delta-conotoxin structure/function through a cladistic analysis

delta -Conotoxins are Conus peptides that inhibit inactivation of voltage-g ated sodium channels. The suggestion that delta -conotoxins might be an ess ential component of the venoms of fish-hunting cone snails which rapidly im mobilize their prey [Terlau, H., Shon, K., Grilley, M., Stocker, M., Stuhme r, W., and Olivera, B. M. (1996) Nature 381, 148-151] has not been tested. On the basis of cDNA cloning, all of the fish-hunting Conus analyzed yielde d at least one delta -conotoxin sequence. In addition, one delta -conotoxin isolated from the venom of Conus striatus had an amino acid sequence ident ical to that predicted from cDNA cloning. This new peptide exhibited proper ties of delta -conotoxins: it targeted sodium channels and potentiated acti on potentials by slowing channel inactivation. Homologous sequences of delt a -conotoxins from two groups (clades) of related fish-hunting Conus specie s share consensus features but differ significantly from the two known delt a -conotoxins from mollusc-hunting Conus venoms. Three large hydrophobic am ino acids were conserved; analogues of the previously described delta -cono toxin PVIA with alanine substituted for the conserved amino acids F9 and I1 2 lost substantial biological activity. In contrast, both the T8A and K13A delta -conotoxin PVIA analogues, where substitutions were at nonconserved l oci, proved to be biologically active. Taken together, our results indicate that a cladistic approach can identify amino acids critical for the activi ty of conotoxins and provide extensive information as to which amino acid s ubstitutions can be made without significant functional consequences.