Co-conotoxins

Olivera BM. (2000) co-Conotoxin MVllA From marine snail venom to analgesic drng. In Fusetani N. (ed), Drugs from the Sea, pp. 74-85. Karger,... 

Schroeder Cl, Smythe ML, Lewis RJ. (2004) Development of small mole-cnles that mimic the binding of co-conotoxins at the A-type voltage-gated calcinm channel. Mol Divers 8 127-134. 

Air oxidation of synthetic fully reduced co-conotoxin GVIA (9) (Scheme 4), a 27-residue peptide, 64 generated a main product that possessed the identical biological activities as the natural product whose cystine framework was determined with the synthetic compound. 65 The choice of buffer system and peptide concentration can, however, dramatically affect the folding efficiency when the DMSO-mediated oxidation method was applied. 661... 

Results similar to those reported for co-conotoxin GVIA were obtained with the Na+, K+-ATPase inhibitor-I (10) J67 a 49 amino acid residue peptide containing four intramolecular disulfide bonds (Scheme 5)J681 Even in this case the addition of redox reagents to the oxidation buffer had a minor effect on the product distribution. 

All the disulfide-folding pathways have the common feature that disulfide formation is initially random and not energetically favored due to the unfolded state of the reduced polypeptide chain. Disulfide formation becomes less random as certain disulfides are favored energetically as a result of the acquisition of nonrandom local conformations. In turn, the disulfides stabilize such conformations, so that disulfide formation and folding become cooperative. Thereby the sequence encoded structural information may fully suffice to direct the correct oxidative refolding as shown for co-conotoxin GVIA (9) (Section 6.1.5.2.1) which assumes the native-type cystine connectivities directly even in absence of redox reagents and... 

Scheme 11 Disulfide Connectivities of Isomers of co-Conotoxin MVIICJ89 ...

Figure 3 HPLC Profile of the Effects of Reaction Temperature and NH4OAc Concentration on the Folding of Reduced co-Conotoxin MVIIC in the Presence of Redox Reagents Buffer NH4OAc pH 7.7 Peptide/GSH/ GSSG 1 100 10 Time 24hl la b...

Figure 4 HPLC Profile of the Progress of the Oxidative Folding of Reduced co-Conotoxin MVIIC and Stability of Isomer 21 in the Presence of Redox Reagents in 50 mM NH4OAc Buffer Containing 2M (NH4)2S04at pH 7.7 (a, c) and in 50 mM NH4OAc Buffer at pH 7.7 (b, d) at 5 °C Aliquots were Analyzed at the Time Shown in Each Paneli891a b...

A similar situation appears to exist in the co-conotoxins, which possess 5-7 net positive charges. Substitution of individual cationic groups had a relatively minor effect on affinity for the voltage-gated calcium channel, whereas replacement of several had a significant effect, greater than that expected from the sum of the individual effects [63,64]. 

Unlike DHP-sensitive L-type channels co-conotoxin-sensitive N-type Ca2+ channels are exclusively expressed in the CNS. L-type channels inactivate very slowly whereas N-type channels inactivate more rapidly and are blocked by co-conotoxin GVIA. co-[125l]conotoxin GVIA is an ideal ligand for binding experiments. The dissociation constant (KD) for this toxin in rat brain membranes is 60 pM (Wagner et al., 1988). 

P-type channels inactivate extremely slowly and are insensitive to both DHPs and co-conotoxin GVIA, but are blocked by the spider venom peptide co-agatoxin IVA, a peptide consisting of 48 amino acids isolated from the American funnel-web spider Agelenopsis aperta. 

The inactivation kinetics of the Q-type channel are similar to the N-type channel but are resistant to DHPs and co-conotoxin GVIA. Q-type channels are inhibited by co-agatoxin IVA but less effectively than co-agatoxin IVA blocks P-type channels (review Miljanich and Ramachandran, 1995). 

Table 4 summarizes the antinociceptive effects of several co-conotoxins and -agatoxin IVA in different animal models. The peptides are administered by the i.t. or i.c.v. route. 

Basilico, L., Parolaro, D., Rubino, T., Gori, E., Giagnoni, G. Influence of co-conotoxin on morphine analgesia and withdrawal syndrome in rats, Eur. J. Pharmacol. 1992, 218, 75-81. 

Wagner,J.A., Snowman, AM., Biswas, A., Olivera, B.M., Snyder, S.H. co-Conotoxin GVIA binding to a high-affinity receptor in brain Characterization, calcium sensitivity, and solubilization, J. Neurosci. 1988, 8, 3354- 3359. 

---