Structure, function and biophysical aspects of the myotoxins from snake venoms

Snake venom myotoxins can be categorized into three types: small, basic polypeptides such as myotoxin a and crotamine; cardiotoxins from cobra venoms; and phospholipase A(2) toxins such as crotoxin and notexin. All three types of myotoxins induce depolarization and contraction of skeletal muscle cells. However, the myonecrosis induced by the small, basic polypeptide myotoxins is different from that induced by the cardiotoxins and phospholipase A(2) myotoxins in that the former do not appear to lyse the sarcolemma whereas the latter two types cause lysis of the sarcolemma which is of rapid onset. Molecular properties of the toxins are similar in that they are all highly basic proteins, and a large portion of their surface charge is positive. Also, they all have considerable beta-sheet structure which may be involved in interaction with the membrane. The purpose of this review is to describe the structure and function of these myotoxins and to evaluate features they might share which could shed light on their mechanism of myotoxic action.