Biodegradation of polyethylene (PE) plastics is environmentally friendly. To obtain the laccases that can efficiently degrade PE plastics, we generated 9 ancestral laccases from 23 bacterial three-domain laccases through ancestral sequence reconstruction. The optimal temperatures of the ancestral laccases were between 60 °C-80 °C, while their optimal pHs were at 3.0 or 4.0. Without substrate pretreatment and mediator addition, all the ancestral laccases can degrade low-density polyethylene (LDPE) films at pH 7.0 and 60 °C. Among them, Anc52, which shared low sequence identity (18 %−41.7 %) with the reported PE-degrading laccases, was the most effective for LDPE degradation. After the catalytic reactions at 90 °C for 14 h, Anc52 (0.2 mg/mL) induced clear wrinkles and deep pits on the PE film surface detected by scanning electron microscope, and its carbonyl and hydroxyl indices reached 2.08 and 2.42, respectively. Then, we identified the residues 203 and 288 critical for PE degradation through site-directed mutation on Anc52. Moreover, Anc52 be activated by heat treatment (60 °C and 90 °C) at pH 7.0, which gave it a high catalytic efficiency (/= 191.73 mM·s) and thermal stability (half-life at 70 °C = 13.70 h). The ancestral laccases obtained here could be good candidates for PE biodegradation.

中文翻译：

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原核三结构域漆酶的祖先序列重建可有效降解聚乙烯


聚乙烯（PE）塑料的生物降解性是环保的。为了获得能够高效降解PE塑料的漆酶，我们通过祖先序列重建，从23个细菌三域漆酶中生成了9个祖先漆酶。祖先漆酶的最适温度在 60°C-80°C 之间，而它们的最适 pH 为 3.0 或 4.0。在不进行底物预处理和添加介体的情况下，所有祖先漆酶都可以在 pH 7.0 和 60 °C 下降解低密度聚乙烯 (LDPE) 薄膜。其中，Anc52 与报道的 PE 降解漆酶序列同一性较低 (18%−41.7%)，对 LDPE 降解最有效。在90°C催化反应14小时后，扫描电镜观察到Anc52（0.2mg/mL）在PE薄膜表面产生了明显的皱纹和深凹坑，其羰基和羟基指数分别达到2.08和2.42。然后，我们通过对 Anc52 进行定点突变，鉴定出对 PE 降解至关重要的残基 203 和 288。此外，Anc52 在 pH 7.0 下通过热处理（60 °C 和 90 °C）被激活，这使其具有较高的催化效率（l= 191.73 mM·s）和热稳定性（70 °C 下的半衰期= 13.70 h） ）。这里获得的祖先漆酶可能是 PE 生物降解的良好候选者。