User:Swanship/adv cell phys

Myotoxins are small, basic peptides found in snake venoms, (e.g. rattlesnakes),  and lizard venoms (e.g. mexican beaded lizard). This involves a non-enzymatic mechanism that leads to severe muscle necrosis, or myonecrosis. These peptides act very quickly, causing instantaneous paralysis to prevent prey from escaping and eventually death due to diaphragmactic paralysis.

Phospholipase A2
Many snake venoms contain toxins with phospholipases A2 (PLA2) activity. These PLA2s weaken the muscle cell plasma membrane by degrading phospholipids. Because the PLA2s lack enzymatic activity, their mechanism of action is hypothesized to be direct hydrolysis of the phospholipid. PLA2 mytoxins have a fairly conserved structure of three α-helices and a β-wing. Major differences in myotoxins between snake species are the length of the H2 helix, length of the C-terminus, and disulfide linkages throughout the peptide. Evidence shows that the main effector of the PLA2 myotoxins are located in the C-terminal region of the proteins.

Crotamine
The first myotoxin to be identified and isolated was crotamine, from the venom of Crotalus durissus terrificus, a tropical South American rattlesnake, by Brazilian scientist José Moura Gonçalves, in the 1950s. Its biological actions, molecular structure and gene responsible for its synthesis were all elucidated in the last two decades. This particular toxin works by changing the inactivation process on sodium channels, ultimately leading to spasms and paralysis. It also has a unique ability to enter the nucleus without the use of a receptor.

Neutralization
The myonecrosis resulting from myotoxins is not efficiently treated with conventional antivenom therapy. Inhibitors of PLA2 activity within venomous snakes (PLIs) have been isolated and categorized as α-, β-, and γ-type inhibitors. PLIαs generally contain a carbohydrate recognition domain-like domain that binds PLA2s and is highly conserved throughout snake speacies. PLIβs is preferential based on PLA2 types and may bind to cover the catalytic center of PLA2s. PLIγs also neutralize PLA2s by forming a complex with the myotoxin. PLIs have been found in mammalian blood as well as plants and are considered to have potential as an alternative treatment for snake bites.