Cloning, Expression and Characterization of a Novel Fructosyltransferase from Aspergillus oryzae ZZ-01 for the Synthesis of Sucrose 6-Acetate

A 1521 bp gene encoding for a novel fructosyltransferase from Aspergillus oryzae ZZ-01 (AoFT) has been amplified by RACE and TAIL PCR, and functionally overexpressed in Escherichia coli BL 21-CodonPlus (DE3)-RIL. The recombinant A. oryzae ZZ-01 fructosyltransferases (r-AoFT) was purified to homogeneity after Ni-NTA affinity and Superdex-200 gel filtration chromatography. SDS-PAGE analysis of the purified r-AoFT revealed a single protein band with an apparent molecular mass of 60.0 kDa. The r-AoFT enzyme exhibited its optimal activity at 55 °C and pH 5.5, and maintained about 63% of its activity even after 60 min of treatment at 60 °C. The addition of Mg2+ led to an increase in the activity of r-AoFT, whereas Zn2+, Cu2+ and Ni2+ led to a reduction in its activity. Six site-directed mutants of r-AoFT (D39A, D164A, E216A, N38L, S99A and Y282A) were constructed and characterized biochemically. The N38L, S99A and Y282A mutants had lower Km and higher Vmax values than the wild-type enzyme, highlighting their higher binding affinity for the substrates. These results therefore suggest that r-AoFT could be used for the enzymatic synthesis of Suc6A from sucrose and glucose 6-acetate.