COMPARED CHEMICAL-PROPERTIES OF DERMONECROTIC AND LETHAL TOXINS FROM SPIDERS OF THE GENUS LOXOSCELES (ARANEAE)

Loxosceles spider venom usually causes a typical dermonecrotic lesion in bitten patients, but it may also cause systemic effects that may be lethal. Gel filtration on Sephadex G-100 of Loxosceles gaucho, L. lae ta, or L. intermedia spider venoms resulted in three fractions (A, con taining higher molecular mass components, B containing intermediate mo lecular mass components, and C with lower molecular mass components). The dermonecrotic and lethal activities were detected exclusively in f raction A of all three species. Analysis by SDS-PAGE showed that the m ajor protein contained in fraction A has molecular weight approximatel y 35 kDa in L. gaucho and L. intermedia, but 32 kDa in L; laeta venom. These toxins were isolated from venoms of L. gaucho, L. laeta, and L. lintermedia by SDS-PAGE followed by blotting to PVDF membrane and seq uencing. A database search showed a high level of identity between eac h toxin and a fragment of the L. reclusa (North American spider) toxin . A multiple sequence alignment of the Loxosceles toxins showed many c ommon identical residues in their N-terminal sequences. Identities ran ged from 50.0% (L. gaucho and L. reclusa) to 61.1% (L. intermedia and L. reclusa). The purified toxins were also submitted to capillary elec trophoresis peptide mapping after in situ partial hydrolysis of the bl otted samples. The results obtained suggest that L. intermedia protein is more similar to L. laeta toxin than L. gaucho toxin and revealed a smaller homology between L. intermedia and L gaucho. Altogether these findings suggest that the toxins responsible for most important activ ities of venoms of Loxosceles species have a molecular mass of 32-35 k Da and are probably homologous proteins.