Ultraviolet Resonance Raman Observations of the Structural Dynamics of Rhizobial Oxygen Sensor FixL on Ligand Recognition

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• 作者：Shinji Yano ; Haruto Ishikawa ; Misao Mizuno ; Hiro Nakamura ; Yoshitsugu Shiro ; Yasuhisa Mizutani
• 刊名：Journal of Physical Chemistry B
• 出版年：2013
• 出版时间：December 12, 2013
• 年：2013
• 卷：117
• 期：49
• 页码：15786-15791
• 全文大小：361K
• 年卷期：v.117,no.49(December 12, 2013)
• ISSN：1520-5207

文摘

FixL is a heme-based oxygen-sensing histidine kinase that induces expression of nitrogen fixation genes under hypoxic conditions. Oxygen binding to heme iron in the sensor domain of FixL initiates protein conformational changes that are transmitted to the histidine kinase domain, inactivating autophosphorylation activity. Although FixL also can bind other diatomic ligands such as CO, the CO-bound FixL represents incomplete inhibition of kinase activity. Ultraviolet resonance Raman (UVRR) spectra revealed that oxygen binding to the truncated sensor domain of FixL markedly decreased the intensity of the Y8a band arising from F_伪-10 Tyr. In contrast, no appreciable change in intensity of the Y8a band occurred after CO binding, and time-resolved UVRR spectra of the sensor domain of FixL upon O₂ dissociation indicated that structural changes near F_伪-10 Tyr occurred at 0.1 渭s. These results suggest that O₂ dissociation from FixL changes the protein conformation near the F_伪-10 Tyr residue within a microsecond. The conformational changes of FixL upon O₂ dissociation and the underlying sensing mechanism also are discussed.