Abstract
BackgroundCellulosic biomass, the earth’s most abundant renewable resource, can be used as substrates for biomanufacturing biofuels or biochemicals via in vitro synthetic enzymatic biosystems in which the first step is the enzymatic phosphorolysis of cellodextrin to glucose 1-phosphate (G1P) by cellodextrin phosphorylase (CDP). However, almost all the CDPs prefer cellodextrin synthesis to phosphorolysis, resulting in the low reaction rate of cellodextrin phosphorolysis for biomanufacturing.ResultsTo increase the reaction rate of cellodextrin phosphorolysis, synthetic enzyme complexes containing CDP and phosphoglucomutase (PGM) were constructed to convert G1P to glucose 6-phosphate (G6P) rapidly, which is an important intermediate for biomanufacturing. Four self-assembled synthetic enzyme complexes were constructed with different spatial organizations based on the high-affinity and high-specific interaction between cohesins and dockerins from natural cellulosomes. Thus, the CDP–PGM enzyme complex with the highest enhancement of initial reaction rate was integrated into an in vitro synthetic enzymatic biosystem for generating bioelectricity from cellodextrin. The in vitro biosystem containing the best CDP–PGM enzyme complex exhibited a much higher current density (3.35-fold) and power density (2.14-fold) than its counterpart biosystem containing free CDP and PGM mixture.ConclusionsHereby, we first reported bioelectricity generation from cellulosic biomass via in vitro synthetic enzymatic biosystems. This work provided a strategy of how to link non-energetically favorable reaction (cellodextrin phosphorolysis) and energetically favorable reaction (G1P to G6P) together to circumvent unfavorable reaction equilibrium and shed light on improving the reaction efficiency of in vitro synthetic enzymatic biosystems through the construction of synthetic enzyme complexes.
Highlights
Cellulosic biomass, the earth’s most abundant renewable resource, can be used as substrates for biomanufacturing biofuels or biochemicals via in vitro synthetic enzymatic biosystems in which the first step is the enzymatic phosphorolysis of cellodextrin to glucose 1-phosphate (G1P) by cellodextrin phosphorylase (CDP)
Designing strategy to accelerate cellulose phosphorolysis In the in vitro synthetic enzymatic biosystems powered by cellodextrin (Fig. 1a), CDP is responsible for the phosphorolysis of cellodextrin with the degree of polymerization (DP) of n (G(n)) to G1P and G (n−1) in the presence of phosphate
PGM [36], Gibbs free energies of converting cellohexaose and phosphate to cellopentaose and G1P by CDP and converting G1P to glucose 6-phosphate (G6P) by PGM are 3.2 ± 3.6 and − 7.4 ± 1.5 kJ mol−1 (Additional file 1: Table S1), respectively. It seems that the glucosyl units in cellodextrin can be converted to G6P efficiently via cascade reactions catalyzed by combination of CDP and PGM
Summary
Cellulosic biomass, the earth’s most abundant renewable resource, can be used as substrates for biomanufacturing biofuels or biochemicals via in vitro synthetic enzymatic biosystems in which the first step is the enzymatic phosphorolysis of cellodextrin to glucose 1-phosphate (G1P) by cellodextrin phosphorylase (CDP). Cellodextrins, which are water-soluble oligosaccharides with degrees of polymerization from two to six, can be prepared by the incomplete acid hydrolysis of cellulose [5] or enzymatic synthesis from glucose 1-phosphate (G1P) by cellodextrin phosphorylase (CDP, EC 2.4.1.49) [6]. Cellodextrins and CDP can be designed in many in vitro synthetic enzymatic biosystems by replacing starch and starch phosphorylase to produce hydrogen [8], bioelectricity [9] and value added chemicals [10]
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