Conantokins inhibit N-methyl-D-aspartate (NMDA) receptors. This toxin has the highest potency for the NR2B/GRIN2B subunit (IC(50)=0.11 uM), followed by NR2D/GRIN2D (IC(50)=0.48 uM), NR2A/GRIN2A (IC(50)=2.1 uM), and NR2C/GRIN2C (IC(50)=6.1 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. The synthetic peptide exists as two interconvertible conformers. Belongs to the conotoxin B superfamily.