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At least 19 recordsLinked to original sources
PubMed1995

Biosynthesis of (1,3)(1,4)-beta-glucan and (1,3)-beta-glucan in barley (Hordeum vulgare L.). Properties of the membrane-bound glucan synthases.

Mixed membrane preparations from the coleoptiles and first leaves of young barley (Hordeum vulgare L. cv. Triumph) plants catalysed the synthesis of 55% methanol-insoluble labelled material from UDP-[U-14C]glucose, the main components of which were identified as (1,3)(1,4)-beta- and (1,3)-beta-D-glucans. The membrane preparations also catalysed the transformation of UDP-glucose into labelled low-molecular-weight products, mainly glucose (by phosphatase action), glucose-1-phosphate (by phosphodiesterase action) and glyco(phospho)lipids (by glycosyltransferase action). The formation of (1,3)(1,4)-beta-glucans, (1,3)-beta-glucans, and the other reactions competing for UDP-glucose, were monitored simultaneously and quantitatively by a novel procedure based on enzymatic analysis, thin-layer chromatography and digital autoradiography. Thus it was possible (i) to optimise conditions to obtain (1,3)(1,4)-beta-glucan synthesis or (1,3)-beta-glucan synthesis in isolation, and (ii) to study the influence of temperature, pH, cofactors, substrate concentration etc. on the (1,3)(1,4)- and (1,3)-beta-glucan synthesis reactions even when both occurred together. The synthesis of both beta-glucans was optimal at 20 degrees C. In Tris-HCl buffer, the pH optima for (1,3)(1,4)-beta-glucan synthesis and (1,3)-beta-glucan synthesis were pH 8.5 and pH 7.0, respectively. Both glucan-synthesis reactions required Mg2+: (1,3)-beta-glucan synthesis was optimal at 2 mM, whereas (1,3)(1,4)-beta-glucan synthesis continued to increase up to 200 mM Mg2+, when the ion was supplied as the sulphate. (1,3)-beta-Glucan synthesis was Ca2+ dependent and this dependence could be abolished by proteinase treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbohydrate Conformation↗
PubMed1991

Yeast beta-glucan synthesis: KRE6 encodes a predicted type II membrane protein required for glucan synthesis in vivo and for glucan synthase activity in vitro.

The KRE6 gene product is required for synthesis of the major beta-glucans of the yeast cell wall, as mutations in this gene confer reduced levels of both the (1----6)- and (1----3)-beta-D-glucan polymers. Cloning and sequencing of KRE6 reveals a gene encoding a predicted 80-kDa protein with a central transmembrane domain and the topology of a type II membrane protein. Null mutants of KRE6 grow slowly, have larger cells, and show a reduction in alkali-insoluble wall glucans. The mutants show good viability and are not osmotically sensitive, but they are more susceptible to beta-glucanase digestion and mechanical stress than wild-type cells. The specific activity of the GTP-dependent, membrane-associated, in vitro (1----3)-beta-glucan synthase is reduced 50% in kre6 null mutants, and this reduction correlates with the mutation in meiotic tetrads. Transformants of kre6 null mutants with a KRE6 gene expressed from a centomere-based vector show a 4- to 5-fold increase in in vitro (1----3)-beta-glucan synthase activity over transformants with the vector alone. The phenotype and structure of the KRE6 product, Kre6p, suggest that Kre6p may be a beta-glucan synthase, and if so, it implies that beta-glucan synthases are functionally redundant in yeast. Alternatively, Kre6p may be part of a single multiprotein glucan synthase or modulate its activity. Use of KRE6 should permit a genetic analysis of eukaryotic (1----3)-beta-glucan synthesis.

Alleles↗
PubMed1999

PGG-glucan, a soluble beta-(1,3)-glucan, enhances the oxidative burst response, microbicidal activity, and activates an NF-kappa B-like factor in human PMN: evidence for a glycosphingolipid beta-(1,3)-glucan receptor.

PGG-Glucan, a soluble beta-(1,6)-branched beta-(1,3)-linked glucose homopolymer derived from the cell wall of the yeast Saccharomyces cerevisiae, is an immunomodulator which enhances leukocyte anti-infective activity and enhances myeloid and megakaryocyte progenitor proliferation. Incubation of human whole blood with PGG-Glucan significantly enhanced the oxidative burst response of subsequently isolated blood leukocytes to both soluble and particulate activators in a dose-dependent manner, and increased leukocyte microbicidal activity. No evidence for inflammatory cytokine production was obtained under these conditions. Electrophoretic mobility shift assays demonstrated that PGG-Glucan induced the activation of an NF-kappaB-like nuclear transcription factor in purified human neutrophils. The binding of 3H-PGG-Glucan to human leukocyte membranes was specific, concentration-dependent, saturable, and high affinity (Kd approximately 6 nM). A monoclonal antibody specific to the glycosphingolipid lactosylceramide was able to inhibit activation of the NF-kappaB-like factor by PGG-Glucan, and ligand binding data, including polysaccharide specificity, suggested that the PGG-Glucan binding moiety was lactosylceramide. These results indicate that PGG-Glucan enhances neutrophil anti-microbial functions and that interaction between this beta-glucan and human neutrophils is mediated by the glycosphingolipid lactosylceramide present at the cell surface.

Adjuvants, Immunologic↗
PubMed1997

Plasma (1-->3)-beta-D-glucan assay and immunohistochemical staining of (1-->3)-beta-D-glucan in the fungal cell walls using a novel horseshoe crab protein (T-GBP) that specifically binds to (1-->3)-beta-D-glucan.

A highly sensitive enzyme-linked immunosorbent assay specific to (1-->3)-beta-D-glucans (GBP-ELISA) has been developed using a novel (1-->3)-beta-D-glucan-binding protein (T-GBP), which was purified from the amebocyte lysate of the Japanese horseshoe crab, Tachypleus tridentatus. This method allowed quantitation of the glucans in a concentration range of 0.1-1,000 ng/ml, regardless of linear and branched structures, and was applied to determine the amounts of (1-->3)-beta-D-glucan in human and animal plasmas for diagnosis of fungemia. High levels of plasma glucan contents in clinical samples were found to be correlated closely with the severity of fungal infection. T-GBP was successfully utilized for indirect immunofluorescence staining of (1-->3)-beta-D-glucan in Candida albicans cell walls.

Animals↗
PubMed1983

Antitumor activity of tetrahydro-2-furanyl- and tetrahydro-2-pyranyl-glucans obtained by chemical modification of (1 leads to 3)-beta-D-glucan from Alcaligenes faecalis var. myxogenes IFO 13140 and its lower molecular weight glucans.

The well-defined (1 leads to 3)-beta-D-glucan with DP (degree of polymerization) 540 and the various chain-length (1 leads to 3)-beta-D-glucans prepared by its hydrolysis were chemically modified to furanyl- and pyranyl-derivatives. As a primary screening, the effect of 20 derivatives thus obtained was tested on Sarcoma 180 solid tumor transplanted sc into allogeneic ICR mice; the dose was 10 mg/kg ip for 10 days. Eleven derivatives that showed a strong antitumor effect on Sarcoma 180 were also tested on Meth-A solid tumor in syngeneic mice. Of the derivatives tested, five furanyl-derivatives (F-4, F-6, F-7, F-10, and F-11) and one pyranyl-derivative (P-5) had potent antitumor effects on this syngeneic tumor system at ip doses of 10 or 30 mg/kg for 10 days. By oral administration, only two derivatives (F-10 and P-3) showed moderate antitumor activity against Sarcoma 180, without complete tumor regression. The mechanism of action of these derivatives was considered to be host-mediated and similar to that of the original glucan, because of a lack of effect in vitro.

Alcaligenes↗
PubMed1965

beta-glucan hydrolases from Aspergillus niger. Isolation of a beta-(1-4)-glucan hydrolase and some properties of the beta-(1-3)-glucan-hydrolase components.

1. The components of an enzyme preparation from Aspergillus niger, which hydrolysed substrates containing beta-(1-->3)- and beta-(1-->4)-glucosidic linkages, were separated by calcium phosphate and Dowex 1 column chromatography. 2. The hydrolytic activity of each fraction from both types of column towards laminaribiose, laminarin, carboxymethylpachyman, pachydextrins, salicin, cellobiose, cellopentaose and swollen cellulose was tested. 3. The activity towards the beta-(1-->3)-glucosidic substrates was found in three well-separated groups of fractions. The differences in action pattern of these groups is discussed. 4. Preparative-scale chromatography that enabled the separation of a beta-(1-->4)-glucan-glucanohydrolase component substantially free of activity towards beta-(1-->3)-glucosidic substrates is described. Residual beta-(1-->3)-glucan-hydrolase activity was removed by adsorption on to insoluble laminarin at pH3.5.

Aspergillus↗
PubMed2000

The influence of glucan polymer structure and solution conformation on binding to (1-->3)-beta-D-glucan receptors in a human monocyte-like cell line.

Glucans are (1-3)-beta-D-linked polymers of glucose that are produced as fungal cell wall constituents and are also released into the extracellular milieu. Glucans modulate immune function via macrophage participation. The first step in macrophage activation by (1-3)-beta-D-glucans is thought to be the binding of the polymer to specific macrophage receptors. We examined the binding/uptake of a variety of water soluble (1-3)-beta-D-glucans and control polymers with different physicochemical properties to investigate the relationship between polymer structure and receptor binding in the CR3- human promonocytic cell line, U937. We observed that the U937 receptors were specific for (1-->3)-beta-D-glucan binding, since mannan, dextran, or barley glucan did not bind. Scleroglucan exhibited the highest binding affinity with an IC(50)of 23 nM, three orders of magnitude greater than the other (1-->3)-beta-D-glucan polymers examined. The rank order competitive binding affinities for the glucan polymers were scleroglucan>>>schizophyllan > laminarin > glucan phosphate > glucan sulfate. Scleroglucan also exhibited a triple helical solution structure (nu = 1.82, beta = 0.8). There were two different binding/uptake sites on U937 cells. Glucan phosphate and schizophyllan interacted nonselectively with the two sites. Scleroglucan and glucan sulfate interacted preferentially with one site, while laminarin interacted preferentially with the other site. These data indicate that U937 cells have at least two non-CR3 receptor(s) which specifically interact with (1-->3)-beta-D-glucans and that the triple helical solution conformation, molecular weight and charge of the glucan polymer may be important determinants in receptor ligand interaction.

Animals↗
PubMed1978

Adherence of glucan-positive and glucan-negative streptococcal strains to normal and damaged heart valves.

The adherence of 18 strains of streptococci to sections of normal canine and human aortic, mitral, and tricuspid valves and to canine interatrial septum was compared in an in vitro system. Quantitative measurements of adherence ratios were performed by two independent methods. Adherence ratios for Streptococcus mutans, S. sanguis, S. bovis, and Group D streptococci were higher (0.0058-0.0101) than for the other streptococcal strains studied (0.0025-0.0041). With the exception of Group D streptococci, adherence ratios for each bacterial strain were similar with the aortic, mitral, and tricuspid valve sections. Adherence ratios with normal human and canine valve leaflets were similar, but adherence ratios with interatrial septum were lower than with normal valve sections. Adherence ratios for glucan-positive and glucan-negative strains of streptococci with normal and with damaged aortic valve leaflets were also compared. The adherence ratios of the glucan-positive streptococci (S. mutans, S. sanguis, and S. bovis) and one glucan-negative enterococcal strain (KG-3) were approximately five times higher with damaged aortic valves (0.039-0.051) than with normal aortic valves (0.009-0.010). For glucan-positive strains, adherence ratios with normal aortic leaflets were similar when bacteria were grown in media which contains or lacks sucrose. In striking contrast, growth of the glucan-positive strains in medium which lacks sucrose, with resultant deficiency of glucan production, decreased the adherence ratios with damaged aortic valve leaflets to those found with normal aortic leaflets. Treatment of glucan-positive strains with dextranase resulted in a decrease in their adherence ratios to levels seen with bacteria grown in medium lacking sucrose, but the higher adherence ratios could be restored in the presence of exogenous dextran.It is concluded that glucan production is one quantitatively important factor that contributes to the greater adherence of glucan-positive streptococci to damaged rather than to normal aortic heart valve leaflets. However, glucan production is not the only factor that determines preferential adherence of streptococci to damaged heart valves, because glucan-negative strains may also show some degree of increased adherence to damaged valves. Thus, bacterial glucan production is one of the factors that could contribute to the pathogenesis of bacterial endocarditis.

Animals↗
PubMed1995

Streptococcal glucan-binding lectins do not recognize methylated alpha-1,6 glucans.

The glucan-binding lectin (GBL) of Streptococcus sobrinus is cell associated, enabling the bacteria to be aggregated by alpha-1,6 glucans. Glucans, such as amylose, pullulan, laminarin and nigeran, have no affinity for the lectin. High molecular weight alpha-1,6 glucans (dextrans) readily aggregate the bacteria, whereas low molecular weight glucans inhibit the aggregation brought about by the high molecular weight species. Methylated glucan T-2000 (an alpha-1,6 glucan with an average molecular weight of 2 x 10(6) Da) aggregated the bacteria very poorly when the extent of methylation (DS, or degree of substitution) was high, and less poorly when the DS was low. Similarly, methylated low molecular weight alpha-1,6 glucan was a poor inhibitor of aggregation induced by the high molecular weight glucan T-2000. Because the methylation occurred primarily on the hydroxyl of C-2, it is suggested that the hydroxyl is needed for formation of the lectin-glucan complex. It appears that the GBL is not only stereospecific in interaction with glucans, but also regio-specific, interacting only with the underivatized alpha-1,6-glucan.

Bacterial Adhesion↗
PubMed1986

Isolation of soluble yeast beta-glucans that inhibit human monocyte phagocytosis mediated by beta-glucan receptors.

The trypsin-sensitive receptor that mediates phagocytosis of unopsonized zymosan particles by human monocytes has been designated as a beta-glucan receptor because of its functional inhibition by specific algal and plant beta-glucans. Soluble ligands that are chemically and structurally identical to beta-glucan constituents of zymosan were isolated from a carbohydrate-enriched fraction of yeast extract by sequential chromatography on DE-cellulose, SP-Sephadex, and Con A-Sepharose. Preincubation of adherent human monocytes with 278, 210, and 2.5 micrograms/ml hexose equivalents in pooled chromatographic fractions from DE-cellulose, SP-Sephadex, and Con A-Sepharose, respectively, effected 50% reductions in subsequent phagocytosis of zymosan particles without affecting Fc-mediated ingestion of IgG-coated sheep erythrocytes (ESIgG). The purified yeast extract-derived beta-glucans, which contained 92% glucose and 8% mannose by gas chromatographic analysis and eluted from a Sephacryl S-200 column as a broad peak with a Kav of 0.39 and estimated molecular sizes of from 20,000 to 70,000 m.w., required only 3.5 +/- 0.9 micrograms/ml (mean +/- SD, n = 6), as compared with 31.5 micrograms/ml of the algal beta-glucan laminarin to achieve 50% decreases in zymosan ingestion. Alternatively, soluble yeast beta-glucans with estimated molecular sizes of from 2 X 10(5) to 2 X 10(6) were prepared from yeast glucan particles, which contained 98% glucose and 0% mannose, by sonication and sequential centrifugation at 15,000 and 100,000 X G for 30 and 60 min, respectively. Monocyte ingestion of zymosan was reduced by 50% by pretreatment with 60 ng/ml of the soluble beta-glucans in 15,000 X G supernatants, whereas ingestion of ESIgG was unaffected by as much as 50 micrograms/ml of this material. Partial acid hydrolysis of soluble glucan-derived beta-glucans in 15,000 X G supernatants followed by gel filtration on Bio-Gel P-4 revealed two well-defined peaks within the inclusion volume of the column with phagocytosis-inhibiting activity. Oligoglucosides that eluted at a Kav of 0.46 had an estimated molecular size of 2,000 m.w. and effected a 48% reduction in zymosan ingestion at inputs of 2 to 5 micrograms/ml, and smaller oligoglucosides with a Kav of 0.82 and an estimated molecular size of 1,000 m.w. effected a 50% reduction at inputs of 25 micrograms/ml. Preincubation of monocytes for 2 min with 25 micrograms/ml of the oligoglucosides with estimated molecular size of 1,000 m.w. and with 50 ng/ml of soluble glucan-derived beta-glucans in 100,000 X G supernatants reduced zymosan ingestion by 41% +/- 4 and 44% +/- 3 (mean +/- SD, n = 3), respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Complement Pathway, Alternative↗
PubMed2003

Modulation of liver fibrosis and pathophysiological changes in mice infected with Mesocestoides corti (M. vogae) after administration of glucan and liposomized glucan in combination with vitamin C.

The effects of glucan and liposomized glucan, alone or co-administered with vitamin C, and empty liposomes on hepatic fibrosis in mice infected with Mesocestoides corti (M. vogae) tetrathyridia were studied. Preparations were administered every third day from day 7 to day 31 post-infection (p.i.), nine doses in total. Activities of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and cholesterol levels were measured in sera collected on days 11, 15, 21, 28, 32, 42, 50 and 65 p.i. Liver fibrosis was studied on the same days by measuring hydroxyproline concentration, which is considered a marker for collagen content. Larvicidal effects of the glucan and liposome preparations were estimated on day 65 p.i. in the liver and peritoneal cavity. Glucan formulations significantly enhanced collagen content, most prominently after administration of liposomized glucan in combination with vitamin C. Activities of both enzymes and cholesterol levels were slightly modified after administration of glucan alone. Liposomized glucan with vitamin C significantly increased ALT and AST activity and cholesterol levels up to days 28-32 p.i., after which they plateaued or declined. The most pronounced decrease was after administration of liposomized glucan and vitamin C. The same pattern of biochemical parameters in serum was observed after administration of empty liposomes, however, collagen content was not modified significantly. Larval counts in the liver and the peritoneal cavity were significantly reduced after treatment with either glucan formulation, but were unaffected following treatment with empty liposomes. In summary, intense fibrosis in the liver of mice treated with liposomized glucan and vitamin C did not result in the most extensive parenchymal cell injury but, rather in the highest efficacy of treatment. Liposomal lipids were probably utilized in the reparation of the damaged parenchymal cells, while glucan stimulated phagocytic cells.

Alanine Transaminase↗
PubMed1992

Stimulation of human monocyte beta-glucan receptors by glucan particles induces production of TNF-alpha and IL-1 beta.

beta-glucans are pharmacologic agents that rapidly enhance host resistance to a variety of biologic insults through mechanisms involving macrophage activation. To determine whether stimulation of the beta-glucan receptors on human monocytes resulted in cytokine production, monolayers of monocytes were incubated with purified yeast glucan particles and measured for tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) mRNA and protein. By Northern blot analysis, TNF-alpha mRNA was detected within 30 min of incubation with glucan particles, peaked at 2 h, and remained elevated for at least 8 h. Glucan induction of IL-1 beta mRNA followed a similar time-course of initiation and accumulation. By enzyme-linked immunosorbent assays (ELISAs), significant levels of TNF-alpha and IL-1 beta were present in supernatants of glucan-treated cells within 1 h and plateau levels of both cytokines were approached within 4 h. At particle-to-cell ratios of from 0.4 to 18, glucan particles induced dose-dependent increases in TNF-alpha and IL-1 beta mRNA and corresponding increases in TNF-alpha and IL-1 beta proteins. Exposure of monocytes to glucan particles for 0-30 min and washing before continued incubation for 4 h in particle-free buffer induced production and secretion of TNF-alpha and IL-1 beta in a time-dependent fashion compatible with phagocytosis. The pretreatment of monocyte monolayers with trypsin reduced glucan-induced production of TNF-alpha and IL-1 beta in a dose-dependent manner with 5 micrograms/ml of trypsin effecting reductions of greater than 50%. Thus, glucan particles induce human monocyte production of TNF-alpha and IL-1 beta by a mechanism that is dependent on trypsin-sensitive beta-glucan receptors.

Cells, Cultured↗
PubMed1978

Mechanism of glucan-induced agglutination in Streptococcus mutans. I. Binding of radioactive glucan to whole cells of S. mutans OMZ-176.

The binding of radioactive glucan to Streptococcus mutans cells, which are agglutinated by dextrans, was examined. The glucan was synthesized from sucrose by extracellular glucosyltransferases from S. mutans FA-1 and was highly branched at C-3 and C-6 of D-glucose residues, containing 17% of a (1 leads to 3)inter-chain residues. Binding of glucan to whole cells of S. mutans OMZ-176, which were agglutinated by addition of glucan or Dextran T2000, was irreversible and followed saturation type kinetics; saturation was achieved at approximately 110 ng of glucan per ml. About 14 ng of glucan were bound per mg of the cells at the saturated concentration. The heated cells of this organism, however, had a relatively low ability of glucan-binding, compared with the freshly prepared and lyophilized cells. Binding to the heated cells was entirely of a non-saturation type. Binding of Dextran T2000 or T10 was determined by competition between the labeled glucan and unlabeled Dextrans for the binding site(s). Both Dextrans and glucan from S. mutans FA-1 were bound to the same site(s). Other organisms, which did not undergo glucan- and Dextran-induced agglutination, had a relatively lower ability of glucan-binding than S. mutans, which was agglutinated.

Agglutination↗
PubMed2000

The first description of a (1--> 6)-beta-D-glucan in prokaryotes: (1 --> 6)-beta-D-glucan is a common component of actinobacillus suis and is the basis for a serotyping system.

The chemical and antigenic properties of the cell-surface lipopolysaccharides (LPSs) and capsular polysaccharides (CPSs) of seven representative strains of Actinobacillus suis from healthy and diseased pigs were investigated. Four strains produced a linear (1 --> 6)-beta-D-glucan homopolymer, beta-D-Glcp-(1-[ --> 6)-beta-D-Glcp-(1-]n -->, as a LPS-O-chain (O1) and as a CPS (K1). Polyclonal antisera prepared against a (1 --> 6)-beta-D-glucan-containing strain showed a positive reaction against both LPSs and CPSs derived from the above strains (designated serotype O1/K1). One strain carried the (1 --> 6)-beta-D-glucan solely as a LPS-O-chain (serotype O1) and two strains did not express the (1 --> 6)-beta-D-glucan, but, instead, produced a different O-chain (designated serotype 02); these three strains expressed their own characteristic CPSs. (1 --> 6)-beta-D-Glucan structures are common cell wall components of yeast, fungi and lichens, but, to our knowledge, this is the first time a (1 --> 6)-beta-D-glucan has been described in a prokaryotic organism. Conformational and nuclear magnetic resonance analyses showed that the beta-D-Glcp-(1 --> 6)-beta-D-Glcp linkage was flexible and two distinct glycosidic conformers are described. Cross-reactive antibodies to the A. suis (1 --> 6)-beta-D-glucan could be detected in sera from a variety of species and in sera from specific pathogen free pigs. This cross-reactivity may arise from immuno-stimulation of organisms present in the surrounding environment that contain (1 --> 6)-beta-D-glucan, which may also explain the high incidence of false positive results in previous serological tests for A. suis. In addition, these (1 --> 6)-beta-D-glucan background antibodies may be protective against A. suis infection. The characterization herein of (1 --> 6)-beta-D-glucan is the foundation for the development of a serotyping system for A. suis.

Actinobacillus↗
PubMed2004

At low serum glucan concentrations there is an inverse correlation between serum glucan and serum cytokine levels in ICU patients with infections.

Glucans are fungal cell wall glucose polymers that are released into the blood of infected patients. The role of glucans in infection is unknown. We examined serum glucan and cytokine levels in intensive care unit (ICU) patients with infections. There was an inverse correlation (p<0.001) between serum glucan levels and interleukin (IL)-2), IL-4, tumor necrosis factoralpha (TNFalpha) and granulocyte macrophage-colony stimulating factor (GM-CSF) levels in infected ICU patients. The correlation between serum cytokines and serum glucan was only observed at glucan concentrations <40 pg/ml. No change was observed at serum glucan levels of >40 pg/ml. There was no correlation between serum glucan levels and systemic levels of IL-1beta, IL-5, IL-6, IL-8, IL-10 or IFNgamma. Interestingly, blood borne glucans did not suppress systemic cytokine levels in infected ICU patients, instead they were maintained at control levels. We conclude that circulating glucans may prevent cytokine upregulation in response to infection. This may represent an adaptive response to septic injury.

Adrenocorticotropic Hormone↗
PubMed1994

Synthesis of yeast cell wall glucan and evidence for glucan metabolism in a Saccharomyces cerevisiae whole cell system.

The synthesis and metabolism of yeast cell wall glucan were studied using a Saccharomyces cerevisiae construct in which radiolabelled galactose is metabolized to UDP-glucose and preferentially incorporated into glucan. Greater than 85% of the incorporated radiolabel was found within insoluble cell wall material. Our study also demonstrated that radiolabelled wall glucan is released from cells growing exponentially, and that the released radiolabel is reutilizable low molecular mass material. Size exclusion chromatography and enzymic analysis indicate that laminaribiose comprises approximately 50% of the released fraction. This is consistent with in vitro findings that laminaribiose is a by-product of a newly identified glucosyltransferase (R. P. Hartland, G. W. Emerson & P. A. Sullivan, 1991, Proc R Soc Lond B 246, 155-160) associated with fungal cell walls. Our results also suggest that pre-existing glucan undergoes less metabolic processes than newly synthesized material as evidenced by a decrease in released radiolabel over time. Pulse double labelling of glucan and total cellular protein indicate that glucan metabolism and protein synthesis (ps) are not tightly coupled although they do parallel each other during exponential growth. Inhibitors of glucan synthesis (gs) decrease the glucan to protein ratio. Measurement of ps allows normalization for non-specific decreases in the rate of cell wall synthesis due to general cessation of growth. Cilofungin and papulacandin B, two putative inhibitors of gs, inhibited galactose incorporation into glucan and thus showed a decrease in the glucan to protein ratio, although ps was affected.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminoglycosides↗
PubMed1996

Cell-associated glucans of Burkholderia solanacearum and Xanthomonas campestris pv. citri: a new family of periplasmic glucans.

The cell-associated glucans produced by Burkholderia solanacearum and Xanthomonas campestris pv. citri were isolated by trichloroacetic acid treatment and gel permeation chromatography. The compounds obtained were characterized by compositional analysis, matrix-assisted laser desorption ionization mass spectrometry, and high-performance anion-exchange chromatography. B. solanacearum synthesizes only a neutral cyclic glucan containing 13 glucose residues, and X. campestris pv. citri synthesizes a neutral cyclic glucan containing 16 glucose residues. The two glucans were further purified by high-performance anion-exchange chromatography. Methylation analysis revealed that these glucans are linked by 1,2-glycosidic bonds and one 1,6-glycosidic bond. Our 600-MHz homonuclear and 1H-13C heteronuclear nuclear magnetic resonance experiments revealed the presence of a single alpha-1,6-glycosidic linkage, whereas all other glucose residues are beta-1,2 linked. The presence of this single alpha-1,6 linkage, however, induces such structural constraints in these cyclic glucans that all individual glucose residues could be distinguished. The different anomeric proton signals allowed complete sequence-specific assignment of both glucans. The structural characteristics of these glucans contrast with those of the previously described osmoregulated periplasmic glucans.

Burkholderia↗