Tagged: DFT

Elucidating the Structures of the Low- and High-pH Mo(V) Species in Respiratory Nitrate Reductase: A Combined EPR, 14,15N HYSCORE, and DFT Study

Julia Rendon, Frédéric Biaso, Pierre Ceccaldi, René Toci, Farida Seduk, Axel Magalon, Bruno Guigliarelli, and Stéphane Grimaldi. Inorg. Chem., 2017, 56 (8), pp 4422–4434. DOI: 10.1021/acs.inorgchem.6b03129

Combining multiple isotope-enrichment strategies in 98Mo and 15N nuclei together with EPR, HYSCORE spectroscopy, and DFT modeling, we propose a structural model of the low-pH Mo(V) species in respiratory nitrate reductase that implies coordination of the metal by a monodentate Asp222 ligand and a hydroxyl moiety. Furthermore, we unveil the peculiar involvement of the conserved Asn52 to the H-bond network around the Mo-cofactor in both low- and high-pH species.

ic-2016-031292_0010

Advertisements

DFT Investigation of the Molybdenum Cofactor in Periplasmic Nitrate Reductases : Structure of the Mo(V) EPR-Active Species

Biaso F., Burlat B., Guigliarelli B

Inorg Chem. 2012 Mar 19;51(6):3409-19. doi: 10.1021/ic201533p. Epub 2012 Mar 7.

The periplasmic nitrate reductase NAP belongs to the DMSO reductase family that regroups molybdoenzymes housing a bis-molybdopterin cofactor as the active site. Several forms of the Mo(V) state, an intermediate redox state in the catalytic cycle of the enzyme, have been evidenced by EPR spectroscopy under various conditions, but their structure and catalytic relevance are not fully understood. On the basis of structural data available from the literature, we built several models that reproduce the first coordination sphere of the molybdenum cofactor and used DFT methods to make magneto-structural correlations on EPR-detected species. “High-g” states, which are the most abundant Mo(V) species, are characterized by a low-anisotropy g tensor and a high gmin value. We assign this signature to a six-sulfur coordination sphere in a pseudotrigonal prismatic geometry with a partial disulfide bond. The “very high-g” species is well described with a sulfido ion as the sixth ligand. The “low-g” signal can be successfully associated to a Mo(V) sulfite–oxidase-type active site with only one pterin moiety coordinated to the molybdenum ion with an oxo or sulfido axial ligand. For all these species we investigate their catalytic activity using a thermodynamic point of view on the molybdenum coordination sphere. Beyond the periplasmic nitrate reductase case, this work provides useful magneto-structural correlations to characterize EPR-detected species in mononuclear molybdoenzymes.