Structural, Biological and Biochemical Studies of MyotoxinaAnd Homologous Myotoxins

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Abstract
Myotoxin a and a group of closely related, small, basic toxins cause myonecrotic destruction of muscle tissue upon envenomation. The sarcoplasmic reticulum swells and eventually breaks down to small vesicles. Degeneration of myofibrils and myofilaments ensues and loss of the classic striation pattern is apparent. These toxins exhibit high sequence similarity as well as sequence microheterogeneity. A conformational heterogeneity was recently discovered in myotoxin a. The existence of myotoxin a in two forms in equilibrium in solution hinders the generation of a well defined three-dimensional structure. The difference, if any, in the biological activity of the two forms has not been established yet. Recent biochemical studies indicate that myotoxin a is a potent Ca2+ releasing agent that binds to calsequestrin in the lumen of the sarcoplasmic reticulum.