Highly alkali-stable and cellulase-free xylanases from Fusarium sp. 21: Heterologous expression, purification and biochemical comparison

Xylanases play an important role in the food, biobleaching and biofuel industries. Here, three new xylanases of the glycosyl hydrolase 11 (GH11) family, named Xyn11A, Xyn11B, and Xyn11C, from the fungus Fusarium sp. 21, were heterologously expressed in E. coli and characterized. These three xylanases displayed a strong specificity towards beechwood and corncob xylan, with no activity for other substrates such as CMC (carboxymethylcellulose), locust bean gum and pNPX (p-nitrophenyl-β-D-xylopyranoside). Xyn11A showed much a higher activity against corncob xylan, while Xyn11B and Xyn11C presented higher activities against beechwood xylan. Beechwood xylan hydrolysates produced by these three xylanases contained xylobiose (DP2), xylotriose (DP3) and xylooligosaccharides (XOS). As Xyn11A, Xyn11B and Xyn11C, have good pH stability and high substrate specificity, these might be widely utilized in pulp and paper biobleaching industries, wine and fruit juice clarification processes and xylooligosaccharide production.

木聚糖酶（Xylanases）在食品加工、生物漂白及生物燃料产业中发挥着关键作用。本研究从镰刀菌属菌株21（Fusarium sp. 21）中获得3个全新的糖苷水解酶11家族（Glycosyl Hydrolase 11, GH11）木聚糖酶，分别命名为Xyn11A、Xyn11B与Xyn11C，并将其在大肠杆菌（E. coli）中进行异源表达与功能表征。该3种木聚糖酶对山毛榉木聚糖与玉米芯木聚糖展现出极强的底物特异性，而对羧甲基纤维素（carboxymethylcellulose，CMC）、刺槐豆胶、对硝基苯基-β-D-吡喃木糖苷（p-nitrophenyl-β-D-xylopyranoside，pNPX）等其他底物均无催化活性。其中Xyn11A对玉米芯木聚糖的酶活显著更高，而Xyn11B与Xyn11C则对山毛榉木聚糖表现出更优的催化活性。经这3种木聚糖酶水解得到的山毛榉木聚糖水解产物中，含有木二糖（DP2）、木三糖（DP3）以及低聚木糖（XOS）。鉴于Xyn11A、Xyn11B与Xyn11C具备良好的pH稳定性与极高的底物特异性，它们有望被广泛应用于制浆造纸生物漂白、葡萄酒与果汁澄清工艺以及低聚木糖生产等领域。