title: A PAS domain with an oxygen labile [4Fe-4S](2+) cluster in the oxygen sensor kinase NreB of Staphylococcus carnosus.
abstract: The cytoplasmic histidine sensor kinase NreB of Staphylococcus carnosus responds to O(2) and controls together with the response regulator NreC the expression of genes of nitrate/nitrite respiration. nreBC homologous genes were found in Staphylococcus strains and Bacillus clausii, and a modified form was found in some Lactobacillus strains. NreB contains a sensory domain with similarity to heme B binding PAS domains. Anaerobically prepared NreB of S. carnosus exhibited a (diamagnetic) [4Fe-4S](2+) cluster when assessed by Mossbauer spectroscopy. Upon reaction with air, the cluster was degraded with a half-life of approximately 2.5 min. No significant amounts of Mossbauer or EPR detectable intermediates were found during the decay, but magnetic Mossbauer spectra revealed formation of diamagnetic [2Fe-2S](2+) clusters. After extended exposure to air, NreB was devoid of a FeS cluster. Photoreduction with deazaflavin produced small amounts of [4Fe-4S](+), which were degraded subsequently. The magnetically perturbed Mossbauer spectrum of the [4Fe-4S](2+) cluster corroborated the S = 0 spin state and revealed uniform electric field gradient tensors of the iron sites, suggesting full delocalization of the valence electrons and binding of each of the Fe ions by four S ligands, including the ligand to the protein. Mutation of each of the four Cys residues inactivated NreB function in vivo in accordance with their role as ligands. [4Fe-4S](2+) cluster-containing NreB had high kinase activity. Exposure to air decreased the kinase activity and content of the [4Fe-4S](2+) cluster with similar half-lives. We conclude that the sensory domain of NreB represents a new type of PAS domain containing a [4Fe-4S](2+) cluster for sensing and function.
authors.affiliation: Institut fur Mikrobiologie and Weinforschung, Universitat Mainz, Becherweg 15, 55099 Mainz, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Müllner
authors.forename: Oliver
authors.initials: O
authors.lastname: Hammel
authors.forename: Bernd
authors.initials: B
authors.lastname: Mienert
authors.forename: Steffen
authors.initials: S
authors.lastname: Schlag
authors.forename: Eckhard
authors.initials: E
authors.lastname: Bill
authors.forename: Gottfried
authors.initials: G
authors.lastname: Unden
mesh_terms: D000388:Air; D006207:Half-Life; D000071677:Histidine Kinase; D007506:Iron-Sulfur Proteins / Q000737:chemistry*; D008280:Magnetics; D010100:Oxygen / Q000737:chemistry / Q000494:pharmacology*; D011494:Protein Kinases / Q000737:chemistry*; D015204:Spectroscopy, Mossbauer; D013210:Staphylococcus / Q000201:enzymology*
chemical_list: D007506:Iron-Sulfur Proteins; D011494:Protein Kinases; D000071677:Histidine Kinase; D010100:Oxygen