Characterisation of Dyp-type peroxidases from Pseudomonas fluorescens Pf-5: Oxidation of Mn(II) and polymeric lignin by Dyp1B.

Members of the DyP family of peroxidases in Gram-positive bacteria have recently been shown to oxidise Mn(II) and lignin model compounds. Gram-negative pseudomonads, which also show activity for lignin oxidation, also contain dyp-type peroxidase genes. Pseudomonas fluorescens Pf-5 contains three dyp-type peroxidases (35, 40 and 55kDa), each of which has been overexpressed in Escherichia coli, purified, and characterised. Each of the three enzymes shows activity for oxidation of phenol substrates, but the 35kDa Dyp1B enzyme also shows activity for oxidation of Mn(II) and Kraft lignin. Treatment of powdered lignocellulose with Dyp1B in the presence of Mn(II) and hydrogen peroxide leads to the release of a low molecular weight lignin fragment, which has been identified by mass spectrometry as a β-aryl ether lignin dimer containing one G unit and one H unit bearing a benzylic ketone. A mechanism for release of this fragment from lignin oxidation is proposed.