Department of Entomology, Genetics and Neuroscience Programs, Michigan State University, East Lansing, MI 48824, USA.
Mol Pharmacol. 2011 Sep;80(3):426-33. doi: 10.1124/mol.111.072504. Epub 2011 Jun 16.
Batrachotoxin (BTX), a steroidal alkaloid, and pyrethroid insecticides bind to distinct but allosterically coupled receptor sites on voltage-gated sodium channels and cause persistent channel activation. BTX presumably binds in the inner pore, whereas pyrethroids are predicted to bind at the lipid-exposed cavity formed by the short intracellular linker-helix IIS4-S5 and transmembrane helices IIS5 and IIIS6. The alkylamide insecticide (2E,4E)-N-(1,2-dimethylpropyl)-6-(5-bromo-2-naphthalenyl)-2,4-hexadienamide (BTG 502) reduces sodium currents and antagonizes the action of BTX on cockroach sodium channels, suggesting that it also binds inside the pore. However, a pyrethroid-sensing residue, Phe(3i17) in IIIS6, which does not face the pore, is essential for the activity of BTG 502 but not for BTX. In this study, we found that three additional deltamethrin-sensing residues in IIIS6, Ile(3i12), Gly(3i14), and Phe(3i16) (the latter two are also BTX-sensing), and three BTX-sensing residues, Ser(3i15) and Leu(3i19) in IIIS6 and Phe(4i15) in IVS6, are all critical for BTG 502 action on cockroach sodium channels. Using these data as constraints, we constructed a BTG 502 binding model in which BTG 502 wraps around IIIS6, probably making direct contacts with all of the above residues on the opposite faces of the IIIS6 helix, except for the putative gating hinge Gly(3i14). BTG 502 and its inactive analog DAP 1855 antagonize the action of deltamethrin. The antagonism was eliminated by mutations of Ser(3i15), Phe(3i17), Leu(3i19), and Phe(4i15) but not by mutations of Ile(3i12), Gly(3i14), and Phe(3i16). Our analysis revealed a unique mode of action of BTG 502, its receptor site overlapping with those of both BTX and deltamethrin.
蛙毒素 (BTX)，一种甾体生物碱，和拟除虫菊酯类杀虫剂结合在电压门控钠离子通道的不同但变构偶联的受体部位，并导致持续的通道激活。BTX 可能结合在内腔，而拟除虫菊酯类杀虫剂被预测结合在由短的细胞内连接环 IIS4-S5 和跨膜螺旋 IIS5 和 IIS6 形成的暴露在脂质中的腔内。烷基酰胺杀虫剂（2E，4E）-N-（1，2-二甲基丙基）-6-（5-溴-2-萘基）-2，4-己二烯酰胺（BTG 502）减少钠离子电流并拮抗 BTX 对蟑螂钠离子通道的作用，表明它也结合在内腔。然而，一个拟除虫菊酯感应残基，位于 IIS6 中的 Phe(3i17)，它不面向孔，对于 BTG 502 的活性是必需的，但不是对于 BTX。在这项研究中，我们发现 IIS6 中的另外三个溴氰菊酯感应残基，Ile(3i12)、Gly(3i14)和 Phe(3i16)（后两个也是 BTX 感应残基），以及 IIS6 中的三个 BTX 感应残基，Ser(3i15)和 Leu(3i19)和 IVS6 中的 Phe(4i15)，对于 BTG 502 对蟑螂钠离子通道的作用都是至关重要的。利用这些数据作为约束条件，我们构建了一个 BTG 502 结合模型，其中 BTG 502 缠绕在 IIS6 周围，可能与 IIS6 螺旋对面的所有上述残基直接接触，除了假定的门控铰链 Gly(3i14)。BTG 502 和其无活性类似物 DAP 1855 拮抗溴氰菊酯的作用。这种拮抗作用被 Ser(3i15)、Phe(3i17)、Leu(3i19)和 Phe(4i15)的突变消除，但 Ile(3i12)、Gly(3i14)和 Phe(3i16)的突变没有消除。我们的分析揭示了 BTG 502 的独特作用模式，其受体部位与 BTX 和溴氰菊酯的受体部位重叠。
