TY - JOUR

T1 - Structural determinants of agonist-specific kinetics at the ionotropic glutamate receptor 2

AU - Holm, Mai Marie

AU - Lunn, Marie-Louise

AU - Traynelis, Stephen F

AU - Kastrup, Jette Sandholm Jensen

AU - Egebjerg, Jan

PY - 2005/8/23

Y1 - 2005/8/23

N2 - Glutamate receptors (GluRs) are the most abundant mediators of the fast excitatory neurotransmission in the human brain. Agonists will, after activation of the receptors, induce different degrees of desensitization. The efficacy of agonists strongly correlates with the agonist-induced closure of the ligand-binding domain. However, the differences in desensitization properties are less well understood. By using high-resolution x-ray structure of the GluR2 flop (GluR2o) ligand-binding core protein in complex with the partial glutamate receptor agonist (S)-2-amino-3-(3-hydroxy-5-tert-butyl-4-isothiazolyl)propionic acid [(S)-thio-ATPA], we show that (S)-thio-ATPA induces an 18 degrees closure of the binding core similar to another partial agonist, (S)-2-amino-3-(4-bromo-3-hydroxy-5-isoxazolyl)propionic acid [(S)-Br-HIBO]. Despite the similar closure of the ligand-binding domain, we find in electrophysiological studies that (S)-thio-ATPA induced a 6.4-fold larger steady-state current than (RS)-Br-HIBO, and rapid agonist applications show that (S)-thio-ATPA induces a 3.6-fold higher steady-state/peak ratio and a 2.2-fold slower desensitization time constant than (RS)-Br-HIBO. Structural comparisons reveal that (S)-Br-HIBO, but not (S)-thio-ATPA, induces a twist of the ligand-binding core compared with the apostructure, and the agonist-specific conformation of Leu-650 correlates with the different kinetic profiles pointing at a key role in defining the desensitization kinetics. We conclude that, especially for intermediate efficacious agonists, the desensitization properties are influenced by additional ligand-induced factors beyond domain closure.

AB - Glutamate receptors (GluRs) are the most abundant mediators of the fast excitatory neurotransmission in the human brain. Agonists will, after activation of the receptors, induce different degrees of desensitization. The efficacy of agonists strongly correlates with the agonist-induced closure of the ligand-binding domain. However, the differences in desensitization properties are less well understood. By using high-resolution x-ray structure of the GluR2 flop (GluR2o) ligand-binding core protein in complex with the partial glutamate receptor agonist (S)-2-amino-3-(3-hydroxy-5-tert-butyl-4-isothiazolyl)propionic acid [(S)-thio-ATPA], we show that (S)-thio-ATPA induces an 18 degrees closure of the binding core similar to another partial agonist, (S)-2-amino-3-(4-bromo-3-hydroxy-5-isoxazolyl)propionic acid [(S)-Br-HIBO]. Despite the similar closure of the ligand-binding domain, we find in electrophysiological studies that (S)-thio-ATPA induced a 6.4-fold larger steady-state current than (RS)-Br-HIBO, and rapid agonist applications show that (S)-thio-ATPA induces a 3.6-fold higher steady-state/peak ratio and a 2.2-fold slower desensitization time constant than (RS)-Br-HIBO. Structural comparisons reveal that (S)-Br-HIBO, but not (S)-thio-ATPA, induces a twist of the ligand-binding core compared with the apostructure, and the agonist-specific conformation of Leu-650 correlates with the different kinetic profiles pointing at a key role in defining the desensitization kinetics. We conclude that, especially for intermediate efficacious agonists, the desensitization properties are influenced by additional ligand-induced factors beyond domain closure.

KW - Alanine

KW - Alternative Splicing

KW - Animals

KW - Brain

KW - Crystallization

KW - Dose-Response Relationship, Drug

KW - Ibotenic Acid

KW - Kinetics

KW - Models, Molecular

KW - Mutagenesis

KW - Oocytes

KW - Patch-Clamp Techniques

KW - Protein Binding

KW - Protein Structure, Tertiary

KW - Receptors, AMPA

KW - Synaptic Transmission

KW - Thiazoles

KW - Xenopus laevis

U2 - 10.1073/pnas.0505522102

DO - 10.1073/pnas.0505522102

M3 - Journal article

C2 - 16099829

VL - 102

SP - 12053

EP - 12058

JO - Proceedings of the National Academy of Sciences of the United States of America

JF - Proceedings of the National Academy of Sciences of the United States of America

SN - 0027-8424

IS - 34

ER -