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.
abstract: 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 (13)CO 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 vibrational "shake" 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.
authors.affiliation: Institut für Chemie, Technische Universität Berlin , 10623 Berlin, Germany.
authors.forename: Aubrey D
authors.initials: AD
authors.lastname: Scott
authors.forename: Vladimir
authors.initials: V
authors.lastname: Pelmenschikov
authors.forename: Yisong
authors.initials: Y
authors.lastname: Guo
authors.forename: Lifen
authors.initials: L
authors.lastname: Yan
authors.forename: Hongxin
authors.initials: H
authors.lastname: Wang
authors.forename: Simon J
authors.initials: SJ
authors.lastname: George
authors.forename: Christie H
authors.initials: CH
authors.lastname: Dapper
authors.forename: William E
authors.initials: WE
authors.lastname: Newton
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Yoda
authors.forename: Yoshihito
authors.initials: Y
authors.lastname: Tanaka
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Cramer
mesh_terms: D016948:Azotobacter vinelandii / Q000201:enzymology; D002248:Carbon Monoxide / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008983:Molybdoferredoxin / Q000378:metabolism; D009154:Mutation; D009591:Nitrogenase / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D011789:Quantum Theory; D017550:Spectroscopy, Fourier Transform Infrared; D056928:X-Ray Absorption Spectroscopy
chemical_list: D004791:Enzyme Inhibitors; D008983:Molybdoferredoxin; D002248:Carbon Monoxide; D009591:Nitrogenase