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Enzymatic demethylation of lignin for potential biobased polymer applications

机译：木质素的酶促去甲基化用于潜在的生物化聚合物应用

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Lignin is a highly methylated, recalcitrant biopolymer available aplenty in nature, and is highly heteropolymer in nature, but yet it has been an under-utilized biopolymer. Modifying it chemically, biologically or enzymatically could render it a good candidate for phenol formaldehyde resin or into fine chemicals, fuels, and plastics applications. Lignin demethylation is facilitated by the enzymes called the O-demethylases, which are able to strip-off of the -OCH3 group in lignin, that give rise to the more widely accessible phenolic hydroxyls groups. Biological demethylation of lignins can be accomplished by means of the microorganisms, such as the white-rot, soft-rot and brown-rot fungi, besides some species of bacteria. Although the enzymes responsible for the lignin demethylation process have not been identified and purified adequately, it is perhaps possible that the O-demethylases, which have the ability to remove the O-methyl groups at the C-3 and (or) C-4 positions of the benzyl ring of low molecular weight lignin-like model compounds (LMCs) and lignin makes them the suitable candidate. These LMCs resemble the aromatic moieties inherent in the molecular structure of lignins, such as the vanillate, syringate, and veratrate. Thus, these enzymes are known as vanillate-O-demethylases, syringate O-demethylases, veratrate O-demethylases and Tetrahydrofolate (THF)-dependent O-demethylase (LigM), respectively. Whereas, some ligninolytic enzymes are known to cause damage to the structure of lignins (e.g., laccases, manganese-dependent peroxidase and lignin peroxidases). The O-demethylase enzymes are believed to be capable of removing the O-methyl groups from the lignins without affecting the complex backbone structure of the lignins. The mechanism of action of O-demethylases on lignin degradation is still largely unexplored, and their ability to remove the O-methyl groups from lignins has not been elucidated sufficiently. In this review, the recent advances made on the molecular approaches in the lignin demethylation (O-demethylases and ligninolytic enzymes), degradation and the probable strategies to tone up the lignin quality have been discussed in detail. The demethylation process of lignins by means of enzymes is envisaged to open up new vistas for its application as a biopolymer in various bioprocess and biorefinery process. (C) 2019 British Mycological Society. Published by Elsevier Ltd. All rights reserved.
机译：木质素是一种高度甲基化的顽皮的生物聚合物，本质上是高度的，并且具有高度杂化聚合物本质上，但它已经是一种利用的生物聚合物。化学，生物学或酶促改性它可以使其成为酚醛树脂或精细化学品，燃料和塑料应用的良好候选者。通过称为O-去甲基酶的酶促进木质素去甲基化，其能够在木质素中脱离-OCH3基团，其产生更广泛可接近的酚羟基。除了一些细菌之外，可以通过微生物，例如白腐，软腐肉和棕腐真菌的微生物来实现荔枝的生物去甲基化。虽然尚未充分鉴定并纯化负责木质素去甲基化过程的酶，但是O-脱甲基酶可能能够除去C-3和（或）C-4中的O-甲基低分子量木质素样模型化合物（LMC）和木质素的苄基环的位置使它们成为合适的候选者。这些LMC类似于木质素的分子结构固有的芳族部分，例如香毒，注射器和钙质。因此，这些酶被称为香草酸盐-O-去甲基酶，注射器O-脱甲基酶，酸酯O-脱甲基酶和四氢溶胶（THF） - 依赖性O-脱甲基酶（Ligm）。然而，已知一些木质素溶解酶导致木质素的结构损伤（例如，漆酶，酰胺类过氧化物酶和木质素过氧化物酶）。据信O-去甲基酶酶能够从木质素中除去O-甲基而不影响木质素的复杂骨干结构。 O-脱甲基酶对木质素降解的作用机制仍然很大程度上是未探测的，并且它们除去来自木质素的O-甲基的能力尚未充分阐明。在本综述中，详细讨论了对木质素去甲基化（O-脱甲基酶和木质素溶解的酶），降解和调整木质素质量的分子方法的最新进展。设想通过酶的木质素的去甲酰化过程，以将其应用作为各种生物过程和生物料理过程中的生物聚合物开辟了新的vistas。 （c）2019年英国Mycological社会。 elsevier有限公司出版。保留所有权利。

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