A New Family of Conotoxins That Blocks Voltage-gated Sodium Channels

Abstract

Conus peptides, including omega-conotoxins and alpha-conotoxins (targeting calcium channels and nicotinic acetylcholine receptors, respectively) have been useful ligands in neuroscience. In this report, we describe a new family of sodium channel ligands, the mu-O-conotoxins. The two peptides characterized, mu-O-conotoxins MrVIA and MrVIB from Conus marmoreus potently block the sodium conductance in Aplysia neurons. This is in marked contrast to standard sodium channel blockers that are relatively ineffective in this system. The sequences of the peptides are as follows. mu-O-conotoxin MrVIA: ACRKKWEYCIVPIIGFIYCCPGLICGPFVCV mu-O-conotoxin MrVIB: ACSKKWEYCIVPILGFVYCCPGLICGPFVCV mu-O-conotoxin MrVIA was chemically synthesized and proved indistinguishable from the natural product. Surprisingly, the mu-O-conotoxins show no sequence similarity to the mu-O-conotoxins. However, ananalysis of cDNA clones encoding the mu-O-conotoxin MrVIB demonstrated striking sequence similarity to omega- and delta-conotoxin precursors. Together, the omega-, delta-, and mu-O-conotoxins define the O-superfamily of Conus peptides. The probable biological role and evolutionary affinities of these peptides are discussed.

Structures of μO-conotoxins from Conus marmoreus

“…The O-conotoxins, MrVIA and MrVIB from the venom of Conus marmoreus (11), are a particularly interesting family of conotoxins, because they block voltage-sensitive sodium channels (VSSC) 1 but also interact with the calcium channel in molluscan neurons. MrVIA and MrVIB have been shown to block tetrodotoxin (TTX)-resistant (TTX-R) Na ϩ current in molluscan neurons (11), the TTX-sensitive (TTX-S) Na ϩ current through Na v 1.2 expressed in Xenopus oocytes, and the TTX-S Na ϩ current in hippocampal neurons (12).…”

“…MrVIA and MrVIB have been shown to block tetrodotoxin (TTX)-resistant (TTX-R) Na ϩ current in molluscan neurons (11), the TTX-sensitive (TTX-S) Na ϩ current through Na v 1.2 expressed in Xenopus oocytes, and the TTX-S Na ϩ current in hippocampal neurons (12). Despite the high sequence conservation between MrVIA and MrVIB (only three residues differ) the peptides behave differently at the calcium channel in molluscan neurons.…”

“…To date, there is no structural information available on the O-conotoxin family despite their sequences being discovered nearly a decade ago (11). This is likely the case because only limited amounts of native peptides may be isolated, and synthetic derivatives of the peptides are difficult to oxidize to the correct disulfide connectivity and appear to aggregate in aqueous solution.…”

“…These similarities involve the spacings between the cysteine residues ( Fig. 1) and similar precursor sequences, and consequently all three families have been placed in the O superfamily (11). Although the sequence homology in the mature peptides is restricted to the cysteine residues for these three families, the O-conotoxins are active at both the sodium and calcium channels similar to the ␦-and -conotoxins, respectively.…”

Developmental Biology of Neoplastic Growth

“…μO-conotoxins MrVIA and MrVIB from Conus marmoreus (Table 4) were originally identified as novel hydrophobic peptide blockers of Aplysia VGSCs (Fainzilber et al 1995;McIntosh et al 1995). More recently, μO-conotoxins were found to preferentially (tenfold selective) inhibit mammalian Na v 1.8 over other neuronal VGSC subtypes ).…”