Molecular characterization of a novel thermostable laccase PPLCC2 from the brown rot fungus Postia placenta MAD-698-R

Abstract

Background: Laccase has been considered important for the degradation of lignocellulose by wood rot fungi. The properties and functions of laccase in white rot fungi have been investigated extensively, but those from brown rot fungi remain largely unknown. In this paper, a laccase isoforms Pplcc2 from the brown rot fungus Postia placenta MAD-698-R was expressed heterologously in Pichia pastoris GS115, purified and the properties of the enzyme were determined.

Results: The molecular weight of the protein was determined to be 67 kDa using SDS-PAGE. It cannot oxidize syringaldazine (SGZ), but it can oxidize 2,2'-azino-di-(3-ethylbenzothialozin-6-Sulfonic acid) (ABTS) and 2,6-dimethoxyphenol (DMP). Specific activity for ABTS was 1960 ± 19 Unit/mg. The catalytic constant (k_cat) was 1213 ± 18.3 s^- 1 for ABTS and 293.2 ± 21.9 s^- 1 for DMP. K_m was 22.08 μM for ABTS and 11.62 μM for DMP. The optimal pH for the oxidation of ABTS and DMP was 3.5 and 5.0 respectively. The optimal temperature for the oxidation of ABTS and DMP was 60°C.

Conclusions: This is the first identified thermo activated and thermostable laccase in brown rot fungi. This investigation will contribute to the understanding the roles played by laccases in brown rot fungi.