Fluorimetric estimation of exo-cellobiohydrolase and β-d-glucosidase activities in cellulase from Aspergillus fumigatus Fresenius

Enzymatic Activities of Polycatalytic Complexes with Nonprocessive Cellulases Immobilized on the Surface of Magnetic Nanoparticles

Polycatalytic enzyme complexes made by immobilization of industrial enzymes on polymer- or nanoparticle-based scaffolds are technologically attractive due to their recyclability and their improved substrate binding and catalytic activities. Herein, we report the synthesis of polycatalytic complexes by the immobilization of nonprocessive cellulases on the surface of colloidal polymers with a magnetic nanoparticle core and the study of their binding and catalytic activities. These polycatalytic cellulase complexes have increased binding affinity for the substrate. But due to their larger size, these complexes were unable to access to the internal surfaces of cellulose and have significantly lower binding capacity when compared to those of the corresponding free enzymes. Analysis of released soluble sugars indicated that the formation of complexes may promote the prospect of having consistent, multiple attacks on cellulose substrate. Once bound to the substrate, polycatalytic complexes tend to remain on the surface with very limited mobility due to their strong, multivalent binding to cellulose. Hence, the overall performance of polycatalytic complexes is limited by its substrate accessibility as well as mobility on the substrate surface.

Isolation of aerobic cultivable cellulolytic bacteria from different regions of the gastrointestinal tract of giant land snail Achatina fulica

The enzymatic hydrolysis of cellulose by cellulases is one of the major limiting steps in the conversion of lignocellulosic biomass to yield bioethanol. To overcome this hindrance, significant efforts are underway to identify novel cellulases. The snail Achatina fulica is a gastropod with high cellulolytic activity, mainly due to the abundance of glycoside hydrolases produced by both the animal and its resident microbiota. In this study, we partially assessed the cellulolytic aerobic bacterial diversity inside the gastrointestinal tract of A. fulica by culture-dependent methods and evaluated the hydrolytic repertoire of the isolates. Forty bacterial isolates were recovered from distinct segments of the snail gut and identified to the genus level by 16S rRNA gene sequence analysis. Additional phenotypic characterization was performed using biochemical tests provided by the Vitek2 identification system. The overall enzymatic repertoire of the isolated strains was investigated by enzymatic plate assays, containing the following substrates: powdered sugarcane bagasse, carboxymethylcellulose (CMC), p-nitrophenyl-β-D-glucopyranoside (pNPG), p-nitrophenyl-β-D-cellobioside (pNPC), 4-methylumbelliferyl-β-D-glucopyranoside (MUG), 4-methylumbelliferyl-β-D-cellobioside (MUC), and 4-methylumbelliferyl-β-D-xylopyranoside (MUX). Our results indicate that the snail A. fulica is an attractive source of cultivable bacteria that showed to be valuable resources for the production of different types of biomass-degrading enzymes.

Adsorption and hydrolytic activity of the polycatalytic cellulase nanocomplex on cellulose

The formation of polycatalytic enzyme complexes may enhance the effectiveness of enzymes due to improved substrate interaction and synergistic actions of multiple enzymes in proximity. Much effort has been made to develop highly efficient polycatalytic cellulase complexes by immobilizing cellulases on low-cost polymer or nanoparticle scaffolds, aiming at their potential applications in biomass conversion to fuels. However, some key cellulases carry out the hydrolytic reaction on crystalline cellulose in a directional, processive manner. A large, artificial polycatalytic complex is unlikely to undergo a highly coordinated motion to slide on the cellulose surface as a whole unit. The mechanism underlying the activity enhancements observed in some artificial cellulase complexes and the limit of this approach remain elusive. Herein, we report the synthesis of polycatalytic cellulase complexes bound to colloidal polymer nanoparticles with a magnetic core and describe their unique adsorption, hydrolytic activities, and motions on cellulose. The polycatalytic clusters of cellulases on colloidal polymers show an increased rate of hydrolytic reactions on cellulose, but this was observed mainly at relatively low cellulase-to-cellulose ratios. Enhanced efficiency is mainly attributed to increased local concentrations of cellulases on the scaffolds and their polyvalent interactions with cellulose. However, once bound, the polycatalytic complexes can only carry out reactions locally and are not capable of relocating to new sites rapidly due to their lack of long-range surface mobility and their extremely tight binding. The development of highly optimized polycatalytic complexes may arise by developing novel nanoscaffolds that induce concerted motion of the complex as a whole.

Analysis of transgenic glycoside hydrolases expressed in plants: T. reesei CBH I and A. cellulolyticus EI

Plant cell walls are composed of three basic structural biomolecules: cellulose, hemicellulose, and lignin with cellulose being the most abundant biopolymer on earth. Cellulose is composed of cellodextrins, which are linear polymers of glucose, and considered to be microcrystalline in structure. The conversion of cellulose to free glucose is one of the primary steps in the fermentative conversion of biomass to fuels and chemicals. However, the crystalline nature of this complex, noncovalent structure is highly resistant to enzymatic hydrolysis. Thus, the substantial cost currently associated with biomass saccharification primarily represents the cost of biomass degrading enzymes. Despite the fact that the microbial cellulose hydrolytic "machinery" for the recycling of carbon from plant biomass already exists in nature, the natural enzymatic degradation of plant material is typically a slow and complex process. Thus, if commercial biofuels production is to become a reality, it must be more cost-effective. One method proposed for achieving this objective is to express all or some of the requisite cellulolytic enzymes in planta, thus reducing both enzyme and thermochemical pretreatment costs.

Characterization of a bifunctional cellulase and its structural gene. The cell gene of Bacillus sp. D04 has exo- and endoglucanase activity

Bacillus sp. D04 secreted a bifunctional cellulase that had a molecular weight of 35,000. This cellulase degraded Cm-cellulose, cellotetraose, cellopentaose, p-nitrophenyl-beta-D-cellobioside, and avicel PH101. Based on the high performance liquid chromatography analysis of the degradation products, this cellulase randomly cleaved internal beta-1, 4-glycosidic bonds in cellotetraose and cellopentaose as an endoglucanase. It also hydrolyzed the aglycosidic bond in p-nitrophenyl-beta-D-cellobioside and cleaved avicel to cellobiose as an exoglucanase. Cellobiose competitively inhibited the p-nitrophenyl-beta-D-cellobioside degrading activity but not Cm-cellulose degrading activity. Ten mM p-chloromercuribenzoate inhibited p-nitrophenyl-beta-D-cellobioside degrading activity completely, but Cm-cellulose degrading activity incompletely. Cm-cellulose increased p-nitrophenyl-beta-D-cellobioside degrading activity, and vice versa, whereas methylumbelliferyl-beta-D-cellobiose strongly inhibited p-nitrophenyl-beta-D-cellobioside degrading activity. The cellulase gene (cel gene), 1461 base pairs, of Bacillus sp. D04 was cloned. The nucleotide sequence of the cel gene was highly homologous to those of Bacillus subtilis DLG and B. subtilis BSE616. The cel gene was overexpressed in Escherichia coli, and its product was purified. The substrate specificity and substrate competition pattern of the purified recombinant cellulase were the same as those of the purified cellulase from Bacillus sp. D04. These results suggest that a single polypeptide cellulase had both endo- and exoglucanase activities and each activity exists in a separate site.

Purification and properties of a beta-1,4-xylanase from a cellulolytic extreme thermophile expressed in Escherichia coli

1. An endoxylanase (EC 3.2.1.8) was purified from an Escherichia coli strain carrying a xylanase gene from the extreme thermophile "Caldocellum saccharolyticum" strain Tp8T6.3.3.1. It was found to have an M(r) of 42,000 and an isoelectric point of approx. 5.0. 2. The enzyme showed optimum activity at pH 5.0-7.7 and had an activation energy of 44 kJ mol-1. It was stable at room temperature at pH 4.5-11.5 in the presence of 0.5 mg ml-1 bovine serum albumin. The half-life of the enzyme at 75 degrees C was 20 min at pH 6.0 in the presence of 0.5 mg ml-1 bovine serum albumin. 3. The xylanase had highest activity on oat spelts xylan, releasing xylobiose and some xylotriose. The Km for oat spelts xylan was 0.021% (w/v) at pH 6.0. 4. The enzyme had high activity on sugar cane bagasse hemicelluloses A and B, lower activity on larchwood xylan and also hydrolysed carboxymethylcellulose, 4-methylumbelliferyl beta-D-cellobioside and p-nitrophenyl beta-D-cellobioside, but could not hydrolyse xylobiose. 5. It showed transferase activity on p-nitrophenyl beta-D-xylopyranoside. Xylose did not inhibit the enzyme.

Cellobiose dehydrogenases of Sporotrichum (Chrysosporium) thermophile

Both cellobiose dehydrogenases of Sporotrichum (Chrysosporium) thermophile, ATCC 42464, obtained after fractionation with DEAE-Trisacryl chromatography and named cellobiose dehydrogenase I and II have been purified to homogeneity by different chromatographic techniques. Both enzymes are slightly glycosylated flavocytochrome-b proteins with similar catalytic properties but with distinct molecular masses (91 kDa and 192 kDa for enzymes I and II, respectively) and isoelectric point (4.1 versus 3.45). Examination by SDS/PAGE clearly showed that the larger enzyme II is a homodimer, whose subunit is close to, but different from dehydrogenase I which is homogeneous by this technique. After limited digestion of both enzymes with papain, two main fractions with residual activity are formed, one carrying the heme, the other being the flavin component; each fraction is characterized by its particular chromatographic behaviour. The flavin carrying component shows an atypical (for flavoprotein) three-banded spectrum indicative of the presence of a flavin derivative. Both enzymes react very slowly with oxygen clearly forming some superoxide radicals and possibly hydrogen peroxide. Cellobiose and other cellodextrins are oxidized at their reducing glycosyl moiety to the corresponding aldonic acid. With the use of the autooxidable phenazinemethosulphate, cellulose (either in a hydrated form or crystalline) is also oxidized at free reducing ends so that appreciable amounts of cellobionic acid are released upon enzymatic hydrolysis.