Covalitoxin-II (Cvtx-II) is a toxin in the venom of Coremiocnemis validus (Singapore or Blue femur tarantula).
It has six cysteine residues which form three disulphide bonds, between the specific amino acid locations 2&16, 19&21 and 15&28.
Near the C-terminus there is a positively charged surface formed by conserved basic residues, which is thought to interact with an ion channel.
[1][3] The inhibitor cystine knot motif that is formed by the cysteine residues shows analogy to other spider toxins and can also be found in ω-conotoxins, which are present in the venom of cone snails.
Based on its effect on behavior, it has been speculated that Cvtx-II targets sodium channel inactivation, analogous to some excitotoxins.