title: Structure--activity relationships of hainantoxin-IV and structure determination of active and inactive sodium channel blockers.
abstract: Hainantoxin-IV (HNTX-IV) can specifically inhibit the neuronal tetrodotoxin-sensitive sodium channels and defines a new class of depressant spider toxin. The sequence of native HNTX-IV is ECLGFGKGCNPSNDQCCKSSNLVCSRKHRWCKYEI-NH(2). In the present study, to obtain further insight into the primary and tertiary structural requirements of neuronal sodium channel blockers, we determined the solution structure of HNTX-IV as a typical inhibitor cystine knot motif and synthesized four mutants designed based on the predicted sites followed by structural elucidation of two inactive mutants. Pharmacological studies indicated that the S12A and R26A mutants had activities near that of native HNTX-IV, while K27A and R29A demonstrated activities reduced by 2 orders of magnitude. (1)H MR analysis showed the similar molecular conformations for native HNTX-IV and four synthetic mutants. Furthermore, in the determined structures of K27A and R29A, the side chains of residues 27 and 29 were located in the identical spatial position to those of native HNTX-IV. These results suggested that residues Ser(12), Arg(26), Lys(27), and Arg(29) were not responsible for stabilizing the distinct conformation of HNTX-IV, but Lys(27) and Arg(29) were critical for the bioactivities. The potency reductions produced by Ala substitutions were primarily due to the direct interaction of the essential residues Lys(27) and Arg(29) with sodium channels rather than to a conformational change. After comparison of these structures and activities with correlated toxins, we hypothesized that residues Lys(27), Arg(29), His(28), Lys(32), Phe(5), and Trp(30) clustered on one face of HNTX-IV were responsible for ligand binding.
authors.affiliation: College of Life Sciences, Peking University, Beijing 100871, China.
authors.forename: Dongling
authors.initials: D
authors.lastname: Li
authors.forename: Yucheng
authors.initials: Y
authors.lastname: Xiao
authors.forename: Xia
authors.initials: X
authors.lastname: Xu
authors.forename: Xia
authors.initials: X
authors.lastname: Xiong
authors.forename: Shanyun
authors.initials: S
authors.lastname: Lu
authors.forename: Zhonghua
authors.initials: Z
authors.lastname: Liu
authors.forename: Qi
authors.initials: Q
authors.lastname: Zhu
authors.forename: Meichi
authors.initials: M
authors.lastname: Wang
authors.forename: Xiaocheng
authors.initials: X
authors.lastname: Gu
authors.forename: Songping
authors.initials: S
authors.lastname: Liang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D051381:Rats; D017386:Sequence Homology, Amino Acid; D026941:Sodium Channel Blockers / Q000737:chemistry* / Q000378:metabolism*; D013111:Spider Venoms / Q000737:chemistry* / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D026941:Sodium Channel Blockers; D013111:Spider Venoms; C474037:hainantoxin-IV, Seleconosmia hainana