Molecular characteristics of two laccase from the basidiomycete fungus Polyporus brumalis.

Two laccase cDNAs, pblac1 and pblac2, were cloned from a white-rot fungus strain, Polyporus brumalis (KFRI 20912). The cloned cDNAs consisted of 1,829 bp and 1,804 bp, and their open reading frames encoded proteins of 520 and 524 amino acids, with calculated molecular masses of approximately 55.9 kDa and 56 kDa, respectively. The deduced amino acid sequences of each protein showed 70% similarity. The copper binding regions were conserved in both proteins, as in other fungal laccases. RT-PCR analysis revealed that the transcript levels of the two laccases increased progressively in shallow stationary culture liquid medium. The transcript level of each laccase was induced when the fungus was exposed to di-butyl phthalate (DBP), suggesting that the two laccases are involved in DBP degradation. The overexpression of the pblac1 gene was derived by the promoter of a gene for glyceraldehyde-3-phosphate dehydrogenase, using a homologous system. The activity of laccase in the transformants was significantly higher than that of the wild type. The identification of these laccase cDNAs was a first step to characterize the molecular events related to the lignin degradation ability of this basidiomycetous fungus, as well as the degradation of many recalcitrant xenobiotics.