PROSITE documentation PDOC60004

Conotoxin families signatures

Cone snail toxins, conotoxins, are small peptides with disulfide connectivity, that target ion-channels or G-protein coupled receptors. Based on the number and pattern of disulfide bonds and biological activities, conotoxins can be classified into several families [1]. Omega, delta and kappa families of conotoxins have a knottin or inhibitor cystine 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 [2,E1].

Conotoxins represent a unique arsenal of neuropharmacologically active peptides that have been evolutionarily tailored to afford unprecedented and exquisite selectivity for a wide variety of ion-channel subtypes. The toxins derived from cone snails are currently being investigated for the treatment of chronic pain, epilepsy, cardiovascular diseases, psychiatric and movement disorders, spasticity, cancer, stroke as well as an anesthetic agent. Several potential analgesic and anti-inflammatory peptides from conotoxin families have been identified and patented [3,4]:

• Conus magus omega-conotoxin MVIIa (Ziconotide) is used for the treatment of chronic pain.
• Conus catus omega-conotoxin CVID is tested for treating severe morphine- resistant pain stress.
• Conus geographus omega-conotoxin GVIA may exert antagonistic effects against β-endorphin induced anti-nociception.

The disulfide bonding network as well as specific amino acids in inter-cysteine loops provide specificity of conotoxins [5]. The cysteine arrangement [C-C-CC-C-C] is the same for omega and delta families, which belong to the O-superfamily. The omega conotoxins are calcium channel blockers, whereas delta conotoxins delay the inactivation of sodium channels [1]. The M-superfamily Mu conotoxins have two types of cysteine arrangement [CC-C-C-CC] and [CC-C-C-C-C], but knottin scaffold is not observed. Mu conotoxins target the voltage-gated sodium channels [1] and are useful probes for investigating voltage-dependent sodium channels of excitable tissues [6]. α conotoxins belong to the A-superfamily and have two types of cysteine arrangement [CC-C-C] and [CCC-C-C-C] [7]. α conotoxins are competitive nicotinic acetylcholine receptor antagonists. The I-superfamily of conotoxins is characterized by a pattern of eight cysteine residues that form four disulfide bridges. The arrangement of cysteine residues is similar to the Janus-faced atracotoxin peptides characterized from spider venoms (see <PDOC60020>) [8,9].

Three signature patterns were developed for omega, delta and mu conotoxin families. The patterns each include six conserved cysteines thought to be important for the maintenance of the tertiary structure of the conotoxins. We have defined a pattern for the common part of the cysteine arrangement [CC-C-C] in all members of α conotoxin family. The pattern includes four conserved cysteines thought to be important for the maintenance of the tertiary structure of α conotoxins. The pattern for the I-superfamily conotoxin covers the eight conserved cysteines.