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CRYSTAL STRUCTURES OF FERRIC-NO COMPLEXES OF FUNGAL NITRIC OXIDE REDUCTASE AND THEIR SER286 MUTANTS AT CRYOGENIC TEMPERATURE
Structural highlights
FunctionNOR_FUSOX Nitric oxide reductase which is involved in a dissimilatory reduction of nitrite. Acts as a nitric oxide reductase. Is able to reduce nitrate and nitrite to a gaseous form of N(2)O when oxygen supply is limited or discontinued. May function as a detoxification mechanism.[1] [2] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedFungal nitric-oxide reductase (NOR) is a heme enzyme that catalyzes the reduction of NO to N(2)O through its ferric-NO complex, the first intermediate of the catalysis. Crystal structures of the ferric-NO forms of wild type (WT) fungal NOR, and of the Ser(286) --> Val and Ser(286) --> Thr mutant enzymes were determined to 1.7-A resolution at cryogenic temperature (100 K). This shows a slightly tilted and bent NO binding to the heme iron, in sharp contrast to the highly bent NO coordination found in ferrous hemoproteins. In the WT structure, a specific hydrogen-bonding network that connects the active site to the solvent was identified, H(2)O(Wat(74))-Ser(286)-H(2)O(Wat(33))-Asp(393)-solvent. Wat(74) is located 3.10 A from the iron-bound NO. Replacement of Ser(286) with Val or Thr scarcely alters the NO coordination structure but expels the water molecules, Wat(74) from the active site. The Asp(393) mutation does not influence the position of Wat(74), but disrupts the hydrogen-bonding network at Wat(33), as evidenced by enzymatic, kinetic, and spectroscopic (resonance Raman and IR) results. The structural changes observed upon the Ser(286) or the Asp(393) mutation are consistent with the dramatic loss of the enzymatic activity for the NO reduction of fungal NOR. We have conclusively identified the water molecule, Wat(74), adjacent to the iron-bound NO as a proton donor to the Fe-NO moiety. In addition, we find the hydrogen-bonding network, H(2)O(Wat(74))-Ser(286)-H(2)O(Wat(33))-Asp(393), as a proton delivery pathway in the NO reduction reaction by fungal NOR. Proton delivery in NO reduction by fungal nitric-oxide reductase. Cryogenic crystallography, spectroscopy, and kinetics of ferric-NO complexes of wild-type and mutant enzymes.,Shimizu H, Obayashi E, Gomi Y, Arakawa H, Park SY, Nakamura H, Adachi S, Shoun H, Shiro Y J Biol Chem. 2000 Feb 18;275(7):4816-26. PMID:10671516[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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