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Title: Structural Characterization of CO-Inhibited Mo-Nitrogenase by Combined Application of Nuclear Resonance Vibrational Spectroscopy, Extended X-ray Absorption Fine Structure, and Density Functional Theory: New Insights into the Effects of CO Binding and the Role of the Interstitial Atom

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–1 mode associated with symmetric breathing of the central cage of the FeMo-cofactor. Similar changes are reproduced with the α-H195Q N2ase variant. In the frequency region above 450 cm–1, 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 Å in the resting enzyme. A DFT model with both a terminal ₋CO and a partially reduced ₋CHO 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 α-H195Q variant NRVS. The calculations also shed light on the vibrationalmore » “shake” modes of the interstitial atom inside the central cage, and their interaction with the Fe-CO modes. We discuss implications for the CO and N2 reactivity of N2ase.« less
Authors:
 [1] ;  [2] ;  [3] ;  [1] ;  [4] ;  [1] ;  [5] ;  [5] ;  [6] ;  [7] ;  [8]
  1. Univ. of California, Davis, CA (United States). Dept. of Chemistry
  2. Technical Univ. Berlin (Germany). Dept. of Chemistry
  3. Carnegie Mellon Univ., Pittsburgh, PA (United States). Dept. of Chemistry
  4. Univ. of California, Davis, CA (United States). Dept. of Chemistry; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Physical Biosciences Division
  5. Virginia Polytechnic Inst. and State Univ. (Virginia Tech), Blacksburg, VA (United States). Dept. of Biochemistry
  6. Japan Synchrotron Radiation Research Institute (JASRI), Hyogo (Japan). SPring-8
  7. RIKEN, Hyogo (Japan). SPring-8 Center
  8. Univ. of California, Davis, CA (United States). Dept. of Chemistry; awrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Physical Biosciences Division
Publication Date:
Grant/Contract Number:
CHE 1308384; GM-65440
Type:
Published Article
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 136; Journal Issue: 45; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
OSTI Identifier:
1163247
Alternate Identifier(s):
OSTI ID: 1257353