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PubMed1974

[Test of cellulose and cellulose derivatives for carcinogenic activity in rats, mice and rabbits].

Activated cellulose, p-aminobenzylcellulose, p-hydroxybenzylcellulose, cellulose-m-aminobenzoxymethylether and cellulose-m-hydroxybenzoxymethylether which are used as highmolecular inert components for the preparation of immunoadsorbents, have been tested for carcinogenic activity in Wistar-rats and CBA-mice by the subcutaneous and intramuscular route of administration. In the same manner the coupling products have been tested in rats, mice and rabbits of diazotized p-aminobenzylcellulose and cellulose-m-aminobenzoxymethylether with a) human gammaglobulin [(cellulose-p-benzylether)-azogammaglobulin and (cellulose-m-benzoxymethylether)-azogammaglobulin respectively] and b) 1-(m-hydroxyphenyl)-flavozole derivatives of saccharides of the isomaltodextrin- and maltodextrin series [saccharide-1-(3 ft.-hydroxy-4 ft.-(resp.-6 ft.-or-2 ft.-) [cellulose-p-benzylether]-azophenyl)-flavazoles and saccharide-1-(3 ft.-hydroxy-4 ft.-(resp. -6 ft;-or-2 ft.-) [cellulose-m-benzoxymethylether]-azophenyl)-flavazoles with isomaltotriose, isomaltotetraose, isomaltopentaose, isomaltohexaose, isomaltooctaose, maltotriose, maltotetraose, maltopentaose, maltohexaose and maltooctaose as saccharide moieties]. No tumours were found in rabbits. No statistical significant difference could be stated between the tumour incidence of experimental animals and controls in the rat and mouse groups.

Animals↗
PubMed2002

Sporulation of Clostridium cellulolyticum while grown in cellulose-batch and cellulose-fed continuous cultures on a mineral-salt based medium.

Clostridium cellulolyticum sporulation was investigated during growth on cellulose fibers in a mineral-salt based medium which corresponds to conditions linked to its natural ecological niche. At steady state of the continuous cultures under limitation and with an excess of cellulose and/or ammonium, bacterial cells mainly sporulated at low dilution rates (D), at least 10% sporulation being observed at the lowest D tested. Increasing the cellulose concentration in the feed-medium reservoir increased the percentage of spores in the bioreactor. It appeared that the remaining undigested cellulose could serve as an exogenous carbon source supply at a continuous but limited rate throughout the sporulation process. In addition to the proportion of carbon and nitrogen, the influence of the environmental pH on spore formation was studied. In cellulose-fed continuous cultures at a constant D and a pH decreasing from 7.2 to 6.4, the percentage of spores increased to 14% at the lowest pH tested. When C. cellulolyticum was grown in batch culture, the level of sporulation was dramatically higher in unregulated-pH fermentation compared to pH-controlled growth conditions at pH 7.2 since in the former it reached 45% within 5 days of cultivation. It then appeared that a low specific growth rate and a low environmental pH in the presence of an insoluble carbon substrate were the major factors inducing sporulation in C. cellulolyticum. Furthermore, since the spores adhere to the carbon substrate (the cellulose) the bacteria gain advantages when the environment allows germination thanks to the recovery of suitable growth conditions. By allowing the maintenance and the integrity of the bacteria in the microbiota, spore formation could then explain the successful survival of C. cellulolyticum in cellulosic anaerobic habitats where low environmental pH conditions are often found.

Adaptation, Physiological↗
PubMed2005

Interaction forces between cellulose microspheres and ultrathin cellulose films monitored by colloidal probe microscopy-effect of wet strength agents.

Colloidal probe microscopy was employed to study forces between cellulose surfaces upon addition of a series of cationic copolymers in aqueous solution, as model compounds for wet strength agents. The content of quaternary ammonium groups and primary amines was systematically varied in the cationic polymers, to distinguish between the importance of electrostatical and H-bonding effects. Cellulose microspheres were glued at the apex of tipless microfabricated cantilevers and used as colloidal probes. Ultra thin cellulose films and cellulose fibres were employed as model surfaces. The cellulose films of a thickness of about 5 nm were spin-coated from cellulose solution onto silicon substrates. The root-mean-square-roughness (RMS) was 0.3-0.8 nm. The cationic model polymers were compared to Servamine, a polymer employed as standard wet strength resin in papermaking industries. Force versus separation measurements showed a detailed picture of adhesion and contact breaking. Relatively strong adhesion of the order of 0.3 mJ/m(2) was observed with Servamine within a range of approximately 10 nm. At larger distances weak bond breaking and elastic chain pulling were identified. When approaching the surface one to two small jump-in's possibly related to strong binding of Servamine and subsequent attraction could be found in the case of Servamine. In contrast, all the model copolymers showed only a weak adhesion of 8-30 micro/m(2), i.e., an order of magnitude less than that of Servamine and subsequent elastic rupture domains. The contour length, persistence length and characteristic rupture distances were calculated by means of applying the WLC model. Measurements against cellulose fibres obtained from the production process proved the relevance of the model systems.

Amines↗
PubMed1999

Rheological characterization of microcrystalline cellulose and silicified microcrystalline cellulose wet masses using a mixer torque rheometer.

The rheological properties of silicified microcrystalline cellulose (Prosolv 50) were compared with those of standard grades of microcrystalline cellulose (Emcocel 50 and Avicel PH 101). Cellulose samples were analyzed using nitrogen adsorption together with particle size, flowability, density and swelling volume studies. The rheological behaviour of the wet powder masses was studied as a function of mixing time using a mixer torque rheometer (MTR). Silicified microcrystalline cellulose exhibited improved flow characteristics and increased specific surface area compared to standard microcrystalline cellulose grades. Although the silicification process affected the swelling properties and, furthermore, the mixing kinetics of microcrystalline cellulose, the source of the microcrystalline cellulose had a stronger influence than silicification on the liquid requirement at peak torque.

Cellulose↗
PubMed1982

Alteration of in vivo cellulose ribbon assembly by carboxymethylcellulose and other cellulose derivatives.

In vivo cellulose ribbon assembly by the Gram-negative bacterium Acetobacter xylinum can be altered by incubation in carboxymethylcellulose (CMC), a negatively charged water-soluble cellulose derivative, and also by incubation in a variety of neutral, water-soluble cellulose derivatives. In the presence of all of these substituted celluloses, normal fasciation of microfibril bundles to form the typical twisting ribbon is prevented. Alteration of ribbon assembly is most extensive in the presence of CMC, which often induces synthesis of separate, intertwining bundles of microfibrils. Freeze-etch preparations of the bacterial outer membrane suggest that particles that are thought to be associated with cellulose synthesis or extrusion may be specifically organized to mediate synthesis of microfibril bundles. These data support the previous hypothesis that the cellulose ribbon of A. xylinum is formed by a hierarchical, cell-directed, self-assembly process. The relationship of these results to the regulation of cellulose microfibril size and wall extensibility in plant cell walls is discussed.

Acetobacter↗
PubMed2002

Cloning of cellulose synthesis related genes from Acetobacter xylinum ATCC23769 and ATCC53582: comparison of cellulose synthetic ability between strains.

About 14.5 kb of DNA fragments from Acetobacter xylinum ATCC23769 and ATCC53582 were cloned, and their nucleotide sequences were determined. The sequenced DNA regions contained endo-beta-1,4-glucanase, cellulose complementing protein, cellulose synthase subunit AB, C, D and beta-glucosidase genes. The results from a homology search of deduced amino acid sequences between A. xylinum ATCC23769 and ATCC53582 showed that they were highly similar. However, the amount of cellulose production by ATCC53582 was 5 times larger than that of ATCC23769 during a 7-day incubation. In A. xylinum ATCC53582, synthesis of cellulose continued after glucose was consumed, suggesting that a metabolite of glucose, or a component of the medium other than glucose, may be a substrate of cellulose. On the other hand, cell growth of ATCC23769 was twice that of ATCC53582. Glucose is the energy source in A. xylinum as well as the substrate of cellulose synthesis, and the metabolic pathway of glucose in both strains may be different. These results suggest that the synthesis of cellulose and the growth of bacterial cells are contradictory.

Amino Acid Sequence↗
PubMed1995

Molecular dynamics simulation of fungal cellulose-binding domains: differences in molecular rigidity but a preserved cellulose binding surface.

A total of 23 fungal cellulose-binding domain (CBD) sequences were aligned. Structural models of the cellulose-binding domain of an exoglucanase (CBHII) and of three endoglucanases (EGI, EGII and EGV) from Trichoderma reesei cellulases were homology modelled based on the NMR structure of the fungal cellobiohydrolase CBHI, from the same organism. The completed models and the known structure of the CBHI cellulose-binding domain were refined by molecular dynamics simulations in water. All four models were found to be very similar to the structure of the CBHI cellulose-binding domain and sequence comparison indicated that in general the three-dimensional structures of fungal cellulose-binding domains are very similar. In all the CBDs studied, two disulphide bridges apparently stabilize the polypeptide fold. From the models, and additional disulphide bridge was predicted in EGI and CBHII, and in eight further CBDs from other organisms. Three highly conserved aromatic residues on the hydrophilic side of the wedge make this surface flat. This surface is expected to make contact with the substrate. Three invariant amino acids, Gln7, Asn29 and Gln34, on this flat face are in suitable positions for hydrogen bonding with the cellulose surface. Analysis of the differences in the protein surface properties indicated that the endoglucanases tend to be more hydrophilic than the exoglucanases. The largest structural variation was found around positions 12-16. The fungal CBD sequences are discussed in relation to variations in function and pH dependence. Comparison of the modelled structures with experimental binding data for the CBHI and EGI allowed the formulation of a qualitative relationship to cellulose affinity.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1994

Mutation analysis of the cellulose-binding domain of the Clostridium cellulovorans cellulose-binding protein A.

Cellulose-binding protein A (CbpA) has been previously shown to mediate the interaction between crystalline cellulose substrates and the cellulase enzyme complex of Clostridium cellulovorans. CbpA contains a family III cellulose-binding domain (CBD) which, when expressed independently, binds specifically to crystalline cellulose. A series of N- and C-terminal deletions and a series of small internal deletions of the CBD were created to determine whether the entire region previously described as a CBD is required for the cellulose-binding function. The N- and C-terminal deletions reduced binding affinity by 10- to 100-fold. Small internal deletions of the CBD resulted in substantial reduction of CBD function. Some, but not all, point mutations throughout the sequence had significant disruptive effects on the binding ability of the CBD. Thus, mutations in any region of the CBD had effects on the binding of the fragment to cellulose. The results indicate that the entire 163-amino-acid region of the CBD is required for maximal binding to crystalline cellulose.

Amino Acid Sequence↗
PubMedDate not supplied

Differential thermal and thermogravimetric analyses of bound water content in cellulosic substrates and its significance during cellulose hydrolysis by alkaline active fungal cellulases.

Various cellulosic substrates were examined for bound water content by differential thermal analysis (DTA) and thermogravimetry (TG). Samples were heated in the range of 30-100 degrees C at a rate of 3 degrees C/min. DTA vaporization curves for different cellulose samples indicated that the bound water (Wf) was vaporized at higher temperature than free water (Wf) at the surface. Weight loss was observed in two stages, corresponding to Wf and Wb in TG curves. The bound water content was dependent on the degree of crystallinity of cellulose. Among different cellulosic substrates, Walseth cellulose showed the highest bound water content, and it also was found to be the least crystalline. The alkaline-active, alkali-stable cellulase was obtained from the alkalotolerant Fusarium sp. The substrate specificity and viscometric characteristics confirmed the enzyme to be an endoglucanase. The Wb content of Walseth cellulose was lowered during the enzymatic hydrolysis. The possible application of bound water analysis in understanding the hydrolysis of cellulosic substrates of different crystallinity is discussed.

Cellulases↗
PubMed1999

Cellulose as an inert matrix for presenting cytokines to target cells: production and properties of a stem cell factor-cellulose-binding domain fusion protein.

A chimaera of stem cell factor (SCF) and a cellulose-binding domain from the xylanase Cex (CBDCex) effectively immobilizes SCF on a cellulose surface. The fusion protein retains both the cytokine properties of SCF and the cellulose-binding characteristics of CBDCex. When adsorbed on cellulose, SCF-CBDCex is up to 7-fold more potent than soluble SCF-CBDCex and than native SCF at stimulating the proliferation of factor-dependent cell lines. When cells are incubated with cellulose-bound SCF-CBDCex, activated receptors and SCF-CBDCex co-localize on the cellulose matrix. The strong binding of SCF-CBDCex to the cellulose surface permits the effective and localized stimulation of target cells; this is potentially significant for long-term perfusion culturing of factor-dependent cells. It also permits the direct analysis of the effects of surface-bound cytokines on target cells.

Animals↗
PubMed2006

Cell suspension cultures of Populus tremula x P. tremuloides exhibit a high level of cellulose synthase gene expression that coincides with increased in vitro cellulose synthase activity.

Compared to wood, cell suspension cultures provide convenient model systems to study many different cellular processes in plants. Here we have established cell suspension cultures of Populus tremula L. x P. tremuloides Michx. and characterized them by determining the enzymatic activities and/or mRNA expression levels of selected cell wall-specific proteins at the different stages of growth. While enzymes and proteins typically associated with primary cell wall synthesis and expansion were detected in the exponential growth phase of the cultures, the late stationary phase showed high expression of the secondary-cell-wall-associated cellulose synthase genes. Interestingly, detergent extracts of membranes from aging cell suspension cultures exhibited high levels of in vitro cellulose synthesis. The estimated ratio of cellulose to callose was as high as 50 : 50, as opposed to the ratio of 30 : 70 so far achieved with membrane preparations extracted from other systems. The increased cellulose synthase activity was also evidenced by higher levels of Calcofluor white binding in the cell material from the stationary-phase cultures. The ease of handling cell suspension cultures and the improved capacity for in vitro cellulose synthesis suggest that these cultures offer a new basis for studying the mechanism of cellulose biosynthesis.

Benzenesulfonates↗
PubMed1993

Visualization of the adsorption of a bacterial endo-beta-1,4-glucanase and its isolated cellulose-binding domain to crystalline cellulose.

Endo-beta-1,4-glucanase A (CenA), a cellulase from the bacterium Cellulomonas fimi, is composed of two domains: a catalytic domain and a cellulose-binding domain. Adsorption of CenA and its isolated cellulose-binding domain (CBD.PTCenA) to Valonia cellulose microcrystals was examined by transmission electron microscopy using an antibody sandwich technique (CenA/CBD.PTCenA-alpha CenA IgG-protein A-gold conjugate). Adsorption of both CenA and CBD.PTCenA occurred along the lengths of the microcrystals, with an apparent preference for certain crystal faces or edges. CenA or CBD.PTCenA, but not the isolated catalytic domain, were shown to prevent the flocculation of microcrystalline bacterial cellulose. The cellulose-binding domain may assist crystalline cellulose hydrolysis in vitro by promoting substrate dispersion.

Actinomycetales↗
PubMed1975

Cellulose synthesis by Acetobacter xylinum. III. Matrix, primer and lipid requirements and heat stability of the cellulose-forming enzymes.

The addition of soluble cellodextrins of increasing size to a cell envelope preparation of Acetobacter xylinum stimulated cellulose synthesis from UDPG. This stimulation was attributed to both acceptor and activator effects. Enzymes required for cellulose synthesis were found to be heat-unstable and those required for synthesis of glycosylated lipid components from UDPG, heat-stable. Both heat-inactivated envelope fragments and supernatant fluid from whole cells were necessary for cellulose synthesis from UDPG. Cellulose was not formed from UDPG in the presence of either supernatant fluid alone or heat-inactivated envelopes alone. The combined results of this and previous studies suggest that either the cell envelope is necessary for synthesis of a more immediate precursor to cellulose than UDPG, or that the synthesis from UDPG requires a matrix. The former suggestion and its possible link with lipid intermediate involvement was strengthened by the observation of inefficient glycosylated lipid formation by a celluloseless mutant strain of A. xylinum. The possible locations of various enzyme activities required for the synthesis of the cellulose precursor are indicated and a possible microfibril nucleation process is discussed.

Cell Wall↗
PubMed2000

The mechanical properties of compacts of microcrystalline cellulose and silicified microcrystalline cellulose.

The mechanical properties of compacts of unlubricated microcrystalline cellulose and silicified microcrystalline cellulose were evaluated using the diametric tensile test. The results suggested that, under comparable testing conditions, compacts of silicified microcrystalline cellulose exhibited greater strength than those of microcrystalline cellulose. In addition to enhanced strength, silicified microcrystalline cellulose compacts exhibited greater stiffness and required considerably more energy for tensile failure to occur. Comparison of the data with that obtained for a dry blend of silicon dioxide/microcrystalline cellulose suggested that the functionality benefits of silicification were not due to a simple composite material model.

Cellulose↗
PubMed1996

Characterization of a double cellulose-binding domain. Synergistic high affinity binding to crystalline cellulose.

Most cellulose-degrading enzymes have a two-domain structure that consists of a catalytic and a cellulose-binding domain (CBD) connected by a linker region. The linkage and the interactions of the two domains represent one of the key questions for the understanding of the function of these enzymes. The CBDs of fungal cellulases are small peptides folding into a rigid, disulfide-stabilized structure that has a distinct cellulose binding face. Here we describe properties of a recombinant double CBD, constructed by fusing the CBDs of two Trichoderma reesei cellobiohydrolases via a linker peptide similar to the natural cellulase linkers. After expression in Escherichia coli, the protein was purified from the culture medium by reversed phase chromatography and the individual domains obtained by trypsin digestion. Binding of the double CBD and its single CBD components was investigated on different types of cellulose substrates as well as chitin. Under saturating conditions, nearly 20 micromol/g of the double CBD was bound onto microcrystalline cellulose. The double CBD exhibited much higher affinity on cellulose than either of the single CBDs, indicating an interplay between the two components. A two-step model is proposed to explain the binding behavior of the double CBD. A similar interplay between the domains in the native enzyme is suggested for its binding to cellulase.

Amino Acid Sequence↗
PubMed2001

EndB, a multidomain family 44 cellulase from Ruminococcus flavefaciens 17, binds to cellulose via a novel cellulose-binding module and to another R. flavefaciens protein via a dockerin domain.

The mechanisms by which cellulolytic enzymes and enzyme complexes in Ruminococcus spp. bind to cellulose are not fully understood. The product of the newly isolated cellulase gene endB from Ruminococcus flavefaciens 17 was purified as a His-tagged product after expression in Escherichia coli and found to be able to bind directly to crystalline cellulose. The ability to bind cellulose is shown to be associated with a novel cellulose-binding module (CBM) located within a region of 200 amino acids that is unrelated to known protein sequences. EndB (808 amino acids) also contains a catalytic domain belonging to glycoside hydrolase family 44 and a C-terminal dockerin-like domain. Purified EndB is also shown to bind specifically via its dockerin domain to a polypeptide of ca. 130 kDa present among supernatant proteins from Avicel-grown R. flavefaciens that attach to cellulose. The protein to which EndB attaches is a strong candidate for the scaffolding component of a cellulosome-like multienzyme complex recently identified in this species (S.-Y. Ding et al., J. Bacteriol. 183:1945-1953, 2001). It is concluded that binding of EndB to cellulose may occur both through its own CBM and potentially also through its involvement in a cellulosome complex.

Amino Acid Sequence↗
PubMed1996

Crystal structure of a bacterial family-III cellulose-binding domain: a general mechanism for attachment to cellulose.

The crystal structure of a family-III cellulose-binding domain (CBD) from the cellulosomal scaffoldin subunit of Clostridium thermocellum has been determined at 1.75 A resolution. The protein forms a nine-stranded beta sandwich with a jelly roll topology and binds a calcium ion. conserved, surface-exposed residues map into two defined surfaces located on opposite sides of the molecule. One of these faces is dominated by a planar linear strip of aromatic and polar residues which are proposed to interact with crystalline cellulose. The other conserved residues are contained in a shallow groove, the function of which is currently unknown, and which has not been observed previously in other families of CBDs. On the basis of modeling studies combined with comparisons of recently determined NMR structures for other CBDs, a general model for the binding of CBDs to cellulose is presented. Although the proposed binding of the CBD to cellulose is essentially a surface interaction, specific types and combinations of amino acids appear to interact selectively with glucose moieties positioned on three adjacent chains of the cellulose surface. The major interaction is characterized by the planar strip of aromatic residues, which align along one of the chains. In addition, polar amino acid residues are proposed to anchor the CBD molecule to two other adjacent chains of crystalline cellulose.

Amino Acid Sequence↗
PubMed2006

The cellulose synthase gene superfamily and biochemical functions of xylem-specific cellulose synthase-like genes in Populus trichocarpa.

Wood from forest trees modified for more cellulose or hemicelluloses could be a major feedstock for fuel ethanol. Xylan and glucomannan are the two major hemicelluloses in wood of angiosperms. However, little is known about the genes and gene products involved in the synthesis of these wood polysaccharides. Using Populus trichocarpa as a model angiosperm tree, we report here a systematic analysis in various tissues of the absolute transcript copy numbers of cellulose synthase superfamily genes, the cellulose synthase (CesA) and the hemicellulose-related cellulose synthase-like (Csl) genes. Candidate Csl genes were characterized for biochemical functions in Drosophila Schneider 2 (S2) cells. Of the 48 identified members, 37 were found expressed in various tissues. Seven CesA genes are xylem specific, suggesting gene networks for the synthesis of wood cellulose. Four Csl genes are xylem specific, three of which belong to the CslA subfamily. The more xylem-specific CslA subfamily is represented by three types of members: PtCslA1, PtCslA3, and PtCslA5. They share high sequence homology, but their recombinant proteins produced by the S2 cells exhibited distinct substrate specificity. PtCslA5 had no catalytic activity with the substrates for xylan or glucomannan. PtCslA1 and PtCslA3 encoded mannan synthases, but PtCslA1 further encoded a glucomannan synthase for the synthesis of (1-->4)-beta-D-glucomannan. The expression of PtCslA1 is most highly xylem specific, suggesting a key role for it in the synthesis of wood glucomannan. The results may help guide further studies to learn about the regulation of cellulose and hemicellulose synthesis in wood.

Animals↗