Disaccharide Side Chain Research Articles

Convergent emergence of Glucomannan β-galactosyltransferase activity in Asterids and Rosids.

β-Galactoglucomannan (β-GGM) is a primary cell wall polysaccharide in rosids and asterids. The β-GGM polymer has a backbone of repeating β-(1,4)-glucosyl and mannosyl residues, usually with mono- α-(1,6)-galactosyl substitution or β-(1,2)-galactosyl α-galactosyl disaccharide sidechains on the mannosyl residues. Mannan β-GalactosylTransferases (MBGTs) are therefore required for β-GGM synthesis. The single MBGT identified so far, AtMBGT1, lies in glycosyltransferase family 47A subclade VII, and was identified in Arabidopsis. However, despite the presence of β-GGM, an orthologous gene is absent in tomato (Solanum lycopersicum), a model asterid. In this study, we screened candidate MBGT genes from the tomato genome, functionally tested the activities of encoded proteins, and identified the tomato MBGT (SlMBGT1) in GT47A-III. Interestingly therefore, AtMBGT1 and SlMBGT1 are located in different GT47A subclades. Further, phylogenetic and glucomannan structural analysis from different species raised the possibility that various asterids possess conserved MBGTs in an asterid-specific subclade of GT47A-III, indicating that MBGT activity has been acquired convergently among asterids and rosids. The present study highlights the promiscuous emergence of donor and acceptor preference in GT47A enzymes. The independent acquisition of the activity also suggests an adaptive advantage for eudicots to acquire β-GGM β-galactosylation, and hence also suggests the disaccharide side chains are important for β-GGM function.

Structural Characterization and Anticoagulant Activities of a Keratan Sulfate-like Polysaccharide from the Sea Cucumber Holothuria fuscopunctata.

A sulfated polysaccharide (AG) was extracted and isolated from the sea cucumber H. fuscopunctata, consisting of GlcNAc, GalNAc, Gal, Fuc and lacking any uronic acid residues. Importantly, several chemical depolymerization methods were used to elucidate the structure of the AG through a bottom-up strategy. A highly sulfated galactose (oAG-1) and two disaccharides labeled with 2,5-anhydro-D-mannose (oAG-2, oAG-3) were obtained from the deaminative depolymerized product along with the structures of the disaccharide derivatives (oAG-4~oAG-6) identified from the free radical depolymerized product, suggesting that the repeating building blocks in a natural AG should comprise the disaccharide β-D-GalS-1,4-D-GlcNAc6S. The possible disaccharide side chains (bAG-1) were obtained with mild acid hydrolysis. Thus, a natural AG may consist of a keratan sulfate-like (KS-like) glycosaminoglycan with diverse modifications, including the sulfation types of the Gal residue and the possible disaccharide branches α-D-GalNAc4S6S-1,2-α/β-L-Fuc3S linked to the KS-like chain. Additionally, the anticoagulant activities of the AG and its depolymerized products (dAG1-9) were evaluated in vitro using normal human plasma. The AG could prolong activated partial thromboplastin time (APTT) in a dose-dependent manner, and the activity potency was positively related to the chain length. The AG and dAG1-dAG3 could prolong thrombin time (TT), while they had little effect on prothrombin time (PT). The results indicate that the AG could inhibit the intrinsic and common coagulation pathways.

The structure of Klebsiella pneumoniae K108 capsular polysaccharide is similar to Escherichia coli colanic acid

The clinical isolate of Klebsiella pneumoniae 1333/P225 was revealed as containing a KL108 K. pneumoniae K locus for capsule biosynthesis. The gene cluster demonstrated a high level of sequence and arrangement similarity with that of the E. coli colanic acid biosynthesis gene cluster. The KL108 gene cluster includes a gene of WcaD polymerase responsible for joining oligosaccharide K units into capsular polysaccharide (CPS), acetyltransferase, pyruvyltransferasefive and genes for glycosyltransferases (Gtrs), four of which have homologues in genetic units of the colanic acid synthesis. The fifth Gtr is specific to this cluster. The work involved the use of sugar analysis, Smith degradation and one- and two-dimensional 1H and 13C NMR spectroscopy to establish the structure of the K108 CPS. The CPS repetitive K unit is composed of branched pentasaccharide with three monosaccharides in the backbone and a disaccharide side chain. The main chain is the same as for colanic acid but the side chain differs. Two bacteriophages infecting K. pneumoniae strain 1333/P225 were isolated and structural depolymerase genes were determined; depolymerases Dep108.1 and Dep108.2 were cloned, expressed and purified. It was demonstrated that both depolymerases specifically cleave the β-Glcp-(1→4)-α-Fucp linkage between K108 units in the CPS.

Structural Elucidation of a Glucan from Trichaster palmiferus by Its Degraded Products and Preparation of Its Sulfated Derivative as an Anticoagulant.

Echinoderms have been attracting increasing attention for their polysaccharides, with unique chemical structure and enormous potential for preparing drugs to treat diseases. In this study, a glucan (TPG) was obtained from the brittle star Trichaster palmiferus. Its structure was elucidated by physicochemical analysis and by analyzing its low-molecular-weight products as degraded by mild acid hydrolysis. The TPG sulfate (TPGS) was prepared, and its anticoagulant activity was investigated for potential development of anticoagulants. Results showed that TPG consisted of a consecutive α1,4-linked D-glucopyranose (D-Glcp) backbone together with a α1,4-linked D-Glcp disaccharide side chain linked through C-1 to C-6 of the main chain. The TPGS was successfully prepared with a degree of sulfation of 1.57. Anticoagulant activity results showed that TPGS significantly prolonged activated partial thromboplastin time, thrombin time, and prothrombin time. Furthermore, TPGS obviously inhibited intrinsic tenase, with an EC50 value of 77.15 ng/mL, which was comparable with that of low-molecular-weight heparin (LMWH) (69.82 ng/mL). TPGS showed no AT-dependent anti-FIIa and anti-FXa activities. These results suggest that the sulfate group and sulfated disaccharide side chains play a crucial role in the anticoagulant activity of TPGS. These findings may provide some information for the development and utilization of brittle star resources.

Deaminative-cleaved S. monotuberculatus fucosylated glycosaminoglycan: Structural elucidation and anticoagulant activity

Stichopus monotuberculatus is a tropical sea cucumber species and used as a folk medicine and tonic food. In this study, a fucosylated glycosaminoglycan (SmFG), the depolymerized SmFG (dSmFG) and its oligosaccharide fractions were prepared. The SmFG and its depolymerized products were comprised of a chondroitin-sulfate-E backbone, and various sulfated fucose side chains, including an unusual disaccharide side chain connected to the C-3 position of D-glucuronic acid (GlcA) or GlcA-ol. A peeling reaction occurred during the deaminative depolymerization process. The dSmFG and its fractions showed strong anticoagulant activity by selectively inhibiting intrinsic tenase complex, and had no anti-factor IIa, Xa and VIIa activity. The anticoagulant activity reduced with the decrease of molecular weight, and the unusual branch and novel reducing end may enhance the anticoagulant activity. These findings can provide significant information for development and utilization of depolymerized products from SmFG in food and pharmaceutical industries.

Identification of xylan arabinosyl 2-O-xylosyltransferases catalyzing the addition of 2-O-xylosyl residue onto arabinosyl side chains of xylan in grass species.

Grass xylan, the major hemicellulose in both primary and secondary cell walls, is heavily decorated with α-1,3-linked arabinofuranosyl (Araf) residues that may be further substituted at O-2 with xylosyl (Xyl) or Araf residues. Although xylan 3-O-arabinosyltransferases (XATs) catalyzing 3-O-Araf addition onto xylan have been characterized, glycosyltransferases responsible for the transfer of 2-O-Xyl or 2-O-Araf onto 3-O-Araf residues of xylan to produce the Xyl-Araf and Araf-Araf disaccharide side chains remain to be identified. In this report, we showed that a rice GT61 member, named OsXAXT1 (xylan arabinosyl 2-O-xylosyltransferase 1) herein, was able to mediate the addition of Xyl-Araf disaccharide side chains onto xylan when heterologously co-expressed with OsXAT2 in the Arabidopsis gux1/2/3 (glucuronic acid substitution of xylan 1/2/3) triple mutant that lacks any glycosyl substitutions. Recombinant OsXAXT1 protein expressed in human embryonic kidney 293 cells exhibited a xylosyltransferase activity catalyzing the addition of Xyl from UDP-Xyl onto arabinosylated xylooligomers. Consistent with its function as a xylan arabinosyl 2-O-xylosyltransferase, CRISPR-Cas9-mediated mutations of the OsXAXT1 gene in transgenic rice plants resulted in a reduction in the level of Xyl-Araf disaccharide side chains in xylan. Furthermore, we revealed that XAXT1 close homologs from several other grass species, including switchgrass, maize, and Brachypodium, possessed the same functions as OsXAXT1, indicating functional conservation of XAXTs in grass species. Together, our findings establish that grass XAXTs are xylosyltransferases catalyzing Xyl transfer onto O-2 of Araf residues of xylan to form the Xyl-Araf disaccharide side chains, which furthers our understanding of genes involved in xylan biosynthesis.

Impact of borate on structure of antifreeze glycoproteins

Antifreeze glycoproteins (AFGPs) facilitate the survival of various organisms in the polar region by preventing internal ice accumulation via an adsorption-inhibition mechanism. Inhibition of AFGP antifreeze activity by the borate buffers has been widely acknowledged as the direct experimental evidence supporting the hydroxyl, rather than methyl, binding mechanism. On the other hand, perturbation of borate binding on the AFGP configuration, which might have considerable influence on the binding efficiency of not only the hydroxyl but also the methyl groups, has rarely been quantitatively examined. Herein we studied, using molecular dynamics simulations, the perturbation on the configuration of a solvated AFGP8 protein induced by the binding of one single borate anion. Near the freezing point, this binding not only makes the disaccharide groups adjacent to the borate-binding disaccharide close to each other but also affects the entire AFGP8 conformation. The structural changes induced by the binding of borate on different disaccharide sidechains exhibit clear site-specificities and the effect of borate binding on the structural changes is significantly reduced at higher temperatures. Our study is valuable for further understanding the relationship between the structure and antifreeze activity of these antifreeze glycoproteins.

Rheology of sphingans in EPS–surfactant systems

A model-based rheological characterization of four sphingans in combination with four prominent surfactants of cosmetic formulations of cationic, anionic, zwitterionic and neutral headgroup characteristics was performed. The impact of the surfactants on the rheological properties, based on changes in the mechanical models was evaluated in respect to the closely related structural differences of the polysaccharides, to give an insight on the structure-function relationship of these interactions. The side chains of the sphingans Welan, Diutan and S-88 seem to be involved in the masking of the anionic charge of the polysaccharide backbone, making them highly compatible even with cationic surfactants. The effect of a disaccharide side chain of Diutan also impacts its intermolecular interactions opposed to Welan and S-88, resulting in different surfactant interactions as well as temperature stability. The lack of a side chain in Gellan leads to large incompatibilities with zwitterionic and cationic surfactants due to high polysaccharide-surfactant interactions.

Elucidation of the K32 Capsular Polysaccharide Structure and Characterization of the KL32 Gene Cluster of Acinetobacter baumannii LUH5549.

Capsular polysaccharide (CPS), isolated from Acinetobacter baumannii LUH5549 carrying the KL32 capsule biosynthesis gene cluster, was studied by sugar analysis, Smith degradation, and one- and two-dimensional 1H and 13C NMR spectroscopy. The K32 CPS was found to be composed of branched pentasaccharide repeats (K units) containing two residues of β-D-GalpNAc and one residue of β-D-GlcpA (β-D-glucuronic acid) in the main chain and one residue each of β-D-Glcp and α-D-GlcpNAc in the disaccharide side chain. Consistent with the established CPS structure, the KL32 gene cluster includes genes for a UDP-glucose 6-dehydrogenase (Ugd3) responsible for D-GlcA synthesis and four glycosyltransferases that were assigned to specific linkages. Genes encoding an acetyltransferase and an unknown protein product were not involved in CPS biosynthesis. Whilst the KL32 gene cluster has previously been found in the global clone 2 (GC2) lineage, LUH5549 belongs to the sequence type ST354, thus demonstrating horizontal gene transfer between these lineages.

Structure of the K128 capsular polysaccharide produced by Acinetobacter baumannii KZ-1093 from Kazakhstan

The structure of the K128 capsular polysaccharide (CPS) produced by Acinetobacter baumannii isolate KZ-1093 from Kazakhstan was established by sugar analysis and Smith degradation along with 1D and 2D 1H and 13C NMR spectroscopy. The CPS was found to consist of branched pentasaccharide repeating units containing only neutral sugars, and its composition and topology are closely related to those of the A. baumannii K116 CPS. The K128 and K116 oligosaccharide units differ in the linkage between the disaccharide side chain and the main chain, with a β-(1 → 6) linkage in K128 replacing a β-(1 → 4) linkage in K116. The linkages between the repeating units in the K128 and K116 CPSs are also different, with K128 units linked by β-d-GalpNAc-(1 → 4)-d-Galp, and β-d-GalpNAc-(1 → 3)-d-Galp linkages between K116 units. The KZ-1093 genome was sequenced and the CPS biosynthesis gene cluster at the chromosomal K locus was designated KL128. Consistent with the CPS structures, KL128 differs from KL116 in one glycosyltransferase gene and the gene for the Wzy polymerase. In KL128, the gtr200 glycosyltransferase gene replaces gtr76 in KL116, and Gtr200 was therefore assigned to the different β-d-GalpNAc-(1 → 6)-d-Galp linkage in K128. Similarly, the WzyK128 polymerase could be assigned to the β-d-GalpNAc-(1 → 4)-d-Galp linkage between the K128 units.

Acinetobacter baumannii K116 capsular polysaccharide structure is a hybrid of the K14 and revised K37 structures

The genome of Acinetobacter baumannii clinical isolate, MAR-303, recovered in Russia was sequenced and found to contain a novel gene cluster at the A. baumannii K locus for capsule biosynthesis. The gene cluster, designated KL116, included four genes for glycosyltransferases (Gtrs) and a gene for a Wzy polymerase responsible for joining oligosaccharide K units into the capsular polysaccharide (CPS). The arrangement of KL116 was a hybrid of previously described A. baumannii gene clusters, with two gtr genes and the wzy gene shared by KL37 and the two other gtr genes found in KL14. The structure of the K116 CPS was established by sugar analysis and Smith degradation, along with one- and two-dimensional 1H and 13C NMR spectroscopy. The CPS is composed of branched pentasaccharide K units containing only neutral sugars, with three monosaccharides in the main chain and a disaccharide side chain. The K116 unit shares internal sugar linkages with the K14 and K37 units, corresponding to the presence of shared gtr genes in the gene clusters. However, the specific linkage formed by Wzy was discrepant between K116 and the previously reported K37 CPS produced by A. baumannii isolate NIPH146. The K37 structure was therefore revised in this study, and the corrected Wzy linkage found to be identical to the Wzy linkage in K116. The KL116, KL14 and KL37 gene clusters were found in genomes of a variety of A. baumannii strain backgrounds, indicating their global distribution.

Rheological behaviors of microbial polysaccharides with different substituents in aqueous solutions: Effects of concentration, temperature, inorganic salt and surfactant

Rheological behaviors of microbial polysaccharides with different substituents in aqueous solutions have been systematically investigated. Both the saccharide side chains and acetyl substituents improve the gelation of welan gum (WG), diutan gum (DG) and gellan gum (GG) in pure water at 25 °C. For the polysaccharides with saccharide side chains (WG and DG), the relationship between the apparent viscosity and concentration conforms to the linear equation, while that of the polysaccharide with acetyl (GG) is exponential. More importantly, the roles of substituents on the stability of the molecular conformation of polysaccharides are significantly depended on the surrounding environment. Disaccharide side chains promote the stability of helical conformation and gel aggregates of GG at high temperature (85 °C) or in the presence of inorganic salts with the ionic strength of 2.0 mol L−1. The stability of gel structure containing acetyl (GG) shows higher temperature/salt sensitivity. Additionally, deacylated gellan gum (GG(d)) solutions transform into hydrogels in the presence of dodecyltrimethylammonium bromide (DTAB). This study will help to obtain a better understanding on the rheological properties of polysaccharides with respect to the conformation and applications.

The K90 capsular polysaccharide produced by Acinetobacter baumannii LUH5553 contains di-N-acetylpseudaminic acid and is structurally related to the K7 polysaccharide from A. baumannii LUH5533

Acinetobacter baumannii isolate LUH5553 carries the KL90 capsule gene cluster, which includes genes for three glycosyltransferases (Gtrs) and the ItrA3 initiating transferase, as well as a set of genes for synthesis of a higher sugar, 5,7-diacetamido-3,5,7,9-tetradeoxy-l-glycero-l-manno-non-2-ulosonic (di-N-acetylpseudaminic) acid (Pse5Ac7Ac). The K90 capsular polysaccharide (CPS) has a tetrasaccharide repeat (K90 unit), which begins with d-GlcpNAc and contains Pse5Ac7Ac. The higher sugar was cleaved by mild acid hydrolysis of the CPS, and structures of the initial and modified polysaccharides were established by 1D and 2D 1H and 13C NMR spectroscopy. K90 contains α-d-Galp-(1 → 6)-d-GlcpNAc and α-d-GlcpNAc-(1 → 3)-d-GlcpNAc fragments, and formation of these glycosidic linkages is catalysed respectively by Gtr14 and Gtr15. The gtr14 and gtr15 genes occur in several A. baumannii KL gene clusters, including KL5 and KL7 that carry itrA2 rather than itrA3. As ItrA2 introduces d-GalpNAc rather than d-GlcpNAc as the first monosaccharide, Gtr15 can transfer d-GlcpNAc to either of these amino sugars, suggesting that this enzyme has relaxed specificity. Consequently, the third, novel glycosyltransferase, Gtr163, forms the β-(2 → 3) linkage between Pse5Ac7Ac and d-Galp. Wzy polymerases encoded by KL90 and KL7 are 54% identical and form the same linkage between the K units to give branched polysaccharides with the same main chain but different disaccharide side chains, β-Pse5Ac7Ac-(2 → 3)-d-Galp in K90 and α-Leg5Ac7Ac-(2 → 6)-d-Galp in K7.

Synthesis and Antibacterial Evaluation of a Series of 11,12-Cyclic Carbonate Azithromycin-3-O-descladinosyl-3-O-carbamoyl Glycosyl Derivatives.

A novel series of 11,12-cyclic carbonate azithromycin-3-O-descladinosyl-3-O-carbamoyl glycosyl derivatives were designed, synthesized, and evaluated for their antibacterial activities in vitro. Most of these compounds had significant antibacterial activity against seven kinds of susceptible strains. In particular, compound G1 exhibited the most potent activity against methicillin-resistant Streptococcus pneumoniae 943 (MIC: 1 μg/mL), Staphylococcus pneumoniae 746 (MIC: 2 μg/mL), Streptococcus pyogenes 447 (MIC: 8 μg/mL), and Escherichia coli 236 (MIC: 32 μg/mL), which were two-, four-, four-, four-, and eight-fold stronger activity than azithromycin, respectively. Additionally, compound G2 exhibited improved activity against methicillin-resistant Staphylococcus aureus MRSA-1 (MIC: 8 μg/mL), Streptococcus pneumoniae 943 (MIC: 2 μg/mL), Staphylococcus pneumoniae 746 (MIC: 2 μg/mL), and Escherichia coli 236 (MIC: 32 μg/mL), which were two-, two-, four-, and eight-fold better activity than azithromycin, respectively. As for methicillin-resistant Staphylococcus aureus MRSA-1, compound G6 presented the most excellent activity (MIC: 4 μg/mL), showing four-fold higher activity than azithromycin (MIC: 16 μg/mL) and erythromycin (MIC: 16 μg/mL). However, compared with other compounds, compounds G7 and G8 with the disaccharide side chain were observed the lower activity against seven strains.

Water-soluble polysaccharide from Erythronium sibiricum bulb: Structural characterisation and immunomodulating activity

A water-soluble polysaccharide named ESBP2-1 was isolated from Erythronium sibiricum bulb through anion-exchange and size-exclusion chromatography. ESBP2-1 is a neutral polysaccharide fraction with an average molecular weight of 9.4×105Da and is composed of glucose, galactose and arabinose in a ratio of 24.3:1.1:1. Methylation analysis, partial hydrolysis and NMR studies revealed that the backbone of ESBP2-1 primarily consists of repeating →1)-α-d-Glcp-(4→ units where the disaccharide side chains of Arap-(1→6)-α-d-Galp-(1→ residue are attached to the O-6 position of Glc. An in vitro assay showed that ESBP2-1 significantly promoted the proliferation and neutral red phagocytosis of RAW 264.7 macrophage cells. In addition, ESBP2-1 stimulated the production of secretory molecules (nitric oxide, TNF-α and IL-1β) of RAW264.7 cells in a dose-dependent manner. These results suggest that ESBP2-1 is a potential immunostimulator.

Synthesis of three OSW-1 analogs with maltose side chains bearing different protection groups

In order to simplify the synthesis of OSW-1's disaccharide side chain and explore the structure–activity relationship of OSW-1, three 16α-O-maltose OSW-1 analogs carrying three maltose side chains bearing different protections were designed and synthesized.

Structure of perosamine-containing polysaccharide, a component of the sheath of Thiothrix fructosivorans

A sheath-forming and sulfur-oxidizing bacterium, Thiothrix fructosivorans, was heterotrophically cultured. The sheath, which is an extracellular microtube, was prepared by selectively removing the cells using lysozyme, sodium dodecyl sulfate, and sodium hydroxide. Solid-state 13C-nuclear magnetic resonance (NMR) spectrum revealed that the sheath is assembled from a glycan possessing acetyl and methyl groups. When the sheath was deacetylated, the original microtube structure was lost and the sheath became soluble under acidic conditions, revealing the importance of acetyl groups in maintaining the sheath structure. Equimolar d-glucose, d-glucosamine, and l-fucose were detected in the acid hydrolysate of the sheath by gas liquid chromatography. In addition to these sugars, β-GlcN-(1→4)-Glc and unidentified sugar were detected by analyzing the hydrolysate using high-performance liquid chromatography analysis. 1H and 13C NMR spectroscopy was used to identify a disaccharide composed of 4-deoxy-4-aminorhamnose (perosamine, Rha4N) and fucose. N-Acetyl-perosamine prepared from the disaccharide was polarimetric and exhibited a d-configuration. The previously unidentified disaccharide was found to be α-d-Rhap4N-(1→3)-d-Fuc. According to 1H and 13C NMR analyses, the deacetylated sheath-forming polysaccharide was found to h have a main chain of [→4)-β-d-GlcpN-(1→4)-β-d-Glcp-(1→]n, to which disaccharide side chains of α-d-Rhap4N-(1→3)-α-l-Fucp-(1→ were attached at position 3 of Glc.

Revision of the O-polysaccharide structure of Yersinia pseudotuberculosis O:1a; confirmation of the function of WbyM as paratosyltransferase

An O-polysaccharide was isolated by mild acid degradation at pH 4.5 of the long-chain lipopolysaccharide of Yersinia pseudotuberculosis PB1 (serotype O:1a) and studied using 2D NMR spectroscopy. It was found to contain two uncommon monosaccharides: paratose (3,6-dideoxy-d-ribo-hexose, Par) in the furanose form and 6-deoxy-d-manno-heptose (d-6dmanHep). The following structure of a branched tetrasaccharide repeat (O-unit) with a disaccharide side chain was established:▪This structure is at variance with the O-polysaccharide structure of Y. pseudotuberculosis O:1a reported earlier (Komandrova, N. A.; Gorshkova, R. P.; Isakov, V. V.; Ovodov, Y. S. Bioorg. Khim.1984, 10, 232–237). A comparative study by high-resolution ESI MS of the short-chain lipopolysaccharides from strain PB1 and a wbyM mutant thereof confirmed the function of wbyM as the paratosyltransferase gene.

Heterogeneous structure of O-antigenic part of lipopolysaccharide of Salmonella telaviv (Serogroup O:28) containing 3-acetamido-3,6-dideoxy-D-glucopyranose

The O-polysaccharide of Salmonella Telaviv was obtained by mild acid degradation of the lipopolysaccharide and studied by chemical methods (sugar and methylation analyses, Smith degradation, de-O-acetylation) and NMR spectroscopy. The structure of the O-polysaccharide was established. The repeating units that are proximal to the lipopolysaccharide core region mostly have a digalactose side chain and lack glucose, whereas those at the other end of the chain mostly do bear glucose but are devoid of the disaccharide side chain. This is the first structure established for the O-polysaccharide of a Salmonella serogroup O:28 (formerlyM) strain characterized by subfactors O28(1) and O28(2). Knowledge of this structure and the structure of the O-polysaccharide of Salmonella Dakar (O28(1), O28(3)) established earlier is crucial for determination of the exact structures associated with subfactors O28(1), O28(2), and O28(3) and elucidation of the genetic basis of the close relationship between Escherichia coli O71 and S. enterica O:28 O-antigens.

Polysaccharides of basidiomycetes. Alkali-soluble polysaccharides from the mycelium of white rot fungus Ganoderma lucidum (Curt.: Fr.) P. Karst

Two polysaccharides were isolated from submergedly cultured mycelium of the basidiomycete Ganoderma lucidum by extraction with alkali followed by fractionation with Fehling reagent. The polysaccharides were shown to be a linear (1-->3)-alpha-D-glucan and a highly branched xylomannan containing a backbone built up of (1-->3)-linked alpha-D-mannopyranose residues, the majority of which are substituted at O-4 by single beta-D-xylopyranose residues or by disaccharide fragments beta-D-Manp-(1-->3)-beta-D-Xylp-(1-->. Polysaccharide structures were elucidated by NMR spectroscopy in combination with methylation analysis and periodate oxidation. An interesting feature of the xylomannan is the simultaneous presence of alpha-D-mannopyranose and beta-D-mannopyranose residues, the first forming the backbone, and the second being the non-reducing terminal units of disaccharide side chains.