Bombyx mori ABC transporter C2 structures responsible for the receptor function of Bacillus thuringiensis CrylAa toxin

Because Bombyx mori ABC transporter C2 (BmABCC2) has 1000-fold higher potential than B. mori cadherin-like protein as a receptor for Bacillus thuringiensis CrylAa toxin (Tanaka et al., 2013), the gate opening ability of the latent pore under six extracellular loops (ECLs) of BmABCC2 was expected to be the reason for its higher potential (Heckel, 2012). In this study, cell swelling assays in Sf9 cells showed that BmABCC2 mutants lacking substrate-excreting activity retained receptor activity, indicating that the gate-opening activity of BmABCC2 is not responsible for CrylAa toxicity. The analysis of 29 BmABCC2 mutants demonstrated that (DYWL773)-D-770 of ECL 4 comprise a putative binding site to CrylAa. This suggests that specific toxicity of CrylAa toxin to a restricted range of lepidopteran insects is dependent on conservation and variation in the amino acid residues around (DYWL773)-D-770 of ECL 4 in the ABCC2. (C) 2017 Elsevier Ltd. All rights reserved.