The role of covalent heme to protein bonds in the formation and reactivity of redox intermediates of a bacterial peroxidase with high homology to human peroxidases

Oral presentatio

Intracellular catalase/peroxidase from the phytopathogenic rice blast fungus Magnaporthe grisea: expression analysis and biochemical characterization of the recombinant protein

Phytopathogenic fungi such as the rice blast fungus Magnaporthegrisea are unique in having two catalase/peroxidase (KatG)paralogues located either intracellularly (KatG1) or extracellularly(KatG2). The coding genes have recently been shownto derive from a lateral gene transfer from a (proteo)bacterialgenome followed by gene duplication and diversification. Here wedemonstrate thatKatG1 is expressed constitutively in M. grisea. Itis the first eukaryotic catalase/peroxidase to be expressed heterologouslyin Escherichia coli in high amounts, with high purity andwith almost 100% haem occupancy. Recombinant MagKatG1is an acidic, mainly homodimeric, oxidoreductase with a predominantfive-co-ordinated high-spin haem b. At 25◦C andpH 7.0, the E0 (standard reduction potential) of the Fe(III)/Fe(II)couple was found to be −186+−10 mV. It bound cyanidemonophasically with an apparent bimolecular rate constant of(9.0+−0.4)×105 M−1 · s−1 at pH 7.0 and at 25◦C and with aKd value of 1.5 μM. Its predominantly catalase activity wascharacterized by a pH optimum at 6.0 and kcat and Km valuesof 7010 s−1 and 4.8 mM respectively. In addition, it acts as aversatile peroxidase with a pH optimum in the range 5.0–5.5using both one-electron [2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) o-dianisidine, pyrogallol or guaiacol] andtwo-electron (Br−, I− or ethanol) donors. Structure–functionrelationships are discussed with respect to data reported forprokaryotic KatGs, as is the physiological role of MagKatG1.Phylogenetic analysis suggests that (intracellular) MagKatG1 canbe regarded as a typical representative for catalase/peroxidase ofboth phytopathogenic and saprotrophic fungi

Chlorite to chloride and O2 conversion: new lessons from structural and mechanistic investigations of chlorite dismutase

Oral Presentatio

Mechanistic studies on a new functional dimeric chlorite dismutase

Poster presentatio

New highly stable chlorinating bacterial peroxidase with autocatalytically formed covalent heme to protein bonds

Here, for the first time, an ancestral bacterial heme peroxidase has been cloned and purified. It is shown to catalyse (besides conventional peroxidase activity) bromide and chloride oxidation more efficiently than LPO and MPO. The structure-function relationships of this new peroxidase in relation to its mammalian counterparts and its putative physiological role are discussed

Understanding Chlorite Dismutase from Candidatus Nitrospira defluvii

Chlorite dismutases (Clds) are heme b containing oxidoreductases that convert chlorite to chloride and molecular oxygen. In order to elucidate the role of conserved heme cavity residues in the catalysis of this reaction comprehensive mutational and biochemical analyses of Cld from “Candidatus Nitrospira defluvii” (NdCld) were performed, using UV-vis spectroscopy, spectroelectrochemistry, pre-steady-state and steady-state kinetics as well as X-ray crystallography. The results obteined are described