Modelling insecticide-binding sites in the voltage-gated sodium channel

Abstract

A homology model of the housefly voltage-gated sodium channel was developed to predict the location of binding sites for the insecticides fenvalerate, a synthetic pyrethroid, and DDT an early generation organochlorine. The model successfully addresses the state-dependent affinity of pyrethroid insecticides, their mechanism of action and the role of mutations in the channel that are known to confer insecticide resistance. The sodium channel was modelled in an open conformation with the insecticide-binding site located in a hydrophobic cavity delimited by the domain II S4-S5 linker and the IIS5 and IIIS6 helices. The binding cavity is predicted to be accessible to the lipid bilayer and therefore to lipid-soluble insecticides. The binding of insecticides and the consequent formation of binding contacts across different channel elements could stabilize the channel when in an open state, which is consistent with the prolonged sodium tail currents induced by pyrethroids and DDT. In the closed state, the predicted alternative positioning of the domain II S4-S5 linker would result in disruption of pyrethroid-binding contacts, consistent with the observation that pyrethroids have their highest affinity for the open channel. The model also predicts a key role for the IIS5 and IIIS6 helices in insecticide binding. Some of the residues on the helices that form the putative binding contacts are not conserved between arthropod and non-arthropod species, which is consistent with their contribution to insecticide species selectivity. Additional binding contacts on the II S4-S5 linker can explain the higher potency of pyrethroid insecticides compared with DDT.

Multiple origins of pyrethroid insecticide resistance across the species complex of a nontarget aquatic crustacean, Hyalella azteca

“…An amino acid substitution at M918 to a non-sulfur-containing residue reduces susceptibility to pyrethroids (7), and disassociation of pyrethroids from a mutated M918 is 200 times faster than WT (21). The L925I mutation is considered conservative because of the similarity in structure of leucine and isoleucine; however, this small change is sufficient to reduce pyrethroid binding (20,22).…”

“…The M918L mutation was first observed in pyrethroid-resistant cotton aphids, Aphis gossypii (18), whereas the L925I mutation was first identified in resistant whiteflies, Bemisia tabaci (19), and has been characterized extensively in several insects (8). Sites M918 and L925 are two of several residues critical for pyrethroid binding to the VGSC (20), and in vitro assays have shown mutations at these sites retain VGSC gate function in the presence of pyrethroids (21,22). An amino acid substitution at M918 to a non-sulfur-containing residue reduces susceptibility to pyrethroids (7), and disassociation of pyrethroids from a mutated M918 is 200 times faster than WT (21).…”

Footprints of positive selection associated with a mutation ( N1575Y ) in the voltage-gated sodium channel of Anopheles gambiae

“…gambiae), a significant additive benefit of 1575Y was detectable. 1014F and 1014S, although not directly in the binding pocket, are thought to produce their resistance phenotype through altering the confirmation of the VGSC, preventing binding of insecticide (9,24). By contrast, N1575Y occurs within the linker between domains III and IV, the site of the inactivation particle, a sequence of three amino acids (MFM in mammals and IFM in insects), which closes the sodium channel pore following activation, stopping influx of sodium ions into the cell so permitting restoration of the membrane resting potential.…”

“…The presence of kdr has been conclusively linked to reduced mortality following exposure to both DDT and pyrethroids in a large number of studies (3,8). Pyrethroids and DDT target the insect voltage-gated sodium channel (VGSC), binding to the open (activated) sodium channel pore and preventing inactivation (9). Several mutations within the sodium channel have been identified in an array of insects and cause varying degrees of resistance (reviewed in ref.…”

“…10). Many of these mutations occur at key residues within the so-called binding pocket enclosed by the IIS4-S5 linker and IIS5/III6 helices (9). In An.…”