Heterologous Expression of a New Acetyl Xylan Esterase from Aspergillus niger BE-2 and its Synergistic Action with Xylan-Degrading Enzymes in the Hydrolysis of Bamboo Biomass

Efficient utilization of plant biomass by enzymatic hydrolysis is currently studied worldwide but still faces enormous challenges because of the inability to break down lignocellulosic materials with high sugar yields and low enzyme dosage. Therefore, the synergistic action between various enzymes plays an important role in reaching this goal. The synergistic cooperation between a novel acetyl xylan esterase (heterologous expressed at high levels in this study) and four other xylan-degrading enzymes (reported previously) were performed in this study. The acetyl xylan esterase (AnAxe) gene was cloned from Aspergillus niger BE-2 and expressed in Pichia pastoris GS115. The deduced amino acid (aa) sequence consisted of 304-aa and included a 23-aa signal peptide and 281-aa mature protein. The AnAxe was extracellularly expressed with a molecular weight of ca. 31 kDa. The purified AnAxe exhibited maximal specific activity of 480.2 IU/mg at pH 7.0 and 40 °C and was still thermostable below 50 °C. The metal ions used in this study and EDTA showed a slight effect on the AnAxe. A significant synergistic effect was determined between AnAxe and the other four xylan-degrading enzymes, including endo-Beta-1,4-xylanases, Beta-xylosidases, alpha-L-arabinofurano-sidases, and alpha-glucuronidases, on the degradation of bamboo biomass. The highest degree of synergism was obtained between AnAxe and endo-Beta-1,4-xylanases/Beta-xylosidases.