Adsorption of enzyme onto lignins of liquid hot water pretreated hardwoods

Abstract

The adsorption of cellulase enzymes onto lignin is shown to be non-productive and therefore reduces enzymatic hydrolysis of liquid hot water pretreated cellulose. Among the enzyme components of Trichoderma reesei cellulase cocktail, β-glucosidase showed the strongest adsorption onto lignin. Only 2-18% of the initial β-glucosidase activity remained in the supernatant while 50-60% of cellobiohydrolase and endoglucanase activities were recovered after incubation with lignin. By increasing the pH to 5.5 and adding NaCl to a 200 mM, the free enzymes in the supernatant were increased but hydrolysis was not enhanced since optimal pH for enzymatic hydrolysis is at 4.8. Electrostatic interactions contributed to enzyme adsorption and their effect was most pronounced for T. reesei β-glucosidase which had high molecular weights (78-94 kDa) and high isoelectric points (pI 5.7-6.4). Since the enzyme components which are required to synergistically hydrolyze cellulose have different profiles (molecular weight, hydrophobicity and pI), they exhibit different adsorption behaviors with lignin, and thereby change the ratio of enzyme activities needed for synergism during cellulose hydrolysis. β-glucosidase from Aspergillus niger exhibits less adsorption than β-glucosidase from T. reesei. Supplemental addition of A. niger β-glucosidase to the enzyme mixture increases hydrolysis of pretreated hardwood by a factor of two. The analysis presented in this paper shows that lignins with higher guaiacyl content adsorb more cellulase enzymes, particularly β-glucosidase, and that adsorption of β-glucosidase onto lignin indirectly suppresses enzymatic hydrolysis of cellulose in pretreated hardwoods due to decreased hydrolysis of cellobiose which in turn accumulates and inhibits CBH.

On-Site Production of Enzymatic Cocktails Using a Non-conventional Fermentation Method with Agro-Industrial Residues as Renewable Feedstocks

“…The absorption bands related to lignin and phenolic compounds were less intense in the wheat bran spectrum than in the spectra for the other materials. Lignin can cause a decrease in cellulase activity due to its unproductive binding with enzymes [43]. Furthermore, phenolic compounds are well-known cellulase inhibitors and deactivators, and significantly affect cellulase activity [44,45].…”

Manipulation of Guaiacyl and Syringyl Monomer Biosynthesis in an Arabidopsis Cinnamyl Alcohol Dehydrogenase Mutant Results in Atypical Lignin Biosynthesis and Modified Cell Wall Structure

“…Lignin polymers interact with wall polysaccharides, adding to the structural integrity of the cell wall, and are responsible for rendering certain cell types impermeable to water (Boerjan et al, 2003); however, the interactions between lignin and cell wall polysaccharides and the enzymes that hydrolyze them greatly impede the conversion of these polymers for industrial and agricultural purposes (Pauly and Keegstra, 2010;Somerville et al, 2010;Carpita, 2012;Jung et al, 2012;Kim et al, 2015;Ko et al, 2015). To overcome this challenge, many strategies to reduce lignin content or alter lignin composition and structure have been implemented with the overall goal of increasing cell wall degradability (Vanholme et al, 2008;Van Acker et al, 2013).…”

Open Fermentative Production of L-Lactic Acid from Distillers’ Grains by Lactobacillus casei CICC 6056

“…In addition to temperature, pH can also affect both the cellulase hydrolysis and L. casei growth. The optimal pH for cellulase hydrolysis is 4.8 (Shang et al 2014;Ko et al 2015), which is within the range of pH change (pH 4.0 to 6.5) in the optimized pH condition (pH 6.5-24 h) for lactic acid production described above. Thus, the effect of pH on cellulase activity can be considered negligible within this specific pH range during lactic acid production.…”