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E A Bayer

Publications and source records attributed to E A Bayer.

At least 19 recordsLinked to original sources
PubMed1992

Identification of the cellulose-binding domain of the cellulosome subunit S1 from Clostridium thermocellum YS.

The 3' region of a gene designated cipB, which shows strong homology with cipA that encodes the cellulosome SL subunit of Clostridium thermocellum ATCC 27405, was isolated from a gene library of C. thermocellum strain YS. The truncated S1 protein encoded by the cipB derivative bound tightly to cellulose. The cellulose-binding domain in this polypeptide consisted of a C-terminal proximal 167 residue sequence which showed complete identity with residues 337-503 of mature SL from C. thermocellum strain ATCC 27405. The cellulose-binding domain interacted with both crystalline and amorphous cellulose, but not with xylan.

Amino Acid Sequence↗
PubMed1992

Novel oligosaccharide constituents of the cellulase complex of Bacteroides cellulosolvens.

The multiple cellulase-containing protein complex, isolated from the cellulolytic bacterium Bacteroides cellulosolvens, contains oligosaccharides which are O-linked mainly to a 230-kDa subunit. The oligosaccharide chains were liberated by alkaline-borohydride treatment and fractionated as oligosaccharide alditols via gel-permeation chromatography and HPLC. The fractions were investigated by one- and two-dimensional (correlation, homonuclear Hartmann-Hahn, rotating-frame nuclear Overhauser enhancement) 500-MHz 1H-NMR spectroscopy in combination with monosaccharide and methylation analyses and with fast-atom-bombardment mass spectrometry. The following carbohydrate structures could be established: [formula: see text] The results indicate an interesting similarity between the oligosaccharide moieties of the cellulase complex of B. cellulosolvens and of Clostridium thermocellum [Gerwig, G. J., Kamerling, J. P., Vliegenthart, J. F. G., Morag (Morgenstern), E., Lamed, R. & Bayer, E. A. (1991) Eur. J. Biochem. 196, 115-122], having 3, 5 and 6 as common elements. The furanose form of a terminal alpha-D-galactose residue demonstrated an inhibitory effect on the interaction of Griffonia simplicifolia I isolectin B4 with the cellulosome-like entity of B. cellulosolvens.

Amidohydrolases↗
PubMed1992

The cellulose paradox: pollutant par excellence and/or a reclaimable natural resource?

The various aspects of cellulose as a pollutant are considered in view of its lack of toxicity on the one hand and its recalcitrant durable nature on the other. The microbial degradation of cellulosics is discussed, and the contrast between its success in handling natural cellulosic wastes versus its failure to cope with man-made refuse is described. Research carried out in the past decade has demonstrated that cellulolytic organisms are provided with cell surface multifunctional multienzyme conglomerates, called cellulosomes, which are capable of solubilizing solid cellulosic substrates. The intriguing properties of such complexes include their cohesive nature, their many enzymatic components, and a characteristic glycosylated cellulose-binding, 'scaffolding' component. The latter appears to serve as a substrate-targeting carrier, which delivers the other (hydrolytic) components to the cellulose. Progress in establishing efficient model systems for in vitro solubilization of purified cellulose or natural cellulosic substrates has been achieved using purified cellulosome preparations, fortified with beta-glucosidase and pectinase. The latter enzymes were required in order to alleviate the phenomenon of product inhibition which reduces the efficiency of the free cellulosome. Such combined enzyme systems are proposed as examples of future tailor-made cellulolytic systems for the degradation of natural cellulosics.

Biodegradation, Environmental↗
PubMed1992

Cell-adhesive properties of streptavidin are mediated by the exposure of an RGD-like RYD site.

The interaction of streptavidin with various cell systems was studied using fluorescent derivatives of the protein. The native unprocessed form of streptavidin bound to cells at low levels and in a nonspecific manner. In contrast, both the truncated "core" streptavidin (the commercially available form) and the biotin-blocked unprocessed protein bound to cells in enhanced levels and in a specific, saturable manner. This suggests that the binding of biotin or cleavage of the terminal portion(s) of the native protein molecule causes conformational changes which lead to the exposure of sites which presumably interact with cell surface receptors. Peptide inhibition studies demonstrated that the majority of binding to cells appears to be dependent on RGD-like specificity, suggesting that the GRYDS sequence of the streptavidin molecule may exhibit such specificity. Indirect immunofluorescence assays revealed that the protein is associated mainly with the cell surface. Moreover, streptavidin was demonstrated to compete with specific monoclonal antibodies to the RGD-binding site on the GpIIbIIIa integrin of activated platelets, thus suggesting that streptavidin may facilitate binding to ubiquitous cell-surface adhesion receptors via RGD mimicry.

Amino Acid Sequence↗
PubMed1991

Studies on the biotin-binding site of avidin. Minimized fragments that bind biotin.

The object of this study was to define minimized biotin-binding fragments, or 'prorecognition sites', of either the egg-white glycoprotein avidin or its bacterial analogue streptavidin. Because of the extreme stability to enzymic hydrolysis, fragments of avidin were prepared by chemical means and examined for their individual biotin-binding capacity. Treatment of avidin with hydroxylamine was shown to result in new cleavage sites in addition to the known Asn-Gly cleavage site (position 88-89 in avidin). Notably, the Asn-Glu and Asp-Lys peptide bonds (positions 42-43 and 57-58 respectively) were readily cleaved; in addition, lesser levels of hydrolysis of the Gln-Pro (61-62) and Asn-Asp (12-13 and 104-105) bonds could be detected. The smallest biotin-binding peptide fragment, derived from hydroxylamine cleavage of either native or non-glycosylated avidin, was identified to comprise residues 1-42. CNBr cleavage resulted in a 78-amino acid-residue fragment (residues 19-96) that still retained activity. The data ascribe an important biotin-binding function to the overlapping region (residues 19-42) of avidin, which bears the single tyrosine moiety. This contention was corroborated by synthesizing a tridecapeptide corresponding to residues 26-38 of avidin; this peptide was shown to recognize biotin. Streptavidin was not susceptible to either enzymic or chemical cleavage methods used in this work. The approach taken in this study enabled the experimental distinction between the chemical and structural elements of the binding site. The capacity to assign biotin-binding activity to the tyrosine-containing domain of avidin underscores its primary chemical contribution to the binding of biotin by avidin.

Amino Acid Sequence↗
PubMed1991

The quaternary structure of streptavidin in urea.

We report on the interactions of urea and guanidinium salts with streptavidin. Gel filtration chromatography in 0, 4, 6, and 7 M urea indicates that the streptavidin tetramer remains intact in urea. Biotin alters the electrophoretic mobility of streptavidin whether or not 6 M urea is present. The intrinsic fluorescence of streptavidin is increased and blue-shifted in 6 M urea. The fluorescence changes indicate the absence of unfolding. A conformational response to urea is possible, but much of the fluorescence change is due to urea binding as a weak biotin analog (Ka approximately 1.3 M-1). The resistance to structural perturbation by urea reflects the structural stability of streptavidin's anti-parallel beta-barrel motif. Unfolding is sluggish in 6 M guanidinium hydrochloride (half-time, approximately 50 days). After guanidinium thiocyanate unfolding, streptavidin can be refolded, but the unfolding and refolding transitions are centered at different concentrations of perturbant. Slow unfolding, with a 15th power dependence on guanidinium thiocyanate concentration, may be partially responsible for the noncoincidence of the unfolding and refolding processes. Nonequilibrium behavior is also seen in 6 M urea, as native streptavidin does not unfold and guanidinium thiocyanate unfolded streptavidin does not refold. Refolding does occur at lower concentrations of urea. Guanidinium thiocyanate only slowly unfolds the biotin-streptavidin complex. In the presence of biotin, unfolded streptavidin does not refold in 6 M guanidinium thiocyanate or in 6 M urea.

Bacterial Proteins↗
PubMed1991

Primary structure of O-linked carbohydrate chains in the cellulosome of different Clostridium thermocellum strains.

The cell-free forms of the multiple cellulase-containing protein complex (cellulosome), isolated from the cellulolytic bacterium Clostridium thermocellum strains YS, ATCC 27405 and LQRI, have a total carbohydrate content of 5-7% (by mass), consisting of O-linked oligosaccharide chains. The carbohydrate chains were liberated by alkaline-borohydride treatment and fractionated as oligosaccharide alditols via gel-permeation chromatography and HPLC. The fractions were investigated by 500-MHz 1H-NMR spectroscopy in combination with monosaccharide and methylation analysis and with fast-atom-bombardment mass spectrometry (FAB-MS). In addition to the previously described major oligosaccharide, (formula; see text) [Gerwig, G. J., de Waard, P., Kamerling, J. P., Vliegenthart, J. F. G., Morgenstern, E., Lamed, R. & Bayer, E. A. (1989) J. Biol. Chem. 264, 1027-1035], the following partial structures of this compound could be established: (formula; see text). Cell-free and cell-associated forms of the cellulosome of C. thermocellum, as determined for strain YS, have the same oligosaccharide pattern. Based on the oligosaccharide structures, a biosynthetic pathway is suggested.

Bacterial Proteins↗
PubMed1991

Anomalous dissociative behavior of the major glycosylated component of the cellulosome of Clostridium thermocellum.

The cellulosome of Clostridium thermocellum is a highly cohesive multienzyme complex that is capable of completely solubilizing insoluble cellulose. One of the major cellulosomal components, the glycosylated S1 subunit, is believed to play an important structural role and normally migrates in sodium dodecyl sulfate-polyacrylamide gel electrophoresis with an Mr of 210,000. It is shown here that by simply altering the conditions (pH or ionic strength) of the environment prior to electrophoresis, a different migratory profile for S1 emerges, yielding a collection of bands, all of which migrate faster than the parent band. The original electrophoretic behavior of S1 can be reproduced on restoration of the original pH and ionic strength. These results may bear important significance for the physiological role of the S1 subunit in facilitating the observed synergistic action of the other (cellulolytic) components of the cellulosome.

Biotechnology↗
PubMed1991

A coupled enzyme assay for measurement of sialidase activity.

A multi-coupled enzyme assay system for determining sialidase activity is described. Enzymes, substrates and chromogens are reacted in situ and determined spectrophotometrically in ELISA microtiter plates. Sialidase is assayed by the extent of desialylated galactose on an appropriate sialoglycoconjugate (fetuin), which is otherwise unavailable for oxidation by galactose oxidase. The oxidation is monitored by the coupling of H2O2 released to a third enzyme, peroxidase. The rate of change of absorbance at 405 nm, resulting from the oxidized chromogen is a measure of the reaction rate of the coupled enzyme system. A similar system can be used for determining galactose oxidase in solution, or on blots using galactose as substrate. Due to the small-scale single-step measurement, the described assay is a sensitive, convenient, and inexpensive alternative to the classic colorimetric determination.

Acetylgalactosamine↗
PubMed1991

Isolation and properties of a major cellobiohydrolase from the cellulosome of Clostridium thermocellum.

In the anaerobic, thermophilic, cellulolytic bacterium Clostridium thermocellum, efficient solubilization of the insoluble cellulose substrate is accomplished largely through the action of a cellulose-binding multienzyme complex, the cellulosome. A major cellobiohydrolase activity from the cellulosome has been traced to its Mr 75,000 S8 subunit, and an active fragment of this subunit was prepared by a novel procedure involving limited proteolytic cleavage. The truncated Mr 68,000 fragment, termed S8-tr, was purified by gel filtration and high-performance ion-exchange chromatography. The purified protein adsorbed weakly to amorphous cellulose, and its enzymatic action yielded cellobiose as the major end product from both amorphous and crystalline cellulose preparations. The high ratio of exo- to endo-beta-glucanase activities was supported by viscosimetric measurements. The use of model substrates showed that the smallest cellodextrin to be degraded was cellotetraose, but cellopentaose was degraded at a much greater rate. Cellobiose dramatically inhibited the cellulolytic activities. In the absence of calcium or other bivalent metal ions, both the truncated cellobiohydrolase activity of S8-tr and the true cellulase activity of the parent cellulosome were relatively unstable at temperatures above 50 degrees C. Cysteine further enhanced the stabilizing effect of calcium. This is the first report of a defined cellobiohydrolase in C. thermocellum. Its association with the cellulosome and the correspondence of several of their major distinctive properties suggest that this cellobiohydrolase plays a key role in the solubilization of cellulose by the intact cellulosomal complex.

Animals↗
PubMed1990

Affinity cleavage and targeted catalysis of proteins using the avidin-biotin system.

The avidin-biotin system was used in order to target enzymes to their substrates in complex mixtures of proteins in solution. The approach described here thus mimics natural systems in which enzymes usually act in selective fashion, due, perhaps, to proximity effects. For affinity cleavage studies, biotinyl transferrin was used as a model target substrate. Avidin or streptavidin was then employed to bridge between the biotinylated target protein and a biotinyl protease. Bovine serum albumin was included in the reaction mixtures to assess the level of nonspecific cleavage. In the case of an unbiotinylated target protein, avidin could be used to inhibit the hydrolytic action of the biotinyl protease. In some systems, a biotinyl antibody could be used to direct the avidin-bridged biotinyl protease to an unbiotinylated target antigen. The data support the contention that preferential cleavage reflects two separate phenomena: (i) avidin confers a conformational alteration of the biotinylated target protein, and (ii) the biotinyl protease is targeted (via the avidin bridge) to the proximity of the biotinylated target protein, thereby promoting cleavage of the conformationally altered molecule. This is the first report in which a proteolytic enzyme could be selectively targeted to specifically hydrolyze a defined protein substrate in solutions containing a complex mixture of other proteins. The approach appears to be a general phenomenon for "targeted catalysis", appropriate for other applications, particularly for affinity cleavage and targeted catalysis of cell-based macromolecules.

Affinity Labels↗
PubMed1990

Streptavidin contains an RYD sequence which mimics the RGD receptor domain of fibronectin.

Streptavidin binds at low levels and high affinity to cell surfaces, the cause of which can be traced to the occurrence of a sequence containing RYD (Arg-Tyr-Asp) in the protein molecule. This binding is enhanced in the presence of biotin. Cell-bound streptavidin can be displaced by fibronectin, as well as by RGD- and RYD-containing peptides. In addition, streptavidin can displace fibronectin from cell surfaces. The RYD sequence of streptavidin thus mimics RGD (Arg-Gly-Asp), the universal recognition domain present in fibronectin and other adhesion-related molecules. The observed adhesion to cells has no relevance to biotin-binding since the RYD sequence is not part of the biotin-binding site of streptavidin. Since the use of streptavidin in avidin-biotin technology is based on its biotin-binding properties, researchers are hereby warned against its indiscriminate use in histochemical and cytochemical studies.

Amino Acid Sequence↗
PubMed1990

Studies on the biotin-binding sites of avidin and streptavidin. Tyrosine residues are involved in the binding site.

The involvement of tyrosine in the biotin-binding sites of the egg-white glycoprotein avidin and the bacterial protein streptavidin was examined by using the tyrosine-specific reagent p-nitrobenzenesulphonyl fluoride (Nbs-F). Modification of an average of about 0.5 mol of tyrosine residue/mol of avidin subunit caused the complete loss of biotin binding. This indicates that the single tyrosine residue (Tyr-33) in the avidin subunit is directly involved in the biotin-binding site and that its modification by Nbs also abolishes the binding properties of a neighbouring subunit. This suggests that the tyrosine residues of the egg-white protein may also contribute to the stabilization of the native protein structure. In streptavidin, however, the modification of an average of 3 mol of tyrosine residue/mol of subunit was required to inactivate completely the biotin-binding activity of the protein, but only 1 mol (average) of tyrosine residue/mol of subunit was protected in the presence of biotin. The difference between the h.p.l.c. elution profiles of the enzymic digests of Nbs-modified streptavidin and the Nbs-modified streptavidin-biotin complex revealed two additional fractions in the unprotected protein that contain Nbs-modified tyrosine residues. These residues, Tyr-43 (major fraction) and Tyr-54 (minor fraction), appear to contribute to the biotin-binding site in streptavidin.

Amino Acid Sequence↗
PubMed1990

Application of avidin-biotin technology to affinity-based separations.

During the last decade, avidin-biotin technology has become a commercially viable tool for research, medical and industrial applications. From the beginning, mediation via the avidin-biotin complex was proposed for affinity-based separations. This particular application, however, has been slow in gaining acceptance. One of the reasons is that the strength of binding between avidin and biotin is sometimes inappropriate for the desired affinity system. Another problem involves certain "undesirable" structural properties in the avidin molecule which may lead to high levels of "non-specific" binding. Recent progress in understanding the molecular requirements for binding biotin may eventually lead to the design of avidin-like proteins which will exhibit preferred recognition properties according to the desired application.

Animals↗
PubMed1990

Avidin column as a highly efficient and stable alternative for immobilization of ligands for affinity chromatography.

The avidin/biotin system was applied as a general mediator in the adsorption/desorption or immobilization of biologically active macromolecules to solid supports. In this context, model biotinylated proteins (lectins and antibodies) were attached to avidin-coupled Sepharose. As examples for affinity chromatography, peanut agglutinin and anti-transferrin antibody were used to isolate asialofetuin and transferrin, respectively. The capacity and product yields were significantly better than those achieved with conventional affinity chromatography on CNBr-activated Sepharose columns containing the same lectin or antibody. Moreover, the columns were characterized by improved stability properties exhibiting remarkably low levels of leakage.

Antibodies↗
PubMed1990

Biotin binding changes the conformation and decreases tryptophan accessibility of streptavidin.

Biotin binding reduces the tryptophan fluorescence emissions of streptavidin by 39%, blue shifts the emission peak from 333 to 329 nm, and reduces the bandwidth at half height from 53 to 46 nm. The biotin-induced emission difference spectrum resembles that of a moderately polar tryptophan. Streptavidin fluorescence can be described by two lifetime classes: 2.6 nsec (34%) and 1.3 nsec (66%). With biotin bound, lifetimes are 1.3 nsec (26%) and 0.8 nsec (74%). Biotin binding reduces the average fluorescence lifetime from 1.54 to 0.88 nsec. Biotin does not quench the fluorescence of indoles. The fluorescence changes are consistent with biotin binding causing a conformational change which moves tryptophans into proximity to portions of streptavidin which reduce the quantum yield and lifetimes. Fluorescence quenching by acrylamide revealed two classes of fluorophores. Analysis indicated a shielded component comprising 20-28% of the initial fluorescence with (KSV + V) less than or equal to 0.55 M-1. The more accessible component has a predominance of static quenching. Measurements of fluorescence lifetimes at different acrylamide concentrations confirmed the strong static quenching. Since static quenching could be due to acrylamide binding to streptavidin, a dye displacement assay for acrylamide binding was constructed. Acrylamide does bind to streptavidin (Ka = 5 M-1), and probably binds within the biotin-binding site. In the absence of biotin, none of streptavidin's fluorescence is particularly accessible to iodide. In the presence of biotin, iodide neither quenches fluorescence nor alters emission spectra, and acrylamide access is dramatically reduced. We propose that the three tryptophans which always line the biotin site are sufficiently close to the surface of the binding site to be quenched by bound acrylamide. These tryptophans are shielded from iodide, most probably due to steric or ionic hindrances against diffusion into the binding site. Most of the shielding conferred by biotin binding can be attributed to the direct shielding of these residues and of a fourth tryptophan which moves into the binding site when biotin binds, as shown by X-ray studies (Weber et al., 1989).

Acrylamides↗