Description of a versatile peroxidase involved in the natural degradation of lignin that has both manganese peroxidase and lignin peroxidase substrate interaction sites

Two major peroxidases are secreted by the fungus Pleurotus eryngii in ligno cellulose cultures. One is similar to Phanerochaete chrysosporium manganese -dependent peroxidase, The second protein (PS1), although catalyzing the ox idation of Mn2+ to Mn3+ by H2O2, differs from the above enzymes by its mang anese-independent activity enabling it to oxidize substituted phenols and s ynthetic dyes, as well as the lignin peroxidase (LiP) substrate veratryl al cohol. This is by a mechanism similar to that reported for LiP, as evidence d by p-dimethoxybenzene oxidation yielding benzoquinone. The apparent kinet ic constants showed high activity on Mn2+, but methoxyhydroquinone was the natural substrate with the highest enzyme affinity (this and other phenolic substrates are not efficiently oxidized by the P, chrysosporium peroxidase s). A three-dimensional model was built using crystal models from four fung al peroxidase as templates. The model suggests high structural affinity of this versatile peroxidase with LiP but shows a putative Mn2+ binding site n ear the internal heme propionate, involving G1u(36), Glu(40), and Asp(181). A specific substrate interaction site for Mn2+ is supported by kinetic dat a showing noncompetitive inhibition with other peroxidase substrates, Moreo ver, residues reported as involved in LiP interaction with veratryl alcohol and other aromatic substrates are present in peroxidase PS1 such as His(82 ) at the heme-channel opening, which is remarkably similar to that of P, ch rysosporium LiP, and Trp(170) at the protein surface, These residues could be involved in two different hypothetical long range electron transfer path ways from substrate (His(82)-Ala(83)-Asn(84)-His(47)-heme and Trp(170)-Leu( 171)-heme) similar to those postulated for LiP.