Enzyme Science Programme (ESP), Department of Biochemistry and Microbiology, Rhodes University, Grahamstown 6140, Eastern Cape, South Africa.
Enzyme Science Programme (ESP), Department of Biochemistry and Microbiology, Rhodes University, Grahamstown 6140, Eastern Cape, South Africa.
Enzyme Microb Technol. 2019 Mar;122:74-81. doi: 10.1016/j.enzmictec.2018.12.010. Epub 2018 Dec 19.
Xylan, the most abundant hemicellulose in lignocellulosic biomass, requires a consortium of xylanolytic enzymes to achieve its complete de-polymerisation. As global interest in using xylan-containing lignocellulosic feedstocks for biofuel production increases, an accompanying knowledge on how to efficiently depolymerise these feedstocks into fermentable sugars is required. Since it has been observed that the same enzyme [i.e. an enzyme with the same EC (Enzyme Commission) classification] from different GH families can display different substrate specificities and properties, we evaluated GH10 (XT6) and 11 (Xyn2A) xylanase performance alone, and in combination, during xylan depolymerisation. Synergistic enhancement with respect to reducing sugar release was observed when Xyn2A at 75% loading was supplemented with 25% loading of XT6 for both beechwood glucuronoxylan (1.14-fold improvement) and wheat arabinoxylan (1.1-fold improvement) degradation. Following this, the optimised xylanase mixture was dosed with an oligosaccharide reducing-end xylanase (Rex8A) from either Bifidobacterium adolescentis or Bacillus halodurans for further synergistic enhancement. Dosing 75% of the xylanase mixture (Xyn2A:XT6 at 75:25%) with 25% loading of Rex8A led to an enhancement of reducing sugar (up to an 1.1-fold improvement) and xylose release (up to an 1.5-fold improvement); however, this effect was both xylan and Rex8A specific. Using thin layer chromatography, synergism appeared to be a result of the GH10 and 11 xylanases liberating xylo-oligomers that are preferred substrates of the processive Rex8As. Rex8As then hydrolysed xylo-oligomers to xylose - and xylobiose which was the preferred substrate for xylosidase, SXA. This likely explains why there was a significant improvement in xylose release in the presence of Rex8As. Here, it was shown that Rex8As are key enzymes in the efficient saccharification of hetero-xylan into xylose, a major component of lignocellulosic substrates.
木聚糖是木质纤维素生物质中最丰富的半纤维素，需要木聚糖酶的协同作用才能实现其完全解聚。随着全球对利用含木聚糖的木质纤维素饲料进行生物燃料生产的兴趣增加，人们对如何有效地将这些饲料解聚成可发酵糖的了解也随之增加。由于观察到来自不同 GH 家族的同一种酶（即具有相同 EC（酶委员会）分类的酶）可能具有不同的底物特异性和性质，因此我们单独评估了 GH10（XT6）和 11（Xyn2A）木聚糖酶的性能，以及它们在木聚糖解聚过程中的组合性能。当 Xyn2A 的负载量为 75%，并补充负载量为 25%的 XT6 时，观察到对于桦木木聚糖（提高 1.14 倍）和小麦阿拉伯木聚糖（提高 1.1 倍）的降解，还原糖释放均表现出协同增强。在此之后，用来自双歧杆菌或嗜盐杆菌的寡糖还原端木聚糖酶（Rex8A）对优化后的木聚糖酶混合物进行了加药，以进一步实现协同增强。用 25%的 Rex8A 处理 75%的木聚糖酶混合物（Xyn2A：XT6 为 75：25%）可提高还原糖（提高 1.1 倍）和木糖的释放（提高 1.5 倍）；然而，这种效果是木聚糖和 Rex8A 特异性的。通过薄层色谱法，协同作用似乎是 GH10 和 11 木聚糖酶释放出更偏好于过程性 Rex8As 的木寡糖的结果。然后，Rex8As 将木寡糖水解成木糖和木二糖，木二糖是木糖苷酶 SXA 的首选底物。这可能解释了为什么在 Rex8As 存在的情况下木糖的释放有显著提高。在这里，结果表明 Rex8As 是将异木聚糖高效糖化为木糖的关键酶，木糖是木质纤维素底物的主要成分。
