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Structural basis for tetrodotoxin-resistant sodium channel binding by mu-conotoxin SmIIIA


Keizer, DW; West, PJ; Lee, EF; Yoshikami, D; Olivera, BM; Bulaj, G; Norton, RS
2003-11-21
JOURNAL OF BIOLOGICAL CHEMISTRY
Journal Article
278
47
46805-46813
SmIIIA is a new mu-conotoxin isolated recently from Conus stercusmuscarum. Although it shares several biochemical characteristics with other mu-conotoxins ( the arrangement of cysteine residues and a conserved arginine believed to interact with residues near the channel pore), it has several distinctive features, including the absence of hydroxyproline, and is the first specific antagonist of tetrodotoxin-resistant voltage-gated sodium channels to be characterized. It therefore represents a potentially useful tool to investigate the functional roles of these channels. We have determined the three-dimensional structure of SmIIIA in aqueous solution. Consistent with the absence of hydroxyprolines, SmIIIA adopts a single conformation with all peptide bonds in the trans configuration. The spatial orientations of several conserved Arg and Lys side chains, including Arg(14) ( using a consensus numbering system), which plays a key role in sodium channel binding, are similar to those in other mu-conotoxins but the N-terminal regions differ, reflecting the trans conformation for the peptide bond preceding residue 8 in SmIIIA, as opposed to the cis conformation in mu-conotoxins GIIIA and GIIIB. Comparison of the surfaces of SmIIIA with other mu-conotoxins suggests that the affinity of SmIIIA for TTX-resistant channels is influenced by the Trp(15) side chain, which is unique to SmIIIA. Arg(17), which replaces Lys in the other mu-conotoxins, may also be important. Consistent with these inferences from the structure, assays of two chimeras of SmIIIA and PIIIA in which their N- and C-terminal halves were recombined, indicated that residues in the C-terminal half of SmIIIA confer affinity for tetrodotoxin-resistant sodium channels in the cell bodies of frog sympathetic neurons. SmIIIA and the chimera possessing the C-terminal half of SmIIIA also inhibit tetrodotoxin-resistant sodium channels in the postganglionic axons of sympathetic neurons, as indicated by their inhibition of C-neuron compound action potentials that persist in the presence of tetrodotoxin.
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
NUCLEAR-MAGNETIC-RESONANCE; SKELETAL-MUSCLE; SYMPATHETIC-GANGLIA; POTASSIUM CHANNELS; AQUEOUS-SOLUTIONS; POTENT INHIBITOR; H-3 SAXITOXIN; SHK TOXIN; GIIIA; NMR
10.1074/jbc.M309222200
Refer to copyright notice on published article.

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Creation Date 2003-11-21 12:00:00