Ablomin

Ablomin is a toxin present in the venom of the Japanese Mamushi snake, which blocks L-type voltage-gated calcium channels.

Etymology
The protein ablomin is a component of the venom of the Japanese Mamushi snake, Gloydius blomhoffii. The term ‘ablomin’ is an acronym derived from Agkistrodon blomhoffi, an old name for this snake.

Chemistry
Ablomin is part of the Cystein-Rich Secretory Protein (CRISP) family. CRISPs comprise a particular group of snake venom proteins distributed among the venom of several families of snakes, such as elapids, colubrids and vipers.

The protein exists of 240 amino acids, coded by an mRNA of 1336 base pairs. Structurally, it is composed of three distinct regions: an N-terminal protein domain, a hinge region and a C-terminal cystein-rich domain. It has a molecular mass of 25 kDa.

Ablomin shows great sequence homology with triflin (83.7%) and latisemin (61.5%), two other snake venom components of the CRISP family, which also target voltage-dependent calcium channels. In addition, it shows partial homology with helothermine (52.8%), a venom protein of the Mexican beaded lizard; this protein, however, targets other ion channels than ablomin.

Target
Ablomin reduces potassium-induced contraction of smooth muscles, suggesting that it blocks L-type voltage-gated calcium channels. Moreover, ablomin may slightly inhibit rod-type cyclic nucleotide-gated ion channels (CNGA1) channels.

Toxicity
Ablomin affects high potassium-induced contraction of arterial smooth muscle in rat-tails in a concentration-dependent matter. Reduction of arterial smooth muscle contraction in a rat-tail results in vasodilation of the rat-tails artery, which may lead to hypothermia. Blocking other L-type voltage gated Ca2+ channels, for instance in the heart, may lead to arrhythmias and even cardiac arrest.