Crotamine

Crotamine is a toxin present in the venom of the South American rattlesnake (Crotalus durissus terrificus). It is a 42-residue long protein containing 11 basic residues (9 lysines, 2 arginines) and 6 cysteines. It has also been isolated from the venom of North American prairie rattlesnake, Crotalus viridis viridis. It was first isolated and purified by Brazilian scientist José Moura Gonçalves, and later intensively studied by his group of collaborators at the Medical School of Ribeirão Preto of the University of São Paulo.

Crotamine has a number of biological actions: it acts on cell membrane's sodium channels, is slightly analgesic and is myotoxic, i.e., it penetrates the cells of muscles and promotes necrosis. Crotamine is homologous with other venom myotoxins and is similar to α-,β-defensins.

The amino acid sequence, YKQCHKKGGHCFPKEKICLPPSSDFGKMDCRWRWKCCKKGS—G, and the 3D molecular structure of crotamine have already been determined.

The protein structure of crotamine could not be initially determined through protein crystallization nor X-ray diffraction. It was speculated that the difficulty was because crotamine has so many isoforms, leading to the formation of aggregates and different possible conformations of the protein. The structure and the shape of the protein was proposed through a 3D model generated by Siqueira et al. (2002) based on computational calculations that were supported with intensive molecular dynamics simulations and homology modeling procedures. Afterwards, Nicastro et al. (2003) discovered the structure of crotamine through nuclear magnetic resonance spectroscopy. Crotamine has a topology that was never before seen in active toxins that target ion channels; the protein is composed of a short N-terminal alpha helix, a type of protein formation, and a small antiparallel triple-stranded beta-sheet, another type of protein formation, arranged in an ab1b2b3 topology. Crotamine has similar structural fold conformations to the human b-defensin family as well as identical disulfide bridges arrangement.

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