Conotoxin

Conotoxin is a neurotoxic peptides .It is isolated from the venom of marine cone snail,genus Conus,Its consist of 10 to 30 aminoacid residues,Typically have one or more dilsulfde bonds,Conotoxins have a variety of mechanisms of action like ion channels. Types and biological activities of conotoxins 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

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* α-conotoxin inhibits acetylcholine receptors at nerves and muscles. * δ-conotoxin inhibits the inactivation of voltage-dependent sodium channels. * κ-conotoxin inhibits potassium channels. * μ-conotoxin inhibits voltage-dependent sodium channels in muscles. * ω-conotoxin inhibits N-type voltage-dependent calcium channels. Because N-type voltage-dependent calcium channels are related to algesia (sensitivity to pain) in the nervous system, ω-conotoxin has an analgesic effect: the effect of ω-conotoxin M VII A is 100 to 1000 times that of morphine.[7] Therefore a synthetic version of ω-conotoxin M VII A has found application as an analgesic drug ziconotide (Prialt).

Types of conotoxins also differ in the number and pattern of disulfide bonds [9]. The disulfide bonding network, as well as specific amino acids in inter-cysteine loops, provide the specificity of conotoxins. Omega, delta and kappa conotoxins Omega, delta and kappa families of conotoxins have a knottin or inhibitor cysteine knot scaffold. The knottin scaffold is a very special disulfide-through-disulfide knot, in which the III-VI disulfide bond crosses the macrocycle formed by two other disulfide bonds (I-IV and II-V) and the interconnecting backbone segments, where I-VI indicates the six cysteine residues starting from the N-terminus. The cysteine arrangements are the same for omega, delta and kappa families, even though omega conotoxins are calcium channel blockers, whereas delta conotoxins delay the inactivation of sodium channels, and kappa conotoxins are potassium channel blockers. Mu conotoxins Mu conotoxins have two types of cysteine arrangements, but the knottin scaffold is not observed. Mu conotoxins target the voltage-gated sodium channels[9], and are useful probes for investigating voltage-dependent sodium channels of excitable tissues