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

Author:

Zamocky Marcel12,Furtmüller Paul G.1,Bellei Marzia3,Battistuzzi Gianantonio3,Stadlmann Johannes4,Vlasits Jutta1,Obinger Christian1

Affiliation:

1. Metalloprotein Research Group, Division of Biochemistry, Department of Chemistry, University of Natural Resources and Applied Life Sciences, Muthgasse 18 A-1190 Vienna, Austria

2. Institute of Molecular Biology, Slovak Academy of Sciences, Bratislava, Slovakia

3. Department of Chemistry, University of Modena and Reggio Emilia, Modena, Italy

4. Glycobiology Research Group, Division of Biochemistry, Department of Chemistry, University of Natural Resources and Applied Life Sciences, Muthgasse 18 A-1190 Vienna, Austria

Abstract

Phytopathogenic fungi such as the rice blast fungus Magnaporthe grisea are unique in having two catalase/peroxidase (KatG) paralogues located either intracellularly (KatG1) or extracellularly (KatG2). The coding genes have recently been shown to derive from a lateral gene transfer from a (proteo)bacterial genome followed by gene duplication and diversification. Here we demonstrate that KatG1 is expressed constitutively in M. grisea. It is the first eukaryotic catalase/peroxidase to be expressed heterologously in Escherichia coli in high amounts, with high purity and with almost 100% haem occupancy. Recombinant MagKatG1 is an acidic, mainly homodimeric, oxidoreductase with a predominant five-co-ordinated high-spin haem b. At 25 °C and pH 7.0, the E0′ (standard reduction potential) of the Fe(III)/Fe(II) couple was found to be −186±10 mV. It bound cyanide monophasically 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 a Kd value of 1.5 μM. Its predominantly catalase activity was characterized by a pH optimum at 6.0 and kcat and Km values of 7010 s−1 and 4.8 mM respectively. In addition, it acts as a versatile peroxidase with a pH optimum in the range 5.0–5.5 using both one-electron [2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) o-dianisidine, pyrogallol or guaiacol] and two-electron (Br−, I− or ethanol) donors. Structure–function relationships are discussed with respect to data reported for prokaryotic KatGs, as is the physiological role of MagKatG1. Phylogenetic analysis suggests that (intracellular) MagKatG1 can be regarded as a typical representative for catalase/peroxidase of both phytopathogenic and saprotrophic fungi.

Publisher

Portland Press Ltd.

Subject

Cell Biology,Molecular Biology,Biochemistry

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