N-ACETYL GALACTOSAMINE IS PART OF THE RECEPTOR IN INSECT GUT EPITHELIA THAT RECOGNIZES AN INSECTICIDAL PROTEIN FROM BACILLUS-THURINGIENSIS

Proteins synthesized by the bacterium Bacillus thuringiensis are potent insecticides. When ingested by susceptible larvae they rapidly lyse epithelial cells lining the midgut. In vitro the toxins lyse certain insect cell lines and show saturable, high-affinity binding to brush-border membrane vesicles (BBMVS) prepared from insect midguts. We observed that the sugar N-acetyl galactosamine (GalNAc) specifically decreased the cytolytic activity of a CryIA (c) toxin towards Choristoneura fumiferana CF1 cells, completely abolished toxin binding to Manduca sexta BBMVs, partially inhibited binding to Heliothis virescens BBMVs and had no apparent effect on binding to Pieris brassicae BBMVs. In ligand blotting experiments the toxin bound proteins of 120 kDa in M. sexta, 125 kDa in P. brassicae and numerous proteins in H. zea. Toxin binding to these proteins was specifically inhibited by GalNAc. The toxin binding proteins of M. sexta and H. zea also bound the lectin soybean agglutinin. Taken together these findings suggest that N-acetyl galactosamine might be a component of a CryIA (c) toxin receptor of CF1 cells and of at least two of the insects tested.