title: Effect of mutation on the dissociation and recombination dynamics of CO in transcriptional regulator CooA: a picosecond infrared transient absorption study.
abstract: The CO ligation process in a mutant (H77G) of CooA, the CO-sensing transcriptional regulator in Rhodospirillum rubrum, is studied with femtosecond time-resolved transient absorption spectroscopy in the mid-infrared region. Following photolyzing excitation, a transient bleach in the vibrational region of bound CO due to the CO photodissociation is detected. In contrast to the spectra of the wild-type (WT) CooA, the transient bleach spectra of H77G CooA show a bimodal shape with peaks shifting to the lower frequency during spectral evolution. The CO recombination dynamics show single-exponential behavior, and the CO escaping yield is higher than that of the WT CooA. A reorientation process of CO relative to the heme plane during recombination is revealed by anisotropy measurements. These phenomena indicate changes in the protein response to the CO ligation and suggest an alteration to the CO environment caused by the mutation. On the basis of these results, the role of His77 in the CO-dependent activation of CooA and a possible activation mechanism involving collaborative movement of the heme and the amino residues at both sides of the heme plane are discussed.
authors.affiliation: School of Materials Science, Japan Advanced Institute of Science and Technology, Tatsunokuchi, Ishikawa 923-1292, Japan. zhangti@mail.nih.gov
authors.forename: Tieqiao
authors.initials: T
authors.lastname: Zhang
authors.forename: Igor V
authors.initials: IV
authors.lastname: Rubtsov
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nakajima
authors.forename: Shigetoshi
authors.initials: S
authors.lastname: Aono
authors.forename: Keitaro
authors.initials: K
authors.lastname: Yoshihara
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D002248:Carbon Monoxide / Q000737:chemistry* / Q000378:metabolism; D005998:Glycine / Q000235:genetics; D006418:Heme / Q000737:chemistry; D006420:Hemeproteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D006639:Histidine / Q000235:genetics; D008956:Models, Chemical; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011995:Recombination, Genetic; D050436:Regulatory Elements, Transcriptional / Q000502:physiology*; D012247:Rhodospirillum rubrum / Q000737:chemistry / Q000235:genetics; D019265:Spectroscopy, Near-Infrared / Q000379:methods; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; C108776:CooA protein, Rhodospirillum rubrum; D006420:Hemeproteins; D015534:Trans-Activators; D006418:Heme; D006639:Histidine; D002248:Carbon Monoxide; D005998:Glycine