Structural and Functional Diversities among μ-Conotoxins Targeting TTX-resistant Sodium Channels

Abstract

mu-Conotoxins are peptides that block sodium channels. Molecular cloning was used to identify four novel mu-conotoxins: CnIIIA, CnIIIB, CIIIA, and MIIIA from Conus consors, C. catus and C. magus. A comparison of their sequences with those of previously characterized mu-conotoxins suggested that the new mu-conotoxins were likely to target tetrodotoxin-resistant (TTX-r) sodium channels. The four peptides were chemically synthesized, and their biological activities were characterized. The new conotoxins all blocked, albeit with varying potencies, TTX-r sodium currents in frog dorsal-root-ganglion (DRG) neurons. The more potent of the four new mu-conotoxins, CnIIIA and CIIIA, exhibited a strikingly different selectivity profile in blocking TTX-r versus TTX-sensitive channels, as determined by their ability to block extracellularly recorded action potentials in three preparations from frog: skeletal muscle, cardiac muscle and TTX-treated C-fibers. CnIIIA was highly specific for TTX-r sodium channels, whereas CIIIA was nonselective. Both peptides appeared significantly less potent in blocking TTX-r sodium currents in rat and mouse DRG neurons. When CnIIIA and CIIIA were injected intracranially into mice, both induced seizures, but only CIIIA caused paralysis. This is the most comprehensive characterization to date of the structural and functional diversities of an emerging group of mu-conotoxins targeting TTX-r sodium channels.

μ-Conotoxins that differentially block sodium channels NaV1.1 through 1.8 identify those responsible for action potentials in sciatic nerve

“…In contrast, none of the μ-conopeptides tested thus far has been found to block rat Na V 1.8 (Table 1). This is consistent with the observation that KIIIA (as well as CIIIA and CnIIIA) have minimal, if any, effects on TTX-resistant sodium currents (TTX-r I Na ), as a result of Na V 1.8, in rodent DRG neurons (15,24); similarly, SmIIIA does not block human Na V 1.8 expressed in oocytes (25). A Na V 1.9 clone was not available for testing in oocytes, and we have no information concerning its susceptibility to μ-conopeptides.…”

“…Discussion This is a comprehensive report of the susceptibilities of Na V 1.1 through 1.8 to the 11 μ-conopeptides used in this study. Previously, we reported that KIIIA, SIIIA, and SmIIIA (as well as CIIIA and CnIIIA) readily blocked TTX-resistant currents in neurons in frog sympathetic and dorsal root ganglion (DRG) neurons (23,24). In contrast, none of the μ-conopeptides tested thus far has been found to block rat Na V 1.8 (Table 1).…”

Conus Venom Peptide Pharmacology

“…In recent years, the Na v subtype selectivity of -conotoxins has been studied with renewed interest; many have now shown subtype selectivity for neuronal subtypes, including PIIIA, KIIIA, MIIIA, CIIIA, CnIIIA, CnIIIB, SIIIA, SmIIIA, and TIIIA. To date, no -conotoxins have been identified with affinity for the TTX-resistant mammalian subtypes Na v 1.5, -1.9, and -1.8 Schroeder et al, 2008;Leipold et al, 2011;Wilson et al, 2011a) despite a number showing activity at amphibian TTX-resistant isoforms (Zhang et al, 2006b) (see Table 5). The least susceptible isoforms include Na v 1.3, -1.7, and -1.5, and no -conotoxins have yet been found to block recombinantly expressed Na v 1.8 Schroeder et al, 2008;Leipold et al, 2011;Wilson et al, 2011a).…”

Conotoxins: from the biodiversity of gastropods to new drugs

“…Всего на данный момент известно не менее 7 m-конотоксинов, ингибирующих ТТХ устойчивые натриевые каналы амфибий [63], и не менее двух, взаимодействующих на ТТХ устойчивые натриевые каналы млекопитающих [64].…”