Discovering a thermophilic xylanase and a β-xylosidase for synergistic degradation of corncob

Corncob, as an agricultural waste rich in hemicellulose, plays a crucial role in the effective utilization for biomass conversion and biorefinery. Here, we report a thermophilic GH11 xylanase (Xyn11B) and a β-xylosidase (Xyl43B) in the compost metatranscriptome database, with optimal temperature of 75 ℃ and 70 ℃, respectively, utilized for the synergistic degradation of corncob. Xyn11B consists of a catalytic domain (CD) and a carbohydrate-binding module 60 (CBM60). After deleting CBM60, the T_m of the remaining CD_Xyn increased by 2.4 ℃ and the half-life at 80 ℃ increased threefold. After 10-h hydrolysis on the NaOH-treated corncob using Xyn11B and CD_Xyn, the conversion yield reached 78 and 94 mg sugar/g raw corncob, respectively. Interestingly, in the absence of alkali pretreatment, the conversion yield can reach 107 mg sugar/g raw corncob using 0.1% (mg enzyme/mg corncob) Xyn11B, which is two times higher than that of CD_Xyn. Our analysis shows that CBM60 can reduce the non-catalytic adsorption to lignin, which increases the capability of the full-length enzyme to hydrolyze hemicellulose without alkali pretreatment. Furthermore, synergistic hydrolysis with both 0.1% Xyn11B and 0.1% Xyl43B considerably elevates the conversion yield to 296 mg sugar/g raw corncob, which is 2.8-fold higher than that achieved using Xyn11B alone, and comparable to the enzymatic effect observed with the combination of CD_Xyn and Xyl43B in alkali pretreatment. Our strategy demonstrates a good example of green hydrolysis of lignocellulosic biomass using enzymes without chemical pretreatment.