Understanding Laccase–Ionic Liquid Interactions toward Biocatalytic Lignin Conversion in Aqueous Ionic Liquids
Understanding Laccase–Ionic Liquid Interactions toward Biocatalytic Lignin Conversion in Aqueous Ionic Liquids
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DOI：
10.1021/acssuschemeng.9b02151
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发表时间：
2019-09
影响因子：
8.4
通讯作者：
Joseph C. Stevens;Lalitendu Das;Justin K. Mobley;Shardrack O Asare;B. Lynn;D. Rodgers;Jian Shi
中科院分区：
文献类型：
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作者：
Joseph C. Stevens;Lalitendu Das;Justin K. Mobley;Shardrack O Asare;B. Lynn;D. Rodgers;Jian Shi
木质素是植物物质的重要组分;然而，当进行预处理过程时，它也是木质纤维素生物质的降解的主要原因。木质素作为来自造纸和制浆工业以及纤维素生物炼制的废物大量产生。因此，木质素的价值稳定对于成功实施纤维素生物燃料至关重要。为此，我们研究了三种离子液体（ILs）和木质素分解酶漆酶之间的相互作用，以生物催化木质素转化为芳香族单体。漆酶在10%二乙胺硫酸氢盐（[DEA][HSO_4]）中表现出最小的活性损失。漆酶的V_（max）和K_（max）随IL浓度的变化表明，[DEA][HSO_4]是一种非竞争性抑制剂，而[Ch][Lys]和[C_（max）C_（max）Im][OAc]是混合抑制剂。对接模拟表明，[Ch][Lys]和[C → C → Im][OAc]破坏了导致活性位点的残基。用β-O-4′连接的模型二聚体进行的实验表明，漆酶在[C]-[C]-[Im]-[Ac]和[Ch]-[Lys]中需要2，2 ′-连氮基-双（3-乙基苯并噻唑啉-6-磺酸）（ABTS）的存在来氧化β-O-4′连接，导致模型二聚体的聚合。用漆酶、ABTS和水性离子液体（AILs）处理的碱性木质素显示出很少的结构变化，尽管木质素部分溶解并转化为降解产物。从碱木质素中得到的主要产物是香草醛、乙酰香草酮、香草醛和乙酰香草酮。本研究的结果首次深入解释了漆酶与AIL之间为木质素增值而发生的相互作用。
Lignin is a crucial component of plant matter; however, it is also largely responsible for the recalcitrance of lignocellulosic biomass when subjected to pretreatment processes. Lignin is generated in large volumes as a waste product from paper and pulping industry as well as cellulosic biorefineries. As a result, lignin valorization is critical to the successful implementation of cellulosic biofuels. To this end, we investigated interactions between three ionic liquids (ILs) and the lignolytic enzyme laccase toward biocatalytic lignin conversion to aromatic monomers. Laccase exhibited minimal loss of activity in 10% diethylamine hydrogensulfate ([DEA][HSO₄]). Changes in Vₘₐₓ and Kₘ of laccase with respect to IL concentration indicate that [DEA][HSO₄] is a noncompetitive inhibitor, whereas cholinium lysinate ([Ch][Lys]) and [C₂C₁Im][OAc] are mixed inhibitors. Docking simulations suggested that [Ch][Lys] and [C₂C₁Im][OAc] disrupt residues leading to the active site. Experiments with a β-O-4′ linked model dimer revealed that laccase in [C₂C₁Im][OAc] and [Ch][Lys] requires the presence of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) to oxidize the β-O-4′ linkage, leading to polymerization of the model dimer. Alkaline lignin treated with laccase, ABTS, and the aqueous ILs (AILs) showed few structural changes, although the lignin was partially solubilized and converted to degradation products. The major products obtained from alkaline lignin were vanillin, acetosyringone, syringaldehyde, and acetovanillone. The results of this study provide, for the first time, an in-depth explanation of the interactions between laccase and AILs for the purpose of lignin valorization.