title: Ligand-bound S = 1/2 FeMo-cofactor of nitrogenase: hyperfine interaction analysis and implication for the central ligand X identity.
abstract: Broken symmetry density functional theory (BS-DFT) has been used to address the hyperfine parameters of the single atom ligand X, proposed to be coordinated by six iron ions in the center of the paramagnetic FeMo-cofactor (FeMoco) of nitrogenase. Using the X = N alternative, we recently found that any hyperfine signal from X would be small (calculated A(iso)(X = (14)N) = 0.3 MHz) due to both structural and electronic symmetry properties of the [Mo-7Fe-9S- X] FeMoco core in its resting S = 3/2 state. Here, we extend our BS-DFT approach to the 2e(-) reduced S = 1/2 FeMoco state. Alternative substrates coordinated to this FeMoco state effectively perturb the electronic and/or structural symmetry properties of the cofactor. Using an example of an allyl alcohol (H2C=CH-CH2-OH) product ligand, we consider three different binding modes at single iron site and three different BS-DFT spin state structures and show that this binding would enhance the key hyperfine signal A(iso)(X) by at least 1 order of magnitude (3.8 < or = A(iso)(X = (14)N) < or = 14.7 MHz), and this result should not depend strongly on the exact identity of X (nitrogen, carbon, or oxygen). The interstitial atom, when the nucleus has a nonzero magnetic moment, should therefore be observable by ESR methods for some ligand-bound FeMoco states. In addition, our results illustrate structural details and likely spin-coupling patterns for models for early intermediates in the catalytic cycle.
authors.affiliation: The Scripps Research Institute, Department of Molecular Biology TPC-15, 10550 North Torrey Pines Road, La Jolla, California 92037, USA. vovan@scripps.edu
authors.forename: Vladimir
authors.initials: V
authors.lastname: Pelmenschikov
authors.forename: David A
authors.initials: DA
authors.lastname: Case
authors.forename: Louis
authors.initials: L
authors.lastname: Noodleman
mesh_terms: D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D008983:Molybdoferredoxin / Q000737:chemistry*; D009591:Nitrogenase / Q000737:chemistry*
chemical_list: D008024:Ligands; D008983:Molybdoferredoxin; D009591:Nitrogenase