Synthesis and biological characterization of a series of analogues of omega-conotoxin GVIA.

The 27-residue polypeptide omega-conotoxin GVIA (omega-CgTx), from the venom of the cone shell Conus geographus, blocks N-type neuronal calcium channels. It contains three disulphide bridges. We report here the synthesis and biological characterization of a series of analogues in which one disulphide has been replaced by substitution of appropriate Cys residues with Ser, viz. [Ser1,16]-omega -CgTx, [Ser8,19]-omega-CgTx, [Ser15,26)-omega-CgTx, [Ser16]-omega-CgTx8-27 and [Ser15]-omega-CgTx1-19. All syntheses were conducted manually using either Boc or Fmoc methodology. Deprotected peptides were oxidized to their bridged forms using either aerial oxidation or aqueous dimethyl sulphoxide. Peptides were purified using RP-HPLC, and their purity and identity were checked by RP-HPLC, capillary electrophoresis and mass spectrometry. Inhibition of neuronal N-type calcium channels was assessed as the inhibition of the twitch responses of rat vas deferens stimulated with single electrical pulses at 20 second intervals. None of these analogues was biologically active, suggesting that the disulphides play an important role in maintaining biological activity.