Lignin biodegradation has been extensively studied in white-rot fungi, which largely belong to order Polyporales. Among the enzymes that wood-rotting polypores secrete, lignin peroxidases (LiPs) have been labeled as the most efficient. Here, we characterize a similar enzyme (ApeLiP) from a fungus of the order Agaricales (with ~13,000 described species), the soil-inhabiting mushroom Agrocybe pediades. X-ray crystallography revealed that ApeLiP is structurally related to Polyporales LiPs, with a conserved heme-pocket and a solvent-exposed tryptophan. Its biochemical characterization shows that ApeLiP can oxidize both phenolic and non-phenolic lignin model-compounds, as well as different dyes. Moreover, using stopped-flow rapid spectrophotometry and 2D-NMR, we demonstrate that ApeLiP can also act on real lignin. Characterization of a variant lacking the above tryptophan residue shows that this is the oxidation site for lignin and other high redox-potential substrates, and also plays a role in phenolic substrate oxidation. The reduction potentials of the catalytic-cycle intermediates were estimated by stopped-flow in equilibrium reactions, showing similar activation by H₂O₂, but a lower potential for the rate-limiting step (compound-II reduction) compared to other LiPs. Unexpectedly, ApeLiP was stable from acidic to basic pH, a relevant feature for application considering its different optima for oxidation of phenolic and nonphenolic compounds.

中文翻译：

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蘑菇木质素过氧化物酶：从结构-功能到降解能力

木质素生物降解在白腐真菌中得到了广泛的研究，白腐真菌主要属于多孔菌目。在木材腐烂多孔菌分泌的酶中，木质素过氧化物酶 (LiPs) 被认为是最有效的。在这里，我们表征了一种类似的酶 (ApeLiP)，来自一种蘑菇目真菌（具有约 13,000 个描述的物种），即栖息在土壤中的蘑菇Agrocybe pediades. X 射线晶体学显示 ApeLiP 在结构上与 Polyporales LiPs 相关，具有保守的血红素袋和暴露于溶剂的色氨酸。其生化特性表明 ApeLiP 可以氧化酚类和非酚类木质素模型化合物，以及不同的染料。此外，使用停流快速分光光度法和 2D-​​NMR，我们证明 ApeLiP 也可以作用于真正的木质素。缺乏上述色氨酸残基的变体的表征表明，这是木质素和其他高氧化还原电位底物的氧化位点，也在酚类底物氧化中起作用。催化循环中间体的还原电位通过平衡反应中的停止流动来估计，显示出类似的 H ₂ O ₂活化，但与其他 LiP 相比，限速步骤（化合物 II 还原）的潜力较低。出乎意料的是，ApeLiP 在从酸性到碱性 pH 值范围内都是稳定的，这是考虑到其对酚类和非酚类化合物氧化的不同优化的应用相关特征。