Structural Insights into Pyrethroid Recognition by Anopheles Chemosensory Proteins

Mosquito-borne diseases, particularly malaria, remain a major global health challenge. Among different mosquitoes, Anopheles are solely responsible for malaria. Insecticide-based interventions such as insecticide-treated nets (ITNs) and indoor residual spraying (IRS) are central to mosquito control. However, the widespread emergence of insecticide resistance, especially to pyrethroids, the most commonly used insecticides for mosquito worldwide, threatens their effectiveness. While genetic and metabolic mechanisms of resistance are well characterized, behavioral and sequestration-based mechanisms, particularly those involving chemosensory proteins (CSPs), are less understood. CSPs and odorant-binding proteins (OBPs) are integral components of the mosquito olfactory system, mediating host-seeking and other behavioral processes by transporting odorant molecules to olfactory receptors. Recent evidence suggests that CSPs may also bind insecticides like pyrethroids, contributing to resistance through sequestration. In this study, we investigated the structural and functional roles of CSPs in Anopheles mosquitoes. We determined three high-resolution X-ray crystal structures (apo-form) of CSPs (<2 Å) from Anopheles culicifacies and Anopheles gambiae, representing the first crystal structures of CSPs from any Anopheles species reported to date. Using structural, biophysical and computational approaches, we assessed CSP-ligand recognition of various insecticides, specifically pyrethroids and identified key residues potentially involved in pyrethroid interaction through site-directed mutagenesis. The moderate micromolar binding affinities of deltamethrin and permethrin, compared to other insecticides, support the role of CSPs in pyrethroid sequestration. Our findings offer mechanistic insights into pyrethroid sequestration and provide a foundation for developing novel vector control strategies that target CSP-insecticide interactions to combat pyrethroid resistance.