Max Planck Institute for Marine Microbiology, Bremen, Germany.
Biochemistry, Faculty of Chemistry, University of Kaiserslautern-Landau, Kaiserslautern, Germany.
产甲烷古菌是碳循环的主要参与者，但对活性亚硫酸盐很敏感。一些产甲烷菌使用亚硫酸盐解毒系统，该系统结合了 F 420 H 2 -氧化酶和亚硫酸盐还原酶，这两种酶都被认为是现代酶的前体。在这里，我们展示了这个名为辅酶 F 420的偶联系统的快照依赖亚硫酸盐还原酶（I 组 Fsr），从两种海洋产甲烷菌中获得。Fsr 组织为同源四聚体，包含一个以光谱学为特征的交织六 [4Fe–4S] 簇中继。跨越 5.4 nm 的导线将黄素电子连接到 siroheme 中心。尽管结构类似于异化亚硫酸盐还原酶，但 Fsr 显示出与同化亚硫酸盐还原酶相同的 siroheme 配位和反应机制。因此，Fsr 的反应是单向的，用 F 420 H 2还原亚硫酸盐或亚硝酸盐。我们的结果为这种独特的融合提供了结构上的见解，在这种融合中，一种原始的亚硫酸盐还原酶将毒物转化为生命的基本组成部分。
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Structures of the sulfite detoxifying F420-dependent enzyme from Methanococcales
Methanogenic archaea are main actors in the carbon cycle but are sensitive to reactive sulfite. Some methanogens use a sulfite detoxification system that combines an F420H2-oxidase with a sulfite reductase, both of which are proposed precursors of modern enzymes. Here, we present snapshots of this coupled system, named coenzyme F420-dependent sulfite reductase (Group I Fsr), obtained from two marine methanogens. Fsr organizes as a homotetramer, harboring an intertwined six-[4Fe–4S] cluster relay characterized by spectroscopy. The wire, spanning 5.4 nm, electronically connects the flavin to the siroheme center. Despite a structural architecture similar to dissimilatory sulfite reductases, Fsr shows a siroheme coordination and a reaction mechanism identical to assimilatory sulfite reductases. Accordingly, the reaction of Fsr is unidirectional, reducing sulfite or nitrite with F420H2. Our results provide structural insights into this unique fusion, in which a primitive sulfite reductase turns a poison into an elementary block of life.
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