title: Spectroscopic and redox properties of a CooA homologue from Carboxydothermus hydrogenoformans.
abstract: CooA is a CO-sensing transcriptional activator that contains a b-type heme as the active site for sensing its physiological effector, CO. In this study, the spectroscopic and redox properties of a new CooA homologue from Carboxydothermus hydrogenoformans (Ch-CooA) were studied. Spectroscopic and mutagenesis studies revealed that His-82 and the N-terminal alpha-amino group were the axial ligands of the Fe(III) and Fe(II) hemes in Ch-CooA and that the N-terminal alpha-amino group was replaced by CO upon CO binding. Two neutral ligands, His-82 and the N-terminal alpha-amino group, are coordinated to the Fe(III) heme in Ch-CooA, whereas two negatively charged ligands, a thiolate from Cys-75 and the nitrogen atom of the N-terminal Pro, are the axial ligands of the Fe(III) heme in Rr-CooA. The difference in the coordination structure of the Fe(III) heme resulted in a large positive shift of redox potentials of Ch-CooA compared with Rr-CooA. Comparing the properties of Ch-CooA and Rr-CooA demonstrates that the essential elements for CooA function will be: (i) the heme is six-coordinate in the Fe(III), Fe(II), and Fe(II)-CO forms; (ii) the N-terminal is coordinated to the heme as an axial ligand, and (iii) CO replaces the N-terminal bound to the heme upon CO binding.
authors.affiliation: Department of Structural Molecule Science, The Graduate University for Advanced Studies, 38 Nishigo-naka, Myodaiji, Okazaki 444-8585, Japan.
authors.forename: Sayaka
authors.initials: S
authors.lastname: Inagaki
authors.forename: Chiaki
authors.initials: C
authors.lastname: Masuda
authors.forename: Tetsuhiro
authors.initials: T
authors.lastname: Akaishi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nakajima
authors.forename: Shiro
authors.initials: S
authors.lastname: Yoshioka
authors.forename: Takehiro
authors.initials: T
authors.lastname: Ohta
authors.forename: Biswajit
authors.initials: B
authors.lastname: Pal
authors.forename: Teizo
authors.initials: T
authors.lastname: Kitagawa
authors.forename: Shigetoshi
authors.initials: S
authors.lastname: Aono
mesh_terms: D001421:Bacteria, Anaerobic / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics; D036781:Fimbriae Proteins / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D006420:Hemeproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D016296:Mutagenesis; D010084:Oxidation-Reduction; D017434:Protein Structure, Tertiary; D013054:Spectrophotometry, Atomic; D013059:Spectrum Analysis, Raman; D015534:Trans-Activators / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; C088904:CooA protein, E coli; C108776:CooA protein, Rhodospirillum rubrum; D029968:Escherichia coli Proteins; D006420:Hemeproteins; D015534:Trans-Activators; D036781:Fimbriae Proteins