Toward combined delignification and saccharification of wheat straw by a laccase-containing designer cellulosome

Abstract

Efficient breakdown of lignocellulose polymers into simple molecules is a key technological bottleneck limiting the production of plant-derived biofuels and chemicals. In nature, plant biomass degradation is achieved by the action of a wide range of microbial enzymes. In aerobic microorganisms, these enzymes are secreted as discrete elements in contrast to certain anaerobic bacteria, where they are assembled into large multienzyme complexes termed cellulosomes. These complexes allow for very efficient hydrolysis of cellulose and hemicellulose due to the spatial proximity of synergistically acting enzymes and to the limited diffusion of the enzymes and their products. Recently, designer cellulosomes have been developed to incorporate foreign enzymatic activities in cellulosomes so as to enhance lignocellulose hydrolysis further. In this study, we complemented a cellulosome active on cellulose and hemicellulose by addition of an enzyme active on lignin. To do so, we designed a dockerin-fused variant of a recently characterized laccase from the aerobic bacterium Thermobifida fusca. The resultant chimera exhibited activity levels similar to the wild-type enzyme and properly integrated into the designer cellulosome. The resulting complex yielded a twofold increase in the amount of reducing sugars released from wheat straw compared with the same system lacking the laccase. The unorthodox use of aerobic enzymes in designer cellulosome machinery effects simultaneous degradation of the three major components of the plant cell wall (cellulose, hemicellulose, and lignin), paving the way for more efficient lignocellulose conversion into soluble sugars en route to alternative fuels production.

Genome sequencing and functional characterization of aDictyopanus pusillusfungal extract offers a promising alternative for lignocellulose pretreatment of oil palm residues

“…Reducing sugar release was observed when the cellulolytic enzymatic extract from T. reesei was used alone (20.84 ± 0.7 g.g -1 ). Higher reducing sugar release from EFB was also observed when the cellulolytic enzymatic extract from T. reesei was used with the commercial laccase enzyme from T. versicolor (46.47 ± 5.9 g.g -1 ) or the enzymatic extract from D. pusillus (44.80 ± 5.21 g.g -1 ), confirming that ligninolytic enzymes such as laccases favor cellulose hydrolysis, as previously reported (72,73). These results suggest that a combination of cellulolytic and ligninolytic enzymes enhance the release of reducing sugars.…”

Laccases as a Potential Tool for the Efficient Conversion of Lignocellulosic Biomass: A Review

“…Not investigated Reducing sugar yields increased 2.0-fold [121] Milled sugarcane bagasse Bacterial laccase from T. fusca SEM analysis of laccase-treated sample shows smaller shatters 2-fold increment in sugar production [122] Steam-exploded wheat straw…”

“…AH28-2 laccase in T. reesei. With a similar concept, Davidi et al [121] have recently incorporated laccase activity into a cellulase-and xylanase-containing cellulosome. For that, authors designed a dockerin-fused variant of a recently characterized laccase from the aerobic bacterium Thermobifida fusca [122].…”

Bringing plant cell wall‐degrading enzymes into the lignocellulosic biorefinery concept

“…Enhanced cellulosome activity has been achieved by incorporating accessory enzymes and proteins such as β‐glucosidases, LPMOs, and expansins . Moreover, the inclusion of a laccase in a designer cellulosome bearing endoglucanase, exoglucanase, and xylanase subunits has been shown to have a synergistic effect on wheat straw decomposition, combining holocellulose and lignin breakdown …”