A novel arrangement of Cys residues in a paralytic peptide of Conus cancellatus (jr. syn.: Conus austini), a worm-hunting snail from the Gulf of Mexico

The present study details the purification, the amino acid sequence determination, and a preliminary characterization of the biological effects in mice of a new conotoxin from the venom of Conus cancellatus (jr. syn.: Conus austini), a worm-hunting cone snail collected in the western Gulf of Mexico (Mexico). The 23-amino acid peptide, called as25a, is characterized by the sequence pattern CX1CX2CX8CX1CCX5, which is, for conotoxins, a new arrangement of six cysteines (framework XXV) that form three disulfide bridges. The primary structure (CKCPSCNFNDVTENCKCCIFRQP*; *, amidated C-terminus; calculated monoisotopic mass, 2644.09 Da) was established by automated Edman degradation after reduction and alkylation, and MALDI-TOF and ESI mass spectrometry (monoisotopic mass, 2644.12/2644.08 Da). Upon intracranial injection in mice, the purified peptide provokes paralysis of the hind limbs and death with a dose of 240 pmol (∼0.635 μg, ∼24.9 ng/g). In addition, a post-translational variant of this peptide (as25b) was identified and determined to contain two hydroxyproline residues. These peptides may represent a novel conotoxin gene superfamily.

► Two six Cys-peptides (as25a and as25b) were purified from Conus cancellatus venom.
► Peptides as25a and as25b have a novel arrangement of Cys residues.
► Peptide as25a has paralytic and lethal activities.
► Peptide as25b has two hydroxyproline residues.
► Peptides as25a and as25b might represent a novel gene superfamily.