1e39

Flavocytochrome C3 from Shewanella frigidimarina histidine 365 mutated to alanine

spinqualitylabelsall models 1e39, resolution 1.80Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Structural highlights 1e39 is a 1 chain structure with sequence from Shewanella frigidimarina. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance. Method: X-ray diffraction, Resolution 1.8Å Ligands: FAD, FUM, GOL, HEC, NA Resources: FirstGlance, OCA, PDBe, RCSB, PDBsum, ProSAT Function FRDA_SHEFR Catalyzes fumarate reduction using artificial electron donors such as methyl viologen. The physiological reductant is unknown, but evidence indicates that flavocytochrome c participates in electron transfer from formate to fumarate and possibly also to trimethylamine oxide (TMAO). This enzyme is essentially unidirectional. 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 PubMed The active sites of respiratory fumarate reductases are highly conserved, indicating a common mechanism of action involving hydride and proton transfer. Evidence from the X-ray structures of substrate-bound fumarate reductases, including that for the enzyme from Shewanella frigidimarina [Taylor, P., Pealing, S. L., Reid, G. A., Chapman, S. K., and Walkinshaw, M. D. (1999) Nat. Struct. Biol. 6, 1108-1112], indicates that the substrate is well positioned to accept a hydride from N5 of the FAD. However, the identity of the proton donor has been the subject of recent debate and has been variously proposed to be (using numbering for the S. frigidimarina enzyme) His365, His504, and Arg402. We have used site-directed mutagenesis to examine the roles of these residues in the S. frigidimarina enzyme. The H365A and H504A mutant enzymes exhibited lower k(cat) values than the wild-type enzyme but only by factors of 3-15, depending on pH. This, coupled with the increase in K(m) observed for these enzymes, indicates that His365 and His504 are involved in Michaelis complex formation and are not essential catalytic residues. In fact, examination of the crystal structure of S. frigidimarina fumarate reductase has led to the proposal that Arg402 is the only plausible active site acid. Consistent with this proposal, we report that the R402A mutant enzyme has no detectable fumarate reductase activity. The crystal structure of the H365A mutant enzyme shows that, in addition to the replacement at position 365, there have been some adjustments in the positions of active site residues. In particular, the observed change in the orientation of the Arg402 side chain could account for the decrease in k(cat) seen with the H365A enzyme. These results demonstrate that an active site arginine and not a histidine residue is the proton donor for fumarate reduction. Identification of the active site acid/base catalyst in a bacterial fumarate reductase: a kinetic and crystallographic study.,Doherty MK, Pealing SL, Miles CS, Moysey R, Taylor P, Walkinshaw MD, Reid GA, Chapman SK Biochemistry. 2000 Sep 5;39(35):10695-701. PMID:10978153 From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See Also Flavocytochrome 3D structures

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