Ophanin

Ophanin is a toxin found in the venom of the King Cobra (Ophiophagus hannah), which lives throughout South East Asia. This toxin belongs to the cysteine-rich secretory protein (CRISP) family. Ophanin weakly blocks the contraction of smooth muscles elicited by high potassium-induced depolarization, suggesting that it inhibits voltage-dependent calcium channels. Ophanin is a toxin found in the venom of the King Cobra (Ophiophagus hannah), which lives throughout South East Asia. This toxin belongs to the cysteine-rich secretory protein (CRISP) family. Ophanin weakly blocks the contraction of smooth muscles elicited by high potassium-induced depolarization, suggesting that it inhibits voltage-dependent calcium channels. The toxin was named ophanin after the snake whose venom it is derived from, the King Cobra (Ophiophagus hannah). Ophanin is produced in the venom glands of the King Cobra (O. Hannah). Although the venom has relatively low toxicity, this is compensated by the high amounts of it injected into the prey for each bite. Ophanin was successfully isolated from O. Hannah venom by gel filtration and cation-exchange chromatography. Its molecular weight is 25 kDa (from positions 19 – 239), which conforms to the molecular mass predicted from its cDNA sequences. Ophanin is a cysteine-rich secretory protein and therefore belongs to the CRISP family. These proteins possess 16 strictly conserved cysteines and contain 8 disulfide bonds. Ten of the 16 cysteine residues are clustered at the C-terminal end of the protein. Ophanin belongs to the “long” CRISPs subgroup, which consists of the 9 CRISPs with the longest sequences. Snake venom CRISPs belonging to different subgroups act on different biological targets, contributing in this way to the diversity of damaging effects of snake venoms. The phylogenetic tree constructed from the nucleotide sequences of all known snake venom CRISPs shows that ophanin is more closely related to the Viperidae branch than the Elapidae branch even though O. Hannah belongs to the Elapidae snakes. Ophanin, along with other specific snake toxins like triflin and ablomin, is also a helothermine-related venom protein (Helveprin) which was originally isolated from the skin of the Mexican beaded lizard. Ophanin is a weak blocker of the high potassium-induced contraction of smooth muscles. Snake venom CRISP family proteins inhibit depolarization-induced smooth muscle contraction to different extents. Compared to the normal contraction of smooth muscle, ophanin is able to reduce their force of contractility to 84% ± 1%, which is less than most other CRISPs.