Identification of Key Metabolic Pathways and Biomarkers Underlying Flowering Time of Guar (Cyamopsis tetragonoloba (L.) Taub.) via Integrated Transcriptome-Metabolome Analysis

Guar (Cyamopsis tetragonoloba (L.) Taub.) is an annual legume crop native to India and Pakistan. Seeds of the plant serve as a source of galactomannan polysaccharide (guar gum) used in the food industry as a stabilizer (E412) and as a gelling agent in oil and gas fracturing fluids. There were several attempts to introduce this crop to countries of more northern latitudes. However, guar is a plant of a short photoperiod, therefore, its introduction, for example, to Russia is complicated by a long day length during the growing season. Breeding of new guar varieties insensitive to photoperiod slowed down due to the lack of information on functional molecular markers, which, in turn, requires information on guar genome. Modern breeding strategies, e.g., genomic predictions, benefit from integration of multi-omics approaches such as transcriptome, proteome and metabolome assays. Here we present an attempt to use transcriptome-metabolome integration to understand the genetic determination of flowering time variation among guar plants that differ in their photoperiod sensitivity. This study was performed on nine early- and six delayed-flowering guar varieties with the goal to find a connection between 63 metabolites and 1,067 differentially expressed transcripts using Shiny GAM approach. For the key biomarker of flowering in guar myo-inositol we also evaluated the KEGG biochemical pathway maps available for Arabidopsis thaliana. We found that the phosphatidylinositol signaling pathway is initiated in guar plants that are ready for flowering through the activation of the phospholipase C (PLC) gene, resulting in an exponential increase in the amount of myo-inositol in its free form observed on GC-MS chromatograms. The signaling pathway is performed by suppression of myo-inositol phosphate kinases (phosphorylation) and alternative overexpression of phosphatases (dephosphorylation). Our study suggests that metabolome and transcriptome information taken together, provide valuable information about biomarkers that can be used as a tool for marker-assisted breeding, metabolomics and functional genomics of this important legume crop.

Mechanistic insights from plant heteromannan synthesis in yeast

Heteromannan (HM) is one of the most ancient cell wall polymers in the plant kingdom, consisting of β-(1-4)-linked backbones of glucose (Glc) and mannose (Man) units. Despite the widespread distribution of HM polysaccharides, their biosynthesis remains mechanistically unclear. HM is elongated by glycosyltransferases (GTs) from the cellulose synthase-like A (CSLA) family. MANNAN-SYNTHESIS RELATED (MSR) putative GTs have also been implicated in (gluco)mannan synthesis, but their roles have been difficult to decipher in planta and in vitro. To further characterize the products of the HM synthases and accessory proteins, we chose a synthetic biology approach to synthesize plant HM in yeast. The expression of a CSLA protein in Pichia pastoris led to the abundant production of plant HM: up to 30% of glycans in the yeast cell wall. Based on sequential chemical and enzymatic extractions, followed by detailed structural analyses, the newly produced HM polymers were unbranched and could be larger than 270 kDa. Using CSLAs from different species, we programmed yeast cells to produce an HM backbone composed exclusively of Man or also incorporating Glc. We demonstrate that specific MSR cofactors were indispensable for mannan synthase activity of a coffee CSLA or modulated a functional CSLA enzyme to produce glucomannan instead of mannan. Therefore, this powerful platform yields functional insight into the molecular machinery required for HM biosynthesis in plants.

Regulation of galactomannan biosynthesis in coffee seeds

The seed of Coffea arabica accumulates large amounts of cell wall storage polysaccharides (CWSPs) of the mannan family in the cell walls of the endosperm. The variability induced by the growing environment and extensive pairwise correlation analysis with stringent significance thresholds was used to investigate transcript-transcript and transcript-metabolite relationships among 26 sugar-related genes, and the amount of CWSPs and seven soluble low molecular weight carbohydrates in the developing coffee endosperm. A dense module of nine quantitatively co-expressed genes was detected at the mid-developmental stage when CWSPs accumulate. This module included the five genes of the core galactomannan synthetic machinery, namely genes coding for the enzymes needed to assemble the mannan backbone (mannan synthase, ManS), and genes that introduce the galactosyl side chains (galactosyltransferase, GMGT), modulate the post-depositional degree of galactose substitution (α-galactosidase), and produce the nucleotide sugar building blocks GDP-mannose and UDP-galactose (mannose-1P guanyltransferase and UDP-glucose 4'-epimerase, respectively). The amount of CWSPs stored in the endosperm at the onset of their accumulation was primarily and quantitatively modulated at the transcriptional level (i.e. positively correlated with the expression level of these key galactomannan biosynthetic genes). This analysis also suggests a role for sorbitol and raffinose family oligosaccharides as transient auxiliary sources of building blocks for galactomannan synthesis. Finally, a microarray-based analysis of the developing seed transcriptome revealed that all genes of the core galactomannan synthesis machinery grouped in a single cluster of 209 co-expressed genes. Analysis of the gene composition of this cluster revealed remarkable functional coherence and identified transcription factors that putatively control galactomannan biosynthesis in coffee.

Deep sequencing of voodoo lily (Amorphophallus konjac): an approach to identify relevant genes involved in the synthesis of the hemicellulose glucomannan

A Roche 454 cDNA deep sequencing experiment was performed on a developing corm of Amorphophallus konjac--also known as voodoo lily. The dominant storage polymer in the corm of this plant is the polysaccharide glucomannan, a hemicellulose known to exist in the cell walls of higher plants and a major component of plant biomass derived from softwoods. A total of 246 mega base pairs of sequence data was obtained from which 4,513 distinct contigs were assembled. Within this voodoo lily expressed sequence tag collection genes representing the carbohydrate related pathway of glucomannan biosynthesis were identified, including sucrose metabolism, nucleotide sugar conversion pathways for the formation of activated precursors as well as a putative glucomannan synthase. In vivo expression of the putative glucomannan synthase and subsequent in vitro activity assays unambiguously demonstrate that the enzyme has indeed glucomannan mannosyl- and glucosyl transferase activities. Based on the expressed sequence tag analysis hitherto unknown pathways for the synthesis of GDP-glucose, a necessary precursor for glucomannan biosynthesis, could be proposed. Moreover, the results highlight transcriptional bottlenecks for the synthesis of this hemicellulose.

Side-chain structure of cell surface polysaccharide, mannan, affects hypocholesterolemic activity of yeast

We previously reported that Kluyveromyces marxianus YIT 8292 exhibited more potent hypocholesterolemic activity than other yeasts containing Saccharomyces cerevisiae . To clarify the reason for the higher hypocholesterolemic activity, we examined the side-chain structure of cell surface polysaccharide, mannan, of K. marxianus YIT 8292. The result shows that K. marxianus YIT 8292 had shorter alpha-(1,2)-linked oligomannosyl side chains and lower phosphate content in mannan than S. cerevisiae. The association between its structural features and hypocholesterolemic activity was investigated by comparing the hypocholesterolemic activities of S. cerevisiae mannan mutants in rats fed a high-cholesterol diet. S. cerevisiae mnn5 mutant with deficiencies in the phosphorylation and elongation of mannan side chains showed higher hypocholesterolemic activity than the wild-type strain. These results show that the side-chain length and phosphate contents of mannan affect hypocholesterolemic activity.

Mannan-modified adenovirus as a vaccine to induce antitumor immunity

Tumor vaccine is a useful strategy for cancer therapy. However, priming of the immune system requires the relevant antigen to be presented by antigen-presenting cells (APCs). Here, we employed telomerase reverse transcriptase as a model antigen to explore the feasibility of using mannan-modified adenovirus as a tumor vaccine. We found that tumor immunogene therapy with the vaccine was effective at protective antitumor immunity in mice. The antigen-specific cytotoxic T lymphocytes were found in in vitro cytotoxicity assay. The elevation of the killing activity could be abrogated by anti-CD8 or anti-major histocompatibility complex-I antibodies. Adoptive transfer of purified CD8+ cells, and CD4+ cells to a less extent, was effective at antitumor activity. In vivo antitumor activity could be abrogated by depleting CD4+ T lymphocytes. A possible explanation for the antitumor effects may be the antigen was transferred to APCs in the presence of mannan. These observations provide insights into the design of novel vaccine strategies and might be important for the future application of antigens identified in other diseases.

Mechanisms of resistance of Porphyromonas gingivalis to killing by serum complement

The complement system plays an important role in the host defense against infection, and the formation of the terminal complement complex on the bacterial surface has been shown to be particularly important in killing of gram-negative bacteria. The gram-negative periodontal pathogen Porphyromonas gingivalis is resistant to complement killing, and possible mechanisms suggested for this resistance include protease production and capsule formation. In this study, P. gingivalis Arg- and Lys-gingipain deletion mutants and polysaccharide synthesis deletion mutants have been used to investigate these hypotheses. When Arg- and Lys-gingipain protease mutants were incubated in 20% normal human serum, deposition of complement components on the cell surface was significantly increased compared to that for the wild-type organism. However, despite the increased deposition, the protease mutants maintained resistance to killing and their viability was equal to that seen with heat-inactivated serum. Similar data were obtained when the wild-type organism was treated with gingipain protease inhibitors. K-antigen expression mutants were also resistant to killing. However, mutants which no longer synthesized a surface anionic polysaccharide (APS) (a phosphorylated branched mannan) were extremely sensitive to serum killing. These mutants lack the organized dense glycan surface layer present on the parent strain on the basis of electron microscopy. We conclude that the production of APS at the surface of P. gingivalis rather than Arg- and Lys-gingipain synthesis is the principal mechanism of serum resistance in P. gingivalis.

New method of DNA isolation from two food additives suitable for authentication in polymerase chain reaction assays

Locust bean gum and guar gum are galactomannans used as additives (E 410 and E 412, respectively) in the food industry as stabilizing agents. Analytical discrimination between the two additives in gums and foods is now feasible by molecular techniques. However, only complex and time-consuming DNA isolation protocols are available to date. We have developed simple improved protocols to obtain enough DNA suitable for PCR amplification from a few milligrams of commercial E 410 and E 412 additives (containing more than 75% polysaccharides). The suspension of additives in water or 10 mM Tris-HCl, pH 8.5, efficiently recovers DNA suitable for authentication in PCR assays. However, the Tris method was much more efficient for the extraction of DNA from E 410 than for E 412 additives. Conversely, the water method was the most suitable for detecting DNA extracted from E 412 or from E 410/E 412 mixtures. Combined with the use of the two specific ribosomal primer pairs previously designed, our methods are well-suited for a fast and simple high-throughput sample treatment of commercial gums for molecular certification.

Five Genes Involved in Biosynthesis of the Pyruvylated Galβ1,3-Epitope in Schizosaccharomyces pombe N-Linked Glycans

The N-linked galactomannans of Schizosaccharomyces pombe have pyruvylated Galbeta1,3-(PvGal) caps on a portion of the Galalpha1,2-residues in their outer chains (Gemmill, T. R., and Trimble, R. B. (1998) Glycobiology 8, 1087-1095). PvGal biosynthesis was investigated by ethyl methanesulfonate mutagenesis of S. pombe, followed by the isolation of cells devoid of negatively charged N-glycans by Q-Sepharose exclusion and failure to bind human serum amyloid P component, which acts as a lectin for terminal PvGal residues. Mutant glycans were characterized by lectin binding, saccharide composition, exoglycosidase sensitivity, and NMR spectroscopy. Restoration of the cell surface negative charge by complementation with an S. pombe genomic library led to the identification of five genes involved in PvGal biosynthesis, which we designated pvg1-pvg5. Pvg1p may be a pyruvyltransferase, since NMR of pvg1(-) mutant N-glycans revealed the absence of only the pyruvyl moiety. Pvg2p-Pvg5p are crucial for attachment of the Galbeta1,3-residue that becomes pyruvylated. Pvg3p is predicted to be a member of the beta1,3-galactosyltransferase family, and Pvg3p-green fluorescent protein labeling was consistent with Golgi localization. Predicted Pvg1p and Pvg3p functions imply that Galbeta1,3-is added to the galactomannans and is then pyruvylated in situ, rather than by an en bloc addition of PvGalbeta1,3-caps to the outer chain. Pvg4p-green fluorescent protein targeted to the nucleus, and its sequence contains a MADS-box DNA-binding and dimerization domain; however, it does not appear to solely control transcription of the other identified genes. Pvg2p and/or Pvg5p may contribute to an enzyme complex. Whereas a functional role for the PvGal epitope in S. pombe remains unclear, it is nonessential for either cell growth or mating under laboratory conditions.

Nonreducing Terminal Modifications Determine the Chain Length of Polymannose O Antigens of Escherichia coli and Couple Chain Termination to Polymer Export via an ATP-binding Cassette Transporter

The chain length of bacterial lipopolysaccharide O antigens is regulated to give a modal distribution that is critical for pathogenesis. This paper describes the process of chain length determination in the ATP-binding cassette (ABC) transporter-dependent pathway, a pathway that is widespread among Gram-negative bacteria. Escherichia coli O8 and O9/O9a polymannans are synthesized in the cytoplasm, and an ABC transporter exports the nascent polymer across the inner membrane prior to completion of the LPS molecule. The polymannan O antigens have nonreducing terminal methyl groups. The 3-O-methyl group in serotype O8 is transferred from S-adenosylmethionine by the WbdD(O8) enzyme, and this modification terminates polymerization. Methyl groups are added to the O9a polymannan in a reaction dependent on preceding phosphorylation. The bifunctional WbdD(O9a) catalyzes both reactions, but only the kinase activity controls chain length. Chain termination occurs in a mutant lacking the ABC transporter, indicating that it precedes export. An E. coli wbdD(O9a) mutant accumulated O9a polymannan in the cytoplasm, indicating that WbdD activity coordinates polymannan chain termination with export across the inner membrane.

Mannan mucin-1 peptide immunization: influence of cyclophosphamide and the route of injection

The mucin MUC1 is greatly increased in breast cancer and is a potential target for immunotherapy. In mice, MUCI conjugated to oxidized mannan (MUC1-mannan fusion protein [M-FP]) targets the mannose receptor and induces a high frequency of cytotoxic T lymphocytes and anti-tumor responses. On this basis, three phase I trials were performed in patients with adenocarcinoma to evaluate the toxicity and the immunologic responses to mannan MUCI. Forty-one patients with metastatic or locally advanced carcinoma of the breast (trial 1), colon (trial 2), and various adenocarcinomas (trial 3) received increasing doses of M-FP (1 to 300 microg). The immunizations were given at weekly intervals (weeks 1 to 3) and repeated in weeks 7 to 9. Cyclophosphamide (to increase cellular immunity) was given on weeks 1 and 4. M-FP was given intramuscularly in trial 1 and intraperitoneally in trial 2. No toxic effects occurred, and delayed-type hypersensitivity responses were present only as a microscopic lymphocytic infiltration. Overall, approximately 60% of the patients had high-titer MUC1 immunoglobulin G1 antibody responses, with the intraperitoneal route yielding approximately 10-fold higher responses. Cellular responses (proliferation, cytotoxic T cells, or CD8 T cells secreting tumor necrosis factor-alpha alphand interferon-gamma in response to MUC1 stimulation in vitro) were found in 28% of the patients, which was similar to that seen without cyclophosphamide. In most patients, disease progressed, but in five it remained stable. In addition, there were no objective responses. M-FP is not toxic and induces immune responses that were amplified by the intraperitoneal route of immunization. Cyclophosphamide was of no benefit.

Gastrodianin-like mannose-binding proteins: a novel class of plant proteins with antifungal properties

The orchid Gastrodia elata depends on the fungus Armillaria mellea to complete its life cycle. In the interaction, fungal hyphae penetrate older, nutritive corms but not newly formed corms. From these corms, a protein fraction with in vitro activity against plant-pathogenic fungi has previously been purified. Here, the sequence of gastrodianin, the main constituent of the antifungal fraction, is reported. Four isoforms that encoded two different mature proteins were identified at the cDNA level. Another isoform was detected in sequenced peptides. Because the antifungal activity of gastrodianins produced in and purified from Escherichia coli and Nicotiana tabacum was comparable to that of gastrodianin purified from the orchid, gastrodianins are the active component of the antifungal fractions. Gastrodianin accumulation is probably an important part of the mechanism by which the orchid controls Armillaria penetration. Gastrodianin was found to be homologous to monomeric mannose-binding proteins of other orchids, of which at least one (Epipactis helleborine mannose-binding protein) also displayed in vitro antifungal activity. This establishes the gastrodianin-like proteins (GLIPs) as a novel class of antifungal proteins.

[Immunology in the medical practice. XXVII. Mannose-binding lectin, an important link for nonspecific or hereditary immune reaction]

In the course of the past two decennia, a 3rd route of complement activation (next to the classical and the alternative routes) has been identified: the lectin route in which mannose-binding lectin (MBL) plays an essential role. MBL is produced in the liver. From the phylogenetic and functional points of view, complement activation via MBL falls in between the alternative and the classical routes and combines the advantages of the former (an early response, without the intervention of antibodies) with those of the latter (high specificity). The binding of MBL to the surface of a microorganism results in the activation of two serine proteases (MASP1 and MASP2) that are coupled to MBL. These enzymes can activate C4 and C2 so that, via the MBL route, the C3-convertase of the classical route (C4b2b) is produced long before there are any specific antibodies. The gene for MBL is located on the long arm of chromosome 10 and consists of a promoter gene and 4 exons coding for the protein. The prevalence of mutations in the MBL gene is about 10%, but in Africa South of the Sahara it is as high as 30%. MBL deficiency predisposes both children and adults to all sorts of infectious diseases, chronic diarrhoea, tonsillitis, otitis media, pneumonia, (meningococcal) meningitis, sepsis and osteomyelitis. Remarkably, MBL deficiency may actually be advantageous in some infections, because certain microorganisms use MBL or complement to invade the cell.

Isolation and characterization of non-labeled and 13C-labeled mannans from Pichia pastoris yeast

Mannans from genetically modified Pichia pastoris yeast, used for overproduction of neural cell adhesion molecule protein, grown on normal media or on uniformly 13C-labeled glucose and methanol, were isolated and characterized by high-field (750 MHz) NMR spectroscopy. Fully 13C-labeled oligosaccharide fragments were prepared from mannans by acetolysis. According to the data obtained, the mannan is made up of a main chain of alpha-(1-->6)-linked mannopyranosyl residues, substituted at 0-2 with alpha-mannopyranosyl or a alpha-D-Manp-(1-->2)-beta-D-Manp-(1-->2)-beta-D-Manp-( 1-->2)-alpha-D-Manp- group, and with much lower content of substitution with beta-D-Manp-(1-->2)-alpha-D-Manp-. A fraction of these oligosaccharide side chains is again substituted with alpha-D-Glcp or alpha-D-GlcpNAc through a phosphodiester linkage to the 6 position of the first mannopyranosyl residue. Improved conditions of acetolysis, cleaving all alpha-(1-->6) linkages, but not beta-mannoside linkages, are proposed.

Molecular defects in variant forms of mannose-binding protein associated with immunodeficiency

Distinct molecular mechanisms underlying immunodeficiency caused by three different naturally occurring point mutations within the collagen-like domain of human mannose-binding protein (MBP; also known as mannose-binding lectin) have been revealed by introduction of analogous mutations into rat serum MBP. The change Arg23-->Cys results in a lower proportion of the large oligomers most efficient at activating the complement cascade. The presence of cysteine at position 23, which forms aberrant interchain disulfide bonds, causes disruption of the normal oligomeric state. The deficiency in MBPs containing Gly25-->Asp and Gly28-->Glu substitutions also results in part from reduced formation of higher oligomers. However, decreased ability to interact with downstream components of the complement cascade due to changes in both the N-terminal disulfide-bonding arrangement and the local structure of the collagenous domain make more important contributions to the loss of activity in these mutants.

Different molecular events result in low protein levels of mannan-binding lectin in populations from southeast Africa and South America

Previous studies have shown that three point mutations in exon 1 and a particular promoter haplotype of the mannan-binding lectin (MBL) gene lead to a dramatic decrease in the serum concentration of MBL. In this study, MBL genotypes and serum concentrations were determined in unrelated individuals in a population from Mozambique (n = 154) and in two native Indian tribes from Argentina (i.e., the Chiriguanos (n = 43) and the Mapuches (n = 25)). In both populations, the MBL concentrations were low compared with those found in Eskimo, Asian, and European populations. In Africans, the low serum concentrations were due to a high allele frequency (0.24) of the codon 57 (C) variant, which resulted in a high frequency of individuals with MBL deficiency (0.06), and were also due to the effect of a relatively high frequency (0.13) of low-producing promoter haplotypes. The low concentrations in the South American populations were primarily due to an extremely high allele frequency of the codon 54 (B) variant in both the Chiriguanos (0.42) and the Mapuches (0.46), resulting in high frequencies of individuals with MBL deficiency (0.14 and 0.16, respectively). In the search for additional genetic variants, we found five new promoter mutations that might help to elucidate the evolution of the MBL gene. Taken together, the results of this study show that different molecular mechanisms are the basis for low MBL levels on the two continents.

Susceptibility to HIV infection and progression of AIDS in relation to variant alleles of mannose-binding lectin

BACKGROUND

Low serum concentrations of mannose-binding lectin (MBL) are associated with increased susceptibility to recurrent infection. Three variant alleles in the MBL gene (B, C, and D), cause low serum concentrations of the protein. We investigated whether variant alleles of MBL affect susceptibility to infection with HIV and progression of AIDS.

METHODS

Between 1983 and 1986, all men who attended two clinics in Copenhagen for HIV screening were invited to take part in our study. We investigated the prevalence of variant alleles of MBL (detected by PCR) and assessed the prognostic value of these alleles and the corresponding serum MBL concentrations (measured by ELISA) in 96 homosexual men with HIV infection and in two control groups (123 healthy adults and 36 HIV-negative homosexual men at high risk of HIV infection because of their sexual behaviour). Follow-up was for up to 10 years.

FINDINGS

Eight (8%) of the HIV-infected men were homozygous for the variant MBL alleles compared with one (0.8%) of the healthy controls (p = 0.005) and none of the high-risk homosexual controls (p = 0.05). We found no significant association between MBL genotype and time from first positive HIV test to progression of AIDS (p = 0.8). However, in the 61 HIV-infected men who developed AIDS, the median survival time was significantly shorter after the AIDS diagnosis for men who were carriers of the variant alleles (both homozygous and heterozygous) than for men homozygous for the normal MBL allele (11 [IQR 4-21] vs 18 months [9-44], p = 0.007). Among men who developed AIDS, there was a significant difference in survival time between those with serum MBL concentrations below the lower quartile, those within the IQR, and those above the upper quartile (p = 0.02). Multivariate analysis showed that men who developed AIDS and had low serum MBL concentrations had an increased rate of rapid death, independently of CD4 T-cell counts at AIDS diagnosis.

INTERPRETATION

Our findings suggest that homozygous carriers of variant MBL alleles are at increased risk of HIV infection, either directly or indirectly because of increased susceptibility to coinfections. These alleles are also associated with a significantly shorter survival time after a diagnosis of AIDS.

Age-dependent variation in the serum concentration of mannan-binding protein

Mannan-binding protein (MBP) is an acute phase reactant, and its deficiency is associated with the common opsonic defect and suspectibility to infections and atopic constitution. The aim of this study was to investigate the changes occurring in the serum level of MBP in infancy and during later childhood. We studied the serum concentration of MBP in 611 Finnish children of different ages and 110 adults by using an enzyme immunoassay. In an analysis of successive serum samples from infants at the day of birth and at the ages of 1 and 5 months, and at 1 and 2 years, the serum concentration of MBP increased significantly after birth, and was at its highest (the mean and median were 8.13 and 8.49 mgl-1, respectively) at the age of 1 month. After that, it declined to the initial level until the age of 5 months. The MBP concentration continued to decrease during childhood, and after the age of 12 years the MBP values reached the adult level. In Finnish adults the mean and median concentrations of MBP were 4.48 and 4.02 mgl-1, respectively, which seem to be higher than those reported previously in other populations. The high concentration of MBP in infants may best be explained by exposure to novel environmental antigens in early childhood, which suggests a protective role for MBP during the period of immaturity of the immunosystem. In older children the high level of MBP can probably be explained by childhood infections and the ensuing need of MBP.

Characterization of epitopes recognized by Candida factor 1 and 9 antisera by use of Saccharomyces cerevisiae mnn mutants

The use of Saccharomyces cerevisiae mnn mutants has facilitated the study of the epitopes recognized by antisera against several antigenic factors of the genus Candida (Candida Check; Iatron Laboratories, Tokyo, Japan). We have taken advantage of the very well characterized structure of the mannans of the different mnn mutants to compare their reactivities with the factor antisera used in the identification of different species of the genus Candida. The results of this study provide evidence that one of the antigenic determinants recognized by factor 1 antisera is the O-linked mannose chains of the cell wall mannoproteins, while that recognized by factor 9 antiserum is the alpha 1-6-linked mannose backbone of the outer chain of the N-linked oligosaccharide.

Yeast flocculation: receptor definition by mnn mutants and concanavalin A

Yeast flocculation involves the binding of surface lectins on flocculent yeasts, to carbohydrate receptors present as constituents of yeast cell walls. Receptors were investigated by coflocculation of flocculent strains of Saccharomyces cerevisiae, of both Flo 1 and NewFlo phenotypes, to known mnn mutants which vary in the wall mannan structure. Strong coflocculation was found with mnn1, mnn4, mnn9 and control strains, while very little coflocculation was found with mnn2 and mnn5 strains. In contrast, aggregation of these mutants by concanavalin A, a lectin with similar sugar inhibition to NewFlo phenotype flocculation, showed strong aggregation of mnn1, mnn4 and mnn5 strains and poor aggregation of mnn2 and mnn9 strains. The mmn mutant data suggested that flocculation receptors were the outer-chain mannan side-branches, two or three mannose residues in length, confirming an earlier theory based on sugar inhibition data. The similarities and differences between flocculation and concanavalin A aggregation are discussed.

Analysis of mannans of two relatively avirulent mutant strains of Candida albicans

We previously reported the isolation of two cerulenin-resistant mutant strains of Candida albicans 4918 that differ in adherence properties and are less virulent than the parental strain. In addition, biochemical characterization demonstrated significant differences in both protein and polysaccharide composition of cell wall material between the mutant and wild-type strains. These observations prompted studies concerning the chemical structure of mannans in these strains. After extraction and subsequent purification by ion-exchange chromatography, mannan fractions were subjected to either mild acid hydrolysis, alkali hydrolysis, or acetylation followed by acetolysis. Acid- and alkali-modified mannans were studied by proton magnetic resonance spectroscopy, and released products were analyzed by high-performance liquid chromatography on an Aminex HPX-42A column. The results demonstrated quantitative and qualitative differences between mannooligosaccharides of the wild-type and mutant strains in the identity of released oligosaccharides as well as in linkage of the oligosaccharides to the protein backbone.