Glycosyltransferase mutant, and method for catalytic synthesis of rebaudioside m using glycosyltransferase mutant

A method for synthesizing rebaudioside M using a glycosyltransferase mutant, wherein the glycosyltransferase mutant is a G87D, S147D, S195Q, L200Y, S285W, or G378P mutant of the glycosyltransferase of SEQ ID NO:

• 1, the method comprising the following steps:
• 1) cloning a coding gene for said glycosyltransferase UGT76G1 mutant and a coding gene for sucrose synthase (SuSy) into an expression vector to obtain a recombinant plasmid;
• 2) transforming the recombinant plasmid into Escherichia coli (E. coli) BL21 (DE3) to obtain a recombinant strain, wherein the glycosyltransferase mutant and the SuSy are co-expressed in the recombinant strain;
• 3) inoculating the recombinant strain into an Luria-Bertani (LB) liquid medium, and adding an inducer into the LB liquid medium to induce an expression;
• centrifuging a resulting bacterial solution at 4° C., collecting a resulting bacterial precipitate, and resuspending the bacterial precipitate with a predetermined buffer;
• and subjecting a resulting bacterial suspension to an ultrasonication, centrifuging a resulting ultrasonication system, and collecting a first resulting supernatant, wherein the first resulting supernatant is a crude enzyme solution;
• and
• 4) adding rebaudioside E or rebaudioside D as a substrate, sucrose, and the crude enzyme solution to a catalytic reaction system, and allowing a reaction at a predetermined temperature;
• and
• collecting a sample, inactivating the sample at 95° C., centrifuging an inactivated sample, and collecting a second resulting supernatant, wherein the second resulting supernatant is the rebaudioside M.