Structural chemistry of fungal polysaccharides

Comparative Study of Green and Synthetic Polymers for Enhanced Oil Recovery

Several publications by authors in the field of petrochemical engineering have examined the use of chemically enhanced oil recovery (CEOR) technology, with a specific interest in polymer flooding. Most observations thus far in this field have been based on the application of certain chemicals and/or physical properties within this technique regarding the production of 50-60% trapped (residual) oil in a reservoir. However, there is limited information within the literature about the combined effects of this process on whole properties (physical and chemical). Accordingly, in this work, we present a clear distinction between the use of xanthan gum (XG) and hydrolyzed polyacrylamide (HPAM) as a polymer flood, serving as a background for future studies. XG and HPAM have been chosen for this study because of their wide acceptance in relation to EOR processes. To this degree, the combined effect of a polymer's rheological properties, retention, inaccessible pore volume (PV), permeability reduction, polymer mobility, the effects of salinity and temperature, and costs are all investigated in this study. Further, the generic screening and design criteria for a polymer flood with emphasis on XG and HPAM are explained. Finally, a comparative study on the conditions for laboratory (experimental), pilot-scale, and field-scale application is presented.

The GH130 Family of Mannoside Phosphorylases Contains Glycoside Hydrolases That Target β-1,2-Mannosidic Linkages in Candida Mannan

The depolymerization of complex glycans is an important biological process that is of considerable interest to environmentally relevant industries. β-Mannose is a major component of plant structural polysaccharides and eukaryotic N-glycans. These linkages are primarily cleaved by glycoside hydrolases, although recently, a family of glycoside phosphorylases, GH130, have also been shown to target β-1,2- and β-1,4-mannosidic linkages. In these phosphorylases, bond cleavage was mediated by a single displacement reaction in which phosphate functions as the catalytic nucleophile. A cohort of GH130 enzymes, however, lack the conserved basic residues that bind the phosphate nucleophile, and it was proposed that these enzymes function as glycoside hydrolases. Here we show that two Bacteroides enzymes, BT3780 and BACOVA_03624, which lack the phosphate binding residues, are indeed β-mannosidases that hydrolyze β-1,2-mannosidic linkages through an inverting mechanism. Because the genes encoding these enzymes are located in genetic loci that orchestrate the depolymerization of yeast α-mannans, it is likely that the two enzymes target the β-1,2-mannose residues that cap the glycan produced by Candida albicans. The crystal structure of BT3780 in complex with mannose bound in the -1 and +1 subsites showed that a pair of glutamates, Glu(227) and Glu(268), hydrogen bond to O1 of α-mannose, and either of these residues may function as the catalytic base. The candidate catalytic acid and the other residues that interact with the active site mannose are conserved in both GH130 mannoside phosphorylases and β-1,2-mannosidases. Functional phylogeny identified a conserved lysine, Lys(199) in BT3780, as a key specificity determinant for β-1,2-mannosidic linkages.

Enzymatic synthesis using glycoside phosphorylases

Carbohydrate phosphorylases are readily accessible but under-explored catalysts for glycoside synthesis. Their use of accessible and relatively stable sugar phosphates as donor substrates underlies their potential. A wide range of these enzymes has been reported of late, displaying a range of preferences for sugar donors, acceptors and glycosidic linkages. This has allowed this class of enzymes to be used in the synthesis of diverse carbohydrate structures, including at the industrial scale. As more phosphorylase enzymes are discovered, access to further difficult to synthesise glycosides will be enabled. Herein we review reported phosphorylase enzymes and the glycoside products that they have been used to synthesise.

Expression pattern of glycoside hydrolase genes in Lutzomyia longipalpis reveals key enzymes involved in larval digestion

The sand fly Lutzomyia longipalpis is the most important vector of American Visceral Leishmaniasis. Adults are phytophagous (males and females) or blood feeders (females only), and larvae feed on solid detritus. Digestion in sand fly larvae has scarcely been studied, but some glycosidase activities putatively involved in microorganism digestion were already described. Nevertheless, the molecular nature of these enzymes, as the corresponding genes and transcripts, were not explored yet. Catabolism of microbial carbohydrates in insects generally involves β-1,3-glucanases, chitinases, and digestive lysozymes. In this work, the transcripts of digestive β-1,3-glucanase and chitinases were identified in the L. longipalpis larvae throughout analysis of sequences and expression patterns of glycoside hydrolases families 16, 18, and 22. The activity of one i-type lysozyme was also registered. Interestingly, this lysozyme seems to play a role in immunity, rather than digestion. This is the first attempt to identify the molecular nature of sand fly larval digestive enzymes.

Immunoglobulin G Antibodies Against Environmental Moulds in a Norwegian Healthy Population Shows a Bimodal Distribution for Aspergillus versicolor

Immunoglobulin G (IgG) antibodies against moulds related to indoor dampness problems are used as biomarkers to indicate exposure. In the present study, we evaluated the frequency of mould exposure in an adult healthy population by examining levels of mould-specific IgG antibodies in Norwegian blood donors. Using enzyme-linked immunosorbent assay, 106 blood donor sera were analyzed for IgG antibodies to Aspergillus versicolor, Penicillium chrysogenum, Cladosporium herbarum, Stachybotrys chartarum and Fusarium oxysporum. The levels of specific IgG antibodies to P. chrysogenum, C. herbarum and S. chartarum correlated (r = 0.46-0.62). Responses to A. versicolor were considerably stronger than to the other moulds, and another 996 blood donor sera were analyzed for IgG antibodies to this mould. Women had significantly higher levels of specific IgG antibodies to A. versicolor than men. The concentration of A. versicolor-specific IgG antibodies showed a non-Gaussian, bimodal distribution profile, in which 12.5% were defined as positive to exposure. This suggests that significant mould exposure in a healthy population can be calculated from mean + 1SD. Western blotting analyses showed that antibody responses to A. versicolor were largely directed against carbohydrate antigens of unknown saccharides.

Overview of N- and O-linked oligosaccharide structures found in various yeast species

Yeast and most higher eukaryotes utilize an evolutionarily conserved N-linked oligosaccharide biosynthetic pathway that involves the formation of a Glc3Man9GlcNAc2-PP-dolichol lipid-linked precursor, the glycan portion of which is co-translationally transferred in the endoplasmic reticulum (ER) to suitable Asn residues on nascent polypeptides. Subsequently, ER processing glycohydrolases remove the three glucoses and, with the exception of Schizosaccharomyces pombe, a single, specific mannose residue. Processing sugar transferases in the Golgi lead to the formation of core-sized structures (Hex<15GlcNac2) as well as cores with an extended poly-alpha1,6-Man 'backbone' that is derivatized with various carbohydrate side chains in a species-specific manner (Hex50-200GlnNAc2). In some cases these are short alpha1,2-linked Man chains with (Saccharomyces cerevisiae) or without (Pichia pastoris) alpha1,3-Man caps, while in other yeast (S. pombe), the side chains are alpha1,2-linked Gal, some of which are capped with beta-1,3-linked pyruvylated Gal residues. Charged groups are also found in S. cerevisiae and P. pastoris N-glycans in the form of mannose phosphate diesters. Some pathogenic yeast (Candida albicans) add poly-beta1,2-Man extension through a phosphate diester to their N-glycans, which appears involved in virulence. O-Linked glycan synthesis in yeast, unlike in animal cells where it is initiated in the Golgi using nucleotide sugars, begins in the ER by addition of a single mannose from Man-P-dolichol to selected Ser/Thr residues in newly made proteins. Once transported to the Golgi, sugar transferases add one (C. albicans) or more (P. pastoris) alpha1,2-linked mannose that may be capped with one or two alpha1,3-linked mannoses (S. cerevisiae). S. pombe is somewhat unique in that it synthesizes a family of mixed O-glycans with additional alpha1,2-linked Man and alpha1,2- and 1, 3-linked Gal residues.

Partial purification and characterization of phospholipase C from Yersinia enterocolitica

About 34% of the strains of Yersinia enterocolitica isolated from raw milk were found to produce lecithinase. A selected strain produced phospholipase C at 22 degrees C and 37 degrees C; production was optimum at 37 degrees C in the stationary phase (14-16 h). A decrease in phospholipase C activity at various storage temperatures (-5 degrees C, 4 degrees C, 37 degrees C) was also observed, although the enzyme was active over a wide range of temperature (5-65 degrees C) and pH (3.5-7.5). The phospholipase C was partially purified by ammonium sulphate precipitation and Sephadex column chromatography, and characterized.

Purification and properties of extracellular polysaccharide (EPS) antigens produced by different mould species

Extracellular polysaccharide (EPS) antigens produced by different mould species were purified and partially characterized. Purification included (NH4)2SO4 treatment, Sepharose CL-4B column chromatography and Con A-sepharose chromatography. The EPS of Penicillium digitatum, Mucor racemosus and Cladosporium cladosporioides showed high antigenic capacities. Immunologically the EPS were partially genus-specific, but cross-reactivity was observed. The EPS antigens produced by species of Penicillium, Aspergillus repens and Geotrichum candidum lost their immunological activity upon heating (100 degrees C) at pH 1.8, while the EPS antigen of M. racemosus, Rhizopus oligosporus and C. cladosporioides were stable under the same conditions. The dominant monosaccharides present in the EPS antigen were mannose, galactose and glucose. The EPS obtained from cultures of M. racemosus and R. oligosporus also contained rhamnose. In the EPS produced by Penicillium spp. and A. repens the galactose residues were determined to be immunodominant.

Podospora mutant defective in glucose-dependent growth control

A mutation (modE), previously described as a membrane mutation, results in several modifications of the female developmental cycle: a high density of protoperithecia, the unscheduled development of protoperithecia into sterile perithecia on the homokaryons of each mating type, and the independence of ascospore outgrowth from the substances normally required for germination. Cultured in liquid medium, the modE strain showed two additional specific features: a higher growth yield than that of wild-type cultures (plus 10% of dry weight) and an extreme reduction of cell life span. Both mutant traits were specific to glucose limitation. Despite the large difference existing in the sensitivity of cells to glucose starvation, the glycogen and trehalose reserves of mutant and wild-type cells were nearly identical. Considered together, these results suggest that the primary effect of the mutation lies in the disruption of a glucose-dependent regulation controlling the transition of the metabolic pattern of cells from growth to quiescence.

[Polysaccharide structure of cell wall preparations from the food protein yeast Candida spec. H]

More than 27% of the cell wall are unstably bound components: Proteophosphomannan as a main polysaccharide of the cell wall, mannose and manno-oligosides which are bound to peptides or phosphate. 19% are glycosidically linked with a phosphate bridge or O-glycosidically (Ser/Thr) linked with the protein which is covalently bound to the cell wall. Besides mannose and glucose, manno-oligosides and gluco-oligosides are involved in this linkage. A preparation consisting of glucan and chitin remains after careful degradation. It contains (1,2)-, (1,3)- and (1,6)- linked glucose, (1, 2, 3)-, (1, 2, 6)- or (1, 3, 6)-glucose-branchpoints and (1,4)-linked N-acetylglucosamine.

Variation in average unit chain length of glycogen in relation to developmental stage in Blastocladiella emersonii

Synchronous, single generations of Blastocladiella emersonii were grown along either the ordinary colorless or resistant sporangial plant pathways. Samples of cells were withdrawn at different developmental stages and glycogen was extracted, purified, debranched by isoamylase treatment, and its component unit chains separated by gel permeation chromatography. The elution profiles showed the distribution of unit chains. Average unit chain length was determined for plants at different developmental stages and shown to vary between 9 and 16. Some of these variations were correlated with other developmental events in the fungus.

Serological and cellular immune activity of peptidoglucomannan fractions of Candida albicans cell walls

A two-stage extraction of isolated cell walls of C. albicans resulted in 45% solubilization into antigens of high molecular weight leaving a wall residue which also had antigenic properties. Ice-cold dilute alkali removed 25% of the defatted cell walls. The extract was nondialyzable, had a glucose-to-mannose ratio of 2:3 and an amino acid content of 7.32%, and was designated peptidoglucomannan (PGM). An additional 26% of the walls resistant to stage I were solubilized by sonic treatment yielding a fraction having a glucose-to-mannose ratio of 6:1, termed soluble mannoglucan (sMG). The residue after extraction and sonic treatment contained 10.9% mannose, which was the insoluble mannoglucan. The gel permeation behavior of PGM and sMG on BioGel A5M was similar; each contained two components, one estimated to exceed 5 x 10(6) molecular weight and a second smaller species. The soluble cell wall fractions were active in immunodiffusion and carried antigenic group specificity. Immunoelectrophoresis of PGM, sMG, and mannan revealed some heterogeneity. The insoluble mannoglucan had agglutinating activity. A distinctive immunodiffusion pattern of cell wall antigens was formed with the serum of a leukemic patient with candidiasis. All three cell wall antigens and mannan elicited delayed-type hypersensitivity as measured by skin-test and specific inhibition of macrophage migration. A dose of 25 mug of PGM was sufficient to inhibit 89.9% migration in the peritoneal exudates of guinea pigs immunized with cell walls, and 10 mug of PGM inhibited 91.7% migration in guinea pigs immunized with insoluble mannoglucan.

Structure and immunochemistry of the cell wall mannans from Saccharomyces chevalieri, Saccharomyces italicus, Saccharomyces diastaticus, and Saccharomyces carlsbergensis

The mannans of Saccharomyces chevalieri, S. italicus, S. diastaticus, and S. carlsbergensis, were acetolyzed, and the fragments were separated by gel filtration. All gave similar acetolysis fingerprints, which were distinguished from S. cerevisiae by the presence of a pentasaccharide component in addition to the mono-, di-, tri-, and tetrasaccharides. All oligosaccharide fragments were composed of mannose in alpha-linkage. From methylation analysis and other structural studies, the disaccharide was shown to be alphaMan(1 --> 2)Man; the trisaccharide was shown to be a mixture of alphaMan(1 --> 2)alphaMan (1 --> 2)Man and alphaMan(1 --> 3)alphaMan(1 --> 2)Man; the tetrasaccharide was alphaMan(1 --> 3)alphaMan(1 --> 2)alphaMan(1 --> 2)Man; and the pentasaccharide was alphaMan(1 --> 3)alphaMan(1 --> 3)alphaMan(1 --> 2)alphaMan(1 --> 2)Man. The ratios of the different fragments varied slightly from strain to strain. Mannanase digestion of two of the mannans yielded polysaccharide residues that were unbranched (1 --> 6)-linked polymers, thus establishing the structural relationship between these mannans and that from S. cerevisiae. Antisera raised against the various yeasts cross-reacted with the mannans from each, and also with S. cerevisae mannan. The mannotetraose and mannopentaose acetolysis fragments gave complete inhibition of the precipitin reactions, which indicated that, in these systems as in the S. cerevisiae system, the terminal alpha(1 --> 3)-linked mannose unit was the principal immunochemical determinant on the cell surface.

Comparison of the rhamnomannans from the human pathogen Sporothrix schenckii with those from the Ceratocystis species

Rhamnomannans from several isolates of Sporothrix schenckii and Ceratocystis species were compared. No major differences emerged in the analysis of the carbohydrate composition of polysaccharides from either species. Methylation analysis for the identification of the glycosidic linkages present in the polysaccharides showed that they all were very similar with minor differences being observed among strains and between polysaccharides obtained at 25 and 37 C. Partially methylated derivatives were identified by gas-liquid chromatography and mass spectrometry. Their proportions suggest that polysaccharides from S. schenckii and C. stenoceras have a general structure similar to that of C. ulmi: a (1 --> 6)-linked alpha-d-mannopyranosyl main chain substituted in the 3-positions by alpha-l-rhamnopyranosyl and in many cases by alpha-l-rhamnopyranosyl (1-->2)-l-rhamnopyranosyl side chains. Differences among polysaccharides resided in the proportions of the dirhamnosyl side chains and of 4-O-substituted and 2, 4-di-O-substituted mannose units. Increased proportions of dirhamnosyl side chains were observed in the polysaccharides from S. schenckii strains and from a pathogenic variant of C. stenoceras grown at 25 C. Proton magnetic resonance spectra (H-1 region) of the rhamnomannans showed that S. schenckii strains could be placed in two different groups similar but not identical to any Ceratocystis species. These spectra were very close to those of the polysaccharides from the C. clavata and C. ambrosia groups of Ceratocystis species.

The composition of the cell wall of Fusicoccum amygdali

1. The cell wall of Fusicoccum amygdali consisted of polysaccharides (85%), protein (4-6%), lipid (5%) and phosphorus (0.1%). 2. The main carbohydrate constituent was d-glucose; smaller amounts of d-glucosamine, d-galactose, d-mannose, l-rhamnose, xylose and arabinose were also identified, and 16 common amino acids were detected. 3. Chitin, which accounted for most of the cell-wall glucosamine, was isolated in an undegraded form by an enzymic method. Chitosan was not detected, but traces of glucosamine were found in alkali-soluble and water-soluble fractions. 4. Cell walls were stained dark blue by iodine and were attacked by alpha-amylase, with liberation of glucose, maltose and maltotriose, indicating the existence of chains of alpha-(1-->4)-linked glucopyranose residues. 5. Glucose and gentiobiose were liberated from cell walls by the action of an exo-beta-(1-->3)-glucanase, giving evidence for both beta-(1-->3)- and beta-(1-->6)-glucopyranose linkages. 6. Incubation of cell walls with Helix pomatia digestive enzymes released glucose, N-acetyl-d-glucosamine and a non-diffusible fraction, containing most of the cell-wall galactose, mannose and rhamnose. Part of this fraction was released by incubating cell walls with Pronase; acid hydrolysis yielded galactose 6-phosphate and small amounts of mannose 6-phosphate and glucose 6-phosphate as well as other materials. Extracellular polysaccharides of a similar nature were isolated and may be formed by the action of lytic enzymes on the cell wall. 7. About 30% of the cell wall was resistant to the action of the H. pomatia digestive enzymes; the resistant fraction was shown to be a predominantly alpha-(1-->3)-glucan. 8. Fractionation of the cell-wall complex with 1m-sodium hydroxide gave three principal glucan fractions: fraction BB had [alpha](D) +236 degrees (in 1m-sodium hydroxide) and showed two components on sedimentation analysis; fraction AA(2) had [alpha](D) -71 degrees (in 1m-sodium hydroxide) and contained predominantly beta-linkages; fraction AA(1) had [alpha](D) +40 degrees (in 1m-sodium hydroxide) and may contain both alpha- and beta-linkages.

Method for fingerprinting yeast cell wall mannans

Controlled acetolysis of yeast mannans yields mixtures of oligosaccharides with (1-->2) and (1-->3) linkages between the mannose units, whereas the less stable (1-->6) linkages of the polysaccharide backbone are cleaved. The "fingerprints," obtained by gel filtration of the oligosaccharide mixtures, can be used to distinguish between the different yeast mannans. The general method may be useful for determining the taxonomy of yeasts and for making correlations between immunochemical reactivity and mannan structure.