Over Expression and Its Enzymatic Properties of Polygalacturonase in Aspergillus niger

The recombinant strains of Aspergillus niger with high expression of polygalacturonase were constructed by means of genetic engineering. The activity and enzymatic properties of the recombinant enzyme were studied to better realize the important role of polygalacturonase in food processing,feed production and wastewater treatment. The mature peptide coding sequence(1232 bp)of polygalacturonase gene pgaB was amplified from the pectinase producing strain Aspergillus niger GJ-1.glaA multi-copy strong promoter and signal peptide were integrated to construct Aspergillus niger expression vector pSZHG6RS-pgaB,and Aspergillus niger recombinant strain of polygalacturonase was obtained by agrobacterium-mediated transformation of Aspergillus niger. Polyacrylamide gel electrophoresis(SDS-PAGE)detection results showed that the target protein size was about 38 kDa. The maximum enzyme activity reached 4617.8 U·mL^-1 at the 10th day of fermentation. The enzymatic properties results showed that the optimal temperature was 50℃ and the thermal stability was poor at high temperature. The optimal pH was 5.0 while it had strong alkaline tolerance. Ca²⁺,Fe²⁺ and Fe³⁺ all had certain activation effects on recombinant enzymes. The catalytic capacity of the recombinant enzyme was different for different substrates. The higher the degree of methylation,the weaker the degradation ability of enzyme was. The catalytic capacity of the recombinant enzyme was the strongest for the non-methylated polygalacturonic acid with a DE value of 33.04%,while the degradation ability of the enzyme was weaker with higher methylation degree. The recombinant strain had high enzyme production activity and had clear industrial prospects.