Sequencing neurotoxic peptides

The venoms from spiders, scorpions, some marine snails, and certain other animals immobilize victims by blocking ion channels that control nerve cells. The bioactive molecules in the venoms are incredibly diverse—cone snails alone produce more than 50 000 distinct peptide venoms—and researchers hope to mine them for potential pharmaceuticals that, say, kill pain or unblock diseased ion channels. Knowing the amino acid sequences would help in that effort. Researchers typically turn to mass spectrometry, in which the peptides are fragmented and the amino acid sequence deduced, usually in combination with searching a protein database. Unfortunately, the organisms do not have sequenced genomes, so the amino acid sequence has to be determined from mass spectrometry alone. Such de novo sequencing has been hampered by an inability to produce sufficient fragmentation. Now, Beatrix Ueberheide, David Fenyö, and Brian Chait of the Rockefeller University and Paul Alewood of the University of Queensland have devised a method to solve that problem. They realized that a simple chemical trick—the conversion of cysteine, an abundant amino acid in peptide venoms, to a lysine-like charged residue—would put the molecules in a highly positive charged state. The peptides could then be more efficiently fragmented using a technique known as electron transfer dissociation and thereby give rise to a rich mass spectrum. As proof of principle, the team reconstructed the complete sequence for 31 distinct peptide toxins using just 7% of the venom from the gland of a single cone snail. (B. M. Ueberheide et al., Proc. Natl. Acad. Sci. USA 106 , 6910, 2009 http://dx.doi.org/10.1073/pnas.0900745106 .)