Activation of crystalline cellulose to cellulose III_I results in efficient hydrolysis by cellobiohydrolase

Abstract

Cellulose is a linear polymer of b-1,4-linked anhydrous glucose residues, and is the major component of plant cell walls. In nature, cellulose chains are packed into ordered arrays to form insoluble microfibrils, which are stabilized by cross-links involving intermolecular hydrogen bonds. Microfibrils generally consist of a mixture of disordered amorphous cellulose and cellulose I, which forms highly ordered crystalline regions. Cellulose I is further classified into two polymorphs, triclinic cellulose I a , which is found in algal and bacterial celluloses, and monoclinic cellulose I b, called cotton-ramie-type cellulose [1][2][3]. Although the differences in their physiological roles in the cell wall are uncertain, cellulose I a is more susceptible than cellulose I b to hydrolysis by cellulase [4,5].Cellulase is a generic term for enzymes hydrolyzing b-1,4-glucosidic linkages. If we consider the structure of microfibrils, however, cellulases should be subdivided into two categories, as all cellulases can hydrolyze amorphous cellulose, whereas only a limited number can hydrolyze crystalline cellulose [6]. The enzymes that hydrolyze crystalline cellulose are generally called cellobiohydrolases, and share similar twodomain structures, with a catalytic domain (CD) and a cellulose-binding domain (CBD) [7][8][9][10]. As the initial step of the reaction, they are adsorbed on the surface of crystalline cellulose via the CBD, then glucosidic linkages are hydrolyzed by the CD. As the reaction produces mainly cellobiose, a soluble b-1,4-glucosidic dimer, from insoluble substrates, the hydrolysis of crystalline cellulose occurs at a solid ⁄ liquid interface [11][12][13]. To evaluate such reactions, we recently developed a novel analysis based on surface density (q), defined as the amount of adsorbed enzyme (A) divided by the maximum adsorption of the enzyme (A max ) [14]. Using this parameter, we were able to analyze the hydrolysis of crystalline cellulose while taking account of the available substrate The crystalline polymorphic form of cellulose (cellulose I a -rich) of the green alga, Cladophora, was converted into cellulose III I and I b by supercritical ammonium and hydrothermal treatments, respectively, and the hydrolytic rate and the adsorption of Trichoderma viride cellobiohydrolase I (Cel7A) on these products were evaluated by a novel analysis based on the surface density of the enzyme. Cellobiose production from cellulose III I was more than 5 times higher than that from cellulose I. However, the amount of enzyme adsorbed on cellulose III I was less than twice that on cellulose I, and the specific activity of the adsorbed enzyme for cellulose III I was more than 3 times higher than that for cellulose I. When cellulose III I was converted into cellulose I b by hydrothermal treatment, cellobiose production was dramatically decreased, although no significant change was observed in enzyme adsorption. This clearly indicates that the enhanced hydrolysis of cellulose III I is related to the structure of the crystalline...

Traffic Jams Reduce Hydrolytic Efficiency of Cellulase on Cellulose Surface

“…Cellulose and enzyme preparations-Cellulose from green alga Cladophora sp., having more than 95% crystallinity, was used in this study (14,26). Cel7A from T. reesei was purified from a commercial cellulase mixture, Celluclast ® 1.5L (Novozyme, available from Sigma-Aldrich)…”

Enhancement of Ethanol Production from Napiergrass (<i>Pennisetum purpureum</i> Schumach) by a Low-Moisture Anhydrous Ammonia Pretreatment

“…Therefore, the ammonia fiber explosion (AFEX) pretreatment was performed by heating the biomass with ammonia gas at 90˚C under 21 atm [10,11]. This was interpreted as an increase in the cellulose IIII phase which has a high reactivity toward enzymatic degradation [12]. Also, soaking in aqueous ammonia (SAA) at 40˚C -80˚C in a room atmosphere was used as the pretreatment of lignocellulose [13,14].…”

Surface-Induced Frustration in Solid State Polymorphic Transition of Native Cellulose Nanocrystals

“…2,[4][5][6][7][8] Meanwhile, chemical properties are influenced by crystalline packing which often controls the accessibility and energetic state of the molecules, thereby affecting their chemical reactivity. 3,5,9 The extent (degree) of crystallinity and the quality of the polymorphs can be tuned in various ways, e.g., by helical inducers for polymers. [10][11][12] The presence of an interface can significantly affect the crystalline structure of materials, small molecules 13 and polymers 14,15 alike.…”