Structural and kinetic characterization of native laccases from Pleurotas ostreatus, Rigidoporus lignosus, and Trametes trogii

A comparative study has been performed on five native laccases purified fro m the three basidiomycete fungi Pleurotus ostreatus, Rigidoporus lignosus, and Trametes trogii to relate their different catalytic capacities to their structural properties. Spectroscopic absorption features and EPR spectra a t various pH values of the five enzymes are very similar and typical of the blue oxidases. The analysis of the dependence of kinetic parameters on pH suggested that a histidine residue is involved in the binding of nonphenoli c substrates, whereas both a histidine and an acidic residue may be involve d in the binding of phenolic compounds. His and an Asp residue are indeed f ound at the bottom of a cavity which may be regarded as a suitable substrat e channel for approaching to type I copper in the 3D homology models of the two laccases from Pleuorotus ostreatus (POXC and POXA1b) whose sequences a re known.