Depolymerization of biorefinery lignin by improved laccases of the white‐rot fungus Obba rivulosa

Abstract

Fungal laccases are attracting enzymes for sustainable valorization of biorefinery lignins. To improve the lignin oxidation capacity of two previously characterized laccase isoenzymes from the white-rot fungus Obba rivulosa, we mutated their substrate-binding site at T1. As a result, the pH optimum of the recombinantly produced laccase variant rOrLcc2-D206N shifted by three units towards neutral pH. O. rivulosa laccase variants with redox mediators oxidized both the dimeric lignin model compound and biorefinery poplar lignin. Significant structural changes, such as selective benzylic aoxidation, were detected by nuclear magnetic resonance analysis, although no polymerization of lignin was observed by gel permeation chromatography. This suggests that especially rOrLcc2-D206N is a promising candidate for lignin-related applications.

The Laccase‐Lig Multienzymatic Multistep System in Lignin Valorization

“…TEMPO has been used in this effort as laccase mediator. β‐O‐4 aryl ether lignin model compounds were oxidized at the Cα secondary position by the laccase‐TEMPO system [32] . The laccase‐TEMPO system has been also reported as being able to oxidize lignin [33] .…”

“…β-O-4 aryl ether lignin model compounds were oxidized at the Cα secondary position by the laccase-TEMPO system. [32] The laccase-TEMPO system has been also reported as being able to oxidize lignin. [33] However, the oxoammonium ion generated upon oxidation of TEMPO by laccase has also been reported to oxidize primary hydroxy groups.…”

Fractionation of Technical Lignin from Enzymatically Treated Steam-Exploded Poplar Using Ethanol and Formic Acid

“…The aim of this work was to produce high-quality lignin for further valorization of biorefinery lignin side stream to fuels or aromatic platform chemicals. − Solvent fractionation methods allow for solvent recycling in closed circulation systems through distillation, while simultaneously, the lignin fraction is isolated as a part of the process. To evaluate the success of the treatments, the following quality criteria were defined for the isolated lignin: (1) Low residual carbohydrate content, which is generally expected to reduce industrial applicability of lignin .…”

Production of Recombinant Laccase From Coprinopsis cinerea and Its Effect in Mediator Promoted Lignin Oxidation at Neutral pH

“…In comparison, VIO showed over 80% yield with NS 51002, but rCcLcc9 was more efficient with SCN and MeS. Previously, we studied the improved laccase variants of the white rot fungus Obba rivulosa with phenolic mediators SCN and MeS at neutral pH, but their ability to oxidize adlerol ( 12) was slightly lower than that of rCcLcc9 (Wallenius et al, 2021). The phenolic mediators (e.g., SCN, MeS and MeOSA) are significantly more environmentally benign compared to the N-OH-type mediators (HBT, VIO, HPI) and ABTS that are suggested to produce toxic degradation products (Cañas and Camarero, 2010).…”