Exploration of receptor binding of Bacillus thuringiensis toxins

Kwak, I.; Lü, Hong; Dean, Donald H.

doi:10.1590/s0074-02761995000100017

Cited by 4 publications

(2 citation statements)

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“…ʈ To whom correspondence should be addressed: (24), while mutations in loop 1 showed no effect on initial binding (25). These studies establish the significance of domain II loop residues in receptor binding.…”

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confidence: 63%

Mutations at Domain II, Loop 3, of Bacillus thuringiensis CryIAa and CryIAb δ-Endotoxins Suggest Loop 3 Is Involved in Initial Binding to Lepidopteran Midguts

Rajamohan¹,

Hussain

Cotrill³

et al. 1996

Journal of Biological Chemistry

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Alanine substitutions of loop 3 residues, 438 SGF-SNS 443 , of CryIAb toxin were constructed to study the functional role of these residues in receptor binding and toxicity to Manduca sexta and Heliothis virescens. Experiments with trypsin and insect gut juice enzyme digestions of mutant toxins showed that these mutations did not produce any gross structural changes to the toxin molecule. Bioassay data showed that mutant G439A (alanine substitution of residue Gly 439 ) and F440A significantly reduced toxicity toward M. sexta and H. virescens. In contrast, mutants S438A, S441A, N442A, and S443A were similar or only marginally less toxic (2-3 times) to the insects compared to the wild-type toxin. Binding studies with brush border membrane vesicles prepared from M. sexta and H. virescens midgut membranes revealed that the loss of toxicity of mutants G439A and F440A was attributable to substantially reduced initial binding. Consistent with the initial binding, mutants G349A and F440A showed 3.5 times less binding to M. sexta and H. virescens brush border membrane vesicles, although the off-rate of bound toxins was not affected. The role of hydrophobic residue, Phe 440 , is distinctly different from our previous observation that alanine substitution of Phe 371 at loop 2 of CryIAb did not affect initial binding but reduced irreversible association of the toxin to the receptor or membrane toward M. sexta (Rajamohan, F., Alcantara, E., Lee, M. K., Chen, X. J., and Dean, D. H. (1995) J. Bacteriol. 177, 2276 -2282). Likewise, deletion of relatively hydrophobic CryIAa loop 3 residues, 440 AAGA 443 (D3a), resulted in reduced toxicity to Bombyx mori (>62 times less) and M. sexta (28 times less). The loss of toxicity was correlated with reduced initial binding to midgut vesicles prepared from these insects. However, alanine substitution of residues 437 LSQ 439 (A3a), contiguous to loop 3, altered neither toxicity nor receptor binding toward B. mori or M. sexta. These results suggest that the loop 3 residues of CryIAb and CryIAa toxins establish hydrophobic interactions with the receptor molecule, and mutations at these hydrophobic residues affect initial binding.

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confidence: 63%

Mutations at Domain II, Loop 3, of Bacillus thuringiensis CryIAa and CryIAb δ-Endotoxins Suggest Loop 3 Is Involved in Initial Binding to Lepidopteran Midguts

Rajamohan¹,

Hussain

Cotrill³

et al. 1996

Journal of Biological Chemistry

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“…The implications of our findings are important for rational design of δ‐endotoxins that overcome insect resistance to these toxins and for altered or improved insecticidal activity, as has been achieved in other Cry toxins [4,27]. For instance, the hydrophobic residues around the loop I region in domain II, F 313 NYW 316 of Cry1Aa, E 313 YYW 316 of Cry1Ab and Y 313 YYW 316 of Cry1Ac toxins, may be identified as the homologue of Y 350 YGND 354 of Cry3A by functional mapping and sequence alignment [49]. Identification of these hydrophobic contact residues provides the potential for constructing genetically enhanced and durable toxins for use as biological pesticides.…”

Section: Discussionmentioning

confidence: 99%