title: A positively charged surface patch is important for hainantoxin-IV binding to voltage-gated sodium channels.
abstract: Hainantoxin-IV (HNTX-IV), isolated from the venom of the spider Ornithoctonus hainana, is a specific antagonist of tetrodotoxin-sensitive (TTX-S) voltage-gated sodium channels in rat dorsal root ganglion (DRG) cells. It adopts an inhibitor cystine knot motif, and structural analysis revealed a positively charged patch consisting of Arg26, Lys27, His28, Arg29 and Lys32 distributed on its molecular surface. Our previous study demonstrated that Lys27 and Arg29 but not Arg26 were critical residues for HNTX-IV binding to TTX-S sodium channels. In the present study, we examined the roles of His28 and Lys32 in the interaction of HNTX-IV with its target. Two mutants, HNTX-IV-H28D and HNTX-IV-K32A, were generated by solid-phase chemical synthesis and purified by reverse-phase HPLC after refolding and oxidation, yielding two compounds of high purity with monoisotopic masses of 3962.66 and 3927.70 Da, respectively, as determined by MALDI-TOF mass spectrometry. This indicated the presence of six cysteine residues forming three disulfide bonds. Moreover, circular dichroism spectroscopy analysis demonstrated that the substitution of His28 or Lys32 did not affect the overall structure of HNTX-IV. The inhibitory activity of HNTX-IV-H28D and HNTX-IV-K32A against TTX-S sodium channels in rat DRG cells was analyzed by whole-cell patch-clamp technique. The IC(50) values for the mutants were 0.57 and 5.80 μM (17-fold and 170-fold lower than the activity of the native toxin), indicating that His28 and Lys32 may be important for the inhibitory activity of HNTX-IV. Taken together, our results suggest that the positively charged patch might be the binding site for the interaction of HNTX-IV with TTX-S sodium channels. These findings might contribute to the elucidation of the structure and function relationship of HNTX-IV.
authors.affiliation: College of Life Science, Hunan Normal University, Changsha, 410081, China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Liu
authors.forename: Dan
authors.initials: D
authors.lastname: Li
authors.forename: Zhe
authors.initials: Z
authors.lastname: Wu
authors.forename: Jing
authors.initials: J
authors.lastname: Li
authors.forename: Dongsong
authors.initials: D
authors.lastname: Nie
authors.forename: Yang
authors.initials: Y
authors.lastname: Xiang
authors.forename: Zhonghua
authors.initials: Z
authors.lastname: Liu
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D005260:Female; D005727:Ganglia, Spinal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008958:Models, Molecular; D008969:Molecular Sequence Data; D051381:Rats; D017207:Rats, Sprague-Dawley; D015222:Sodium Channels / Q000737:chemistry* / Q000378:metabolism; D052616:Solid Phase Extraction; D013111:Spider Venoms / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology; D013112:Spiders; D055672:Static Electricity; D013329:Structure-Activity Relationship; D013499:Surface Properties; D061567:Voltage-Gated Sodium Channel Blockers / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology
chemical_list: D015222:Sodium Channels; D013111:Spider Venoms; D061567:Voltage-Gated Sodium Channel Blockers; C474037:hainantoxin-IV, Seleconosmia hainana