Spider toxins comprising disulfide-rich and linear amphipathic domains: a new class of molecules identified in the lynx spider Oxyopes takobius

In addition to the conventional neurotoxins and cytotoxins, venom of the lynx spider Oxyopestakobius was found to contain two-domain modular toxins named spiderines: OtTx1a, 1b, 2a and 2b. These toxins show both insecticidal activity (a median lethal dose against flesh fly larvae of 75gg(-1)) and potent antimicrobial effects (minimal inhibitory concentrations in the range 0.1-10m). Full sequences of the purified spiderines were established by a combination of Edman degradation, mass spectrometry and cDNA cloning. They are relatively large molecules (similar to 110 residues, 12.0-12.5kDa) and consist of two distinct modules separated by a short linker. The N-terminal part (similar to 40 residues) contains no cysteine residues, is highly cationic, forms amphipathic -helical structures in a membrane-mimicking environment, and shows potent cytolytic effects on cells of various origins. The C-terminal part (similar to 60 residues) is disulfide-rich (five S-S bonds), and contains the inhibitor cystine knot (ICK/knottin) signature. The N-terminal part of spiderines is very similar to linear cytotoxic peptides found in various organisms, whereas the C-terminal part corresponds to the usual spider neurotoxins. We synthesized the modules of OtTx1a and compared their activity to that of full-length mature toxin produced recombinantly, highlighting the importance of the N-terminal part, which retained full-length toxin activity in both insecticidal and antimicrobial assays. The unique structure of spiderines completes the range of two-domain spider toxins. DatabaseThe protein sequences of the spiderines (OtTx) reported in this paper have been submitted to the UniProt Knowledgebase (UniProtKB) under accession numbers P86716-P86719, and the nucleotide sequences encoding OtTx have been submitted to the GenBank under accession numbers JX134894-JX134897.