Full domain closure of the ligand-binding core of the ionotropic glutamate receptor iGluR5 induced by the high affinity agonist dysiherbaine and the functional antagonist 8,9-dideoxyneodysiherbaine

TY - JOUR

T1 - Full domain closure of the ligand-binding core of the ionotropic glutamate receptor iGluR5 induced by the high affinity agonist dysiherbaine and the functional antagonist 8,9-dideoxyneodysiherbaine

AU - Frydenvang, Karla Andrea

AU - Lash, L Leanne

AU - Naur, Peter

AU - Postila, Pekka A

AU - Pickering, Darryl S

AU - Smith, Caleb M

AU - Gajhede, Michael

AU - Sasaki, Makoto

AU - Sakai, Ryuichi

AU - Pentikäinen, Olli T

AU - Swanson, Geoffrey T

AU - Kastrup, Jette Sandholm

PY - 2009

Y1 - 2009

N2 - The prevailing structural model for ligand activation of ionotropic glutamate receptors posits that agonist efficacy arises from the stability and magnitude of induced domain closure in the ligand-binding core structure. Here we describe an exception to the correlation between ligand efficacy and domain closure. A weakly efficacious partial agonist of very low potency for homomeric iGluR5 kainate receptors, 8,9-dideoxy-neodysiherbaine (MSVIII-19), induced a fully closed iGluR5 ligand-binding core. The degree of relative domain closure, ~30 degrees , was similar to that we resolved with the structurally related high-affinity agonist dysiherbaine (DH), and to that of L-glutamate. The pharmacological activity of MSVIII-19 was confirmed in patch-clamp recordings from transfected HEK293 cells, where MSVIII-19 predominantly inhibits iGluR5-2a, with little activation apparent at a high concentration (1 mM) of MSVIII-19 (<1% of mean glutamate-evoked currents). To determine the efficacy of the ligand quantitatively, we constructed concentration-response relationships for MSVIII-19 following potentiation of steady-state currents with concanavalin A (EC50 3.6 muM) and on the non-desensitizing receptor mutant iGluR5-2b(Y506C/L768C) (EC50 8.1 muM). MSVIII-19 exhibited a maximum of 16% of full agonist efficacy as measured in parallel recordings with glutamate. Molecular dynamics simulations and electrophysiological recordings confirm that the specificity of MSVIII-19 for iGluR5 is partly attributable to inter-domain hydrogen bonds residues Glu441 and Ser721 in the iGluR5-S1S2 structure. The weaker interactions of MSVIII-19 with iGluR5 compared to DH, together with altered stability of the inter-domain interaction, may be responsible for the apparent uncoupling of domain closure and channel opening in this kainate receptor subunit.

AB - The prevailing structural model for ligand activation of ionotropic glutamate receptors posits that agonist efficacy arises from the stability and magnitude of induced domain closure in the ligand-binding core structure. Here we describe an exception to the correlation between ligand efficacy and domain closure. A weakly efficacious partial agonist of very low potency for homomeric iGluR5 kainate receptors, 8,9-dideoxy-neodysiherbaine (MSVIII-19), induced a fully closed iGluR5 ligand-binding core. The degree of relative domain closure, ~30 degrees , was similar to that we resolved with the structurally related high-affinity agonist dysiherbaine (DH), and to that of L-glutamate. The pharmacological activity of MSVIII-19 was confirmed in patch-clamp recordings from transfected HEK293 cells, where MSVIII-19 predominantly inhibits iGluR5-2a, with little activation apparent at a high concentration (1 mM) of MSVIII-19 (<1% of mean glutamate-evoked currents). To determine the efficacy of the ligand quantitatively, we constructed concentration-response relationships for MSVIII-19 following potentiation of steady-state currents with concanavalin A (EC50 3.6 muM) and on the non-desensitizing receptor mutant iGluR5-2b(Y506C/L768C) (EC50 8.1 muM). MSVIII-19 exhibited a maximum of 16% of full agonist efficacy as measured in parallel recordings with glutamate. Molecular dynamics simulations and electrophysiological recordings confirm that the specificity of MSVIII-19 for iGluR5 is partly attributable to inter-domain hydrogen bonds residues Glu441 and Ser721 in the iGluR5-S1S2 structure. The weaker interactions of MSVIII-19 with iGluR5 compared to DH, together with altered stability of the inter-domain interaction, may be responsible for the apparent uncoupling of domain closure and channel opening in this kainate receptor subunit.

KW - Former Faculty of Pharmaceutical Sciences

U2 - 10.1074/jbc.M808547200

DO - 10.1074/jbc.M808547200

M3 - Journal article

C2 - 19297335

SN - 0021-9258

VL - 284

SP - 14219

EP - 14229

JO - Journal of Biological Chemistry

JF - Journal of Biological Chemistry

IS - 21

ER -