Jingzhaotoxin-III, a novel spider toxin inhibiting activation of voltage-gated sodium channel in rat cardiac myocytes.
We have isolated a cardiotoxin, denoted jingzhaotoxin-III (JZTX-III), from the venom of the Chinese spider Chilobrachys jingzhao. The toxin contains 36 residues stabilized by three intracellular disulfide bridges (I-IV, II-V, and III-VI), assigned by a chemical strategy of partial reduction and sequence analysis. Cloned and sequenced using 3'-rapid amplification of cDNA ends and 5'-rapid amplification of cDNA ends, the full-length cDNA encoded a 63-residue precursor of JZTX-III. Different from other spider peptides, it contains an uncommon endoproteolytic site (-X-Ser-) anterior to mature protein and the intervening regions of 5 residues, which is the smallest in spider toxin cDNAs identified to date. Under whole cell recording, JZTX-III showed no effects on voltage-gated sodium channels (VGSCs) or calcium channels in dorsal root ganglion neurons, whereas it significantly inhibited tetrodotoxin-resistant VGSCs with an IC(50) value of 0.38 microm in rat cardiac myocytes. Different from scorpion beta-toxins, it caused a 10-mV depolarizing shift in the channel activation threshold. The binding site for JZTX-III on VGSCs is further suggested to be site 4 with a simple competitive assay, which at 10 microm eliminated the slowing currents induced by Buthus martensi Karsch I (BMK-I, scorpion alpha-like toxin) completely. JZTX-III shows higher selectivity for VGSC isoforms than other spider toxins affecting VGSCs, and the toxin hopefully represents an important ligand for discriminating cardiac VGSC subtype.
Xiao
Yucheng
Y
College of Life Sciences, Hunan Normal University, Changsha, Hunan 410081, People's Republic of China.
Tang
Jianzhou
J
Yang
Yuejun
Y
Wang
Meichi
M
Hu
Weijun
W
Xie
Jinyun
J
Zeng
Xiongzhi
X
Liang
Songping
S
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D004220:Disulfides / Q000737:chemistry; D004594:Electrophysiology; D005727:Ganglia, Spinal / Q000187:drug effects; D020128:Inhibitory Concentration 50; D008969:Molecular Sequence Data; D032383:Myocytes, Cardiac / Q000187:drug effects*; D009498:Neurotoxins / Q000737:chemistry / Q000494:pharmacology*; D010455:Peptides / Q000737:chemistry / Q000494:pharmacology*; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D051381:Rats; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D015222:Sodium Channels / Q000378:metabolism*; D013111:Spider Venoms / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology*; D013112:Spiders; D013997:Time Factors
D018076:DNA, Complementary; D004220:Disulfides; D009498:Neurotoxins; D010455:Peptides; D020033:Protein Isoforms; D015222:Sodium Channels; D013111:Spider Venoms; C487820:jingzhaotoxin-III, Chilobrachys jingzhao