Cooccupancy of the Outer Vestibule of Voltage-Gated Sodium Channels by μ-Conotoxin KIIIA and Saxitoxin or Tetrodotoxin
- 1 July 2010
- journal article
- research article
- Published by American Physiological Society in Journal of Neurophysiology
- Vol. 104 (1), 88-97
- https://doi.org/10.1152/jn.00145.2010
Abstract
The guanidinium alkaloids tetrodotoxin (TTX) and saxitoxin (STX) are classic ligands of voltage-gated sodium channels (VGSCs). Like TTX and STX, μ-conotoxin peptides are pore blockers but with greater VGSC subtype selectivity. μ-Conotoxin KIIIA blocks the neuronal subtype NaV1.2 with nanomolar affinity and we recently discovered that KIIIA and its mutant with one fewer positive charge, KIIIA[K7A], could act synergistically with TTX in a ternary peptide·TTX·NaV complex. In the complex, the peptide appeared to trap TTX in its normal binding site such that TTX could not readily dissociate from the channel until the peptide had done so; in turn, the presence of TTX accelerated the rate at which peptide dissociated from the channel. In the present study we examined the inhibition of NaV1.2, exogenously expressed in Xenopus oocytes, by STX (a divalent cation) and its sulfated congener GTX2/3 (with a net +1 charge). Each could form a ternary complex with KIIIA and NaV1.2, as previously found with TTX (a monovalent cation), but only when STX or GTX2/3 was added before KIIIA. The KIIIA·alkaloid·NaV complex was considerably less stable with STX than with either GTX2/3 or TTX. In contrast, ternary KIIIA[K7A]·alkaloid·NaV complexes could be formed with either order of ligand addition and were about equally stable with STX, GTX2/3, or TTX. The most parsimonious interpretation of the overall results is that the alkaloid and peptide are closely apposed in the ternary complex. The demonstration that two interacting ligands (“syntoxins”) occupy adjacent sites raises the possibility of evolving a much more sophisticated neuropharmacology of VGSCs.Keywords
This publication has 44 references indexed in Scilit:
- De Novo Synthesis of Modified Saxitoxins for Sodium Ion Channel StudyJournal of the American Chemical Society, 2009
- AutoDock4 and AutoDockTools4: Automated docking with selective receptor flexibilityJournal of Computational Chemistry, 2009
- A Stereoselective Synthesis of (+)-Gonyautoxin 3Journal of the American Chemical Society, 2008
- Specificity, affinity and efficacy of iota-conotoxin RXIA, an agonist of voltage-gated sodium channels NaV1.2, 1.6 and 1.7Biochemical Pharmacology, 2008
- International Union of Pharmacology. XLVII. Nomenclature and Structure-Function Relationships of Voltage-Gated Sodium ChannelsPharmacological Reviews, 2005
- μ-Conotoxin SmIIIA, a Potent Inhibitor of Tetrodotoxin-Resistant Sodium Channels in Amphibian Sympathetic and Sensory NeuronsBiochemistry, 2002
- The Structure of the Potassium Channel: Molecular Basis of K + Conduction and SelectivityScience, 1998
- Mapping the site of block by tetrodotoxin and saxitoxin of sodium channel IIFEBS Letters, 1991
- Structure of a crystalline derivative of saxitoxin. Structure of saxitoxinJournal of the American Chemical Society, 1975
- Structure of saxitoxinJournal of the American Chemical Society, 1975