Carbohydrate-binding Modules Recognize Fine Substructures of Cellulose

Structural insights into a unique cellulase fold and mechanism of cellulose hydrolysis

“…Indeed, competition experiments between cellulose-specific CBMs indicate that these proteins recognize specific topological features of the polysaccharide. Thus, CBMs belonging to families 4, 17, and 28 recognize distinct amorphous or paracrystalline regions of cellulose (24,25), and CBM2a, CBM3a, and CBM1, which bind to crystalline cellulose, also display distinct specificities (26). Many cellulose-degrading bacteria express a large number of endo-β-1,4-glucanases (27,28), exemplified by C. thermocellum that has the potential to synthesize approximately 30 endoglucanases.…”

The Use of Carbohydrate Binding Modules (CBMs) to Monitor Changes in Fragmentation and Cellulose Fiber Surface Morphology during Cellulase- and Swollenin-induced Deconstruction of Lignocellulosic Substrates

“…Samples were incubated for 60 min at 20°C in a FinePCR Combi-SV12 hybridization incubator at 30 rpm and then centrifuged at 16,000 ϫ g for 10 min in a benchtop centrifuge. The amount of CBM bound to the cotton was calculated by measuring the absorbance of the supernatant at 280 nm and determining the concentration of the residual CBM in the supernatant using the calculated molar extinction coefficients of 27,625 and 27,365 M Ϫ1 cm Ϫ1 for CBM2a and CBM44, respectively (29). The amount of CBM bound to the cotton was calculated by subtracting the amount of the residual CBM in the supernatant from the original amount of CBM added to the sample.…”

“…A Type B CBM (CBM44), which contains a cleft-shaped binding site that preferentially binds to amorphous regions of cellulose (30), was used as a probe to determine the amount of accessible amorphous cellulose, whereas a Type A CBM (CBM2a), with a planar, hydrophobic binding face that preferentially binds to crystalline cellulose regions (29), was used as a probe to determine the amount of accessible crystalline cellulose on the dissolving pulp fibers. The amount of each CBM bound to the variably hydrolyzed dissolving pulp over the course of 6 h was used to determine the relative amounts of accessible amorphous and accessible crystalline cellulose (Fig.…”

“…As described earlier by Boraston et al (28), CBMs can be broadly categorized into the three types: Type A, which binds to well ordered (crystalline) substrates via a planar hydrophobic surface composed of tryptophan and tyrosine residues; Type B, which binds via a binding cleft to individual carbohydrate chains; and Type C, which binds via a binding pocket to chain ends and smaller carbohydrate molecules (28). The CBM adsorption technique used in the work described here compares the adsorption of a Type A and a Type B CBM with cellulose where the Type A CBM has been shown to preferentially adsorb to the more crystalline regions of the cellulose surface (29), whereas the Type B CBM preferentially binds to the more amorphous regions (30). Several previous studies have used CBMs with different specificities for crystalline and amorphous regions of the cellulose to try to reveal the differences in surface morphology between the surrounding fiber and the cellulose within fiber dislocations (21,27,(31)(32)(33).…”

Differential recognition of plant cell walls by microbial xylan-specific carbohydrate-binding modules

“…Recent in vitro studies have started to unravel the possible biological significance for the overlapping specificities displayed by the different CBM families. Carrard et al (11) showed that Type A CBMs in families 1, 2a, and 3a could target different regions of purified crystalline cellulose, whereas McLean et al (12), employing f luorescently tagged CBM4, CBM17, and CBM28, showed that these modules recognize distinct substructures within amorphous cellulose. However, these studies have been restricted to defining the specificities of CBMs for purified polysaccharides that have an invariant chemical structure of ␤-1,4-linked glucose moieties.…”