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Crystallization and preliminary X-ray diffraction of chlorite dismutase from Dechloromonas aromatica RCB.

ABSTRACT: Chlorite dismutase from Dechloromonas aromatica RCB, a novel b-type hemoprotein that catalyzes O-O bond formation, has been crystallized. Synchrotron X-ray diffraction data have been collected to 3.0 A resolution. The crystals belonged to space group P2(1)2(1)2(1), with unit-cell parameters a = 122.7, b = 202.9, c = 247.1 A.

SUBMITTER: Goblirsch BR

PROVIDER: S-EPMC2720342 | biostudies-literature | 2009 Aug

REPOSITORIES: biostudies-literature

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Crystallization and preliminary X-ray diffraction of chlorite dismutase from Dechloromonas aromatica RCB.

Goblirsch Brandon R BR Streit Bennett R BR DuBois Jennifer L JL Wilmot Carrie M CM

Acta crystallographica. Section F, Structural biology and crystallization communications 20090730 Pt 8

Chlorite dismutase from Dechloromonas aromatica RCB, a novel b-type hemoprotein that catalyzes O-O bond formation, has been crystallized. Synchrotron X-ray diffraction data have been collected to 3.0 A resolution. The crystals belonged to space group P2(1)2(1)2(1), with unit-cell parameters a = 122.7, b = 202.9, c = 247.1 A. ...[more]

PMID: 19652348

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Project description:The heme-based chlorite dismutases catalyze the unimolecular decomposition of chlorite (ClO2−) to yield Cl− and O2. The work presented here shows that chlorite dismutase from Dechloromonas aromatica (DaCld) also catalyzes the decomposition of bromite (BrO2−) with the evolution of O2 (kcat = (2.0±0.2)×102 s−1; kcat/KM = (1.2±0.2)×105 M−1 s−1 at pH 5.2). Stopped-flow studies of this BrO2− decomposition as a function of pH show that 1) the two-electron oxidized heme, compound I (Cpd I), is the primary accumulating heme intermediate during O2 evolution in acidic solution, 2) Cpd I and its one-electron reduction product, compound II (Cpd II) are present in varying ratios at intermediate pHs, and 3) only Cpd II is observed at pH 9.0. The pH dependences of Cpd I and Cpd II populations both yield a pKa of 6.7±0.1 in good agreement with the pKa of DaCld activity with ClO2−. The observation of a protein-based amino acid radical (AA•) whose appearance coincides with that of Cpd II supports the hypothesis that conversion of Cpd I to Cpd II occurs via proton-coupled electron transfer (PCET) from a heme-pocket amino acid to the oxidized porphyrinate of Cpd I to yield a dead-end decoupled state in which the holes decay at different rates. The site of the amino acid radical is tentatively assigned to Y118, which serves as a H-bond donor to propionate 6 (P6). The favoring of Cpd II:AA• accumulation in alkaline solution is consistent with the amino acid oxidation being rate limited by transfer of its proton to P6 having pKa 6.7. Examination of reaction mixtures comprising DaCld and ClO2− by resonance Raman and electron paramagnetic resonance spectroscopy reveal formation of Cpd II and •ClO2, which forms in preference to the analogous to AA• in the BrO2− reaction. Addition of ClO− to Cpd II did not yield O2. Together these results are consistent with heterolytic cleavage of the O–BrO− and O–ClO− bonds yielding Cpd I, which is the catalytically active intermediate. The long-lived Cpd II that forms subsequently, is inactive toward O2 production, and diminishes the amount of enzyme available to cycle through the active Cpd I intermediate.

Dataset Information

Crystallization and preliminary X-ray diffraction of chlorite dismutase from Dechloromonas aromatica RCB.

Publications

Crystallization and preliminary X-ray diffraction of chlorite dismutase from Dechloromonas aromatica RCB.

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