DIFFERENT DOMAINS OF BACILLUS-THURINGIENSIS DELTA-ENDOTOXINS CAN BINDTO INSECT MIDGUT MEMBRANE-PROTEINS ON LIGAND BLOTS

We investigated the role of the constituent domains of the CryIA(b) an d CryIA(c) delta-endotoxins in binding to midgut epithelial cell membr ane proteins of Spodoptera exigua and Manduca sexta on ligand blots, A collection of wild-type and CryIC-CryIA hybrid toxins was used for th is purpose, As demonstrated elsewhere (R. A. de Maagd, M. S. G. Kwa, H . van der Klei, T. Yamamoto, B. Schipper, J. M. Vlak, W. J. Stiekema, and D. Bosch, Appl. Environ. Microbiol. 62:1537-1543, 1996), CryIA(b) domain III recognized a 205-kDa protein on S. exigua blots, while no s pecific binding by domain I or II could be detected, In contrast, on l igand blots of M. serta proteins CryIA(b) domain II recognized a 210-k Da protein and CryIA(b) domain III recognized a 250-kDa protein, Domai n III is responsible for the interaction of CryIA(c) with 120-kDa majo r binding proteins of both S. exigua and M. sexta, In addition, in M. serta CryIA(c) also reacts with a 210-kDa binding protein through its domain I and/or domain II, These results show that besides domain II, domain III of delta-endotoxins plays a major role in binding to putati ve receptors on ligand blots, However, for S. exigua there was no clea r correlation between binding of toxins on ligand blots and the in viv o toxicity of the toxins, These and previous results suggest that inte ractions of insect membrane proteins with both domain II and domain II I can occur and that detection of these interactions depends on the ty pe of binding assay used.