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.
Highlights
Lignocellulosic feedstocks have huge economical potential as a source of value-added products (VAPs) and biofuel [1,2,3]
The above information relates to the fungal cellulolytic enzyme cocktails; it is clear that exoglucanase systems of bacterial organisms are different to those of fungal systems; for instance, Cel6A, Cel48A, Cel6B, and Cel9A sourced from Cellulomonas fimi were all processive on the different types of cellulose biomasses utilized, namely, phosphoric acid swollen cellulose (PASC), Avicel, and crystalline celluloses Iα or III from green algae [22]
EG (Cel7B) and MtLPMO9A synergy improved the hydrolysis of Avicel, bacterial cellulose, and sugarcane bagasse (SCB), which resulted in higher glucose production in the presence of Anβ-gl
Summary
Lignocellulosic feedstocks have huge economical potential as a source of value-added products (VAPs) and biofuel [1,2,3]. Several studies have shown that the expansins synergize with cellulases that hydrolyze the crystalline microfibrils of cellulose [4,30,31,33] Fungi possess another non-hydrolytic protein called swollenin, which is similar to the expansins [33]. Gize with cellulases that hydrolyze the crystalline microfibrils of cellulose [4,30,31,33] The lack of investigation of the DS during enzymatic cellulose saccharification is attributed to a focus on hydrolysis yields by researchers It appears that some enzyme combinations do not display a positive DS, yet these combinations demonstrate higher yields, in terms of soluble sugar production, compared to when the individual enzymes are used to hydrolyze the substrate.
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