Efficient Bioconversion of Crystalline α-Chitin to <i>N</i>-Acetyl-D-glucosamine Driven by a Novel β-<i>N</i>-Acetylglucosaminidase and the Promotion Mechanism Analysis

Whole-enzyme cascade degradation of crystalline α-chitin is a long-term pursuit, which has been hampered by low transformation efficiency and heterogeneous products. Here, a novel β-<i>N</i>-acetylglucosaminidase (NAGase) from <i>Sulfuriroseicoccus oceanibius</i>, designated Sohex, was biochemically characterized. The enzyme demonstrated high hydrolytic activity toward <i>N</i>-acetyl chitooligomers (<i>N</i>-acetyl COSs) and exhibited promotive effects on crystalline α-chitin degradation. Furthermore, a whole-enzyme cascade degradation system based on lytic polysaccharide monooxygenases (LPMOs), chitinases, and Sohex was developed for <i>N</i>-acetyl-D-glucosamine (GlcNAc) production. This system achieved a maximum conversion rate of 45.93%, with GlcNAc purity reaching 99.99%. The addition of Sohex significantly enhanced α-chitin degradation efficiency, achieving conversion rates of 1.37-fold and 2.46-fold compared to the LPMOs + chitinases system and the sole chitinases system, respectively. Moreover, the promotion mechanisms of Sohex in conjunction with LPMOs and chitinases were elucidated, making the cascade system a promising strategy for converting crystalline α-chitin into high-purity GlcNAc.