Heterologous expression and characterization of class III chitinases from rice (Oryza sativa L.)

Acidic (OsChib1a) and basic (OsChib1b) class III chitinases from rice (Oryza sativa L.), sharing 70% of the identical amino acid residues each other, were expressed from the corresponding cDNAs in Pichia pastoris and purified homogenously. Both OsChib1a and OsChib1b degraded actively glycol chitin over colloidal chitin at the optimum pH of 4.3 and 8.3, respectively. OsChib1b had lower specific chitinase activity than OsChib1a, but it showed a strong lytic activity and significant antifungal activity: no lytic and antifungal activity was observed for OsChib1a. Experiments with N-acetyl chitooligosaccharides showed that OsChib1a hydrolyzed (GlcNAc)6 efficiently to yield (GlcNAc)2 as the major product, while OsChib1b hydrolyzed (GlcNAc)6 to yield both (GlcNAc)2 and (GlcNAc)4. Possible structures responsible for their distinct catalytic properties are discussed.