title: Spectroscopic and electronic structure studies of symmetrized models for reduced members of the dimethylsulfoxide reductase enzyme family.
abstract: Enzymes belonging to the dimethylsulfoxide reductase (DMSOR) family of pyranopterin Mo enzymes have a unique active-site geometry in the reduced form that lacks a terminal oxo ligand, unlike the reduced active sites of other pyranopterin Mo enzymes. Furthermore, the DMSOR family is characterized by the coordination of two pyranopterin-ene-1,2-dithiolate ligands in their active sites, which is distinctive among the other pyranopterin Mo enzymes but analogous to all of the currently known tungsten-containing enzymes. Electronic absorption, resonance Raman, and ground- and excited-state density functional calculations of symmetrized analogues of the reduced DMSOR active site ([NEt4][Mo(IV)(QAd)(S2C2Me2)2] where Ad = 2-adamantyl; Q = O, S, Se) have allowed for a detailed description of Mo-bisdithiolene electronic structure in the absence of a strong-field oxo ligand. The electronic absorption spectra are dominated by dithiolene S --> Mo charge-transfer transitions, and the totally symmetric Mo-S Raman stretch is observed at approximately 400 cm(-1) for all three complexes. These data indicate that the Mo-bisdithiolene bonding scheme in high-symmetry [Mo(QAd)(S2C2Me2)2]- complexes is not strongly perturbed by the apical QAd- ligands, but instead, the dithiolene ligands define the t(2g) ligand field splitting. The effects of conserved geometric distortions observed in DMSOR, relative to these high-symmetry models, were explored by spectroscopically calibrated bonding calculations, and the results are discussed within the context of electronic structure contributions to ground-state destabilization and transition-state stabilization. The specific electronic structure tuning of the endogenous amino acid ligation on the mechanism of DMSOR is also discussed.
authors.affiliation: Department of Chemistry, The University of New Mexico, MSC03 2060, Albuquerque, New Mexico 87131, USA.
authors.forename: Rebecca L
authors.initials: RL
authors.lastname: McNaughton
authors.forename: Booyong S
authors.initials: BS
authors.lastname: Lim
authors.forename: Sushilla Z
authors.initials: SZ
authors.lastname: Knottenbelt
authors.forename: Richard H
authors.initials: RH
authors.lastname: Holm
authors.forename: Martin L
authors.initials: ML
authors.lastname: Kirk
mesh_terms: D001665:Binding Sites; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D011789:Quantum Theory; D013056:Spectrophotometry, Ultraviolet; D013059:Spectrum Analysis, Raman
chemical_list: D007506:Iron-Sulfur Proteins; D010088:Oxidoreductases; C045664:dimethyl sulfoxide reductase