Identification of a new member of Pleurotus ostreatus laccase family from mature fruiting body

Laccases (benzenediol:oxygen oxidoreductases, EC 1.10.3.2) are blue multicopper oxidases, catalyzing the oxidation of an array of aromatic substrates concomitantly with the reduction of molecular oxygen to water. Most of the known laccases have fungal or plant origins, although few laccases have been also identified in bacteria and insects. Most of the fungal laccases reported thus far are extra-cellular enzymes, whereas only few enzymes from fruiting bodies have been described so far. Multiple isoforms of laccases are usually secreted by each fungus depending on species and environmental conditions. As a fact, a laccase gene family has been demonstrated in the white-rot fungus Pleurotus ostreatus. This work allowed identification and characterization of the first laccase isoenzyme from the fruiting body of P. ostreatus. Discovery through mass spectrometry of LACC12 proves the expression of a functional protein by the related deduced encoding transcript. The topology of phylogenetic tree of fungal laccases proves that LACC12 falls in cluster with the members of P. ostreatus LACC10 (=POXC) subfamily, although lacc12 deduced intron–exon structure differs from that of the subfamily members and the related locus is located in a different chromosome. Results show that the evolutionary pattern of lacc12 and that of the other laccase isozyme genes may have evolved independently, possibly through duplication–divergence events. The reported data add a new piece to the knowledge about P. ostreatus laccase multigene family and shed light on the role(s) played by individual laccase isoforms in P. ostreatus.