A new omega-conotoxin that targets N-type voltage-sensitive calcium channels with unusual specificity

A new specific voltage-sensitive calcium channel (VSCC) blocker has been is olated from the venom of the fish-hunting cone snail Conus consors. This pe ptide, named (omega -Ctx CNVIIA, consists of 27 amino acid residues folded by 3 disulfide bridges. Interestingly, loop 4, which is supposed to be cruc ial for selectivity, shows an unusual sequence (SSSKGR). The synthesis of t he linear peptide was performed using the Fmoc strategy, and the correct fo lding was achieved in the presence of guanidinium chloride, potassium buffe r, and reduced/oxidized glutathione at 4 degreesC for 3 days. Both syntheti c and native toxin caused an intense shaking activity, characteristic of om ega -conotoxins targeting N-type VSCC when injected intracerebroventricular ly to mice. Binding studies on rat brain synaptosomes revealed that the rad ioiodinated omega -Ctx CNVIIA specifically and reversibly binds to high-aff inity sites with a K-d of 36.3 pM. Its binding is competitive with omega -C tx MVIIA at low concentration (K-i = 2 pM). Moreover, omega -Ctx CNVIIA exh ibits a clear selectivity for N-type VSCCs versus P/Q-type VSCCs targeted r espectively by radioiodinated omega -Ctx GVIA and omega -Ctx MVIIC. Althoug h omega -Ctx CNVIIA clearly blocked N-type Ca2+ current in chromaffin cells , this toxin did not inhibit acetylcholine release evoked by nerve stimuli at the frog neuromuscular junction, in marked contrast to omega -Ctx GVIA. omega -Ctx CNVIIA thus represents a new selective tool for blocking N-type VSCC that displays a unique pharmacological profile and highlights the dive rsity of voltage-sensitive Ca2+ channels in the animal kingdom.