@article{HaveliusReschkeHornetal.2011,
  author    = {Havelius, Kajsa G. V. and Reschke, Stefan and Horn, Sebastian and Doerlng, Alexander and Niks, Dimitri and Hille, Russ and Schulzke, Carola and Leimk{\"u}hler, Silke and Haumann, Michael},
  title     = {Structure of the molybdenum site in YedY, a sulfite oxidase homologue from escherichia coli},
  series = {Inorganic chemistry},
  volume    = {50},
  journal   = {Inorganic chemistry},
  number    = {3},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {0020-1669},
  doi       = {10.1021/ic101291j},
  pages     = {741 -- 748},
  year      = {2011},
  abstract  = {YedY from Escherichia coil is a new member of the sulfite oxidase family of molybdenum cofactor (Moco)-containing oxidoreductases. We investigated the atomic structure of the molybdenum site in YedY by X-ray absorption spectroscopy, in comparison to human sulfite oxidase (hSO) and to a Mo(IV) model complex. The K-edge energy was indicative of Mo(V) in YedY, in agreement with X- and Q-band electron paramagnetic resonance results, whereas the hSO protein contained Mo(VI). In YedY and hSO, molybdenum is coordinated by two sulfur ligands from the molybdopterin ligand of the Moco, one thiolate sulfur of a cysteine (average Mo-S bond length of similar to 2.4 angstrom), and one (axial) oxo ligand (Mo=O, similar to 1.7 angstrom). hSO contained a second oxo group at Mo as expected, but in YedY, two species in about a 1:1 ratio were found at the active site, corresponding to an equatorial Mo-OH bond (similar to 2.1 angstrom) or possibly to a shorter M-O(-) bond. Yet another oxygen (or nitrogen) at a similar to 2.6 angstrom distance to Mo in YedY was identified, which could originate from a water molecule in the substrate binding cavity or from an amino acid residue close to the molybdenum site, i.e., Glu104, that is replaced by a glycine in hSO, or Asn45. The addition of the poor substrate dimethyl sulfoxide to YedY left the molybdenum coordination unchanged at high pH. In contrast, we found indications that the better substrate trimethylamine N-oxide and the substrate analogue acetone were bound at a similar to 2.6 angstrom distance to the molybdenum, presumably replacing the equatorial oxygen ligand. These findings were used to interpret the recent crystal structure of YedY and bear implications for its catalytic mechanism.},
  language  = {en}
}
@article{ReschkeNiksWilsonetal.2013,
  author    = {Reschke, Stefan and Niks, Dimitri and Wilson, Heather and Sigfridsson, Kajsa G. V. and Haumann, Michael and Rajagopalan, K. V. and Hine, Russ and Leimk{\"u}hler, Silke},
  title     = {Effect of exchange of the cysteine molybdenum ligand with selenocysteine on the structure and function of the active site in human sulfite oxidase},
  series = {Biochemistry},
  volume    = {52},
  journal   = {Biochemistry},
  number    = {46},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {0006-2960},
  doi       = {10.1021/bi4008512},
  pages     = {8295 -- 8303},
  year      = {2013},
  abstract  = {Sulfite oxidase (SO) is an essential molybdoenzyme for humans, catalyzing the final step in the degradation of sulfur-containing amino acids and lipids, which is the oxidation of sulfite to sulfate. The catalytic site of SO consists of a molybdenum ion bound to the dithiolene sulfurs of one molybdopterin (MPT) molecule, carrying two oxygen ligands, and is further coordinated by the thiol sulfur of a conserved cysteine residue. We have exchanged four non-active site cysteines in the molybdenum cofactor (Moco) binding domain of human SO (SOMD) with serine using site-directed mutagenesis. This facilitated the specific replacement of the active site Cys207 with selenocysteine during protein expression in Escherichia coli. The sulfite oxidizing activity (k(cat)/K-M) of SeSOMD4Ser was increased at least 1.5-fold, and the pH optimum was shifted to a more acidic value compared to those of SOMD4Ser and SOMD4Cys(wt) X-ray absorption spectroscopy revealed a Mow Se bond length of 2.51 A, likely caused by the specific binding of Sec207 to the molybdenum, and otherwise rather similar square-pyramidal S/Se(Cys)(O2MoS2)-S-VI(MPT) site structures in the three constructs. The low-pH form of the Mo(V) electron paramagnetic resonance (EPR) signal of SeSOM4Ser was altered compared to those of SOMD4Ser and SOMD4cy,(,), with g, in particular shifted to a lower magnetic field, due to the Se ligation at the molybdenum. In contrast, the Mo(V) EPR signal of the high-pH form was unchanged. The substantially stronger effect of substituting selenocysteine for cysteine at low pH as compared to high pH is most likely due to the decreased covalency of the Mo Se bond.},
  language  = {en}
}