Two catalytic domains of Chlorella virus CVK2 chitinase

VChti-1 chitinase encoded by the Chlorella virus CVK2 contained two catalyt ic domains belonging to family 18 glycosyl hydrolases. The first catalytic domain on a C-terminal-truncated derivative of vChti-1 generated exclusivel y chitobiose from chitotetraose, chitohexaose, and colloidal high-molecular mass chitin in the enzyme reaction, a typical characteristic of an exochit inase. In contrast, N-acetylglucosamine was produced from chitobiose as wel l as from chitooligosaccharides by the second catalytic do main on an N-ter minal-truncated derivative of vChti-1. Therefore, the second domain possess ed N-acetylglucosaminidase activity as well as endochitinase activity. The presence of two catalytic domains with different enzymatic properties in th e viral enzyme seems to be necessary for hydrolyzing natural substrates in a cooperative fashion.