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µ-conotoxin CnIIIC is a conopeptide that has been isolated from the venom of the marine cone snail Conus consors. µ-conotoxin CnIIIC has been described to exhibit a myorelaxing effect through specific blockade of the skeletal muscle Nav1.4 channels (IC50 = 1.4 nM). µ-conotoxin CnIIIC also appears to block Nav1.2 channels (1 µM) and mildly Nav1.7. In contrast, Nav1.5 and Nav1.8 are insensitive to the action of the toxin. µ-conotoxin CnIIIC is also described to block the α3β2 nicotinic acetylcholine receptor (IC50= 450 nM) and to lesser extents the α7 and α4β2 subtypes and completely inhibits twitch tension in isolated mouse hemidiaphragms (IC50 = 150 nM). This peptide is a valuable tools to study Nav1.4 channels.
AA sequence: Pyr-Gly-Cys3-Cys4-Asn-Gly-Pro-Lys-Gly-Cys10-Ser-Ser-Lys-Trp-Cys15-Arg-Asp-His-Ala-Arg-Cys21-Cys22-NH2
Disulfide bonds: Cys3-Cys15, Cys4-Cys21 and Cys10-Cys22
Length (aa): 22
Formula: C92H141N35O28S6
Molecular Weight: 2375.8 Da
Appearance: White lyophilized solid
Solubility: water and saline buffer
CAS number:
Source: Synthetic
Purity rate: > 95 %
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The µ-conopeptide family is defined by its ability to block voltage-gated sodium channels (VGSCs), a property that can be used for the development of myorelaxants and analgesics. We characterized the pharmacology of a new µ-conopeptide (µ-CnIIIC) on a range of preparations and molecular targets to assess its potential as a myorelaxant.
µ-CnIIIC was sequenced, synthesized and characterized by its direct block of elicited twitch tension in mouse skeletal muscle and action potentials in mouse sciatic and pike olfactory nerves. µ-CnIIIC was also studied on HEK-293 cells expressing various rodent VGSCs and also on voltage-gated potassium channels and nicotinic acetylcholine receptors (nAChRs) to assess cross-interactions. Nuclear magnetic resonance (NMR) experiments were carried out for structural data.
Synthetic µ-CnIIIC decreased twitch tension in mouse hemidiaphragms (IC(50) = 150 nM), and displayed a higher blocking effect in mouse extensor digitorum longus muscles (IC = 46 nM), compared with µ-SIIIA, µ-SmIIIA and µ-PIIIA. µ-CnIIIC blocked Na(V)1.4 (IC(50) = 1.3 nM) and Na(V)1.2 channels in a long-lasting manner. Cardiac Na(V)1.5 and DRG-specific Na(V)1.8 channels were not blocked at 1 µM. µ-CnIIIC also blocked the α3β2 nAChR subtype (IC(50) = 450 nM) and, to a lesser extent, on the α7 and α4β2 subtypes. Structure determination of µ-CnIIIC revealed some similarities to α-conotoxins acting on nAChRs.
µ-CnIIIC potently blocked VGSCs in skeletal muscle and nerve, and hence is applicable to myorelaxation. Its atypical pharmacological profile suggests some common structural features between VGSCs and nAChR channels.
Favreau P., et al. (2012) A novel µ-conopeptide, CnIIIC, exerts potent and preferential inhibition of NaV1.2/1.4 channels and blocks neuronal nicotinic acetylcholine receptors. BJP. PMID: 22229737
Voltage-gated sodium channels (Na(V) channels) are key players in the generation and propagation of action potentials, and selective blockade of these channels is a promising strategy for clinically useful suppression of electrical activity. The conotoxin µ-CnIIIC from the cone snail Conus consors exhibits myorelaxing activity in rodents through specific blockade of skeletal muscle (Na(V) 1.4) Na(V) channels.
We investigated the activity of µ-CnIIIC on human Na(V) channels and characterized its inhibitory mechanism, as well as the molecular basis, for its channel specificity.
Similar to rat paralogs, human Na(V) 1.4 and Na(V) 1.2 were potently blocked by µ-CnIIIC, the sensitivity of Na(V) 1.7 was intermediate, and Na(V) 1.5 and Na(V) 1.8 were insensitive. Half-channel chimeras revealed that determinants for the insensitivity of Na(V) 1.8 must reside in both the first and second halves of the channel, while those for Na(V) 1.5 are restricted to domains I and II. Furthermore, domain I pore loop affected the total block and therefore harbours the major determinants for the subtype specificity. Domain II pore loop only affected the kinetics of toxin binding and dissociation. Blockade by µ-CnIIIC of Na(V) 1.4 was virtually irreversible but left a residual current of about 5%, reflecting a ‘leaky’ block; therefore, Na(+) ions still passed through µ-CnIIIC-occupied Na(V) 1.4 to some extent. TTX was excluded from this binding site but was trapped inside the pore by µ-CnIIIC.
Of clinical significance, µ-CnIIIC is a potent and persistent blocker of human skeletal muscle Na(V) 1.4 that does not affect activity of cardiac Na(V) 1.5.
Markgraf R., et al. (2012) Mechanism and molecular basis for the sodium channel subtype specificity of µ-conopeptide CnIIIC. BJP. PMID: 22537004
