PMID:17724025

Citation	Zhang, MM, Green, BR, Catlin, P, Fiedler, B, Azam, L, Chadwick, A, Terlau, H, McArthur, JR, French, RJ, Gulyas, J, Rivier, JE, Smith, BJ, Norton, RS, Olivera, BM, Yoshikami, D and Bulaj, G (2007) Structure/function characterization of micro-conotoxin KIIIA, an analgesic, nearly irreversible blocker of mammalian neuronal sodium channels. J. Biol. Chem. 282:30699-706
Abstract	Peptide neurotoxins from cone snails continue to supply compounds with therapeutic potential. Although several analgesic conotoxins have already reached human clinical trials, a continuing need exists for the discovery and development of novel non-opioid analgesics, such as subtype-selective sodium channel blockers. Micro-conotoxin KIIIA is representative of micro-conopeptides previously characterized as inhibitors of tetrodotoxin (TTX)-resistant sodium channels in amphibian dorsal root ganglion neurons. Here, we show that KIIIA has potent analgesic activity in the mouse pain model. Surprisingly, KIIIA was found to block most (>80%) of the TTX-sensitive, but only approximately 20% of the TTX-resistant, sodium current in mouse dorsal root ganglion neurons. KIIIA was tested on cloned mammalian channels expressed in Xenopus oocytes. Both Na(V)1.2 and Na(V)1.6 were strongly blocked; within experimental wash times of 40-60 min, block was reversed very little for Na(V)1.2 and only partially for Na(V)1.6. Other isoforms were blocked reversibly: Na(V)1.3 (IC50 8 microM), Na(V)1.5 (IC50 284 microM), and Na(V)1.4 (IC50 80 nM). "Alanine-walk" and related analogs were synthesized and tested against both Na(V)1.2 and Na(V)1.4; replacement of Trp-8 resulted in reversible block of Na(V)1.2, whereas replacement of Lys-7, Trp-8, or Asp-11 yielded a more profound effect on the block of Na(V)1.4 than of Na(V)1.2. Taken together, these data suggest that KIIIA is an effective tool to study structure and function of Na(V)1.2 and that further engineering of micro-conopeptides belonging to the KIIIA group may provide subtype-selective pharmacological compounds for mammalian neuronal sodium channels and potential therapeutics for the treatment of pain.
Links	PubMed Online version:10.1074/jbc.M704616200
Keywords	Amino Acid Substitution; Analgesics, Non-Narcotic/pharmacology; Animals; Conotoxins/genetics; Conotoxins/pharmacology; Ganglia, Spinal/metabolism; Ganglia, Spinal/pathology; Mice; Mutation, Missense; Neurons/metabolism; Neurons/pathology; Oocytes; Pain/drug therapy; Pain/metabolism; Pain/pathology; Peptides/genetics; Peptides/pharmacology; Protein Isoforms/genetics; Protein Isoforms/metabolism; Recombinant Proteins/genetics; Recombinant Proteins/metabolism; Sodium Channel Blockers/pharmacology; Sodium Channels/genetics; Sodium Channels/metabolism; Xenopus laevis
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
CONKI:CM3A		GO:0044740: negative regulation of sensory perception of pain in other organism	ECO:0000314:		P		Figure 2 shows the result of a paw-licking assay with mice. In panel A, injection with KIIIA prior to injection with formalin reduced paw-licking compared to a saline control and a lidocaine injection. Panel B shows the dose-dependence of this pain reduction.	complete CACAO 10911
CONKI:CM3A		GO:0044489: modulation of voltage-gated sodium channel activity in other organism	ECO:0000314:		P		Figures 3 and 4 show KIIIA blocking voltage-gated sodium channels in mice.	complete CACAO 10912

References

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