Bifunctional catalase-peroxidase is secreted by the rice blast fungus Magnaporthe grisea during oxidative burst

Recently, it has been demonstrated that secreted bifunctional catalase-peroxidase is essential for the survival of the rice blast fungus Magnaporthe grisea during oxidative burst induced by theinfected plant (Tanabe et al., Mol. Plat. Microb. Inter. 2011.24:163–171). Magnaporthe grisea expresses several heme peroxidases and catalases of remarkable structural and functional variability.In this work we have focused on heme b containing catalase-peroxidases (KatGs). The fungus expresses an intracellularKatG most likely located in peroxisomes (MagKatG1) as wellas an extracellular variant that is secreted and might participatein host-pathogen interaction. Recombinant MagKatG1 and MagKatG2 have been expressed heterologously in E. coli and purified to homogeneity. We report UV–Vis and resonance Raman spectra of the ferric and ferrous forms as well as the standard reduction potential of the Fe(III)/ Fe(II) couple of both metalloproteins. Kinetic parameters of both catalase and peroxidase activities are reported probing several artificial one- and two electron donors at different pH. Both described KatGs differed slightly in their pH optima for both catalatic and peroxidatic reactions. For probing the peroxidatic reaction mode several (artificial) one and two electron donors (ascorbate, ABTS, 5-amino salicylic acid, L-DOPA, o-dianisidine, guaiacol, resorcinol, catechol, pyrogallol, luminol, tyrosine, tetramethylbenzidine and halides) were tested since the natural substrate is unknown. In addition ligand binding and reaction of the ferric enzymes with various hydrogen peroxide and peroxoacetic acid concentrations were tested by stopped-flow spectroscopy.Similarities and differences between these two KatGs and omologous heme peroxidases will be discussed and related to a putative role of KatG2 in plant-pathogen interaction.