Expression, purification and characterization of a recombinant Lipomyces starkey dextranase in Pichia pastoris

The DEX gene encoding an extracellular dextranase from Lipomyces starkeyi was cloned into vector pPIC9k-His6 and was expressed in Pichia pastoris GS115 strain under the control of AOX1 promoter. After 107 h of the 5 L-scaled fermentation, wet cells weight of the recombinant P. pastoris Mut+ strain reached to 588.6 g/L, and the concentration of dextranase and enzyme activity in the supernatant were 0.46 g/L and 83900 U/L, respectively. The activity of dextranase was improved 17.56-fold by cation-exchange chromatography only with a final yield of 71.61% and the specific activity of the purified enzyme was 181.96 U/mg. The purified dextranase, analyzed by SDS–PAGE and Western blotting, showed only one homogeneous band. Then the factors affecting the dextranase activity were evaluated. The optimal temperature and pH was 30 °C and pH 4.5, respectively. Metal ions Al3+, Cu2+, Fe3+, and SDS could completely inhibit the enzyme activity, whereas Mg2+ enhanced 145% of the enzyme activity. These characters are much different from what was previously reported for the L. starkeyi dextranase that was either expressed in S. cerevisiae or purified from natural L. starkeyi.