Heterologous Expression and Characterization of a pH-Stable Chitinase from Micromonospora aurantiaca with a Potential Application in Chitin Degradation

To promote the bioconversion of marine chitin waste into value-added products, we expressed a novel pH-stableMicromonospora aurantiaca-derived chitinase,MaChi1, inEscherichia coliand subsequently purified, characterized, and evaluated it for its chitin-converting capacity. Our results indicated thatMaChi1 is of the glycoside hydrolase (GH) family 18 with a molecular weight of approximately 57 kDa, consisting of a GH18 catalytic domain and a cellulose-binding domain. We recorded its optimal activity at pH 5.0 and 55 °C. It exhibited excellent stability in a wide pH range of 3.0–10.0. Mg2+(5 mM), and dithiothreitol (10 mM) significantly promotedMaChi1 activity.MaChi1 exhibited broad substrate specificity and hydrolyzed chitin, chitosan, cellulose, soluble starch, andN-acetyl chitooligosaccharides with polymerization degrees ranging from three to six. Moreover,MaChi1 exhibited an endo-type cleavage pattern, and it could efficiently convert colloidal chitin intoN-acetyl-D-glucosamine (GlcNAc) and (GlcNAc)2with yields of 227.2 and 505.9 mg/g chitin, respectively. Its high chitin-degrading capacity and exceptional pH tolerance makes it a promising tool with potential applications in chitin waste treatment and bioactive oligosaccharide production.