The receptor of Bacillus sphaericus binary toxin in Culex pipiens (Diptera: Culicidae) midgut: molecular cloning and expression

Culex pipiens larval midgut is the primary target of the binary toxin (Bin) present in parasporal inclusions of Bacillus sphaericus. Cpm1, a 60-kDa pr otein purified from brush border membranes, has been proposed as the recept or of the Bin toxin in the midgut epithelial cells of mosquitoes. We have c loned and characterized the corresponding cDNA from midgut of Culex pipiens larvae. The open reading frame predicted a 580 amino-acid protein with a p utative signal peptide at the N-terminus and a putative GPI-anchoring signa l at the C-terminus. The amino acid sequence of the cloned Cpm1 exhibited 3 9-43% identities with insect maltases (alpha -glucosidases and alpha -amyla ses). Recombinant Cpm1 expressed in E. coli specifically bound to the Bin t oxin and had a significant alpha -glucosidase activity but no alpha -amylas e activity. These results support the view that Cpm1 is an cc-glucosidase e xpressed in Culex midgut where it constitutes the receptor for the Bin toxi n. To date, this is the first component involved in the mosquitocidal activ ity of the Bacillus sphaericus Bin toxin to be characterized. Its identific ation provides a key step to elucidate the mode of action of the Bin toxin and the mechanisms of resistance developed against it by some mosquito stra ins. (C) 2001 Elsevier Science Ltd. All rights reserved.