Allosteric regulation and spatial distribution of kainate receptors bound to ancillary proteins.
A diverse range of accessory proteins regulates the behaviour of most ligand- and voltage-gated ion channels. For glutamate receptor 6 (GluR6) kainate receptors, two unrelated proteins, concanavalin-A (Con-A) and postsynaptic density protein 95 (PSD-95), bind to extra- and intracellular domains, respectively, but are reported to exert similar effects on GluR6 desensitization behaviour. We have tested the hypothesis that distinct allosteric binding sites control GluR6 receptors via a common transduction pathway. Rapid agonist application to excised patches revealed that neither Con-A nor PSD-95 affect the onset of desensitization. The rate of desensitization elicited by 10 mM L-glutamate was similar in control (taufast = 5.5 +/- 0.4 ms), Con-A-treated patches (taufast = 6.1 +/- 0.5 ms) and patches containing PSD-95 and GluR6 receptors (taufast = 4.7 +/- 0.6 ms). Likewise, the time course of recovery from GluR6 desensitization was similar in both control and Con-A conditions, whereas PSD-95 accelerated recovery almost twofold. Peak and steady-state (SS) dose-response relationships to glutamate were unchanged by lectin treatment (e.g. control, EC50(SS) = 31 +/- 28 microM vs Con-A, EC50(SS) = 45 +/- 9 microM, n = 6), suggesting that Con-A does not convert non-conducting channels with high agonist affinity into an open conformation. Instead, we demonstrate that the effects of Con-A on macroscopic responses reflect a shift in the relative contribution of different open states of the channel. In contrast, the effect of PSD-95 on recovery behaviour suggests that the association between kainate receptors and cytoskeletal proteins regulates signalling at glutamatergic synapses. Our results show that Con-A and PSD-95 regulate kainate receptors via distinct allosteric mechanisms targeting selective molecular steps in the transduction pathway.
Bowie
Derek
D
Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia 30322, USA. dbowie@pharma.mcgill.ca
Garcia
Elizabeth P
EP
Marshall
John
J
Traynelis
Stephen F
SF
Lange
G David
GD
D000494:Allosteric Regulation; D001665:Binding Sites; D002460:Cell Line; D003208:Concanavalin A / Q000378:metabolism* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D018698:Glutamic Acid / Q000008:administration & dosage; D006801:Humans; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009419:Nerve Tissue Proteins / Q000378:metabolism* / Q000494:pharmacology; D018092:Kainic Acid Receptors / Q000819:agonists / Q000378:metabolism* / Q000502:physiology; D015398:Signal Transduction; D014018:Tissue Distribution; D000097806:GluK2 Kainate Receptor
D003208:Concanavalin A; D018698:Glutamic Acid; D009419:Nerve Tissue Proteins; D018092:Kainic Acid Receptors; D000097806:GluK2 Kainate Receptor; C033652:postsynaptic density proteins