Localized Electronic Structure of Nitrogenase FeMoco Revealed by Selenium K-Edge High Resolution X-ray Absorption Spectroscopy.Henthorn, J.T., Arias, R.J., Koroidov, S., Kroll, T., Sokaras, D., Bergmann, U., Rees, D.C., DeBeer, S.
(2019) J.Am.Chem.Soc. 141: 13676-13688
- PubMed: 31356071
- DOI: 10.1021/jacs.9b06988
- Primary Citation of Related Structures:
- PubMed Abstract:
The size and complexity of Mo-dependent nitrogenase, a multicomponent enzyme capable of reducing dinitrogen to ammonia, have made a detailed understanding of the FeMo cofactor (FeMoco) active site electronic structure an ongo-ing challenge. Selective ...
The size and complexity of Mo-dependent nitrogenase, a multicomponent enzyme capable of reducing dinitrogen to ammonia, have made a detailed understanding of the FeMo cofactor (FeMoco) active site electronic structure an ongo-ing challenge. Selective substitution of sulfur by selenium in FeMoco affords a unique probe wherein local Fe-Se in-teractions can be directly interrogated via high-energy resolution fluorescence detected X-ray absorption spectroscop-ic (HERFD XAS) and extended X-ray absorption fine structure (EXAFS) studies. These studies reveal a significant asymmetry in the electronic distribution of the FeMoco, suggesting a more localized electronic structure picture than is typically assumed for iron-sulfur clusters. Supported by experimental small molecule model data in combination with time dependent density functional theory (TDDFT) calculations, the HERFD XAS data is consistent with an assign-ment of Fe2/Fe6 as an antiferromagnetically coupled diferric pair. HERFD XAS and EXAFS have also been applied to Se-substituted CO-inhibited MoFe protein, demonstrating the ability of these methods to reveal electronic and struc-tural changes that occur upon substrate binding. These results emphasize the utility of Se HERFD XAS and EXAFS for selectively probing the local electronic and geometric structure of FeMoco.