PT  - JOURNAL ARTICLE
AU  - Yuzhe Du
AU  - Daniel P Garden
AU  - Bhupinder Khambay
AU  - Boris Zhorov
AU  - Ke Dong
TI  - Batrachotoxin, Pyrethroids and BTG 502 Share Overlapping Binding Sites On Insect Sodium Channels
AID  - 10.1124/mol.111.072504
DP  - 2011 Jun 16
TA  - Molecular Pharmacology
PG  - mol.111.072504
4099  - http://molpharm.aspetjournals.org/content/early/2011/06/16/mol.111.072504.short
4100  - http://molpharm.aspetjournals.org/content/early/2011/06/16/mol.111.072504.full
AB  - A steroidal alkaloid, batrachotoxin (BTX), 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. An alkylamide insecticide 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 likely 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 with its receptor site overlapping with those of both BTX and deltamethrin.