Molecular characteristics of two laccase from the basidiomycete fungus Polyporus brumalis

Preparation and Characterization of High Mechanical Strength Chitosan/Oxidized Tannic Acid Composite Film with Schiff Base and Hydrogen Bond Crosslinking

Chitosan-based composite films with good biodegradability, biocompatibility, and sustainability are extensively employed in the field of food packaging. In this study, novel chitosan/tannic acid (CTA) and chitosan/oxidized tannic acid (COTA) composite films with excellent mechanical and antibacterial properties were prepared using a tape casting method. The results showed that, when 20% tannic acid (TA) was added, the tensile strength of the CTA composite film was 80.7 MPa, which was 89.4% higher than that of the pure chitosan (CS) film. TA was oxidized to oxidized tannic acid (OTA) with laccase, and the phenolic hydroxyl groups were oxidized to an o-quinone structure. With the addition of OTA, a Schiff base reaction between the OTA and CS occurred, and a dual network structure consisting of a chemical bond and hydrogen bond was constructed, which further improved the mechanical properties. The tensile strength of 3% COTA composite film was increased by 97.2% compared to that of pure CS film. Furthermore, these CTA films with significant antibacterial effects against Escherichia coli (E. coli) are likely to find uses in food packaging applications.

Cloning and functional analysis of a laccase gene during fruiting body formation in Hypsizygus marmoreus

The Hypsizygus marmoreus laccase gene (lcc1) sequence was cloned and analyzed. The genomic DNA of lcc1 is 2336 bp, comprising 13 introns and 14 exons. The 1626-bp full-length cDNA encodes a mature laccase protein containing 542 amino acids, with a 21-amino acid signal peptide. Phylogenetic analysis showed that the lcc1 amino acid sequence is homologous to basidiomycete laccases and shares the highest similarity with Flammulina velutipes laccase. A 2021-bp promoter sequence containing a TATA box, CAAT box, and several putative cis-acting elements was also identified. To study the function of lcc1, we first overexpressed lcc1 in H. marmoreus and found that the transgenic fungus producing recombinant laccase displayed faster mycelial growth than the wild-type (wt) strain. Additionally, primordium initiation was induced 3-5 days earlier in the transgenic fungus, and fruiting body maturation was also promoted approximately five days earlier than in the wt strain. Furthermore, we detected that lcc1 was sustainably overexpressed and that laccase activity was also higher in the transgenic strains compared with the wt strain during development in H. marmoreus. These results indicate that the H. marmoreus lcc1 gene is involved in mycelial growth and fruiting body initiation by increasing laccase activity.

Purification and characterization of the extracellular laccase produced by Trametes polyzona WR710-1 under solid-state fermentation

Laccase from Trametes polyzona WR710-1 was produced under solid-state fermentation using the peel from the Tangerine orange (Citrus reticulata Blanco) as substrate, and purified to homogeneity. This laccase was found to be a monomeric protein with a molecular mass of about 71 kDa estimated by SDS-PAGE. The optimum pH was 2.0 for ABTS, 4.0 for L-DOPA, guaiacol, and catechol, and 5.0 for 2,6-DMP. The K(m) value of the enzyme for the substrate ABTS was 0.15 mM, its corresponding V(max) value was 1.84 mM min(-1), and the k(cat)/K(m) value was about 3960 s(-1)  mM(-1). The enzyme activity was stable between pH 6.0 and 8.0, at temperatures of up to 40 °C. The laccase was inhibited by more than 50% in the presence of 20 mM NaCl, by 95% at 5 mM of Fe(2+), and it was completely inhibited by 0.1 mM NaN(3). The N-terminal amino acid sequence of this laccase is AVTPVADLQISNAGISPDTF, which is highly similar to those of laccases from other white-rot basidiomycetes.

Effective induction of pblac1 laccase by copper ion in Polyporus brumalis ibrc05015

Polyporus brumalis ibrc05015 is a strain capable of high laccase (Lac) production. Among several inducers, 0.25 mM copper was most effective for Lac production. One of the Lacs induced by copper was PbLac1, and its transcription was induced within 60 min after copper addition. The promoter region of pblac1 contained six putative metal response elements and one Ace1 consensus cis-element. We cloned the P. brumalis PbAce1 transcription factor, a homologue of Saccharomyces cerevisiae transcription factor Ace1, which regulates metallothionein genes in response to excess copper. PbAce1 complemented the function of Ace1 in an S. cerevisiae Δace strain. The conserved N-terminal copper-fist DNA binding domain of PbAce1 was required for complementation. In the PbAce1 complemented Δace1 strain, the pblac1 promoter was constitutively expressed at a high level, independent of copper concentration. PbAce1 has two Cys-rich repeat motifs (PbC1 and PbC2), which are similar to the Cys-rich repeat domain in metallothionein proteins, and are uniquely conserved in the C-terminal domain of basidiomycetous Ace1 sequences. These C-terminal domains could be involved in copper sensing and concentration-dependent Lac production in basidiomycetous fungi.

Decolorization of Remazol Brilliant Blue R by a purified laccase of Polyporus brumalis

A white rot basidiomycete Polyporus brumalis has been reported to induce two laccase genes under degradation conditions of dibutylphthalate. When this fungus was grown in a minimal medium, one laccase enzyme was detected by the native polyacrylamide gel electrophoresis. A laccase was purified through ammonium sulfate precipitation and ion exchange chromatography, and the estimated molecular weight was 70 kDa. The optimum pH and temperature of the purified laccase was pH 4.0 and 20 °C, respectively. The K (m) value of the enzyme was 685.0 μM, and the V (max) was 0.147 ODmin(-1) unit(-1) for o-tolidine. Purified laccase showed effective decolorization of a dye, Remazol Brilliant Blue R (RBBR), without any laccase mediator. However, this effect was reduced by a laccase inhibitor, kojic acid, which confirmed that the laccase was directly involved in the decolorization of RBBR.