Improvement of lactase secretion level by fusion expression with tag in Pichia pastoris.

Lactase of Bifidobacterium have potential application value in lactose hydrolysis and galactooligosaccharides production,due to its advantages of safety and highly catalysis efficiency.In this study,four protein tag genes,cherry,cbd(cellulose-binding domains),gst(glutathione S-transferase) and mbp(maltose-binding protein),were fused with the gene bg42-106m in vector pPIC9 by genetic technology,respectively.The recombinant plasmids were transformed into Pichia pastoris GS115,respectively.As a result,a high yield strain coexpressed with cherry gene was obtained.The secretion level of bG42-106M in medium achieved 7.42 U/mL,which was 290% higher compared with the wide type strain.However,the CBD,GST and MBP tags had no effect on improvement of expression and secretion level of bG42-106M.