Tannery effluent waste comprises various potentially toxic metals, including chromium (Cr) with varying acute or chronic toxicity. Cr(VI) is known to be a category‐A carcinogen. Reduction of toxic Cr(VI) to Cr(III), which has lesser bioavailability, is one of the mechanisms used by many microbes to withstand Cr(VI) toxicity in the contaminated effluents. Oxidoreductase (OXRs) reduces toxic Cr(VI) to Cr(III); hence a thorough understanding of the OXRs is important for developing a suitable strategy to minimize Cr(VI) toxicity. Therefore, the OXR‐encoding genes were sequenced using metagenomic DNA shotgun sequencing from the tannery effluent‐contaminated soil. Six OXR‐encoding genes were expressed in Escherichia coli, and OXR activity was confirmed by in situ quantitative assays. The six proteins were subjected to phylogenetic and evolutionary analysis. Further, detailed structural analysis of the two OXRs, namely, OXR3 and OXR8 with lowest and highest activity respectively, were investigated in silico for structural characteristics. The results revealed that both the proteins were soluble FMN‐linked oxidoreductases. Eight conserved active site residues (Pro24, Thr26, Ala59, Tyr139, His178, Tyr180, His219, Tyr221, Arg269, and Lys360) in the enzyme OXR3 were predicted. Similarly, nine conserved active site residues (Pro20, Thr22, Ala55, Glu97, His191, Tyr193, Arg241, Cys334, and Arg335) were predicted in OXR8. The tertiary structure of OXR8 was an aldolase TIM barrel structure, like Thermus scotoductus chromate reductase. Docking with FMN revealed the involvement of all the nine predicted active site residues in FMN binding with Pro20, Thr22, and Cys334 as the most important ones.

中文翻译：

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对来自制革废水污染土壤宏基因组的铬还原 OXR 基因进行计算机分析

制革厂废水含有各种潜在有毒金属，包括具有不同急性或慢性毒性的铬 (Cr)。Cr(VI) 已知是 A 类致癌物。将有毒的 Cr(VI) 还原为生物利用度较低的 Cr(III) 是许多微生物用来抵抗受污染废水中 Cr(VI) 毒性的机制之一。氧化还原酶 (OXR) 将有毒的 Cr(VI) 还原为 Cr(III)；因此，全面了解 OXR 对于制定适当的策略以最大限度地减少 Cr(VI) 毒性非常重要。因此，使用宏基因组 DNA 鸟枪法测序对制革厂废水污染的土壤中的 OXR 编码基因进行了测序。六个 OXR 编码基因在大肠杆菌，并通过原位定量测定证实了 OXR 活性。对这六种蛋白质进行了系统发育和进化分析。此外，还通过计算机研究了两种 OXR（即分别具有最低和最高活性的 OXR3 和 OXR8）的详细结构分析，以了解其结构特征。结果表明，这两种蛋白质都是可溶性 FMN 连接氧化还原酶。预测了酶 OXR3 中的 8 个保守活性位点残基（Pro24、Thr26、Ala59、Tyr139、His178、Tyr180、His219、Tyr221、Arg269 和 Lys360）。同样，在 OXR8 中预测了 9 个保守的活性位点残基（Pro20、Thr22、Ala55、Glu97、His191、Tyr193、Arg241、Cys334 和 Arg335）。OXR8的三级结构是醛缩酶TIM桶结构，如暗角栖热菌铬酸还原酶。与 FMN 对接揭示了所有九个预测的活性位点残基都参与了 FMN 与 Pro20、Thr22 和 Cys334 的结合，是最重要的残基。