Coordinated binding of a two-component insecticidal protein from Alcaligenes faecalis to western corn rootworm midgut tissue

Abstract

AfIP-1A/1B is a two-component insecticidal protein identified from the soil bacterium Alcaligenes faecalis that has high activity against western corn rootworm (WCR; Diabrotica virgifera virgifera LeConte). Previous results revealed that AfIP-1A/1B is cross-resistant to the binary protein from Bacillus thuringiensis (Bt), Cry34Ab1/Cry35Ab1 (also known as Gpp34Ab1/Tpp35Ab1; Crickmore et al., 2020), which was attributed to shared binding sites in WCR gut tissue (Yalpani et al., 2017). To better understand the interaction of AfIP-1A/1B with its receptor, we have systematically evaluated the binding of these proteins with WCR brush border membrane vesicles (BBMVs). Our findings show that AfIP-1A binds directly to BBMVs, while AfIP-1B does not; AfIP-1B binding only occurred in the presence of AfIP-1A which was accompanied by the presence of stable, high molecular weight oligomers of AfIP-1B observed on denaturing protein gels. Additionally, we show that AfIP-1A/1B forms pores in artificial lipid membranes. Finally, binding of AfIP-1A/1B was found to be reduced in BBMVs from Cry34Ab1/Cry35Ab1-resistant WCR where Cry34Ab1/Cry35Ab1 binding was also reduced. The reduced binding of both proteins is consistent with recognition of a shared receptor that has been altered in the resistant strain. The coordination of AfIP-1B binding by AfIP-1A, the similar structures between AfIP-1A and Cry34Ab1, along with their shared binding sites and cross-resistance, suggest a similar role for AfIP1A and Cry34Ab1 in receptor recognition and docking site for their cognate partners, AfIP-1B and Cry35Ab1, respectively.