Structural Characterization of CO-Inhibited Mo-Nitrogenase by Combined Application of Nuclear Resonance Vibrational Spectroscopy, Extended X-ray Absorption Fine Structure, and Density Functional Theor

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• 作者：Aubrey D. Scott ; Vladimir Pelmenschikov ; Yisong Guo ; Lifen Yan ; Hongxin Wang ; Simon J. George ; Christie H. Dapper ; William E. Newton ; Yoshitaka Yoda ; Yoshihito Tanaka ; Stephen P. Cramer
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：November 12, 2014
• 年：2014
• 卷：136
• 期：45
• 页码：15942-15954
• 全文大小：803K
• ISSN：1520-5126

文摘

The properties of CO-inhibited Azotobacter vinelandii (Av) Mo-nitrogenase (N₂ase) have been examined by the combined application of nuclear resonance vibrational spectroscopy (NRVS), extended X-ray absorption fine structure (EXAFS), and density functional theory (DFT). Dramatic changes in the NRVS are seen under high-CO conditions, especially in a 188 cm^鈥? mode associated with symmetric breathing of the central cage of the FeMo-cofactor. Similar changes are reproduced with the 伪-H195Q N₂ase variant. In the frequency region above 450 cm^鈥?, additional features are seen that are assigned to Fe-CO bending and stretching modes (confirmed by ¹³CO isotope shifts). The EXAFS for wild-type N₂ase shows evidence for a significant cluster distortion under high-CO conditions, most dramatically in the splitting of the interaction between Mo and the shell of Fe atoms originally at 5.08 脜 in the resting enzyme. A DFT model with both a terminal 鈭扖O and a partially reduced 鈭扖HO ligand bound to adjacent Fe sites is consistent with both earlier FT-IR experiments, and the present EXAFS and NRVS observations for the wild-type enzyme. Another DFT model with two terminal CO ligands on the adjacent Fe atoms yields Fe-CO bands consistent with the 伪-H195Q variant NRVS. The calculations also shed light on the vibrational 鈥渟hake鈥?modes of the interstitial atom inside the central cage, and their interaction with the Fe-CO modes. Implications for the CO and N₂ reactivity of N₂ase are discussed.