A New Nomenclature for Cry1Ab Proteins Reflecting 3-D Structure Differences

Cry1Ab proteins produced by the insecticidal bacterium Bacillus thuringiensis are mostly studied and applied, facing the challenge of insect resistance. The 3-D structure of the toxic core for all available 34 Cry1Ab proteins were constructed by the method of homology modeling. Based on the secondary structure pattern, four different groups were identified and named as Cry1AbⅠ, Cry1AbⅡ, Cry1AbⅢ, and Cry1AbⅣ. The three Cry1Ab proteins, Cry1Ab2, Cry1Ab7 and Cry1Ab28 were recognized as Cry1AbⅡ, Cry1AbⅢ, and Cry1AbⅣ, respectively. The other 31 Cry1Ab proteins were grouped as Cry1AbⅠ, and were further divided into three subgroups based on 3-D structural differences, Cry1AbⅠ3 (Cry1Ab33 only), Cry1AbⅠ2 (Cry1Ab31 only), and Cry1AbⅠ1 (the rest of Cry1AbⅠ). The structural differences among different Cry1Ab groups and subgroups were presented in details. The insecticidal activities of different Cry1Ab groups and subgroups were also discussed. It was worthy to speculate that the only difference in 3-D structure, residues 447-449 form β-sheet in Cry1AbⅠ vs loop in Cry1AbⅢ, resulted in Cry1AbⅠ inactive vs Cry1AbⅢ active against mosquito. The data obtained from the present in silico study provided new insights into structure-function relationship of Cry1Ab proteins.