Researchers isolated and characterized the laccase gene from Phlebia radiata, a lignin-degrading fungus. The gene contains nine introns with typical fungal promoter elements, including heat-shock regulatory sequences. Northern blot analysis demonstrated transcriptional regulation, with mRNA levels correlating with enzyme activity during fungal growth. The derived protein sequence shows homology to plant ascorbate oxidases, suggesting similar basic three-domain architecture. The Phlebia laccase is unique among characterized laccases in containing only two copper atoms and a prosthetic group pyrroloquinoline quinone (PQQ), with Lys193 potentially serving as the PQQ binding site. The intron positions are conserved between Phlebia and Coriolus laccases and cluster near β-strand boundaries, suggesting the enzyme evolved through exon shuffling and domain duplication mechanisms similar to other β-barrel proteins.

Key findings

• The P. radiata laccase gene contains nine introns and shows homology to plant ascorbate oxidases, suggesting conserved three-domain β-barrel structure
• Laccase gene expression is regulated at the transcriptional level, with mRNA abundance correlating with enzyme activity during ligninolytic enzyme production
• The Phlebia laccase uniquely contains two copper atoms and PQQ as a prosthetic group, with lysine-193 as the probable PQQ binding site
• Nine of ten introns in the Coriolus laccase gene are conserved in the Phlebia gene, with five positioned at β-strand boundaries, indicating evolution by exon shuffling