3unc | pdb_00003unc

Crystal Structure of Bovine Milk Xanthine Dehydrogenase to 1.65A Resolution

spinqualitylabelsall models 3unc, resolution 1.65Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Structural highlights 3unc is a 2 chain structure with sequence from Bos taurus. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance. Ligands: CA, CO3, FAD, FES, GOL, MOS, MTE, SAL Related: 1fo4, 3una, 3uni Resources: FirstGlance, OCA, PDBe, RCSB, PDBsum, ProSAT Function [XDH_BOVIN] Key enzyme in purine degradation. Catalyzes the oxidation of hypoxanthine to xanthine. Catalyzes the oxidation of xanthine to uric acid. Contributes to the generation of reactive oxygen species. Publication Abstract from PubMed In mammals, xanthine oxidoreductase can exist as xanthine dehydrogenase (XDH) and xanthine oxidase (XO). The two enzymes possess common redox active cofactors, which form an electron transfer (ET) pathway terminated by a flavin cofactor. In spite of identical protein primary structures, the redox potential difference between XDH and XO for the flavin semiquinone/hydroquinone pair (E(sq/hq)) is ~170 mV, a striking difference. The former greatly prefers NAD(+) as ultimate substrate for ET from the iron-sulfur cluster FeS-II via flavin while the latter only accepts dioxygen. In XDH (without NAD(+)), however, the redox potential of the electron donor FeS-II is 180 mV higher than that for the acceptor flavin, yielding an energetically uphill ET. On the basis of new 1.65, 2.3, 1.9, and 2.2 A resolution crystal structures for XDH, XO, the NAD(+)- and NADH-complexed XDH, E(sq/hq) were calculated to better understand how the enzyme activates an ET from FeS-II to flavin. The majority of the E(sq/hq) difference between XDH and XO originates from a conformational change in the loop at positions 423-433 near the flavin binding site, causing the differences in stability of the semiquinone state. There was no large conformational change observed in response to NAD(+) binding at XDH. Instead, the positive charge of the NAD(+) ring, deprotonation of Asp429, and capping of the bulk surface of the flavin by the NAD(+) molecule all contribute to altering E(sq/hq) upon NAD(+) binding to XDH. Protein conformational gating of enzymatic activity in xanthine oxidoreductase.,Ishikita H, Eger BT, Okamoto K, Nishino T, Pai EF J Am Chem Soc. 2012 Jan 18;134(2):999-1009. Epub 2011 Dec 29. PMID:22145797 From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See Also Xanthine dehydrogenase

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