Protein Engineering of a Novel -Galactosidase from Thermus scotoductus for Efficient Synthesis of Lacto-N-Neotetraose from Chitin Powder

Jianyu Wang, Zhixuan Xiang, Dan Liu,Qiaojuan Yan,Shaoqing Yang,Zhengqiang Jiang


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A novel beta-galactosidase (TsGal48) from Thermus scotoductus was cloned, and the enzyme was biochemically characterized. TsGal48 catalyzed the synthesis of lacto-N-neotetraose (LNnT) from lactose via the transglycosylation reaction with a maximal yield of 20%, which is the highest yield for the synthesis of LNnT so far. To further improve the yield of LNnT, TsGal48 was successfully engineered by directed evolution and site-saturation mutagenesis. A mutated beta-galactosidase (mTsGal48) was selected and characterized. mTsGal48 produced LNnT with a yield of 27.7 g/L, which is 1.4-fold higher than that of TsGal48 (19.7 g/L). Then, a developed strategy for LNnT synthesis from chitin powder was provided in a 30 L bioreactor. The reaction process included chitin powder hydrolysis, lacto-N-triose II (LNT2) synthesis, and LNnT synthesis. The reaction time was reduced from 44 to 17 h in chitin powder hydrolysis and LNT2 synthesis. The content of LNnT was up to 25 g/L in the multienzyme system. The green and efficient route may be suitable for large-scale production of LNnT from chitin powder.
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Key words
beta-galactosidase,Thermus scotoductus,protein engineering,chitin,lacto-N-neotetraose
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