Conantokins inhibit N-methyl-D-aspartate (NMDA) receptors. This toxin has antagonist activity on NR2B/GRIN2B (IC(50)=1.4 uM) and NR2A/GRIN2A (IC(50)=2.9 uM) subunits, 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. Has no antagonist activity on NR2C/GRIN2C, and NR2D/GRIN2D subunits. Belongs to the conotoxin B superfamily.