Structure And Function Study Of Four Voltage-gated Sodium Channel Toxins From Spider Venoms

1.Chilobrachys jingzhao was found in Ledong county,Hainan province in 2001.In this study,we isolated and characterized two novel VGSC toxin named jingzhaotoxin-â…¡(JZTX-â…¡) and Jingzhaotoxin-â…£(JZTX-â…£) from the tarantula Chilobrachys jingzhao venom.(a) JZTX-â…¡consists of 32 amino acid residues including two acidic and two basic residues.Cloned and sequenced using 3'- and 5'-rapid amplification of the cDNA ends,the full-length cDNA for JZTX-â…¡was found to encode a 63-residue precursor.Under whole-cell voltage-clamp conditions,JZTX-â…¡signifycantly slowed rapid inactivation of TTX-resistant (TTX-R) VGSC on cardiac myocytes with the IC₅₀=0.26±0.09μM.In addition,JZTX-â…¡had no effect on TTX-R VGSCs on rat dorsal root ganglion neurons but exerted a concentration-dependent reduction in tetrodotoxin-sensitive(TTX-S) VGSCs accompanied by a slowing of sodium current inactivation similar to delta-ACTXs.It is notable that TTX-S VGSCs on cultured rat hippocampal neurons were resistant to JZTX-â…¡at high dose.Based on its high selectivity for mammalian VGSC subtypes,JZTX-â…¡might be an important ligand for discrimination of VGSC subtypes and for exploration of the distribution and modulation mechanisms of VGSCs.(b) Jingzhaotoxin-â…£(JZTX-â…£) was isolated and characterized.It consists of 34 amino acid residues including six acidic residues clustered with negative charge (pI=4.29).The full-length cDNA of JZTX-â…£encodes an 86-amino acid precursor containing a signal peptide of 21 residues,a mature peptide of 34 residues with terminal Lys-Gly as the signal of amidation.Under whole-cell patch clamp conditions,JZTX-â…£inhibits current and slows the inactivation of sodium channels(IC₅₀=1.77±0.29μM) by shifting the voltage dependence of activation to more depolarized potentials on DRG neurons,therefore,differs from the classic site 4 toxins that shift voltage dependence of activation in the opposite direction.JZTX-â…£(IC₅₀=0.90±0.17μM) potently inhibits current on acutely isolated rat cardiac cell In addition,JZTX-â…£shows a slowing inactivation of sodium channel with a hyperpolarizing shift of the steady-state inactivation on acutely isolated rat cardiac cell and DRG neurons,differs from the classic site 3 toxins that do not affect the steady-state of inactivation.At high concentration,JZTX-â…£has no significant effect on tetrodotoxin-resistant(TTX-R) sodium channels on rat DRG neurons and tetrodotoxin-sensitive(TTX-S) sodium channels on hippocampal neurons.2.HWTX-â… is the most abundant toxic component in the venom of O.huwena.Sequence alignment analysis indicated that HWTX-â… shares identical key residues with HNTX-â…£and HWTX-â…£.In this paper,we investigated the action of huwentoxin-â… (HWTX-â… ) purified from the venom of the Chinese bird spider Omithoctonus huwena on Ca²⁺,Na⁺ channels of adult rat dorsal root ganglion(DRG) neurons.The results showed that huwentoxin-â… could reduce the peak currents of N-type Ca²⁺ channels(IC₅₀≈100 nM) and TTX-S Na⁺ channels(IC₅₀≈55 nM), whereas no effect was detected on TTX-R Na⁺ channels.The comparative studies indicated that the selectivity of HWTX-â… on Ca²⁺ channels was higher that of MVIIA and approximately the same as that of GVIA.HWTX-â… is the first discovered toxin with the cross channel activities from the spider O.huwena venom similar toμO-conotoxins MrVIA and MrVIB.To ensure the cross channel activities was not because of poor purity,we synthesized HWTX-â… and demonstrated that the sodium channel inhibition of synthetic HWTX-â… (sHWTX-â… ) was similar in activity to natural HWTX-â… on rat dorsal root ganglion(DRG) neurons.In addition,we tested the potent sodium channel inhibition of sHWTX-â… on cockroach dorsal unpaired median(DUM) neurons (IC₅₀=4.80±0.58nM) and rat hippocampal neurons(IC₅₀=66.1±5.2nM). The further results showed that sHWTX-â… ,over the IC₅₀ value,had no effect to steady-state activation and steady-state inactivation kinetics of sodium channels on DUM and hippocampal neurons as well as on DRG neurons.As the most abundant toxic component in the venom of O. huwena,the preference of HWTX-â… for insect DUM neurons suggests that it is the most important component in crude venom for prey paralysis.3.Using Reverse-phrase high performance liquid chromatography to isolate the O.hainana crude venom,there were 21 peaks.We collected all the peaks and tested 14 peaks.Three of them were found to inhibit the TTX-R sodium channels on DRG neurons.Further study,a novel toxin,designated Hainantoxin-â…¦(HNTX-â…¦) was isolated from the venom of Chinese spider Ornithoctonus huwena(Selenocosmia hainana).HNTX-â…¦is a 3830.23 Da peptide with 33 amino acid residues containing six conservative cysteines.The full-length cDNA of JZTX-â…£encodes an 85-amino acid precursor.Under whole-cell patch clamps conditions,HNTX-â…¦could reduced the peak current of TTX-S, TTX-R VGSCs on DRG neurons,TTX-S VGSCs on hippocampal neurons in rats and and TTX-S VGSCs on DUM neurons in cockroaches. The IC₅₀ was 0.169±0.046μM,0.676±0.049μM,1.10±0.09μM, 15.1±2.7nM,respectively.HNTX-â…¦did not affect steady-state activation curves and steady-state inactivation curves of VGSCs on DRG neurons.HNTX-â…¦made the steady-state activation curves of VGSCs shift to depolarization direction(10 mV) and steady-state inactivation curves of VGSCs shift to hyperpolafization direction (13.4mV) on hippocampal neurons.HNTX-â…¦selectively affected the kinetics of sodium channel subtype,might be an important tool to explore the structure and functions relationship of voltage gated channels.HNTX-â…¦also inhibit the potassium currents on cockroach DUM neurons with the IC₅₀=13.7±1.2nM.