Crystal Structure and Spectroscopic Studies of a Stable Mixed-Valent State of the Hemerythrin-like Domain of a Bacterial Chemotaxis Protein

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• 作者：Akira Onoda ; Yasunori Okamoto ; Hiroshi Sugimoto ; Yoshitsugu Shiro ; Takashi Hayashi
• 刊名：Inorganic Chemistry
• 出版年：2011
• 出版时间：June 6, 2011
• 年：2011
• 卷：50
• 期：11
• 页码：4892-4899
• 全文大小：910K
• 年卷期：v.50,no.11(June 6, 2011)
• ISSN：1520-510X

文摘

The bacterial chemotaxis protein of Desulfovibrio vulgaris DcrH (DcrH-Hr) functions as an O₂-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 O₂ affinity of DcrH-Hr is 3.3 脳 10⁶ M^鈥?, a value 25-fold higher than that of the Pectinaria gouldii Hr. This high affinity arises from the fast association of the O₂ ligand with DcrH-Hr (k_on = 5.3 脳 10⁸ M^鈥? s^鈥?), which is made possible by a hydrophobic tunnel that accelerates the passage of the O₂ 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 脜) and met-DcrH-Hr (1.4 脜) indicate that the semimet_R- and met-DcrH-Hr species have very similar coordination geometry at the diiron site.