title: Molecular basis of the tarantula toxin jingzhaotoxin-III (β-TRTX-Cj1α) interacting with voltage sensors in sodium channel subtype Nav1.5.
abstract: With conserved structural scaffold and divergent electrophysiological functions, animal toxins are considered powerful tools for investigating the basic structure-function relationship of voltage-gated sodium channels. Jingzhaotoxin-III (β-TRTX-Cj1α) is a unique sodium channel gating modifier from the tarantula Chilobrachys jingzhao, because the toxin can selectively inhibit the activation of cardiac sodium channel but not neuronal subtypes. However, the molecular basis of JZTX-III interaction with sodium channels remains unknown. In this study, we showed that JZTX-III was efficiently expressed by the secretory pathway in yeast. Alanine-scanning analysis indicated that 2 acidic residues (Asp1, Glu3) and an exposed hydrophobic patch, formed by 4 Trp residues (residues 8, 9, 28 and 30), play important roles in the binding of JZTX-III to Nav1.5. JZTX-III docked to the Nav1.5 DIIS3-S4 linker. Mutations S799A, R800A, and L804A could additively reduce toxin sensitivity of Nav1.5. We also demonstrated that the unique Arg800, not emerging in other sodium channel subtypes, is responsible for JZTX-III selectively interacting with Nav1.5. The reverse mutation D816R in Nav1.7 greatly increased the sensitivity of the neuronal subtype to JZTX-III. Conversely, the mutation R800D in Nav1.5 decreased JZTX-III's IC₅₀ by 72-fold. Therefore, our results indicated that JZTX-III is a site 4 toxin, but does not possess the same critical residues on sodium channels as other site 4 toxins. Our data also revealed the underlying mechanism for JZTX-III to be highly specific for the cardiac sodium channel.
authors.affiliation: Key Laboratory of Protein Chemistry and Developmental Biology of Ministry of Education, College of Life Sciences, Hunan Normal University, Changsha, China.
authors.forename: Mingqiang
authors.initials: M
authors.lastname: Rong
authors.forename: Jinjun
authors.initials: J
authors.lastname: Chen
authors.forename: Huai
authors.initials: H
authors.lastname: Tao
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Wu
authors.forename: Peng
authors.initials: P
authors.lastname: Jiang
authors.forename: Ming
authors.initials: M
authors.lastname: Lu
authors.forename: Haibo
authors.initials: H
authors.lastname: Su
authors.forename: Yupeng
authors.initials: Y
authors.lastname: Chi
authors.forename: Tianfu
authors.initials: T
authors.lastname: Cai
authors.forename: Liqun
authors.initials: L
authors.lastname: Zhao
authors.forename: Xiongzhi
authors.initials: X
authors.lastname: Zeng
authors.forename: Yucheng
authors.initials: Y
authors.lastname: Xiao
authors.forename: Songping
authors.initials: S
authors.lastname: Liang
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D005786:Gene Expression Regulation; D057809:HEK293 Cells; D006801:Humans; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D062554:NAV1.5 Voltage-Gated Sodium Channel; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000737:chemistry / Q000235:genetics / Q000633:toxicity*; D011487:Protein Conformation; D015222:Sodium Channels / Q000235:genetics / Q000378:metabolism*; D013111:Spider Venoms / Q000737:chemistry / Q000235:genetics / Q000633:toxicity*; D013112:Spiders / Q000502:physiology*; D013329:Structure-Activity Relationship
chemical_list: D062554:NAV1.5 Voltage-Gated Sodium Channel; D010455:Peptides; C568320:SCN5A protein, human; D015222:Sodium Channels; D013111:Spider Venoms; C487820:jingzhaotoxin-III, Chilobrachys jingzhao