Function and solution structure of Huwentoxin-X, a specific blocker of N-type calcium channels, from the Chinese bird spider Ornithoctonus huwena.
Huwentoxin-X (HWTX-X) is a novel peptide toxin, purified from the venom of the spider Ornithoctonus huwena. It comprises 28 amino acid residues including six cysteine residues as disulfide bridges linked in the pattern of I-IV, II-V, and III-VI. Its cDNA, determined by rapid amplification of 3' and 5' cDNA ends, encodes a 65-residue prepropeptide. HWTX-X shares low sequence homology with omega-conotoxins GVIA and MVIIA, two well known blockers of N-type Ca2+ channels. Nevertheless, whole cell studies indicate that it can block N-type Ca2+ channels in rat dorsal root ganglion cells (IC50 40 nm) and the blockage by HWTX-X is completely reversible. The rank order of specificity for N-type Ca2+ channels is GVIA approximately HWTX-X > MVIIA. In contrast to GVIA and MVIIA, HWTX-X had no detectable effect on the twitch response of rat vas deferens to low frequency electrical stimulation, indicating that HWTX-X has different selectivity for isoforms of N-type Ca2+ channels, compared with GVIA or MVIIA. A comparison of the structures of HWTX-X and GVIA reveals that they not only adopt a common structural motif (inhibitor cystine knot), but also have a similar functional motif, a binding surface formed by the critical residue Tyr, and several basic residues. However, the dissimilarities of their binding surfaces provide some insights into their different selectivities for isoforms of N-type Ca2+ channels.
Liu
Zhonghua
Z
College of Life Sciences, Peking University, Beijing 100087, China.
Dai
Jie
J
Dai
Longjun
L
Deng
Meichun
M
Hu
Zhe
Z
Hu
Weijun
W
Liang
Songping
S
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D002121:Calcium Channel Blockers / Q000008:administration & dosage / Q000633:toxicity*; D002478:Cells, Cultured; D003058:Cockroaches; D017124:Conserved Sequence; D004305:Dose-Response Relationship, Drug; D005260:Female; D005727:Ganglia, Spinal / Q000166:cytology / Q000187:drug effects; D020128:Inhibitory Concentration 50; D007274:Injections, Intraperitoneal; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009474:Neurons / Q000187:drug effects; D017510:Protein Folding; D017433:Protein Structure, Secondary; D051381:Rats; D017207:Rats, Sprague-Dawley; D017386:Sequence Homology, Amino Acid; D012996:Solutions; D013111:Spider Venoms / Q000737:chemistry* / Q000378:metabolism* / Q000633:toxicity*; D013112:Spiders / Q000737:chemistry*
D002121:Calcium Channel Blockers; D012996:Solutions; D013111:Spider Venoms; C510374:hwentoxin-X, Ornithoctonus huwena