Efficient sequential synthesis of lacto-N-triose II and lacto-N-neotetraose by a novel β-N-acetylhexosaminidase from Tyzzerella nexilis

beta-N-acetylhexosaminidases have attracted much attention in recent years due to their potential application in oligosaccharide production, in particular lacto-N-triose II (LNT2) and lacto-N-neotetraose (LNnT) synthesis, which can be further used as backbone precursors for human milk oligosaccharides. A novel beta-N-acetylhexosaminidase gene from Tyzzerella nexilis (TnHex189) was heterologously expressed in Bacillus subtilis. The highest beta-N-acetylhexosaminidase activity of 14.5 U mL(-1) was obtained in a 5-L fermentor by fed-batch fermentation for 27 h. TnHex189 was optimally active at pH 5.0 and 45 degrees C. It efficiently synthesized LNT2 with a conversion ratio of 57.2% (4.7 g L-1). The synthesized LNT2 was further converted to LNnT by a reported beta-galactosidase (BgaD-D) in 8 h, with a conversion ratio of 17.3% (6.1 g L-1). These unique synthesis activities may make this enzyme a good candidate for the food industry.