MoChia1 is a family 18 glycoside hydrolase from the rice blast fungus, Magnaporthe oryzae , that releases reducing-end GlcNAc from chitin oligosaccharides

MoChia1, a family 18 glycoside hydrolase from the rice blast fungus Magnaporthe oryzae , was identified as an enzyme that binds chitin oligosaccharide elicitor to suppress the chitin-induced rice immune response. It hydrolyzed chitin oligosaccharides with a degree of polymerization of at least 3 [(GlcNAc) n ( n ≥3)] in an exo-splitting manner with anomeric retention. HPLC analysis of (GlcNAc) n cleavage by MoChia1 revealed that it specifically recognizes the β -anomer of the substrate at the + 1 subsite and cleaves the terminal glycosidic linkage at the reducing end. It also hydrolyzed the partially deacetylated chitotrisaccharide GlcN-(GlcNAc) 2 to GlcN-GlcNAc and GlcNAc, but not (GlcN) 2 -GlcNAc, indicating the requirement of the N -acetyl group at the −1 subsite for the hydrolytic reaction. MoChia1 released p -nitrophenol from p NP-(GlcNAc) 2 , p -nitrophenyl di- N -acetyl- β -chitotrioside. Furthermore, it hydrolyzed the chitotriose derivatives with a modified GlcNAc residue on the reducing end, (GlcNAc) 2 -G, 4- O - β -di- N -acetylchitobiosyl-2-acetamido-2-deoxy-2,3-anhydro-glucopyranose and (GlcNAc) 2 -L, 4- O - β -di- N -acetylchitobiosyl-2-acetamido-2-deoxy-2,3-anhydro-glucono-δ-lactone, to (GlcNAc) 2 and the modified GlcNAc, respectively. However, it did not hydrolyze 4- O - β -di- N -acetylchitobiosyl moranoline [(GlcNAc) 2 -M], reduced chitotriose (chitotriitol), and α -(GlcNAc) 2 fluoride [( α -(GlcNAc) 2 -F]. MoChia1 did not bind to chitin and barely hydrolyzed the polymeric substrate, glycol chitin. Taken together, we concluded that MoChia1 is a GH18 reducing end GlcNAc-releasing exo-oligochitinase with the β -anomer selectivity. Allosamidin, a potent inhibitor of GH18 chitinases, was found to bind to MoChia1 and inhibit its hydrolytic activity with an IC 50 of 54.4 ± 6.91 μM, indicating that allosamidin may be a potential candidate for a pesticide to prevent rice blast infection by inhibiting the chitinase activity of MoChia1.