBD to that of GluN1 (Fig. 1).

View Article: PubMed Central - PubMed

ABSTRACT

Ionotropic glutamate receptors (iGluRs) are responsible for most of the fast excitatory communication between neurons in our brain. The GluD2 receptor is a puzzling member of the iGluR family: It is involved in synaptic plasticity, plays a role in human diseases, e.g. ataxia, binds glycine and D-serine with low affinity, yet no ligand has been discovered so far that can activate its ion channel. In this study, we show that the hinge region connecting the two subdomains of the GluD2 ligand-binding domain is responsible for the low affinity of D-serine, by analysing GluD2 mutants with electrophysiology, isothermal titration calorimetry and molecular dynamics calculations. The hinge region is highly variable among iGluRs and fine-tunes gating activity, suggesting that in GluD2 this region has evolved to only respond to micromolar concentrations of D-serine.

No MeSH data available.