CD AND FTIR STUDIES OF AN IMMUNOGENIC DISULFIDE CYCLIZED OCTADECAPEPTIDE, A FRAGMENT OF A SNAKE CURAREMIMETIC TOXIN

In a previous paper, the systematic epitope screening of a snake curar emimetic toxin or toxin alpha was described by this group using a pane l of synthetic octadecapeptides. The disulphide cyclized peptide (Cys- 23,40)(23-40) corresponding to loop II of the native toxin was found t o elicit, with no linkage to a carrier, neutralizing antisera against the toxin. We have now undertaken the conformational study of this imm unogenic disulphide cyclized peptide by CD and FTIR. The CD study of t he peptide was carried in aqueous solution under various conditions (p H, temperature, presence of micelles) and in trifluoroethanol solution . Low temperature, SDS micelles and trifluoroethanol were found to ind uce a beta-sheet formation (16 to 39%). FTIR spectra of the peptide in the solid state (dry film) and in D2O solution or deuterated-TFE solu tion (hydrated film) displayed some characteristic bands indicating th e presence of beta-sheet (1623 cm(-1)) and beta-turn (1637 cm(-1); 169 4 cm(-1)). These studies indicate that the immunogenic disulphide cycl ized peptide (23-40) can adopt in solution an ordered structure.