Two xylose-tolerant GH43 bifunctional β-xylosidase/α-arabinosidases and one GH11 xylanase from Humicola insolens and their synergy in the degradation of xylan.

Two β-xylosidases of family 43 (Xyl43A and Xyl43B) and one xylanase of family 11 (Xyn11A) were identified from the genome sequence of Humicola insolens Y1, and their gene products were successfully expressed in heterologous hosts. The optimal activities of the purified Xyl43A, Xyl43B, and Xyn11A were found at pH 6.5-7.0 and 50-60 °C. They were stable over a pH range of 5.0-10.0 and temperatures of 50 °C and below. Xyl43A and Xyl43B had the activities of β-xylosidase, α-arabinosidase and xylanase, and showed xylose tolerance up to 79 and 292 mM, respectively. Xyn11A and Xyl43A or Xyl43B showed significant synergistic effects on the degradation of various xylans, releasing more reduced sugars (up to 1.29 folds) by simultaneous or sequential addition. This study provides several enzymes for synergistic degradation of xylan and contributes to the formulation of optimised enzyme mixtures for the efficient hydrolysis of plant biomass.