Toxin Diversity in the Neotropical Scorpion Genus Tityus (Buthidae) Revealed by Mass Spectrometry and cDNA Sequencing Analyses

¹Borges, A., ¹García, C., ²Op den Camp, H.J.M., and ¹Alfonzo, M.

1 Institute of Experimental Medicine, Central University of Venezuela, Caracas, Venezuela, and 2 Department of Microbiology, University of Nijmegen, The Netherlands.

Envenoming by Tityus species is of considerable medical importance in Tropical America due to their ability to produce toxins active on voltage-gated ion channels. Tityus zulianus (western Venezuela) often produces respiratory arrest and death by pulmonary oedema whereas envenoming by Tityusdiscrepans (northcentral Venezuela) mainly causes pancreatic and gastrointestinal complications. To investigate whether T. zulianus and T. discrepans Na⁺ channel-active toxin repertoires differ structurally, crude venoms were resolved by gel filtration through Sephadex G-50 to isolate TzII (T. zulianus) and TdII (T. discrepans), the most toxic fractions to mice. MALDI-TOF MS analyses of TzII and TdII produced species-specific spectra, with peaks in the m/z 2500-4000 and 6500-8000 ranges. Although peptides with similar mass occur in both venoms, significant dissimilarities are evident in the Na⁺-channel toxin range (6.5-8 kDa) (e.g. Tz1, a major T. zulianus component  ([M+H⁺] 7367.16), present in trace amounts in TdII).  cDNA libraries were also generated from total T. zulianus and T. discrepans venom gland RNA to compare their Na⁺-channel toxin primary structures. A PCR-based strategy was developed to amplify all venom gland transcripts sharing a highly conserved motif located within the pre-toxin leader peptide-encoded region. The most abundant T. discrepans transcript (12 out of 27 sequences) is 68% homologous to Tz1 (8 out 15 sequences). All other novel sequences reveal species-specific components, with non-conservative replacements in the region connecting the conserved secondary structure elements.

Support: FONACIT S1-2001000674, CDCH-UCV 09.33.4371, and CDCH-UCV 09.33.4857.2001 (to A.B.).

Correspondence to: borgesa@rect.ucv.ve