1gu6
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STRUCTURE OF THE PERIPLASMIC CYTOCHROME C NITRITE REDUCTASE FROM ESCHERICHIA COLI
OverviewOverview
The crystal structure and spectroscopic properties of the periplasmic, penta-heme cytochrome c nitrite reductase (NrfA) of Escherichia coli are, presented. The structure is the first for a member of the NrfA subgroup, that utilize a soluble penta-heme cytochrome, NrfB, as a redox partner., Comparison to the structures of Wolinella succinogenes NrfA and, Sulfospirillum deleyianum NrfA, which accept electrons from a, membrane-anchored tetra-heme cytochrome (NrfH), reveals notable, differences in the protein surface around heme 2, which may be the docking, site for the redox partner. The structure shows that four of the NrfA, hemes (hemes 2-5) have bis-histidine axial heme-Fe ligation. The catalytic, heme-Fe (heme 1) has a lysine distal ligand and an oxygen atom proximal, ligand. Analysis of NrfA in solution by magnetic circular dichroism (MCD), suggested that the oxygen ligand arose from water. Electron paramagnetic, resonance (EPR) spectra were collected from electrochemically poised NrfA, samples. Broad perpendicular mode signals at g similar 10.8 and 3.5, characteristic of weakly spin-coupled S = 5/2, S = 1/2 paramagnets, titrated with E(m) = -107 mV. A possible origin for these are the active, site Lys-OH(2) coordinated heme (heme 1) and a nearby bis-His coordinated, heme (heme 3). A rhombic heme Fe(III) EPR signal at g(z) = 2.91, g(y) =, 2.3, g(x) = 1.5 titrated with E(m) = -37 mV and is likely to arise from, bis-His coordinated heme (heme 2) in which the interplanar angle of the, imidazole rings is 21.2. The final two bis-His coordinated hemes (hemes 4, and 5) have imidazole interplanar angles of 64.4 and 71.8. Either, or, both, of these hemes could give rise to a "Large g max" EPR signal at, g(z)() = 3.17 that titrated at potentials between -250 and -400 mV., Previous spectroscopic studies on NrfA from a number of bacterial species, are considered in the light of the structure-based spectro-potentiometric, analysis presented for the E. coli NrfA.
About this StructureAbout this Structure
1GU6 is a Single protein structure of sequence from Escherichia coli with CA, HEC and GOL as ligands. Structure known Active Site: CA1. Full crystallographic information is available from OCA.
ReferenceReference
Structure and spectroscopy of the periplasmic cytochrome c nitrite reductase from Escherichia coli., Bamford VA, Angove HC, Seward HE, Thomson AJ, Cole JA, Butt JN, Hemmings AM, Richardson DJ, Biochemistry. 2002 Mar 5;41(9):2921-31. PMID:11863430
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