Conantokins inhibit N-methyl-D-aspartate (NMDA) receptors. This toxin inhibits NR2 subunits N-methyl-D-aspartate (NMDA) receptor-mediated calcium influx in central nervous system neurons in the following order of preference: NR2B/GRIN2B (IC(50)=0.14 uM), NR2D/GRIN2D (IC(50)=0.31 uM), NR2A/GRIN2A (IC(50)=0.68 uM) and NR2C/GRIN2A (IC(50)=4.9 uM), when tested on rat receptors. Divalent cations stabilize the toxin the in alpha-helix conformation. Expressed by the venom duct. The mature peptide does not contain cysteine residue. Belongs to the conotoxin B superfamily.