Effects of chitin binding domain on enzymatic properties and insecticidal activity of <Emphasis Type="Italic">Bombyx mori</Emphasis> chitinase

Bombyx mori chitinase (Bmchi) possesses a catalytic domain and a cysteine-rich C-terminal domain. Wild-type and a C-terminal truncated form (Bmchi∆c) were expressed and purified from recombinant Pichia pastoris hosts. Loss of the C-teminal domain decreased the ability of the chitinase to bind and degrade insoluble substrates. Differences in optimal pH and temperature, thermostability, and ability to degrade certain oligosaccharide substrates were also observed between Bmchi and Bmchi∆c. To determine whether these proteins could be used to increase virulence of entomopathogenic fungi, Bmchi and Bmchi∆c were introduced into Beauveira bassiana under control of the A. nidulans gpdA constitutive promoter. Insect bioassays using WT and transformed B. bassiana strains revealed expression of Bmchi significantly improved fungal virulence compared to the WT parental strain, whereas expression of Bmchi∆c in B. bassiana had only a nominal effect. These results indicate that the B. mori chitinase can be used to improved fungal efficiency but that the C-terminal domain is essential for this function.