The Effect of Xyloglucans on the Degradation of Cell-Wall-Embedded Cellulose by the Combined Action of Cellobiohydrolase and Endoglucanases from Trichoderma viride

Abstract

l w o endoglucanases of Trichoderma viride, endol and endolV, were assayed for their activity toward alkali-extracted apple xyloglucans. EndolV was shown to have a 60-fold higher activity toward xyloglucan than endol, whereas carboxymethyl cellulose and crystalline cellulose were better substrates for the latter. l h e enzymic degradation of cellulose embedded in the complex cell-wall matrix of apple fruit tissue has been studied using cellobiohydrolase (CBH) and these two different endoglucanases. A high-performance liquid chromatographic method (Aminex HPX-22H) was used to monitor the release of cellobiose and oligomeric xyloglucan fragments. Synergistic action between CBH and endoglucanases on cell-wallembedded cellulose was, with respect to their optimal ratio, slightly different from that reported for crystalline cellulose. l h e combination of endolv and CBH solubilized twice as much cellobiose compared to a combination of endol and CBH. Apparently, the concomitant removal of the xyloglucan coating from cellulose microfibrils by endolV is essential for an efficient degradation of cellulose in a complex matrix. Cellulose degradation slightly enhanced the solubilization of xyloglucans. lhese results indicate optimal degradation of cell-wall-embedded cellulose by a threeenzyme system consisting of an endoglucanase with high affinity toward cellulose (endol), a xyloglucanase (endolV), and CBH.

Standard assays do not predict the efficiency of commercial cellulase preparations towards plant materials

“…The commonly used filter paper activity assay (IUPAC; Decker et al, 2003;Ghose, 1987) is a good measure of the hydrolytic potential of a cellulase preparation. Filter paper is seen as highly crystalline cellulose, of which the degradation is depending on the combination of activities of endoglucanases (EG) and CBH, whereby the EG create new chain ends for the CBH to split of cellobiose (Beldman et al, 1988a;Teeri, 1997;Vincken et al, 1994). In Trichoderma reesei, about 80% of the total cellulolytic protein is consisted of CBH I (60%) and CBH II (20%) (Teeri, 1997).…”

“…The destarched fractions (WUS) of both wheat bran and grass were fractionated further by using 4 M KOH, which is known to selectively dissolve hemicelluloses (Verbruggen, 1995;Vincken et al, 1994). A KOH-soluble fraction was obtained (KOHss) and the remaining solids were collected as KOHres.…”

“…Therefore, enzymatic hydrolysis of the hemicelluloses is essential to facilitate complete cellulose degradation (Vincken et al, 1994(Vincken et al, , 1995. Knowing the diversity in xylanstructures a diversity of hemicellulases, for example endo/ exoxylanases, arabinosidases, acetylesterases, glucuronosidases, should be needed to degrade xylans.…”

Discovery of LPMO activity on hemicelluloses shows the importance of oxidative processes in plant cell wall degradation

“…The biological implications of NcLPMO9C having broad substrate specificity on xyloglucan could be to enable N. crassa to "shave off" hemicelluloses and thereby increase accessibility to otherwise recalcitrant regions of cellulose. Perhaps these enzymes attack junction zones between cellulose and hemicellulose, which may not be good substrates for glycoside hydrolases (39), because the activity of these enzymes depends on interactions with accessible single polysaccharide chains. LPMOs may be better suited to attack these zones because they are adapted to act on surfaces.…”

Degradation of apple cell wall material by commercial enzyme preparations

“…A lot of investigations has been made on the enzymatic degradation of cellulose-xyloglucan networks [32,33]. Cellulolytic enzymes are produced by a large number of microorganisms including fungi, actinomycetes, myxobacteria, and true bacteria.…”