Unden G, Schirawski J
Institut für Mikrobiologie und Weinforschung, Johannes Gutenberg-Universität Mainz, Germany.
Mol Microbiol. 1997 Jul;25(2):205-10. doi: 10.1046/j.1365-2958.1997.4731841.x.
The FNR (fumarate and nitrate reductase regulation) protein of Escherichia coli is an oxygen-responsive transcriptional regulator required for the switch from aerobic to anaerobic metabolism. In the absence of oxygen, FNR changes from the inactive to the active state. The sensory and the regulatory functions reside in separate domains of FNR. The sensory domain contains a Fe-S cluster, which is of the [4Fe-4S]2+ type under anaerobic conditions. It is suggested that oxygen is supplied to the cytoplasmic FNR by diffusion and inactivates FNR by direct interaction. Reactivation under anoxic conditions requires cellular reductants. In vitro, the Fe-S cluster is converted to a [3Fe-4S]+ or a [2Fe-2S]2+ cluster by oxygen, resulting in FNR inactivation. After prolonged incubation with oxygen, the Fe-S cluster is destroyed. Reassembly of the [4Fe-4S]2+ cluster might require cellular proteins, such as the NifS-like protein of E. coli. In this review, the rationale for regulation of alternative metabolic pathways by FNR and other oxygen-dependent regulators is discussed. Only the terminal reductases of respiration, and not the dehydrogenases, are regulated in such a way as to achieve maximal H+/e- ratios and ATP yields.
大肠杆菌的FNR（延胡索酸和硝酸盐还原酶调节）蛋白是一种氧响应转录调节因子，是从有氧代谢转变为无氧代谢所必需的。在无氧条件下，FNR从无活性状态转变为活性状态。传感功能和调节功能分别位于FNR的不同结构域。传感结构域包含一个铁硫簇，在厌氧条件下为[4Fe-4S]2+类型。据推测，氧气通过扩散供应到细胞质中的FNR，并通过直接相互作用使FNR失活。在缺氧条件下重新激活需要细胞还原剂。在体外，铁硫簇被氧气转化为[3Fe-4S]+或[2Fe-2S]2+簇，导致FNR失活。与氧气长时间孵育后，铁硫簇被破坏。[4Fe-4S]2+簇的重新组装可能需要细胞蛋白，如大肠杆菌的NifS样蛋白。在这篇综述中，讨论了FNR和其他氧依赖性调节因子调节替代代谢途径的基本原理。只有呼吸作用的末端还原酶，而不是脱氢酶，以这种方式进行调节，以实现最大的H+/e-比率和ATP产量。
