title: Crystal structure and spectroscopic studies of a stable mixed-valent state of the hemerythrin-like domain of a bacterial chemotaxis protein.
abstract: The bacterial chemotaxis protein of Desulfovibrio vulgaris DcrH (DcrH-Hr) functions as an O(2)-sensing protein. This protein has a hemerythrin-like domain that includes a nonheme diiron center analogous to the diiron center of the hemerythrin (Hr) family. Interestingly, the O(2) affinity of DcrH-Hr is 3.3 × 10(6) M(-1), a value 25-fold higher than that of the Pectinaria gouldii Hr. This high affinity arises from the fast association of the O(2) ligand with DcrH-Hr (k(on) = 5.3 × 10(8) M(-1) s(-1)), which is made possible by a hydrophobic tunnel that accelerates the passage of the O(2) ligand to the diiron site. Furthermore, the autoxidation kinetics indicate that the rate of autoxidation of DcrH-Hr is 54-fold higher than that of P. gouldii Hr, indicating that the oxy form of DcrH-Hr is not stable toward autoxidation. More importantly, a mixed-valent state, semimet(R), which was spectroscopically observed in previous Hr studies, was found to be stable for over 1 week and isolable in the case of DcrH-Hr. The high-resolution crystal structures of the semimet(R)- (1.8 Å) and met-DcrH-Hr (1.4 Å) indicate that the semimet(R)- and met-DcrH-Hr species have very similar coordination geometry at the diiron site.
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan. thayashi@chem.eng.osaka-u.ac.jp
authors.forename: Akira
authors.initials: A
authors.lastname: Onoda
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Okamoto
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Sugimoto
authors.forename: Yoshitsugu
authors.initials: Y
authors.lastname: Shiro
authors.forename: Takashi
authors.initials: T
authors.lastname: Hayashi
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D018360:Crystallography, X-Ray; D016969:Desulfovibrio vulgaris / Q000737:chemistry* / Q000235:genetics; D004578:Electron Spin Resonance Spectroscopy; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D010100:Oxygen / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D001426:Bacterial Proteins; D008024:Ligands; D010100:Oxygen