Addition of Veratryl Alcohol Oxidase Activity to Manganese Peroxidase by Site-Directed Mutagenesis

Abstract

Manganese peroxidase and lignin peroxidase are ligninolytic heme-containing enzymes secreted by the white-rot fungusPhanerochaete chrysosporium.Despite structural similarity, these peroxidases oxidize different substrates. Veratryl alcohol is a typical substrate for lignin peroxidase, while manganese peroxidase oxidizes chelated Mn2+. By a single mutation, S168W, we have added veratryl alcohol oxidase activity to recombinant manganese peroxidase expressed inEscherichia coli.The kcatfor veratryl alcohol oxidation was 11 s−1, Kmfor veratryl alcohol ∼0.49 mM, and Kmfor hydrogen peroxide ∼25 μM at pH 2.3. The Kmfor veratryl alcohol was higher and Kmfor hydrogen peroxide was lower for this manganese peroxidase mutant compared to two recombinant lignin peroxidase isoenzymes. The mutant retained full manganese peroxidase activity and the kcatwas ∼2.6 × 102s−1at pH 4.3. Consistent with relative activities with respect to these substrates, Mn2+strongly inhibited veratryl alcohol oxidation. The single productive mutation in manganese peroxidase suggested that this surface tryptophan residue (W171) in lignin peroxidase is involved in catalysis.