Reversible Protonated Resting State of the Nitrogenase Active Site
| Autor: | Douglas C. Rees, Christine N. Morrison, Thomas Spatzal |
|---|---|
| Rok vydání: | 2017 |
| Předmět: |
inorganic chemicals
chemistry.chemical_element Protonation 010402 general chemistry 01 natural sciences Biochemistry Article Catalysis law.invention Colloid and Surface Chemistry Oxidoreductase law Electron paramagnetic resonance chemistry.chemical_classification biology 010405 organic chemistry Active site Nitrogenase Substrate (chemistry) General Chemistry biology.organism_classification 0104 chemical sciences Crystallography chemistry Azotobacter vinelandii Molybdenum biology.protein |
| Zdroj: | Journal of the American Chemical Society |
| ISSN: | 1520-5126 0002-7863 |
| DOI: | 10.1021/jacs.7b05695 |
| Popis: | Protonated states of the nitrogenase active site are mechanistically significant since substrate reduction is invariably accompanied by proton uptake. We report the low pH characterization by X-ray crystallography and EPR spectroscopy of the nitrogenase molybdenum iron (MoFe) proteins from two phylogenetically distinct nitrogenases (Azotobacter vinelandii, Av, and Clostridium pasteurianum, Cp) at pHs between 4.5 and 8. X-ray data at pHs of 4.5–6 reveal the repositioning of side chains along one side of the FeMo-cofactor, and the corresponding EPR data shows a new S = 3/2 spin system with spectral features similar to a state previously observed during catalytic turnover. The structural changes suggest that FeMo-cofactor belt sulfurs S3A or S5A are potential protonation sites. Notably, the observed structural and electronic low pH changes are correlated and reversible. The detailed structural rearrangements differ between the two MoFe proteins, which may reflect differences in potential protonation sites at the active site among nitrogenase species. These observations emphasize the benefits of investigating multiple nitrogenase species. Our experimental data suggest that reversible protonation of the resting state is likely occurring, and we term this state “E_0H+”, following the Lowe–Thorneley naming scheme. |
| Databáze: | OpenAIRE |
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