Adsorption and mechanism of cellulase enzymes onto lignin isolated from corn stover pretreated with liquid hot water

Abstract

BackgroundIn the bioconversion of lignocellulosic substrates, the adsorption behavior of cellulase onto lignin has a negative effect on enzymatic hydrolysis of cellulose, decreasing glucose production during enzymatic hydrolysis, thus decreasing the yield of fermentation and the production of useful products. Understanding the interaction between lignin and cellulase is necessary to optimize the components of cellulase mixture, genetically engineer high-efficiency cellulase, and reduce cost of bioconversion. Most lignin is not removed during liquid hot water (LHW) pretreatment, and the characteristics of lignin in solid substrate are also changed. To understand the interactions between cellulase and lignin, this study investigated the change in the characteristics of lignin obtained from corn stover, as well as the behavior of cellulase adsorption onto lignin, under various severities of LHW pretreatment.ResultsLHW pretreatment removed most hemicellulose and some lignin in corn stover, as well as improved enzymatic digestibility of corn stover. After LHW pretreatment, the molecular weight of lignin obviously increased, whereas its polydispersity decreased and became more negative. The hydrophobicity and functional groups in lignin also changed. Adsorption of cellulase from Penicillium oxalicum onto lignin isolated from corn stover was enhanced after LHW pretreatment, and increased under increasing pretreatment severity. Different adsorption behaviors were observed in different lignin samples and components of cellulase mixtures, even in different cellobiohydrolases (CBHs), endo-beta-1, 4-glucanases (EGs). The greatest reduction in enzyme activity caused by lignin was observed in CBH, followed by that in xylanase and then in EG and β-Glucosidase (BGL). The adsorption behavior exerted different effects on subsequent enzymatic hydrolysis of various biomass substrates. Hydrophobic and electrostatic interactions may be important factors affecting different adsorption behaviors between lignin and cellulase.ConclusionsLHW pretreatment changed the characteristics of the remaining lignin in corn stover, thus affected the adsorption behavior of lignin toward cellulase. For different protein components in cellulase solution from P. oxalicum, electrostatic action was a main factor influencing the adsorption of EG and xylanase onto lignin in corn stover, while hydrophobicity affected the adsorption of CBH and BGL onto lignin.

Characteristics of Lignin Fractions from Dilute Acid Pretreated Switchgrass and Their Effect on Cellobiohydrolase from Trichoderma longibrachiatum

“…The adsorption data fitted well with the Langmuir isotherm. The maximum adsorptions of CBH were 7.63, 5.53, and 12.32 mg/g for the three lignin fractions, which were similar to the literature (Pareek et al, 2013;Zheng et al, 2013;Machado et al, 2015;Lu et al, 2016;Sun et al, 2016). It should be noted that the binding results could be affected by the different lignin isolation/pretreatment conditions, enzyme and test conditions (temperatures, lignin loading) used for determination.…”

“…It is widely accepted that lignin inhibits enzymatic hydrolysis of lignocellulosic biomass (Zeng et al, 2014;Lu et al, 2016;Saini et al, 2016;Yang et al, 2016). The adsorption of enzymes onto isolated lignins from dilute acid or hot water pretreated biomass has been studied (Zheng et al, 2013;Yu et al, 2014;Li et al, 2016;Lu et al, 2016;Sun et al, 2016). They reported key lignin-enzyme binding effects including the effects of condensed phenolic OH groups, methoxy groups, and the degree of lignin condensation on cellulase binding.…”

“…Lignin is typically derived from three hydroxycinnamyl alcohols (monolignols) that include p-coumaryl, coniferyl, and sinapyl alcohols which are connected via various types of linkages including aryl ether and carbon-carbon bonds (Ralph et al, 2004;Ragauskas et al, 2014). It is widely accepted that lignin inhibits enzymatic hydrolysis of lignocellulosic biomass (Zeng et al, 2014;Lu et al, 2016;Saini et al, 2016;Yang et al, 2016). The adsorption of enzymes onto isolated lignins from dilute acid or hot water pretreated biomass has been studied (Zheng et al, 2013;Yu et al, 2014;Li et al, 2016;Lu et al, 2016;Sun et al, 2016).…”

Hydrolysate-Recycled Liquid Hot Water Pretreatment of Reed Straw and Corn Stover for Bioethanol Production with Fed-Batch, Semi-Simultaneous Saccharification and Fermentation

“…Changes in the Benzene-Alcohol Extractive Contents of the WISs During LHW pretreatment, the water extracts were composed primarily of monosaccharides, a small amount of oligosaccharides, and water-soluble polysaccharides (Lu et al 2016). However, some substances could not be extracted with water, such as the terpene compounds, fats, waxes, and tannins.…”

Structural Characterization and Effect on Enzymatic Hydrolysis of Milled Wood Lignin Isolated from Reed Straw and Corn Stover Pretreated with Liquid Hot Water

“…Several reports have shown that the chemical and physical structures of lignin have a notable function in determining the magnitude of inhibition contributed by lignin to enzymatic hydrolysis (Ko et al 2015;Lu et al 2016). For example, Sewalt et al (1997) demonstrated that increasing the phenolic hydroxyl content of lignin also increases its inhibition activity towards enzymatic hydrolysis.…”