Abstract
Among the scorpion venom components whose function are poorly known or even show contrasting pharmacological results are those called "orphan peptides". The most widely distributed are named beta-KTx or scorpine-like peptides. They contain three disulfide bridges with two recognizable domains: a freely moving N-terminal amino acid sequence and a tightly folded C-terminal region with a cysteine-stabilized alpha/beta (CS-alphabeta) motif. Four such peptides and three cloned genes are reported here. They were assayed for their cytolytic, antimicrobial and K (+) channel-blocking activities. Two main characteristics were found: the existence of an unusual structural and functional diversity, whereby the full-length peptide can lyse cells or kill microorganisms, and a C-terminal domain containing the CS-alphabeta motif that can block K (+) channels. Furthermore, sequence analyses and phylogenetic reconstructions are used to discuss the evolution of this type of peptide and to highlight the versatility of the CS-alphabeta structures.