Structural and functional diversities among mu-conotoxins targeting TTX-resistant sodium channels.
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.
Departments of Biology, University of Utah, Salt Lake City 84112, USA.
Min-Min
MM
Zhang
Brian
B
Fiedler
Brad R
BR
Green
Phillip
P
Catlin
Maren
M
Watkins
James E
JE
Garrett
Brian J
BJ
Smith
Doju
D
Yoshikami
Baldomero M
BM
Olivera
Grzegorz
G
Bulaj
D000200:Action Potentials; D000595:Amino Acid Sequence; D000818:Animals; D002121:Calcium Channel Blockers / Q000378:metabolism / Q000494:pharmacology; D020916:Conotoxins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004351:Drug Resistance; D004594:Electrophysiology; D008297:Male; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000378:metabolism; D010084:Oxidation-Reduction; D017510:Protein Folding; D011894:Rana pipiens / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017385:Sequence Homology; D012908:Snails / Q000378:metabolism; D015222:Sodium Channels / Q000187:drug effects* / Q000378:metabolism; D013329:Structure-Activity Relationship; D013779:Tetrodotoxin / Q000378:metabolism / Q000494:pharmacology*
D002121:Calcium Channel Blockers; D020916:Conotoxins; D015222:Sodium Channels; D013779:Tetrodotoxin