Description

Conotoxins are peptides consisting of 10 to 30 amino acid residues. The disulfide-rich peptides became broadly defined as conotoxins. Conotoxins are relatively small, potent, selective antagonists and agonists of specific cell membrane channel proteins. It represents extremely specific biological probes that offer researchers a tool to understand and differentiate between closely related receptors. Active research in the field of conotoxins involves the isolation, identification, and assessment of biological activity for individual peptides that possess the potential to be made into potent and selective therapeutic drugs.

Types

The number of conotoxins whose activities have been determined so far is five, and they are called the α(alpha)-, δ(delta)-, κ(kappa)-, μ(mu)-, and ω(omega)- types. Each of the five types of conotoxins attacks a different target. μ-conotoxin inhibits voltage-dependent sodium channels in muscles. α-conotoxin inhibits nicotinic acetylcholine receptors in nerves and muscles. κ-conotoxin inhibits potassium channels. ω-conotoxin inhibits N-type voltage-dependent calcium channels[1].

Mu-conotoxin

M-4 μ-conotoxins μ-Conotoxins belong to both the M-4 and M-5 branches of the M-superfamily. These conotoxins differ only in the number of residues in the third loop region and are similar in their common activity as antagonists of voltage-gated sodium channels (VGSCs). μ-Conotoxins have been investigated as therapeutic drugs because of their potency and ability to differentiate between distinct VGSCs[2]. The mu-conotoxins are a group of selective inhibitors of Na+ currents in skeletal muscle. Although related in action to tetrodotoxin (TTX) and Saxitoxin (STX) by their Na-channel blocking activity, the mu-conotoxins are structurally distinct and differ in channel selectivity. The first μ-conotoxins isolated from the venom of Conus geographus were μ-GIIIA, B, and C.

References

[1] Jacob R, et al. The M-superfamily of conotoxins: a review. Cellular and Molecular Life Sciences, 2009; 17–27.

[2] West P, et al. Mu-conotoxin SmIIIA, a potent inhibitor of tetrodotoxin-resistant sodium channels in amphibian sympathetic and sensory neurons. Biochemistry, 2002; 41: 15388–15393.