Human pathogenic and commensal bacteria have evolved the ability to scavenge host-derived sialic acids and subsequently degrade them as a source of nutrition. Expression of the Escherichia coli yjhBC operon is controlled by the repressor protein nanR, which regulates the core machinery responsible for the import and catabolic processing of sialic acid. The role of the yjhBC encoded proteins is not known-here, we demonstrate that the enzyme YjhC is an oxidoreductase/dehydrogenase involved in bacterial sialic acid degradation. First, we demonstrate in vivo using knockout experiments that YjhC is broadly involved in carbohydrate metabolism, including that of N-acetyl-d-glucosamine, N-acetyl-d-galactosamine and N-acetylneuraminic acid. Differential scanning fluorimetry demonstrates that YjhC binds N-acetylneuraminic acid and its lactone variant, along with NAD(H), which is consistent with its role as an oxidoreductase. Next, we solved the crystal structure of YjhC in complex with the NAD(H) cofactor to 1.35 Å resolution. The protein fold belongs to the Gfo/Idh/MocA protein family. The dimeric assembly observed in the crystal form is confirmed through solution studies. Ensemble refinement reveals a flexible loop region that may play a key role during catalysis, providing essential contacts to stabilize the substrate-a unique feature to YjhC among closely related structures. Guided by the structure, in silico docking experiments support the binding of sialic acid and several common derivatives in the binding pocket, which has an overall positive charge distribution. Taken together, our results verify the role of YjhC as a bona fide oxidoreductase/dehydrogenase and provide the first evidence to support its involvement in sialic acid metabolism.

中文翻译：

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关于大肠杆菌YjhC的结构和功能：一种涉及细菌唾液酸代谢的氧化还原酶。

人类致病菌和共生细菌已经进化出清除宿主来源唾液酸并随后降解它们作为营养来源的能力。大肠杆菌yjhBC操纵子的表达受阻遏蛋白nanR的控制，后者可调节负责唾液酸进口和分解代谢过程的核心机制。yjhBC编码的蛋白质的作用尚不清楚-在这里，我们证明了酶YjhC是参与细菌唾液酸降解的氧化还原酶/脱氢酶。首先，我们使用敲除实验在体内证明YjhC广泛参与碳水化合物的代谢，包括N-乙酰基-d-氨基葡萄糖，N-乙酰基-d-半乳糖胺和N-乙酰基神经氨酸。差示扫描荧光法证明YjhC结合N-乙酰神经氨酸及其内酯变体，以及NAD（H），这与其作为氧化还原酶的作用是一致的。接下来，我们将YjhC的晶体结构与NAD（H）辅因子复合解析为1.35Å的分辨率。蛋白质折叠属于Gfo / Idh / MocA蛋白质家族。通过溶液研究证实了以晶体形式观察到的二聚体组装。整体精修显示了一个灵活的环区，该环区在催化过程中可能起关键作用，提供必要的触点来稳定底物-紧密相关结构中YjhC的独特功能。在该结构的指导下，计算机对接实验支持唾液酸与结合口袋中几种常见衍生物的结合，该结合口袋具有整体正电荷分布。在一起