Chitooligosaccharides are converted to N-acetylglucosamine by N-acetyl-β-hexosaminidase from Stenotrophomonas maltophilia

The Stenotrophomonas maltophilia k279a (Stm) Hex gene encodes a polypeptide of 785 amino acid residues, with an N-terminal signal peptide. StmHex was cloned without signal peptide and expressed as an 83.6 kDa soluble protein in Escherichia coli BL21 (DE3). Purified StmHex was optimally active at pH 5.0 and 40 °C. The Vmax, Km and kcat/Km for StmHex towards chitin hexamer were 10.55 nkat (mg protein) −1, 271 μM and 0.246 s−1 mM−1, while the kinetic values with chitobiose were 30.65 nkat (mg protein)−1, 2365 μM and 0.082 s−1 mM−1, respectively. Hydrolytic activity on chitooligosaccharides indicated that StmHex was an exo-acting enzyme and yielded N-acetyl-d-glucosamine (GlcNAc) as the final product. StmHex hydrolysed chitooligosaccharides (up to hexamer) into GlcNAc within 60 min, suggesting that this enzyme has potential for use in large-scale production of GlcNAc from chitooligosaccharides