Production of Lacto-N-triose II and Lacto-N-neotetraose from Chitin by a Novel β-N-Acetylhexosaminidase Expressed in Pichia pastoris

An unstudied beta-N-acetylhexosaminidase (HaHex74) from Halojerula sp. was expressed in Pichia pastoris. HaHex74 displayed the highest similarity (61%) with a beta-N-acetylhexosaminidase from an uncultured Bacteroidetes bacterium. The recombinant P. pastoris secreted the highest enzyme activity of 3500 U mL(-1) after incubation for 168 h in a 5-L fermenter. HaHex74 showed an optimal pH and temperature of 6.5 and 45 degrees C, respectively. HaHex74 displayed high transglycosylation activity, showing a maximal conversion ratio of 13.1% (7.1 g L-1), which is by far the highest conversion ratio for the synthesis of lacto-N-triose II (LNT2) from N-acetyl chitobiose. Thus, an efficient strategy for the production of high value-added LNT2 and lacto-N-neotetraose (LNnT) from chitin by enzyme cocktails was first developed in a 5-L reactor. As a result, the contents of LNT2 and LNnT reached 8.6 and 2.0 g respectively. The novel and environmentally friendly bioprocess may greatly promote the production of LNT2 and LNnT from chitin.