Critical role of extracellular loops in differential modulations of TTX-sensitive and TTX-resistant Nav channels

• 成果类型: Article
• 署名作者: Wu, Tong; Yang, Xinyu; Jin, Xueqin; Yan, Nieng; Li, Zhangqiang
• 署名单位: Tsinghua University; Shenzhen Medical Academy of Research & Translation (SMART); Shenzhen Bay Laboratory
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-14025
• DOI: 10.1073/pnas.2510355122
• 发表日期: 2025-08-06
• 关键词: gated sodium-channels; na(v)1.7; RESOLUTION; biology; scn9a; pain; pore

摘要

The cardiac voltage-gated sodium channel Nav1.5 is resistant to tetrodotoxin (TTXr). Here, we report a cryo-electron microscopy (cryo-EM) structure of wild-type human Nav1.5, coexpressed with the beta 1 auxiliary subunit and treated with high-concentration TTX, at 3.4 & Aring; resolution. Structural comparison reveals the molecular determinants for the distinct responses to TTX as well as beta subunits between TTXr and TTX-sensitive (TTXs) Nav channels. A conserved cation-pi interaction between the guanidinium group of TTX and Tyr or Phe on the P2I helix in TTXs Na-v channels is lost in all TTXr subtypes owing to the replacement by Cys/Ser at the corresponding locus, explaining their differential TTX sensitivities. The beta 1 subunit is invisible in the EM map. Comparison of Na(v)1.5 with Nav1.7 and Na(v)1.8, which are, respectively, TTXs and TTXr, identifies four sites on the extracellular loops (ECLs) that may account for their different beta 1-binding abilities. When the corresponding residues in TTXs Na(v)1.7 are replaced with those from Na-v 1.5, the modulatory effects of beta 1 on channel activation and inactivation are diminished. Consistently, beta 1 is absent in the 3D EM reconstruction of this Nav1.7 mutant. Together with our previous structure-guided discovery that TTXr channels lack a Cys on the ECLII for disulfide bond formation with beta 2 or beta 4, the structure-function relationship studies underscore the importance of the ECLs in the mechanistic distinctions between TTXs and TTXr Nav channels. The ECLs may be further explored for the development of subtype-specific drugs.