title: Probing the hydrogen bonding structure in the Rieske protein.
abstract: The use of the far-infrared spectral range presents a novel approach for analysis of the hydrogen bonding in proteins. Here it is presented for the analysis of Fe--S vibrations (500-200 cm(-1)) and of the intra- and intermolecular hydrogen bonding signature (300-50 cm(-1)) in the Rieske protein from Thermus thermophilus as a function of temperature and pH. Three pH values were adequately chosen in order to study all the possible protonation states of the coordinating histidines. The Fe--S vibrations showed pH-dependent shifts in the FIR spectra in line with the change of protonation state of the histidines coordinating the [2Fe--2S] cluster. Measurements of the low-frequency signals between 300 and 30 K demonstrated the presence of a distinct overall hydrogen bonding network and a more rigid structure for a pH higher than 10. To further support the analysis, the redox-dependent shifts of the secondary structure were investigated by means of an electrochemically induced FTIR difference spectroscopic approach in the mid infrared. The results confirmed a clear pH dependency and an influence of the immediate environment of the cluster on the secondary structure. The results support the hypothesis that structure-mediated changes in the environment of iron--sulfur centers play a critical role in regulating enzymatic catalysis. The data point towards the role of the overall internal hydrogen bonding organization for the geometry and the electronic properties of the cluster.
authors.affiliation: Laboratoire de Spectroscopie Vibrationnelle et Electrochimie des Biomolécules, Institut de chimie Université de Strasbourg, 1 Rue Blaise Pascal 67000 Strasbourg, France.
authors.forename: Youssef
authors.initials: Y
authors.lastname: El Khoury
authors.forename: Aurélien
authors.initials: A
authors.lastname: Trivella
authors.forename: Julien
authors.initials: J
authors.lastname: Gross
authors.forename: Petra
authors.initials: P
authors.lastname: Hellwig
mesh_terms: D014450:Electron Transport Complex III / Q000737:chemistry*; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D016963:Thermus thermophilus / Q000378:metabolism
chemical_list: C037989:Rieske iron-sulfur protein; D014450:Electron Transport Complex III