Characterization of a thermostable alkaline feruloyl esterase from Alternaria alternata and its synergism in dissolving pulp production

Abstract

Feruloyl esterases are of great interest due to their enhancement of the accessibility of xylanase to the backbone of xylan by debranching the side chain decoration of hemicellulose. Alternaria alternata is known for its ability to secrete abundant xylanolytic enzymes, but the pathogenicity greatly limits the production of feruloyl esterase. Herein, we first cloned the thermostable alkaline faeB gene of A. alternata and successfully expressed in Pichia pastoris GS115. The recombinant AaFAEB was purified to homogeneity and the specific activity of purified AaFAEB was 18.39 ± 0.26 U/mg. The optimal temperature and pH for AaFAEB was about 45 °C and 7.0. The recombinant AaFAEB showed excellent thermal stability at 45–60 °C and can retain 71.31% of the maximum activity after incubation for 1 h at 60 °C. In addition, it exhibits broad pH stability and can retain approximately 68% of its maximum activity at pH 10.0 for 2 h. The substrate specificity profiling and phylogenetic analysis confirmed that AaFAEB is a type B FAE. Pretreatment by AaFAEB can synergistically promote the enhancement of the Fock reactivity of dissolving pulp by endoglucanase. In addition, it can increase the α-cellulose content by the cooperation with xylanase, thereby further improving the quality of dissolving pulp. The present results suggested that the recombinant AaFAEB is a promising candidate for dissolving pulp production and biorefining industry.