Conantokins inhibit N-methyl-D-aspartate (NMDA) receptors. This toxin inhibits both NR2A/GRIN2A and NR2B/GRIN2B subunits of N-methyl-D-aspartate (NMDA) receptor-mediated calcium influx in central nervous system neurons. Induces sleep-like symptoms in young mice and hyperactivity in older mice. Expressed by the venom duct. Failed in phase II clinical trial. Was tested by Cognetix Inc. to treat antinociceptive effects in several models of injury-induced pain. Adopts an alpha-helical conformation in presence and in absence of divalent cations. The mature peptide does not contain cysteine residue. Belongs to the conotoxin B superfamily.