Conantokin G Is an NR2B-Selective Competitive Antagonist ofN-Methyl-d-aspartate Receptors

Abstract

Conantokin G (Con G) is a 17-amino-acid peptide antagonist of N-methyl-D-aspartate (NMDA) receptors isolated from the venom of the marine cone snail, Conus geographus. The mechanism of action of Con G has not been well defined; both competitive and noncompetitive interactions with the NMDA-binding site have been proposed. In this study the mechanism of action and subunit selectivity of Con G was examined in whole-cell voltage-clamp recordings from cultured neurons and in two electrode voltage-clamp recordings from Xenopus oocytes expressing recombinant NMDA receptors. Con G was a potent and selective antagonist of NMDA-evoked currents in murine cortical neurons (IC(50) = 480 nM). The slow onset of Con G block could be prevented by coapplication with high concentrations of NMDA or of the competitive antagonist (RS)-3-(2-carboxypiperazine-4-yl)-propyl-1-phosphonic acid. Furthermore, in oocytes expressing NR1a/NR2B receptors, Con G produced a rightward shift in the concentration-response curve for NMDA, providing support for a competitive interaction with the NMDA-binding site. Con G produced an apparent noncompetitive shift in the concentration-response curve for spermine potentiation of NMDA responses, but this was due to spermine-induced enhancement of Con G block. Spermine produced a similar enhancement of DL-2-amino-S-phosphopentanoic acid block. Finally, Con G selectively blocked NMDA receptors containing the NR2B subunit. These results demonstrate that Con G is a subunit-specific competitive antagonist of NMDA receptors. The unique subunit selectivity profile of Con G may explain its favorable in vivo profile compared with nonselective NMDA antagonists.

ConusVenoms: A Rich Source of Novel Ion Channel-Targeted Peptides

“…The block did not show either use dependence or voltage dependence. Furthermore, coapplication of the competitive antagonist (RS)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) prevented development of block by conantokin-G, consistent with competitive antagonism at the NR1a/NR2B subtype (38). With the use of HEK 293 cells expressing cloned rat NMDA receptors, similar results were found by Klein et al (93); conantokin-G blocked the NR1a/NR2B receptor but failed to block the NR1a/NR2a subunit combination, even at a concentration of 50 M. However, this strong selectivity for the NR2B subunit was not found by Wittekindt et al (192).…”

N-Methyl-D-aspartate Receptor Subtype Mediated Bidirectional Control of p38 Mitogen-activated Protein Kinase

“…Mature cultures were treated with either 10 M NMDA or 100 M NMDA for 1 or 5 min to identify the effects of NMDAR subtypes on both p38 activation and deactivation. Pretreatment with 6 M ConG, a competitive inhibitor of the glutamate binding site in NR1/2B and NR1/2A/2B receptors (36,37), inhibited NMDAR-induced p38 phosphorylation (Fig. 3A).…”

Polymodal Regulation of NMDA Receptor-Channels

“…In contrast, (2S*,3R*)-1-(phenanthrene-2-carbonyl)piperizine-2,3-dicarboxylic acid is a NR2C/NR2D selective antagonist. 77 The NR2B subtype selective antagonists include anticonvulsant felbamate, 78 conantokin G, a venom peptide isolated from marine cone snail Conus geographus 79,80 and a noncompetitive antagonist ifenprodil. The latter compound is a good candidate for treatment of stroke, traumatic brain injury, Alzheimer's and Parkinson's diseases.…”