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-stable Micromonospora aurantiaca -derived chitinase, Ma Chi1, in Escherichia coli and subsequently purified, characterized, and evaluated it for its chitin-converting capacity. Our results indicated that Ma Chi1 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. Mg 2+ (5 mM), and dithiothreitol (10 mM) significantly promoted Ma Chi1 activity. Ma Chi1 exhibited broad substrate specificity and hydrolyzed chitin, chitosan, cellulose, soluble starch, and N -acetyl chitooligosaccharides with polymerization degrees ranging from three to six. Moreover, Ma Chi1 exhibited an endo-type cleavage pattern, and it could efficiently convert colloidal chitin into N -acetyl-D-glucosamine (GlcNAc) and (GlcNAc) 2 with 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.