A Novel Conus Peptide Ligand for K+Channels

Abstract

Voltage-gated ion channels determine the membrane excitability of cells. Although many Conus peptides that interact with voltage-gated Na ؉ and Ca 2؉ channels have been characterized, relatively few have been identified that interact with K ؉ channels. We describe a novel Conus peptide that interacts with the Shaker K ؉ channel, M-conotoxin RIIIK from Conus radiatus. The peptide was chemically synthesized. Although M-conotoxin RIIIK is structurally similar to the -conotoxins that are sodium channel blockers, it does not affect any of the sodium channels tested, but blocks Shaker K ؉ channels. Studies using Shaker K ؉ channel mutants with single residue substitutions reveal that the peptide interacts with the pore region of the channel. Introduction of a negative charge at residue 427 (K427D) greatly increases the affinity of the toxin, whereas the substitutions at two other residues, Phe 425 Basic research on voltage-gated ion channels advances on two broad fronts: first, the identification and characterization of the numerous molecular isoforms that comprise each voltage-gated ion channel family. A different stream of research focuses on a few model systems intensively to uncover basic mechanistic insights. For both of these contrasting facets of ion channel research, the small peptides made by predatory cone snails (conotoxins) (1, 2) have considerable potential. Thus, the -conotoxins, one family of conotoxins, have become standard reagents for discriminating among Ca 2ϩ channel subtypes (3), and characterizing the functional role of each subtype. The -conotoxins that block voltage-gated channels are used as probes for the outer vestibule of the channel pore. The subject of this report is a novel conotoxin that has promising properties to be an important reagent for structure/function studies of the Shaker K ϩ channel, arguably the most intensively studied of all voltage-gated ion channels. However, the characterization of the peptide also defines a new family of conotoxins, the M family, that should provide a set of new ligands specific for different K ϩ channel isoforms.The first Conus peptide shown to target a voltage-gated ion channel was -conotoxin GIIIA, which was discovered and characterized two decades ago (4 -8). A characteristic feature of all -conotoxins is the arrangement of disulfide cross-links in the primary sequence, the -conotoxin pattern can be recognized by the following pattern of Cys residues: -CC-C-C-CC-, now defined as a class III (or M-1) conotoxin scaffold (9). After the discovery of the -conotoxins, other groups of Conus peptides with three disulfide bonds (the -conotoxins, ␦-conotoxins, O-conotoxins, and the spasmodic peptides) were characterized, but these had a different arrangement of Cys residues. Only one other family of conopeptides with a class III disulfide framework has been characterized, the -conotoxins (10). The latter are noncompetitive antagonists of nicotinic acetylcholine receptors.In this report, a peptide from Conus radiatus venom ducts that has the same class III...

ConusVenoms: A Rich Source of Novel Ion Channel-Targeted Peptides

“…A new family of conotoxins, the M-conotoxins, has the same class III scaffold as the -and -conotoxins, but an entirely different target specificity: voltage-gated K channels (55). The first peptide belonging to this family, M-RIIIK, was cloned from the venom duct of Conus radiatus.…”

Conotoxins: from the biodiversity of gastropods to new drugs

“…Недавние исследования показали, что разные таксономические группы конусов выделяют несколько отдельных семейств токсинов, взаимодействующих с калиевыми ионными каналами [81,82], однако, точный физиологический эффект и молекулярная специфичность большинства из них, особенно, в системах экспрессии млекопитающих, остаются недостаточно изученными.…”

“…kА-и kМ-конотоксины значительно различаются по строению. kА-Конотоксины представляют собой О-гликозилированные олигопептиды, относящиеся к А-надсемейству [25], тогда как kМ-конотоксины относятся с М-надсемейству и по паттерну дисульфидных связей близки к m-конотоксинам [81].…”

“…Конотоксины, принадлежащие к недавно обнаруженному kМ-семейству, имеют тот же цистеиновый паттерн, что m-конотоксины и y-конотоксины, но демонстрируют другую молекулярную специфичность, обнаруживая высокое сродство к потенциалзависимым калиевым каналам [81]. Первый охарактеризованный токсин этой группы kМ-RIIIK выделен из ядовитой железы C. radiatus.…”

Developmental Biology of Neoplastic Growth

“…Shorter forms of the κA-conotoxins have recently been isolated ). κM-conotoxins have also been isolated from piscivorous species (Ferber et al 2003). These latter K + channel blockers have structures reminiscent of the μ-conotoxins and interact within the pore of the channel through a novel set of interactions (Al-Sabi et al 2004).…”