title: Unexpected NO-dependent DNA binding by the CooA homolog from Carboxydothermus hydrogenoformans.
abstract: CooA, the CO-sensing heme protein from Rhodospirillum rubrum, regulates the expression of genes that encode a CO-oxidation system, allowing R. rubrum to use CO as a sole energy source. To better understand the gas-sensing regulation mechanism used by R. rubrum CooA and its homologs in other organisms, we characterized spectroscopically and functionally the Fe(II), Fe(II)-NO, and Fe(II)-CO forms of CooA from Carboxydothermus hydrogenoformans. Surprisingly, and unlike R. rubrum CooA, C. hydrogenoformans CooA binds NO to form a six-coordinate Fe(II)-NO heme that is active for DNA binding in vitro and in vivo. In contrast, R. rubrum CooA, which is exquisitely specific for CO, forms a five-coordinate Fe(II)-NO adduct that is inactive for DNA binding. Based on analyses of protein variants and temperature studies, NO-dependent DNA binding by C. hydrogenoformans CooA is proposed to result from a greater apparent stability of the six-coordinate Fe(II)-NO adduct at room temperature. Results from the present study strengthen the proposal that CO specificity in the CooA activation mechanism is based on the requirement for a small, neutral distal ligand, which in turn affects the relative positioning of the ligand-bound heme.
authors.affiliation: Departments of Chemistry and Bacteriology, University of Wisconsin, Madison, WI 53706, USA.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Clark
authors.forename: Nicholas D
authors.initials: ND
authors.lastname: Lanz
authors.forename: Andrea J
authors.initials: AJ
authors.lastname: Lee
authors.forename: Robert L
authors.initials: RL
authors.lastname: Kerby
authors.forename: Gary P
authors.initials: GP
authors.lastname: Roberts
authors.forename: Judith N
authors.initials: JN
authors.lastname: Burstyn
mesh_terms: D001671:Biochemistry / Q000379:methods; D004247:DNA / Q000737:chemistry*; D004268:DNA-Binding Proteins / Q000737:chemistry*; D004305:Dose-Response Relationship, Drug; D004578:Electron Spin Resonance Spectroscopy; D029968:Escherichia coli Proteins / Q000737:chemistry*; D036781:Fimbriae Proteins / Q000737:chemistry*; D015964:Gene Expression Regulation, Bacterial; D006418:Heme / Q000737:chemistry; D006420:Hemeproteins / Q000737:chemistry; D007501:Iron / Q000737:chemistry; D008024:Ligands; D008958:Models, Molecular; D009569:Nitric Oxide / Q000737:chemistry / Q000378:metabolism*; D010459:Peptococcaceae / Q000378:metabolism*; D011485:Protein Binding; D013053:Spectrophotometry; D013696:Temperature
chemical_list: C088904:CooA protein, E coli; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D006420:Hemeproteins; D008024:Ligands; D036781:Fimbriae Proteins; D009569:Nitric Oxide; D006418:Heme; D004247:DNA; D007501:Iron