Conformational comparison in the snake toxin family.

A theoretical method was applied to consensus sequences of several members of the snake toxin family as a further approach to examining their conformational homology. Some secondary-structure predictions as well as hydropathy profiles were also examined. A comparison of long neurotoxins themselves reveals a high homology degree. However, their C-terminal fragments show poor homology and the N-terminal fragments appear as the region of maximum variability. Moreover, when the matrix includes the consensus sequence of the genus Laticauda (LNTX1), lacking the disulfide bridge 31-35, the method detects a lower conformational homology in a molecular region centered at position 31. Unlike long neurotoxins, the N-terminal segments of short neurotoxins show a high homology degree, but when comparing short with long neurotoxins, a poor correlation is found in this zone of the molecule. Cytotoxins studied exhibit an excellent conformational homology except when the consensus sequence of cytotoxin homologues CTXE is one of the proteins in the matrix. A comparison between cytotoxins and short neurotoxins reveals homology only in two segments belonging to a beta-sheet structure. A considerable degree of homology is found between the short neurotoxin group and calciseptin and fasciculin as well as between the long neurotoxin group and kappa-neurotoxins.