Importance of Mediators for Lignin Degradation by Fungal Laccase

Abstract

Three of the major ligninolytic enzymes, lignin peroxidase (LiP), manganese peroxidase (MnP), and laccase (LA), as well as the secretome of a white-rot fungi, Grammothele fuligo, are tested on three industrial lignins (organosolv, alkali, and Kraft), to investigate and study the differences in biodegradation reactions and mechanism of these three lignins. Strategies involving additives in laccase mediated systems were also considered to produce small phenolic compounds. Three new or underreported additives including 2,4,6-tri-tert-butylphenol (TTBP), 4-tert-butyl-2,6-dimethylphenol (TBDMP), and 3hydroxyanthranilic acid (HAA) are compared to three classic laccase mediators violuric acid (VA), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and 1-hydroxybenzotriazole (1-HBT). Decrease of molecular weight by up to 73% could be obtained on organosolv lignin with LA−VA systems, and by 49%, 43%, and 39% when LA was used with ABTS, TBDMP, and 1-HBT, respectively. In-depth analysis of the degradation products by quantitative 2D HMQC NMR indicated that the oxidation is mediator-dependent and provides new insights on the enzymatic mechanism.

Full quantum mechanical modeling of the enzyme-substrate system: how laccase detoxifies aflatoxin

“…T. versicolor (or turkey tail, in layman terms) is a Basidiomycetes that grows on rotting wood; it employs laccase to degrade lignin to adhere to the wood and scavenge it for nutrients. Therefore, laccase activity is central to its ecological role, and it is reasonable to assume that it has undergone a constant selective pressure to refine its interaction with lignin, an interaction often mediated by accessory interactors [27]. The progressive evolution of a lignin degrading, laccase-based enzymatic system has led to an active site of the highest redox potential among multi-copper oxidases, which is a good asset to degrade the aromatic moieties of aflatoxins.…”

“…To calculate the binding site, we performed KS-DFT calculations on the docked enzyme-toxin system using the linear scaling mode of the BigDFT code [27], [28] with the PBE approximation, HGH pseudopotentials, and a grid spacing of 0.4 atomic units. The charge of the enzyme was determined by minimizing the energy of the gas phase enzyme with respect to the number of electrons.…”

Applications of Microbial Laccases: Patent Review of the Past Decade (2009–2019)

“…A wide array of compounds has been used in the literature as mediators, such as 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), ABTS ( [14], 1-hydroxybenzotriazole (1-HBT) [38], syringaldehyde, vanillin, α-naphthol [39], and others. The laccase-mediator system (LMS) has been used for the removal of residual lignin in biomass [13,40], or the treatment of recalcitrant pollutants, such as antibiotics [39] or other drugs [41], pesticides [42], industrial textile wastewater [43], and even synthetic fragrances [44]. LMS has been also used for the oxidative synthesis of platform chemicals [45].…”

“…Extensive literature is available on laccases from basidiomycetes, especially white-rot fungi [12], while some laccases have also been characterized from ascomycete saprotrophs and ectomycorrhizal species. Many studies focus on lignin degradation and wood modification by laccases, with or without the use of mediators [13][14][15], and as a result, laccases are now considered essential enzymes in fungal lignocellulose degradation.Most bacterial laccases are active in a wide range of temperatures and pH values (30-85 • C and 3.0-9.0, respectively) [16], but the most extremophilic laccases found so far are of bacterial origin,…”

Designing a bioremediator: mechanistic models guide cellular and molecular specialization

“…In particular, laccase ability to break aromatic moieties makes it promising against the most recalcitrant hydrocarbons. On laccase and its potential applications, existing work [48,[57][58][59][60][61] can be used as a solid ground for further developments.…”