Comparison of enzymatic and antifungal properties between family 18 and 19 chitinases from S. coelicolor A3(2).

Streptomyces coelicolor A3(2) has 13 chitinase genes encoding 11 family 18 and two family 19 chitinases. To compare enzymatic properties of family 19 chitinase and family 18 chitinases produced by the same organism, the four chitinases (Chi18bA, Chi18aC, Chi18aD, and Chi19F), whose genes are expressed at high levels in the presence of chitin, were produced in Escherichia coli and purified. The effect of pH on the hydrolytic activity was very different not only among the four chitinases but also among the substrates. The hydrolytic activity of Chi19F, family 19 chitinase, against soluble substrates was remarkably high as compared with three family 18 chitinases, but was the lowest against crystalline substrates among the four chitinases. On the contrary, Chi18aC, a family 18-subfamily A chitinase, showed highest activity against crystalline substrates. Only Chi19F exhibited significant antifungal activity. Based on these observations, the roles of family 19 chitinases are discussed.