title: The transcription regulator RcoM-2 from Burkholderia xenovorans is a cysteine-ligated hemoprotein that undergoes a redox-mediated ligand switch.
abstract: Spectroscopic characterization of the newly discovered heme-PAS domain sensor protein BxRcoM-2 reveals that this protein undergoes redox-dependent ligand switching and CO- and NO-induced ligand displacement. The aerobic bacterium Burkholderia xenovorans expresses two homologous heme-containing proteins that promote CO-dependent transcription in vivo. These regulators of CO metabolism, BxRcoM-1 and BxRcoM-2, are gas-responsive heme-PAS domain proteins like mammalian neuronal PAS domain protein 2 (NPAS2) and the direct oxygen sensor from Escherichia coli ( EcDos). BxRcoM-2 was studied using electronic absorption, MCD, resonance Raman, and EPR spectroscopies. In the Fe(III) oxidation state, the heme is low-spin and six-coordinate with a cysteine(thiolate) as one of the two ligands. The sixth ligand is a histidine (His (74)), which is present in all states of the protein that were studied. Reduction to the Fe(II) oxidation state results in replacement of the cysteine(thiolate) with a neutral thioether ligand, Met (104). CO and NO bind to the Fe(II) BxRcoM-2 heme opposite the histidine ligand. Thus, BxRcoM-2 employs coordination state changes similar to those known for CO-sensing CooA, with redox-dependent loss of a cysteine(thiolate) ligand and displacement of a relatively weakly bound axial ligand by the effector gas molecule. Like EcDos, the weakly bound axial ligand that is displaced is methionine.
authors.affiliation: Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, USA.
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Marvin
authors.forename: Robert L
authors.initials: RL
authors.lastname: Kerby
authors.forename: Hwan
authors.initials: H
authors.lastname: Youn
authors.forename: Gary P
authors.initials: GP
authors.lastname: Roberts
authors.forename: Judith N
authors.initials: JN
authors.lastname: Burstyn
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D019117:Burkholderia / Q000235:genetics / Q000378:metabolism*; D002248:Carbon Monoxide / Q000737:chemistry / Q000378:metabolism; D003545:Cysteine / Q000737:chemistry / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D006420:Hemeproteins / Q000737:chemistry / Q000378:metabolism*; D006639:Histidine / Q000737:chemistry / Q000378:metabolism; D007501:Iron / Q000737:chemistry / Q000378:metabolism; D015394:Molecular Structure; D009569:Nitric Oxide / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction; D011485:Protein Binding; D013059:Spectrum Analysis, Raman; D015534:Trans-Activators / Q000737:chemistry / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D006420:Hemeproteins; D015534:Trans-Activators; D009569:Nitric Oxide; D006639:Histidine; D002248:Carbon Monoxide; D007501:Iron; D003545:Cysteine