The Lysinibacillus sphaericus Tpp1/2 (BinAB) protein complex is a potent and selective biopesticide targeting Culex and Anopheles mosquitoes. As members of the Toxin_10 family of pore-forming proteins, Tpp1 forms pores in the mosquito midgut, but its uptake depends on Tpp2 binding to the receptor Cqm1. However, the structural basis of this interaction—and why Aedes mosquitoes remain refractory to Tpp1/2—remains unresolved.
Here, we characterize Tpp2 engagement with Cqm1 using single-particle cryo-EM, mass photometry, and protein mutagenesis. Our findings define the receptor-binding interface and key determinants of specificity, providing insight into the mechanism of Tpp2-mediated toxicity. Structural analysis further reveals why Aedes mosquitoes evade Tpp1/2 activity.
By advancing our understanding of pesticidal protein specificity, this work informs the safe and effective use of biopesticides while guiding future efforts to enhance toxin stability, expand host range, and develop next-generation, environmentally friendly insecticides.