Heme binding and peroxidase activity of a secreted minicatalase

Microbial pathogens often require efficient and robust H₂ O₂ scavenger activities to survive in the presence of reactive oxygen species generated by inflammatory responses. In addition to catalases and peroxidases, enzymes known to scavenge H₂ O₂ , a novel class of secreted minicatalases is found in diderm bacteria. Here, we characterize the Helicobacter pylori (Hp) minicatalase: a monomeric hemoprotein with catalase core homology. Overexpression of Hp minicatalase rescued a catalase/peroxidase-deficient Escherichia coli phenotype under aerobic conditions and limited H₂ O₂ stress. The purified enzyme lacks catalase activity, but has strong (k_cat > 100 s^-1 ) H₂ O₂ -dependent peroxidase activity toward a variety of organic substrates. Our investigations into heme binding revealed that the heme cofactor is assembled in the periplasm to form the functional holoprotein. Furthermore, we observed the presence of a disulfide bond near the heme cavity of Hp minicatalase, which is conserved in secreted minicatalases and, therefore, may play a role in heme binding.