Discovery of LPMO activity on hemicelluloses shows the importance of oxidative processes in plant cell wall degradation
Discovery of LPMO activity on hemicelluloses shows the importance of oxidative processes in plant cell wall degradation
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DOI：
10.1073/pnas.1323629111
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发表时间：
2014-04-29
影响因子：
11.1
通讯作者：
Westereng, Bjorge
中科院分区：
文献类型：
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作者：
Agger, Jane W.;Isaksen, Trine;Westereng, Bjorge
最近发现的溶解性多糖单加氧酶（LPMO）已知进行几丁质和纤维素中的糖苷键的氧化裂解，从而提高众所周知的水解解聚酶的活性。由于生物质降解微生物倾向于产生过多的LPMO，并且考虑到植物细胞壁的复杂性和共聚性质，已经推测一些LPMO可能作用于其他底物，特别是束缚于纤维素微纤维的半纤维素。我们证明，来自粗糙脉孢菌的LPMO，NcLPMO 9C，确实降解各种半纤维素，特别是木葡聚糖。使用基于聚糖微阵列的筛选方法检测碳水化合物活性酶的底物特异性发现了这种活性，并使用确定的寡聚半纤维素、分离的聚合半纤维素和细胞壁进一步探索。使用高效阴离子交换色谱和多维质谱分析NcLPMO9C产生的产物。我们表明，NcLPMO9C产生氧化产物从各种基板，其产品的配置文件不同的水解酶作用于相同的基板。该酶特别作用于木葡聚糖的葡萄糖主链，在几乎所有位置接受各种取代（木糖、半乳糖）。因为木葡聚糖与纤维素的连接阻碍了后者的解聚，所以可能存在于目前商业纤维素酶混合物中的LPMO的有益效果部分是由于迄今未检测到的LPMO对柠檬酸半纤维素结构的活性。
The recently discovered lytic polysaccharide monooxygenases (LPMOs) are known to carry out oxidative cleavage of glycoside bonds in chitin and cellulose, thus boosting the activity of well-known hydrolytic depolymerizing enzymes. Because biomass-degrading microorganisms tend to produce a plethora of LPMOs, and considering the complexity and copolymeric nature of the plant cell wall, it has been speculated that some LPMOs may act on other substrates, in particular the hemicelluloses that tether to cellulose microfibrils. We demonstrate that an LPMO from Neurospora crassa, NcLPMO9C, indeed degrades various hemicelluloses, in particular xyloglucan. This activity was discovered using a glycan microarray-based screening method for detection of substrate specificities of carbohydrate-active enzymes, and further explored using defined oligomeric hemicelluloses, isolated polymeric hemicelluloses and cell walls. Products generated by NcLPMO9C were analyzed using high performance anion exchange chromatography and multidimensional mass spectrometry. We show that NcLPMO9C generates oxidized products from a variety of substrates and that its product profile differs from those of hydrolytic enzymes acting on the same substrates. The enzyme particularly acts on the glucose backbone of xyloglucan, accepting various substitutions (xylose, galactose) in almost all positions. Because the attachment of xyloglucan to cellulose hampers depolymerization of the latter, it is possible that the beneficial effect of the LPMOs that are present in current commercial cellulase mixtures in part is due to hitherto undetected LPMO activities on recalcitrant hemicellulose structures.