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 from 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 at 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 nonphenolic substrates, whereas both a histidine and an acidic residue may be involved in the binding of phenolic compounds. His and an Asp residue are indeed found at the bottom of a cavity which may be regarded as a suitable substrate channel for approaching to type I copper in the 3D homology models of the two laccases from Pleuorotus ostreatus (POXC and POXA1b) whose sequences are known.