A low-potential terminal oxidase associated with the iron-only nitrogenase from the nitrogen-fixing bacterium Azotobacter vinelandii.
A low-potential terminal oxidase associated with the iron-only nitrogenase from the nitrogen-fixing bacterium Azotobacter vinelandii.
复制标题
一种低电位末端氧化酶，与固氮细菌 Azotobacter vinelandii 的纯铁固氮酶相关。
DOI：
10.1074/jbc.ra118.007285
复制
发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Varghese F
中科院分区：
文献类型：
--
作者：
Varghese F
氮气进入生物圈的生物途径是通过固氮酶还原成氨，而固氮酶被氧气灭活。存在三种类型的固氮酶，其中研究最少的是仅含铁的固氮酶。荚膜红细菌中的Anf3蛋白是固氮（即固氮）生长所必需的，但其酶活性和功能尚不清楚。在这里，我们的生物化学和结构特征Anf3的模式固氮菌Azotobacter vinelandii。确定Anf3晶体结构的原子分辨率，我们观察到，它是一个二聚体flavocytochrome与血红素和FAD辅因子之间的异常密切的相互作用。通过光谱电化学氧化还原滴定法测量还原电位，我们观察到两种FAD电位的值为−420 ± 10和−330 ± 10 mV，血红素的值为−340 ± 1 mV。我们进一步表明，Anf3接受电子从菠菜铁氧还蛋白和Anf3消耗氧气不产生超氧化物或过氧化氢。我们预测，Anf3保护铁唯一的固氮酶从氧失活作为一种氧化酶在呼吸保护中发挥作用，与黄氧还蛋白或铁氧还蛋白作为生理电子供体。
The biological route for nitrogen gas entering the biosphere is reduction to ammonia by the nitrogenase enzyme, which is inactivated by oxygen. Three types of nitrogenase exist, the least-studied of which is the iron-only nitrogenase. The Anf3 protein in the bacteriumRhodobacter capsulatusis essential for diazotrophic (i.e.nitrogen-fixing) growth with the iron-only nitrogenase, but its enzymatic activity and function are unknown. Here, we biochemically and structurally characterize Anf3 from the model diazotrophic bacteriumAzotobacter vinelandii. Determining the Anf3 crystal structure to atomic resolution, we observed that it is a dimeric flavocytochrome with an unusually close interaction between the heme and the FAD cofactors. Measuring the reduction potentials by spectroelectrochemical redox titration, we observed values of −420 ± 10 and −330 ± 10 mV for the two FAD potentials and −340 ± 1 mV for the heme. We further show that Anf3 accepts electrons from spinach ferredoxin and that Anf3 consumes oxygen without generating superoxide or hydrogen peroxide. We predict that Anf3 protects the iron-only nitrogenase from oxygen inactivation by functioning as an oxidase in respiratory protection, with flavodoxin or ferredoxin as the physiological electron donors.