A unique residue W544 in the beta18-beta19 loop of the Bacillus thuringiensis Cry1Ac toxin has been implicated in its toxicity. In this study, the effects of mutations at this residue on protein stability during protease treatment, UV irradiation, and preservation were examined. Residue 544 of Cry1Ac was involved in maintaining structural stability, and substitution of a polar group at this position was unfavorable to protein stability. One mutant, W544F, produced larger crystals and was more stable. This mutant showed greater resistance to UV radiation than the wild type Cry1Ac but retained equal toxicity. This is the first report showing that residue 544 in the Cry1Ac domain III plays a significant role in toxin structural stability. Our W544F mutant is a significant development in terms of field applications of Cry1Ac toxin.

α-Glucosidases play critical role both in primary metabolism and in glycoconjugate biosynthesis and processing. In this paper, the reasonable three-dimensional molecular model of AglA was generated by homology modeling. This modeled protein is divided into five major structural domains, and the catalytic domain is classical (β/α) 8 barrel with the active site pocket positioned at its C-terminal side. With analyses of conserved residues and overlay of homology structures, the residues Tyr 662, Tyr527, Glu521, His238 and Tyr235 was predicted as the main substrate binding sites, and residues Asp490, Glu493 and Asp660 were deduced to be the acid/base catalytic residues.