Function of a new sensor kinase NreB from Staphylococcus carnosus using a [4Fe4S]2+ cluster for sensing oxygen

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Staphylococcus carnosus uses the cytoplasmic NreBC two-component system for sensing O2 and transcriptional regulation of nitrate respiration. NreB contains a new type of a sensory PAS (Per-Arnt-Sim) domain that binds a [4Fe-4S]2+ cluster. The cluster is degraded by reaction with O2, producing [2Fe-2S]2+ as an intermediate and (FeS-less) apoNreB as the final product. ApoNreB and [2Fe-2S]2+.NreB have lost the kinase activity and the capacity for gene activation. It is shown that apoNreB is the inactive form of NreB in aerobically grown bacteria whereas [2Fe-2S]2+.NreB plays no significant role. Overall, cluster degradation in NreB directly controls kinase activity of NreB, whereas in the O2-sensor FNR the same reaction controls dimerisation and DNA-binding of the protein. The processes at the FeS binding site of NreB and in the signal transfer to the kinase domain will be studied to understand the molecular differences to FNR at the protein level. Bacteria containing NreBC harbour in addition the NreA protein that consists essentially of a GAF domain. NreA fulfils an important role in O2-sensing by NreBC and physically interacts with NreB. We suppose that NreA functions as an accessory protein that controls the function of NreB in O2 sensing, and that NreBC forms together with NreA a three-component system. We will study the role of NreA and the GAF domain for NreBC function in vivo and in vitro.