Siroheme synthase orients substrates for dehydrogenase and chelatase activities in a common active site
Siroheme synthase orients substrates for dehydrogenase and chelatase activities in a common active site
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DOI：
10.1038/s41467-020-14722-1
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发表时间：
2020-02-13
影响因子：
16.6
通讯作者：
Stroupe, M. Elizabeth
中科院分区：
文献类型：
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作者：
Pennington, Joseph M.;Kemp, Michael;Stroupe, M. Elizabeth
Siroheme是亚硫酸盐和亚硝酸盐还原酶的保守类别中的中心辅因子，其催化亚硫酸盐至硫化物和亚硝酸盐至氨的六电子还原。在鼠伤寒沙门氏菌中，siroheme由三功能酶siroheme合酶（CysG）产生。与其甲基转移酶活性不同的双功能活性位点催化最后两个步骤，NAD（+）依赖性脱氢和铁螯合。这种活性位点如何进行这种不同的化学反应是未知的。在这里，我们报告的结构CysG绑定到precorrin-2，初始基板; sirohydrochlorin，脱氢产物/螯合基板;和钴sirohydrochlorin产品。我们确定了所有三种四吡咯的结合姿势，并测试了特定氨基酸在两种活动中的作用，以深入了解双功能活性位点如何催化两种不同的化学反应，并在siroheme合成的最后一步中作为铁特异性螯合酶。西罗血红素是一种重要的细菌铁四吡咯，由西罗血红素依赖的亚硫酸盐和亚硝酸盐还原酶使用。在这里，作者阐明了siroheme合酶的催化机制，通过结合到其底物，前体蛋白-2，产物/底物sirohydrochlorin和钴-sirohydrochlorin的双功能脱氢酶/螯合酶CysG模块的结构。
Siroheme is the central cofactor in a conserved class of sulfite and nitrite reductases that catalyze the six-electron reduction of sulfite to sulfide and nitrite to ammonia. In Salmonella enterica serovar Typhimurium, siroheme is produced by a trifunctional enzyme, siroheme synthase (CysG). A bifunctional active site that is distinct from its methyltransferase activity catalyzes the final two steps, NAD(+)-dependent dehydrogenation and iron chelation. How this active site performs such different chemistries is unknown. Here, we report the structures of CysG bound to precorrin-2, the initial substrate; sirohydrochlorin, the dehydrogenation product/chelation substrate; and a cobalt-sirohydrochlorin product. We identified binding poses for all three tetrapyrroles and tested the roles of specific amino acids in both activities to give insights into how a bifunctional active site catalyzes two different chemistries and acts as an iron-specific chelatase in the final step of siroheme synthesis. Siroheme is an essential bacterial iron tetrapyrrole used by siroheme-dependent sulfite and nitrite reductases. Here the authors shed light on the catalytic mechanisms of siroheme synthase through the structures of the bifunctional dehydrogenase/chelatase CysG module bound to its substrate, precorrin-2, the product/substrate sirohydrochlorin, and cobalt-sirohydrochlorin.