Reassessment of antigenic determinant of Saccharomyces cerevisiae serotype Ia

Enzymatic synthesis of new oligosaccharides using mannosyltransferases from Candida species and their NMR assignments

The outer layer of the cell wall of pathogenic fungi, Candida species, consists of mannan, which plays an important role in infection. In this study, we synthesized several oligosaccharides using mannosyltransferases obtained from Candida parapsilosis and Candida albicans. Namely, we synthesized mannotetraoses [Manalpha1--> 2Manalpha1-->3Manalpha1-->2Man and Manalpha1-->3(Manalpha1-->6)Manalpha1-->2Man] from mannotriose, Manalpha1-->3Manalpha1--> 2Man, and mannohexaoses [Manalpha1-->2Manalpha1-->3Manalpha1-->3Manalpha1-->2Manalpha1-->2Man and Manalpha1-->3(Manalpha1-->6)Manalpha1-->3Manalpha1-->2Manalpha1-->2Man] from mannopentaose, Manalpha1-->3Manalpha1-->3Manalpha1-->2Manalpha1-->2Man. The linkage sequence of these oligosaccharides was identified by a sequential (1)H-NMR assignment method combined with rotating frame nuclear Overhauser enhancement spectroscopy and relayed coherence transfer spectroscopy. The steric effect by the alpha-1,6-linked branching mannose residue to the H-1 proton chemical shift of the neighboring 3-O-substituted mannose residue was different from that of the 2-O-substituted mannose residue. These oligosaccharides having novel structures seem to be useful as the substrate or ligand for glycomics.

Contribution of the mannan backbone of cryptococcal glucuronoxylomannan and a glycolytic enzyme of Staphylococcus aureus to contact-mediated killing of Cryptococcus neoformans

The fungal pathogen Cryptococcus neoformans is killed by the bacterium Staphylococcus aureus, and the killing is inhibited by soluble capsular polysaccharides. To investigate the mechanism of killing, cells in coculture were examined by scanning and transmission electron microscopy. S. aureus attached to the capsule of C. neoformans, and the ultrastructure of the attached C. neoformans cells was characteristic of dead cells. To identify the molecules that contributed to the fungal-bacterial interaction, we treated each with NaIO(4) or protease. Treatment of C. neoformans with NaIO(4) promoted adherence. It was inferred that cleavage of xylose and glucuronic acid side chains of glucuronoxylomannan (GXM) allowed S. aureus to recognize mannose residues in the backbone, which resisted periodate oxidation. On the other hand, treatment of S. aureus with protease decreased adherence, suggesting that protein contributed to attachment in S. aureus. In confirmation, side chain-cleaved polysaccharide or defined alpha-(1-->3)-mannan inhibited the killing at lower concentrations than native GXM did. Also, these polysaccharides reduced the adherence of the two species and induced clumping of pure S. aureus cells. alpha-(1-->3)-Mannooligosaccharides with a degree of polymerization (DP) of >/=3 induced cluster formation of S. aureus in a dose-dependent manner. Surface plasmon resonance analyses showed interaction of GXM and surface protein from S. aureus; the interaction was inhibited by oligosaccharides with a DP of > or =3. Conformations of alpha-(1-->3) oligosaccharides were predicted. The three-dimensional structures of mannooligosaccharides larger than triose appeared curved and could be imagined to be recognized by a hypothetical staphylococcal lectin. Native polyacrylamide gel electrophoresis of staphylococcal protein followed by electroblotting, enzyme-linked immunolectin assay, protein staining, and N-terminal amino acid sequencing suggested that the candidate protein was triosephosphate isomerase (TPI). The enzymatic activities were confirmed by using whole cells of S. aureus. TPI point mutants of S. aureus decreased the ability to interact with C. neoformans. Thus, TPI on S. aureus adheres to the capsule of C. neoformans by recognizing the structure of mannotriose units in the backbone of GXM; we suggest that this contact is required for killing of C. neoformans.

Structural studies of a cell wall polysaccharide of Trichosporon asahii containing antigen II

The structure of a cell-wall polysaccharide containing antigen II from Trichosporon asahii was investigated. A purified glucuronoxylomannan (GXM) antigen was found to contain O-acetyl groups that contribute to the serological reactivity. The structure of GXM was analyzed by partial acid hydrolysis, methylation analysis, controlled Smith degradation, NMR studies, and fluorophore-assisted carbohydrate electrophoresis. GXM has an alpha-(1-->3)-D-mannan backbone with a beta-D-glucopyranosyluronic acid residue bound to O-2 of a mannopyranosyl residue and the same number of beta-D-xylopyranosyl residues as mannose. Side chains of beta-D-xylopyranosyl-D-xylopyranose, forming a nonreducing terminus, and beta-D-xylopyranosyl residues were attached to O-2, O-4, and O-6 of the mannose residues.

Structural studies of the antigen III cell wall polysaccharide of Trichosporon domesticum

Cell wall and soluble polysaccharides that reacted with Trichosporon domesticum factor III serum were isolated from the type strain of T. domesticum. The fractions contained O-acetyl groups, which contributed to the serological reactivity. The antigenic structure was characterized by chromatographic and spectroscopic methods. The polysaccharide has an alpha-(1-->3)-D-mannan backbone with hetero-oligosaccharide side chains consisting of a 2-O-substituted beta-D-glucuronic acid residue bound to O-2 of the mannose residue, beta-D-xylopyranosyl residues located in the middle of the side chain, and a nonreducing terminal alpha-L-arabinopyranosyl residue bound to 0-4 of xylose. The mannan backbone is O-acetylated at O-6 of the mannose residues.

Characterization of beta-1,2-mannosyltransferase in Candida guilliermondii and its utilization in the synthesis of novel oligosaccharides

A particulate insoluble enzyme fraction containing mannosyltransferases from Candida guilliermondii IFO 10279 strain cells was obtained as the residue after extracting a 105,000 x g pellet of cell homogenate with 1% Triton X-100. Incubation of this fraction with a mannopentaose, Manalpha1-->3(Manalpha1-->6)Manalpha1-->2Manalpha1+ ++-->2Man, in the presence of GDP-mannose and Mn2+ ion at pH 6.0 gave a third type of beta-1,2 linkage-containing mannohexaose, Manbeta1-->2Manalpha1-->3(Manalpha1-->6)Manalpha1++ +-->2Manalpha1-->2Man , the structure of which was identified by means of a sequential NMR assignment. The results of a substrate specificity study indicated that the beta-1,2-mannosyltransferase requires a mannobiosyl unit, Manalpha1--> 3Manalpha1-->, at the nonreducing terminal site. We synthesized novel oligosaccharides using substrates possessing a nonreducing terminal alpha-1,3-linked mannose unit prepared from various yeast mannans. Further incubation of the enzymatically synthesized oligosaccharide with the enzyme fraction gave the following structure, Manbeta1-->2Manbeta1-->2Manalpha1-->3(Manalpha1- ->6)Manalpha1--> 2Manalpha1-->2Man, which has been found to correspond to antigenic factor 9. Incubation of Candida albicans serotype B mannan with the enzyme fraction gave significantly transformed mannan, which contains the third type of beta-1,2-linked mannose units.

Production of monoclonal antibody discriminating serological difference in Escherichia coli O9 and O9a polysaccharides

A monoclonal antibody (mAb) with a unique antigenic specificity against Escherichia coli O9 was produced. The O9a mAb was reactive with a part of the strains in E. coli O9. The O9a mAb did not react with LPS from the E. coli O9 test strain Bi316-42. The distribution of the antigen defined by the O9a mAb in E. coli O9 was consistent with that of E. coli O9a present in E. coli O9 strains. The chemical structure of the repeating unit of the O-specific polysaccharide detected by the mAb was demonstrated to be a mannotetraose by two-dimensional nuclear magnetic resonance spectroscopy. It was confirmed that the mAb recognized E. coli O9a serotype in E. coli O9 serotype strains, suggesting that E. coli O9a serotype might be a dominant strain in E. coli O9.

Characterization of alpha-1,6-mannosyltransferase responsible for the synthesis of branched side chains in Candida albicans mannan

A particulate insoluble fraction from Candida albicans NIH B-792 (serotype B) strain cells was obtained as the residue after extracting a 105000 x g pellet of cell homogenate with 1% Triton X-100. Incubation of this fraction with a mannopentaose, Man alpha 1-->3Man alpha 1-->2Man alpha 1-->Man alpha 1-->2Man, in the presence of GDP-mannose and Mn2+ at pH 6.0 gave a branched mannohexaose, [sequence: see text] 6 the structure of which was identified by means of sequential off assignment. However, the enzyme fraction obtained from Candida parapsilosis gave Man alpha 1-->2Man alpha 1-->3Man alpha 1-->2Man alpha 1-->2 Man alpha 1-->2Man under the same conditions. These results demonstrate the finding that the structural difference in the mannans of these two species is due to the presence of alpha-1.6-linked branching mannose units in the C. albicans mannan [Shibata, N., Ikuta, K., Imai, T., Satoh, Y., Satoh, R., Suzuki, A., Kojima, C., Kobayashi, H., Hisamichi, K. & Suzuki, S. (1995) J. Biol. Chem. 270, 1113-1122]. The substrate-specificity study of the enzyme indicated that the structural requirement of the alpha-1,6-mannosyltransferase is Man alpha 1-->3Man alpha 1-->. The alpha-1,6-mannosyltransferase also transferred the alpha-1,6-linked branching mannose unit to the mannan of Saccharomyces cerevisiae. The transformation of the mannan was detected by the appearance of antigenic factor 4 using an enzyme-linked immunosorbent assay and two-dimensional homonuclear Hartmann-Hahn spectroscopy.

Specific antibody response to oligomannosidic epitopes in Crohn's disease

Elevated antibody levels against the yeast Saccharomyces cerevisiae have been reported in sera from patients with Crohn's disease and not with ulcerative colitis. The aim of the study was to identify the nature of the epitopes supporting this antibody response. Whole cells from different S. cerevisiae strains were selected in immunofluorescence assay for their ability to differentiate the antibody responses of patients with Crohn's disease and ulcerative colitis. Their cell wall phosphopeptidomannans were then tested as antigen in enzyme-linked immunosorbent assay (ELISA) against sera from 42 patients with Crohn's disease, 20 patients with ulcerative colitis, and 34 healthy controls. Graded chemical degradations were performed on the most reactive strain phosphopeptidomannan. The discriminating epitope was determined through gas-liquid chromatography-mass spectrometry. The greatest discrimination among patients with Crohn's disease, ulcerative colitis, and controls was obtained with Su1, a S. cerevisiae strain used in brewing of beer. ELISA directed against phosphopeptidomannan of this strain was 64% sensitive and 77% specific for discriminating Crohn's disease versus ulcerative colitis and 71% sensitive and 89% specific for Crohn's disease versus controls. Periodate oxidation and selective degradation demonstrated that the most important polysaccharide epitope was shared by both the acid-stable and the alkali-labile domains of the phosphopeptidomannan. The determination of oligomannose sequences of S. cerevisiae Su1 phosphopeptidomannans suggested that a mannotetraose, Man (1 --> 3)Man(1 --> 2)Man(1 --> 2)Man, supported the serological response seen in Crohn's disease. Further identification of the immunogen eliciting this antibody response as a marker of the disease may help to understand its etiology.

Structure of cell wall mannan of Candida kefyr IFO 0586

We conducted a structural analysis of the antigenic cell wall mannoprotein (mannan) isolated from Candida kefyr (formerly Candida pseudotropicalis) IFO 0586. The result of two-dimensional homonuclear Hartmann-Hahn analysis of this mannan indicates that the molecule is constructed from alpha-1,2- and alpha-1,6-linked mannopyranose residues. Upon alkali treatment (beta-elimination reaction), this mannan released two alpha-1,2-linked mannooligosaccharides, biose and triose. The structure of the alkali-stable mannan (outer chain) moiety was investigated by acetolysis. The structures of the resultant oligosaccharides, biose and triose, from the outer chain moiety were found to be the same as those of the alkali-released ones. Further, the treatment of the parent mannan with an Arthrobacter GJM-1 exo-alpha-mannosidase gave a linear mannan consisting solely of alpha-1,6-linked mannopyranose residues. These results indicate that the mannan forms the long backbone of the alpha-1,6 linkage, with a large number of short alpha-1,2-linked oligomannosyl side chains forming a comblike structure. Moreover, we investigated the serological properties of this mannan by performing an inhibition assay of a slide agglutination reaction with mannooligosaccharides and polyclonal factor sera (Candida Check; Iatron). The result indicates that the factor 1 serum preferentially recognizes the alpha-1,2-linked oligomannosyl side chains in this mannan. On the other hand, the fact that the mannan does not contain an antigenic determinant(s) corresponding to factor 8 suggests that the epitope(s) of this factor resides in other molecules on the cell surface of this strain.

FimH family of type 1 fimbrial adhesins: functional heterogeneity due to minor sequence variations among fimH genes

We recently reported that the type 1-fimbriated Escherichia coli strains CSH-50 and HB101(pPKL4), both K-12 derivatives, have different patterns of adhesion to yeast mannan, human plasma fibronectin, and fibronectin derivatives, suggesting functional heterogeneity of type 1 fimbriae. In this report, we provide evidence that this functional heterogeneity is due to variations in the fimH genes. We also investigated functional heterogeneity among clinical isolates and whether variation in fimH genes accounts for differences in receptor specificity. Twelve isolates obtained from human urine were tested for their ability to adhere to mannan, fibronectin, periodate-treated fibronectin, and a synthetic peptide copying the 30 amino-terminal residues of fibronectin. CSH-50 and HB101(pPKL4) were tested for comparison. Selected isolates were also tested for adhesion to purified fragments spanning the entire fibronectin molecule. Three distinct functional classes, designated M, MF, and MFP, were observed. The fimH genes were amplified by PCR from chromosomal DNA obtained from representative strains and expressed in a delta fim strain (AAEC191A) transformed with a recombinant plasmid containing the entire fim gene cluster but with a translational stop-linker inserted into the fimH gene (pPKL114). Cloned fimH genes conferred on AAEC191A(pPKL114) receptor specificities mimicking those of the parent strains from which the fimH genes were obtained, demonstrating that the FimH subunits are responsible for the functional heterogeneity. Representative fimH genes were sequenced, and the deduced amino acid sequences were compared with the previously published FimH sequence. Allelic variants exhibiting >98% homology and encoding proteins differing by as little as a single amino acid substitution confer distinct adhesive phenotypes. This unexpected adhesive diversity within the FimH family broadens the scope of potential receptors for enterobacterial adhesion and may lead to a fundamental change in our understanding of the role(s) that type 1 fimbriae may play in enterobacterial ecology or pathogenesis.

Fungal polysaccharides

Fungal polysaccharides are cell wall components which may act as antigens or as structural substrates. As antigens, the role of mannans in Saccharomyces cerevisiae and Candida albicans, and of glycoproteins in Aspergillus fumigatus are discussed. Analyses on beta-glucan synthetase in Paracoccidioides brasiliensis and the inhibitory effect of Hansenula mrakii killer toxin on beta-glucan biosynthesis are also considered.

Structural identification of an epitope of antigenic factor 5 in mannans of Candida albicans NIH B-792 (serotype B) and J-1012 (serotype A) as beta-1,2-linked oligomannosyl residues

In previous articles, we reported the presence of phosphate-bound beta-1,2-linked oligomannosyl residues in the mannans of strains of Candida albicans serotypes A and B and Candida stellatoidea. To identify the antigenic factor corresponding to this type of oligomannosyl residue, a relationship between chemical structure and antigenic specificity in the mannans of C. albicans NIH B-792 (serotype B, B-strain) and C. albicans J-1012 (serotype A, J-strain) was investigated by using a combination of two-dimensional 1H nuclear magnetic resonance spectroscopy of H-1, H-2, and H-5 regions in the mannans and an enzyme-linked immunosorbent assay that employed concanavalin A-coated microtiter plates. It was shown in the present 1H nuclear magnetic resonance study that an examination of chemical shifts not only in the H-1 region but also in the H-5 region was useful for the quantitative determination of the phosphate-bound beta-1,2-linked oligomannosyl residues. In the enzyme-linked immunosorbent assay using concanavalin A-coated plates, it was revealed that, of factor sera 1, 4, and 5, only factor serum 5 showed a reactivity proportional to the densities of the beta-1,2-linked oligomannosyl residues of the mannan subfractions of different phosphate contents that had been prepared from the bulk B-strain mannan by DEAE-Sephadex chromatography. The above results indicate that the phosphate-bound beta-1,2-linked oligomannosyl residues, Manp beta 1----(2Manp beta 1----)n2Man (n = 0-5), correspond to antigenic factor 5.

Evidence for oligomannosyl residues containing both beta-1,2 and alpha-1,2 linkages as a serotype A-specific epitope(s) in mannans of Candida albicans

In order to identify the branches containing both beta-1,2 and alpha-1,2 linkages as the serotype A-specific epitope(s) in the mannans of Candida albicans, serotype A strains with oligosaccharides constituting the beta-1,2 linkage, the alpha-1,2 linkage, and both the beta-1,2 and the alpha-1,2 linkages were prepared from the mannans of C. albicans serotype A strains (NIH A-207 and J-1012) and tested for their inhibitory effects in the precipitin and slide agglutination assays. The results indicated that two oligosaccharides containing both beta-1,2 and alpha-1,2 linkages, Manp beta 1-2Manp alpha 1-2Manp alpha 1-2Manp alpha 1-2Man and Manp beta 1-2Manp beta 1-2Manp alpha 1-2Manp alpha 1-2Manp alpha 1-2Man, served as epitopes participating in the serotype A specificity of C. albicans strains.