Molecular cloning and nucleotide sequence analysis of genes from a cDNA library of the scorpion Tityus discrepans

Tityus discrepans is a Venezuelan scorpion known to cause severe human envenomations. It contains toxins that impair proper ion channels function, affect coagulation pathways and interfere with the immunological system, leading to a widespread inflammatory syndrome. This communication reports the results of genes cloned from a cDNA expression library of venomous glands from T. discrepans. A full-length cDNA phagemid library was prepared from which 127 genes were cloned and grouped in 22 clusters showing more than one EST (expressed sequence tag) (74%), and 29 singlets (26%). The identified putative proteins were assorted into two groups. One conformed by precursors similar to gene products implicated in common cellular processes, accounting for 13.4% of transcripts and other comprising putative toxins, representing 50% of total ESTs. A total of 14 sequences are thought to be peptides that recognize or affect Na+-channel function and 6 peptides that affect K+-channels. Among these two classes of venom components are several for which the peptides were previously isolated and characterized. However, based on sequence similarities, three distinct classes of peptides were also identified and are reported: a bradykinin-potentiating peptide, a defensin-like peptide and an acidic peptide of unknown function. The N-terminal amino acid sequence of several peptides is reported here for the first time. A phylogenetic tree analysis is also reported, as well as three three-dimensional models of representative toxins.