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. Author manuscript; available in PMC: 2015 Jun 13.
Published in final edited form as: Metallomics. 2015 Jun 10;7(6):943–956. doi: 10.1039/c5mt00012b

Figure 3. The mechanism of S. Typhimurium NsrR-dependent hmp regulation.

Figure 3

A model of NsrR control of hmp encoding a NO detoxifying flavohaemoglobin under increasing nitric oxide stress. During growth of S. Typhimurium when concentrations of nitric oxide are minimal, such as in the environment outside of the mammalian host, the NsrR [2Fe-2S] cluster is stable. Under these conditions, [2Fe-2S]-NsrR is a functional DNA-binding protein and represses transcription of hmp encoding a nitric oxide detoxifying flavohaemoglobin. However, when S. Typhimurium is exposed to NO stress, such as that generated by host macrophages where S. Typhimurium survives and proliferates during mammalian infection, the NsrR [2Fe-2S] cluster is nitrosylated. These conditions lead to cluster destabilization and abolish NsrR DNA-binding activity. As such, hmp expression is no longer repressed and the resulting NO detoxification by flavohaemoglobin allows for S. Typhimurium persistence within host macrophages.