Cysteine dioxygenase (CDO) plays an essential role in sulfur metabolism by regulating homeostatic levels of cysteine. Human CDO contains a post-translationally generated Cys93–Tyr157 cross-linked cofactor. Here, we investigated this Cys–Tyr cross-linking by incorporating unnatural tyrosines in place of Tyr157 via a genetic method. The catalytically active variants were obtained with a thioether bond between Cys93 and the halogen-substituted Tyr157, and we determined the crystal structures of both wild-type and engineered CDO variants in the purely uncross-linked form and with a mature cofactor. Along with mass spectrometry and ¹⁹F NMR, these data indicated that the enzyme could catalyze oxidative C–F or C–Cl bond cleavage, resulting in a substantial conformational change of both Cys93 and Tyr157 during cofactor assembly. These findings provide insights into the mechanism of Cys–Tyr cofactor biogenesis and may aid the development of bioinspired aromatic carbon–halogen bond activation.

半胱氨酸双加氧酶（CDO）通过调节半胱氨酸的体内平衡水平在硫代谢中起重要作用。人CDO包含翻译后产生的Cys93-Tyr157交联的辅因子。在这里，我们通过遗传方法通过掺入非天然酪氨酸代替Tyr157来研究这种Cys-Tyr交联。获得具有催化活性的变异体，其在Cys93和卤素取代的Tyr157之间具有硫醚键，并且我们确定了纯未交联形式和成熟辅因子的野生型和工程CDO变异体的晶体结构。连同质谱法和¹⁹F NMR，这些数据表明该酶可以催化氧化的CF或C-Cl键裂解，从而导致辅因子组装过程中Cys93和Tyr157的构象发生实质性变化。这些发现提供了对Cys-Tyr辅助因子生物发生机制的见解，并可能有助于生物启发的芳香族碳-卤素键激活的发展。