lambda-conotoxins, a new family of conotoxins with unique disulfide pattern and protein folding - Isolation and characterization from the venom of Conus marmoreus

Conotoxins are multiple disulfide-bonded peptides isolated fk om marine con e snail venom. These toxins have been classified into several families base d on their disulfide pattern and biological properties. Here, we report a n ew family of Conus peptides, which have a novel cysteine motif. Three pepti des of this family (CMrVIA, CMrVIB, and CMrX) have been purified from Conus marmoreus venom, and their structures have been determined. Their amino ac id sequences are VCCGYKLCHOC (CMrVIA), NGVCCGYKLCHOC (CMrVIB), and GICCGVSF CYOC (CMrX), where O represents 4-transhydroxyproline. Two of these peptide s (CMrVIA and CMrX) have been chemically synthesized Using a selective prot ection and deprotection strategy during disulfide bond formation, peptides with both feasible cysteine-pairing combinations were generated. The disulf ide pattern (C-1-C-4, C-2-C-3) in native toxins was identified by their co- elution with the synthetic disulfide-isomeric peptides on reverse-phase hig h pressure liquid chromatography. Although cysteine residues were found in comparable positions with those of alpha -conotoxins, these toxins exhibite d a distinctly different disulfide bonding pattern; we have named this new family "lambda -conotoxins." CMrVIA and CMrX induced different biological e ffects when injected intra-cerebroventricularly in mice; CMrVIA induces sei zures, whereas CMrX induces flaccid paralysis. The synthetic peptide with l ambda -conotoxin folding is about 1150-fold more potent in inducing seizure s than the mispaired isomer with alpha -conotoxin folding Thus it appears t hat the unique disulfide pattern, and hence the "ribbon" conformation, in l ambda -conotoxins is important for their biological activity.