The discovery of lytic polysaccharide monooxygenases (LPMO) has changed our perspective on enzymatic degradation of plant biomass. Through an oxidative mechanism, these enzymes are able to cleave and depolymerize various polysaccharides, acting not only on crystalline substrates such as chitin and cellulose, but also on other polysaccharides, such as xyloglucan, glucomannan and starch. Despite their widespread use, uncertainties related to substrate specificity and stereospecificity, the nature of the co-substrate, in-process stability, and the nature of the optimal reductant challenge their exploitation in biomass processing applications. In this work, we studied the properties of a novel fungal LPMO from the thermophilic fungus Thielavia australiensis, TausLPMO9B. Heterologous expression of TausLPMO9B in Aspergillus niger yielded a glycosylated protein with a methylated N-terminal histidine showing LPMO activity. High sequence identity of the AA9 domain to that of MtLPMO9B (MYCTH_80312) from Myceliophthora thermophila (84%) indicated strictly C1-oxidizing activity on cellulose, which was confirmed experimentally by the analysis of products released from cellulose using HPAEC. The enzyme was stable and active at a pH ranging from 4 to 6, thus matching the conditions commonly used in industrial biomass processing, where a low pH (between 4 and 5) is used due to the pH-optima of commercial cellulases and a desire to limit microbial contamination. While the oxidative cleavage of phosphoric acid swollen cellulose (PASC) by TausLPMO9B was boosted by the addition of H2O2 as a co-substrate, this effect was not observed during the saccharification of acid pretreated corn stover. This illustrates key differences between the lab-scale tests with artificial, lignin-free substrates and industrial settings with lignocellulosic biomass as substrate.

中文翻译：

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从AA9 LPMO的表征土生梭australiensis，TAUS LPMO9B，工业相关的木质纤维素糖化条件下

裂解多糖单加氧酶（LPMO）的发现改变了我们对植物生物质酶促降解的观点。通过氧化机理，这些酶能够裂解和解聚各种多糖，不仅作用于几丁质和纤维素等结晶底物，还作用于其他多糖，如木葡聚糖，葡甘露聚糖和淀粉。尽管它们被广泛使用，但是与底物特异性和立体特异性，共底物的性质，过程中的稳定性以及最佳还原剂的性质有关的不确定性挑战了它们在生物质加工应用中的开发。在这项工作中，我们研究了一种嗜热真菌澳大利亚产Thielavia australiensis的新型真菌LPMO TausLPMO9B的特性。TausLPMO9B在黑曲霉中的异源表达产生具有甲基化的N端组氨酸的糖基化蛋白，显示LPMO活性。AA9结构域与嗜热毁丝霉菌MtLPMO9B（MYCTH_80312）的高度序列同一性（84％）表明对纤维素具有严格的C1氧化活性，这通过使用HPAEC分析从纤维素中释放出的产物进行了实验证实。该酶在4至6的pH范围内稳定且有活性，因此可与工业生物质加工中通常使用的条件相匹配，由于商业纤维素酶的pH最佳值和期望，该条件下使用的pH较低（4至5之间）限制微生物污染。尽管通过添加H2O2作为共底物来促进TausLPMO9B对磷酸溶胀纤维素（PASC）的氧化裂解，在酸预处理的玉米秸秆的糖化过程中未观察到这种作用。这说明了采用人造无木质素底物的实验室规模测试与以木质纤维素生物质为底物的工业环境之间的关键区别。