Liu Jianxin, Knapp Madison, Jo Minshik, Dill Zerick, Bridwell-Rabb Jennifer
Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States.
ACS Cent Sci. 2022 Oct 26;8(10):1393-1403. doi: 10.1021/acscentsci.2c00058. Epub 2022 Jul 27.
Rieske oxygenases perform precise C-H bond functionalization reactions in anabolic and catabolic pathways. These reactions are typically characterized as monooxygenation or dioxygenation reactions, but other divergent reactions are also catalyzed by Rieske oxygenases. Chlorophyll(ide) oxygenase (CAO), for example is proposed to catalyze two monooxygenation reactions to transform a methyl-group into the formyl-group of Chlorophyll . This formyl group, like the formyl groups found in other chlorophyll pigments, tunes the absorption spectra of chlorophyll and supports the ability of several photosynthetic organisms to adapt to environmental light. Despite the importance of this reaction, CAO has never been studied in vitro with purified protein, leaving many open questions regarding whether CAO can facilitate both oxygenation reactions using just the Rieske oxygenase machinery. In this study, we demonstrated that four CAO homologues in partnership with a non-native reductase convert a Chlorophyll precursor, chlorophyllide, into chlorophyllide in vitro. Analysis of this reaction confirmed the existence of the proposed intermediate, highlighted the stereospecificity of the reaction, and revealed the potential of CAO as a tool for synthesizing custom-tuned natural and unnatural chlorophyll pigments. This work thus adds to our fundamental understanding of chlorophyll biosynthesis and Rieske oxygenase chemistry.
铁硫簇氧化酶在合成代谢和分解代谢途径中进行精确的C-H键官能团化反应。这些反应通常被描述为单加氧反应或双加氧反应，但铁硫簇氧化酶也催化其他不同的反应。例如，叶绿素（酯）氧化酶（CAO）被认为催化两个单加氧反应，将一个甲基转化为叶绿素的甲酰基。这个甲酰基，就像在其他叶绿素色素中发现的甲酰基一样，调节叶绿素的吸收光谱，并支持几种光合生物适应环境光的能力。尽管这个反应很重要，但CAO从未在体外使用纯化蛋白进行过研究，关于CAO是否仅使用铁硫簇氧化酶机制就能促进这两个加氧反应，仍有许多悬而未决的问题。在这项研究中，我们证明了四个CAO同源物与一种非天然还原酶合作，在体外将叶绿素前体叶绿素酯转化为叶绿素酯。对该反应的分析证实了所提出的中间体的存在，突出了反应的立体特异性，并揭示了CAO作为合成定制天然和非天然叶绿素色素工具的潜力。因此，这项工作增加了我们对叶绿素生物合成和铁硫簇氧化酶化学的基本理解。
