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1.  Structural Basis of the Divergent Oxygenation Reactions Catalyzed by the Rieske Nonheme Iron Oxygenase Carbazole 1,9a-Dioxygenase 
Carbazole 1,9a-dioxygenase (CARDO), a Rieske nonheme iron oxygenase (RO), is a three-component system composed of a terminal oxygenase (Oxy), ferredoxin, and a ferredoxin reductase. Oxy has angular dioxygenation activity against carbazole. Previously, site-directed mutagenesis of the Oxy-encoding gene from Janthinobacterium sp. strain J3 generated the I262V, F275W, Q282N, and Q282Y Oxy derivatives, which showed oxygenation capabilities different from those of the wild-type enzyme. To understand the structural features resulting in the different oxidation reactions, we determined the crystal structures of the derivatives, both free and complexed with substrates. The I262V, F275W, and Q282Y derivatives catalyze the lateral dioxygenation of carbazole with higher yields than the wild type. A previous study determined the crystal structure of Oxy complexed with carbazole and revealed that the carbonyl oxygen of Gly178 hydrogen bonds with the imino nitrogen of carbazole. In these derivatives, the carbazole was rotated approximately 15, 25, and 25°, respectively, compared to the wild type, creating space for a water molecule, which hydrogen bonds with the carbonyl oxygen of Gly178 and the imino nitrogen of carbazole. In the crystal structure of the F275W derivative complexed with fluorene, C-9 of fluorene, which corresponds to the imino nitrogen of carbazole, was oriented close to the mutated residue Trp275, which is on the opposite side of the binding pocket from the carbonyl oxygen of Gly178. Our structural analyses demonstrate that the fine-tuning of hydrophobic residues on the surface of the substrate-binding pocket in ROs causes a slight shift in the substrate-binding position that, in turn, favors specific oxygenation reactions toward various substrates.
doi:10.1128/AEM.04000-13
PMCID: PMC3993299  PMID: 24584240
2.  Crystallization and preliminary X-ray diffraction analyses of the redox-controlled complex of terminal oxygenase and ferredoxin components in the Rieske nonhaem iron oxygenase carbazole 1,9a-dioxygenase 
A crystal was obtained of the complex between reduced terminal oxygenase and oxidized ferredoxin components of carbazole 1,9a-dioxygenase. The crystal belonged to space group P21 and diffracted to 2.25 Å resolution.
The initial reaction in bacterial carbazole degradation is catalyzed by carbazole 1,9a-dioxygenase, which consists of terminal oxygenase (Oxy), ferredoxin (Fd) and ferredoxin reductase components. The electron-transfer complex between reduced Oxy and oxidized Fd was crystallized at 293 K using the hanging-drop vapour-diffusion method with PEG 3350 as the precipitant under anaerobic conditions. The crystal diffracted to a maximum resolution of 2.25 Å and belonged to space group P21, with unit-cell parameters a = 97.3, b = 81.6, c = 116.2 Å, α = γ = 90, β = 100.1°. The V M value is 2.85 Å3 Da−1, indicating a solvent content of 56.8%.
doi:10.1107/S2053230X14018779
PMCID: PMC4188090  PMID: 25286950
Rieske nonhaem iron oxygenase; electron-transfer complex; terminal oxygenase; ferredoxin; carbazole 1,9a-dioxygenase
3.  Crystallization and preliminary X-ray diffraction studies of a terminal oxygenase of carbazole 1,9a-­dioxygenase from Novosphingobium sp. KA1 
The terminal oxygenase component (Oxy) of carbazole 1,9a-dioxygenase (CARDO) catalyzes dihydroxylation of the aromatic ring. The Oxy of CARDO from Novosphingobium sp. KA1 was crystallized and the crystals diffracted to a resolution of 2.1 Å.
Carbazole 1,9a-dioxygenase (CARDO) is the initial dioxygenase in the carbazole-degradation pathway of Novosphingobium sp. KA1. The CARDO from KA1 consists of a terminal oxygenase (Oxy), a putidaredoxin-type ferredoxin and a ferredoxin reductase. The Oxy from Novosphingobium sp. KA1 was crystallized at 277 K using the hanging-drop vapour-diffusion method with ammonium sulfate as the precipitant. Diffraction data were collected to a resolution of 2.1 Å. The crystals belonged to the monoclinic space group P21. Self-rotation function analysis suggested that the asymmetric unit contained two Oxy trimers; the Matthews coefficient and solvent content were calculated to be 5.9 Å3 Da−1 and 79.1%, respectively.
doi:10.1107/S1744309110034949
PMCID: PMC3001653  PMID: 21045300
carbazole; Novosphingobium; Rieske nonhaem iron oxygenases; sphingomonads; terminal oxygenases
4.  Crystallization and preliminary X-ray diffraction studies of a ferredoxin reductase component of carbazole 1,9a-dioxygenase from Novosphingobium sp. KA1 
The ferredoxin reductase component of carbazole 1,9a-dioxygenase (Red) is involved in electron transfer from NAD(P)H to ferredoxin. The class IIA Red from Novosphingobium sp. KA1 was crystallized and the crystal diffracted to a resolution of 1.58 Å.
Carbazole 1,9a-dioxygenase (CARDO) is the initial enzyme of the carbazole-degradation pathway. The CARDO of Novosphingobium sp. KA1 consists of a terminal oxygenase, a putidaredoxin-type ferredoxin and a ferredoxin-NADH oxidoreductase (Red) and is classified as a class IIA Rieske oxygenase. Red from KA1 was crystallized at 278 K by the hanging-drop vapour-diffusion method using PEG 4000. The crystal diffracted to 1.58 Å resolution and belonged to space group P32, with unit-cell parameters a = b = 92.2, c = 78.6 Å, α = γ = 90, β = 120°. Preliminary analysis of the X-ray diffraction data revealed that the asymmetric unit contained two Red monomers. The crystal appeared to be a merohedral twin, with a twin fraction of 0.32 and twin law (−h, −k, l).
doi:10.1107/S1744309110014491
PMCID: PMC2882777  PMID: 20516607
carbazole; Rieske nonhaem iron oxygenases; ferredoxin reductases
5.  Crystallization and preliminary X-ray diffraction studies of a novel ferredoxin involved in the dioxygenation of carbazole by Novosphingobium sp. KA1 
The ferredoxin component of carbazole 1,9a-dioxygenase (CARDO-F) is involved in an electron-transfer reaction. The CARDO-F from Novosphingobium sp. KA1 was crystallized under anaerobic conditions and diffracted to a resolution of 1.9 Å.
Novosphingobium sp. KA1 uses carbazole 1,9a-dioxygenase (CARDO) as the first dioxygenase in its carbazole-degradation pathway. The CARDO of KA1 contains a terminal oxygenase component and two electron-transfer components: ferredoxin and ferredoxin reductase. In contrast to the CARDO systems of other species, the ferredoxin component of KA1 is a putidaredoxin-type protein. This novel ferredoxin was crystallized at 293 K by the hanging-drop vapour-diffusion method using PEG MME 550 as the precipitant under anaerobic conditions. The crystals belong to space group C2221 and diffraction data were collected to a resolution of 1.9 Å (the diffraction limit was 1.6 Å).
doi:10.1107/S1744309108016278
PMCID: PMC2443972  PMID: 18607094
carbazole; putidaredoxin-type proteins; Rieske nonhaem iron oxygenases

Results 1-5 (5)