Defining the Frontiers of Synergism between Cellulolytic Enzymes for Improved Hydrolysis of Lignocellulosic Feedstocks

Abstract

Lignocellulose has economic potential as a bio-resource for the production of value-added products (VAPs) and biofuels. The commercialization of biofuels and VAPs requires efficient enzyme cocktail activities that can lower their costs. However, the basis of the synergism between enzymes that compose cellulolytic enzyme cocktails for depolymerizing lignocellulose is not understood. This review aims to address the degree of synergism (DS) thresholds between the cellulolytic enzymes and how this can be used in the formulation of effective cellulolytic enzyme cocktails. DS is a powerful tool that distinguishes between enzymes’ synergism and anti-synergism during the hydrolysis of biomass. It has been established that cellulases, or cellulases and lytic polysaccharide monooxygenases (LPMOs), always synergize during cellulose hydrolysis. However, recent evidence suggests that this is not always the case, as synergism depends on the specific mechanism of action of each enzyme in the combination. Additionally, expansins, nonenzymatic proteins responsible for loosening cell wall fibers, seem to also synergize with cellulases during biomass depolymerization. This review highlighted the following four key factors linked to DS: (1) a DS threshold at which the enzymes synergize and produce a higher product yield than their theoretical sum, (2) a DS threshold at which the enzymes display synergism, but not a higher product yield, (3) a DS threshold at which enzymes do not synergize, and (4) a DS threshold that displays anti-synergy. This review deconvolutes the DS concept for cellulolytic enzymes, to postulate an experimental design approach for achieving higher synergism and cellulose conversion yields.

Influence of Cellulose-Cellulase Enzyme Digestibility in the Production of Glucose from Lignocellulosic Biomass Waste

“…The degree of crystallinity of lignocellulosic biomass is an important factor in the substrate enzyme interaction for a successful hydrolytic process [13]. The enzymatic hydrolysis of any cellulosic biomass is a biochemical reaction initiated by highly specific cellulase enzymes [14]. Cellulase enzymes consist of mixture of several enzymes, among which at least three major groups are actively involved in the enzymatic hydrolysis of cellulosic biomaterials [15,16].…”

A Recombinant Thermophilic and Glucose-Tolerant GH1 β-Glucosidase Derived from Hehua Hot Spring

“…Endoglucanase operates by hydrolyzing cellulose chains internally, whereas exoglucanase degrades cellulose from either the reducing or non-reducing end, yielding cellulose oligosaccharides. These oligosaccharides are subsequently hydrolyzed by β-glucosidase to yield glucose [ 3 ]. Serving as the rate-limiting enzyme in cellulose degradation, β-glucosidase mitigates feedback inhibition exerted by cellulose oligosaccharides on both endoglucanase and exoglucanase [ 4 ], a pivotal aspect ensuring the efficient utilization of cellulose.…”

Accumulation of complex oligosaccharides and CAZymes activity under acid conditions constitute the Thatcher+Lr9 defence responses to Puccinia triticina

“…The plant cell wall is composed of a polymeric network of cellulose micro-fibrils cross-linked by hemicellulose and lignin and embedded in pectin (Cosgrove 2000;Mnich et al 2020;Silva-Sanzana et al 2020). Cellulose micro-fibrils consist of β-D-1,4-glucan chains, which are the largest component of the cell wall (Mafa et al 2021). The intra-and intermolecular hydrogen bonds formed between the parallel or overlapping layers of cellulose fibres lead to microcrystalline cellulose (MCF) formation.…”

“…Xyloglucan is the major hemicellulose in dicotyledonous plants, while for most grass species arabinoxylans predominate (Mnich et al 2020). Moreover, cross-linking of xylan to lignin by ferulic acid restricts CWDEs such as xylanases and cellulases from degrading arabinoxylan and MCF, respectively (Mnich et al 2020;Mafa et al 2021).…”

“…Cellulases produced by pathogenic fungi are part of CWDEs classified under the GHs, which catalyse the hydrolysis of the β-1,4-glycosidic bond in cellulose (Cosgrove 2016;Silva-Sanzana et al 2020;Mafa et al 2021). Cellulases can be divided into three groups according to their mode of hydrolysis and substrate specificity, i.e., endoglucanases (EGs), cellobiohydrolase (CBHs), and β-glucosidases (Mafa et al 2021). Generally, β-glucosidases produce glucose from soluble cellooligosaccharides released by the catalytic activity of CBHs and EGs on the cellulose substrates (Kuhad et al 2016).…”