Conantokins inhibit N-methyl-D-aspartate (NMDA) receptors. This toxin has antagonist activity on the NR2B/GRIN2B subunit (IC(50)=0.1 uM) (PubMed:22594498, PubMed:26048991, PubMed:27981829). In vivo, when delivered into the brain, is active has anticonvulsant activity in the model of epilepsy in mice (PubMed:22594498). Divalent cations stabilize the toxin the in alpha-helix conformation. Expressed by the venom duct. Hydroxylation of Pro-88 is important for NR2B/GRIN2B NMDA receptor selectivity (PubMed:26048991, PubMed:27981829). Removal of hydroxylation does not change global NMDA receptor antagonism (tested on WT neurons), but it decreases the inhibitory potency on NR2B/GRIN2B NMDA receptors and increases the inhibitory potency on NR2A/GRIN2A NMDA receptors. Hydroxylation of Pro-88 locally disrupts a small region of the divalent cation-induced alpha-helix but does not destabilize the entire helix (PubMed:26048991, PubMed:27981829). The mature peptide does not contain cysteine residue. Has no or very weak antagonist activity on NR2A/GRIN2A, NR2C/GRIN2C, and NR2D/GRIN2D subunits. Belongs to the conotoxin B superfamily.