Modeling the 3-D structure of a recombinant laccase from Trametes trogii active at a pH close to neutrality

A cDNA encoding a novel laccase from the white-rot fungus Trametes trogii was cloned and expressed in Pichia pastoris. The recombinant protein (Lcc2) exhibited kinetic parameters for both phenolic and non phenolic substrates that were different from the previously described Lcc1, the main laccase isoform expressed by T. trogii; in addition, the pH/activity profiles for phenolic substrates of Lcc2 were shifted upward by 1-1.5 pH units towards neutrality as compared to Lcc1. Comparative modeling of the two laccases (69.2% identity) showed that the overall fold of Lcc2 is very similar to Lcc1 and other laccases. The substrate cavity of Lcc2 contains the Asp residue which is thought to mediate the laccase activity at acidic pHs, whereas two hydrophobic residues (Phe, Ile) on the cavity orifice of Lcc2 replace the two polar residues (Thr, Ser) of Lcc1. These structural differences may be responsible for the unique kinetic performances of Lcc2.