title: The dynamics of the non-heme iron in bacterial reaction centers from Rhodobacter sphaeroides.
abstract: We investigate the dynamical properties of the non-heme iron (NHFe) in His-tagged photosynthetic bacterial reaction centers (RCs) isolated from Rhodobacter (Rb.) sphaeroides. Mössbauer spectroscopy and nuclear inelastic scattering of synchrotron radiation (NIS) were applied to monitor the arrangement and flexibility of the NHFe binding site. In His-tagged RCs, NHFe was stabilized only in a high spin ferrous state. Its hyperfine parameters (IS=1.06±0.01mm/s and QS=2.12±0.01mm/s), and Debye temperature (θ(D0)~167K) are comparable to those detected for the high spin state of NHFe in non-His-tagged RCs. For the first time, pure vibrational modes characteristic of NHFe in a high spin ferrous state are revealed. The vibrational density of states (DOS) shows some maxima between 22 and 33meV, 33 and 42meV, and 53 and 60meV and a very sharp one at 44.5meV. In addition, we observe a large contribution of vibrational modes at low energies. This iron atom is directly connected to the protein matrix via all its ligands, and it is therefore extremely sensitive to the collective motions of the RC protein core. A comparison of the DOS spectra of His-tagged and non-His-tagged RCs from Rb. sphaeroides shows that in the latter case the spectrum was overlapped by the vibrations of the heme iron of residual cytochrome c(2), and a low spin state of NHFe in addition to its high spin one. This enabled us to pin-point vibrations characteristic for the low spin state of NHFe.
authors.affiliation: AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, al. Mickiewicza 30, 30-059 Kraków, Poland.
authors.forename: A
authors.initials: A
authors.lastname: Hałas
authors.forename: A
authors.initials: A
authors.lastname: Orzechowska
authors.forename: V
authors.initials: V
authors.lastname: Derrien
authors.forename: A I
authors.initials: AI
authors.lastname: Chumakov
authors.forename: P
authors.initials: P
authors.lastname: Sebban
authors.forename: J
authors.initials: J
authors.lastname: Fiedor
authors.forename: M
authors.initials: M
authors.lastname: Lipińska
authors.forename: M
authors.initials: M
authors.lastname: Zając
authors.forename: T
authors.initials: T
authors.lastname: Ślęzak
authors.forename: K
authors.initials: K
authors.lastname: Strzałka
authors.forename: K
authors.initials: K
authors.lastname: Matlak
authors.forename: J
authors.initials: J
authors.lastname: Korecki
authors.forename: L
authors.initials: L
authors.lastname: Fiedor
authors.forename: K
authors.initials: K
authors.lastname: Burda
mesh_terms: D001665:Binding Sites; D004579:Electron Transport; D007501:Iron / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism; D012242:Rhodobacter sphaeroides / Q000737:chemistry* / Q000254:growth & development / Q000378:metabolism; D015204:Spectroscopy, Mossbauer; D017356:Synchrotrons; D014732:Vibration
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D007501:Iron