Identification and genetic engineering of pneumococcal capsule-like polysaccharides in commensal oral streptococci.

Capsular polysaccharides (CPS) in Streptococcus pneumoniae are pivotal for bacterial virulence and present extensive diversity. While oral streptococci show pronounced antigenicity toward pneumococcal capsule-specific sera, insights into evolution of capsule diversity remain limited. This study reports a pneumococcal CPS-like genetic locus in Streptococcus parasanguinis, a predominant oral Streptococcus. The discovered locus comprises 15 genes, mirroring high similarity to those from the Wzy-dependent CPS locus of S. pneumoniae. Notably, S. parasanguinis elicited a reaction with pneumococcal 19B antiserum. Through nuclear magnetic resonance analysis, we ascertained that its CPS structure matches the chemical composition of the pneumococcal 19B capsule. By introducing the glucosyltransferase gene cps19cS from a pneumococcal serotype 19C, we successfully transformed S. parasanguinis antigenicity from 19B to 19C. Furthermore, substituting serotype-specific genes, cpsI and cpsJ, with their counterparts from pneumococcal serotype 19A and 19F enabled S. parasanguinis to generate 19A- and 19F-specific CPS, respectively. These findings underscore that S. parasanguinis harbors a versatile 19B-like CPS adaptable to other serotypes. Remarkably, after deleting the locus's initial gene, cpsE, responsible for sugar transfer, we noted halted CPS production, elongated bacterial chains, and diminished biofilm formation. A similar phenotype emerged with the removal of the distinct gene cpsZ, which encodes a putative autolysin. These data highlight the importance of S. parasanguinis CPS for biofilm formation and propose a potential shared ancestry of its CPS locus with S. pneumoniae. IMPORTANCE: Diverse capsules from Streptococcus pneumoniae are vital for bacterial virulence and pathogenesis. Oral streptococci show strong responses to a wide range of pneumococcal capsule-specific sera. Yet, the evolution of this capsule diversity in relation to microbe-host interactions remains underexplored. Our research delves into the connection between commensal oral streptococcal and pneumococcal capsules, highlighting the potential for gene transfer and evolution of various capsule types. Understanding the genetic and evolutionary factors that drive capsule diversity in S. pneumoniae and its related oral species is essential for the development of effective pneumococcal vaccines. The present findings provide fresh perspectives on the cross-reactivity between commensal streptococci and S. pneumoniae, its influence on bacteria-host interactions, and the development of new strategies to manage and prevent pneumococcal illnesses by targeting and modulating commensal streptococci.

Comparative Structural and Antigenic Characterization of Genetically Distinct Flavobacterium psychrophilum O-Polysaccharides.

Little is known about the underlying basis of serotype specificity among strains of Flavobacterium psychrophilum, the agent of rainbow trout fry syndrome and bacterial cold-water disease. The identification of different heat-stable O-serotypes among strains of this gram-negative pathogen does, however, suggest structural variations in the O-polysaccharide (O-PS) moiety of cell surface lipopolysaccharide (LPS). A trisaccharide composed of L-rhamnose (L-Rha), 2-acetamido-2-deoxy-L-fucose (L-FucNAc) and 2-acetamido-4-R-2,4-dideoxy-D-quinovose (D-Qui2NAc4NR), where R represents a dihydroxyhexanamido derivative, was previously identified as the repeating unit of Fp CSF259-93 O-PS. Interestingly, the O-PS gene cluster of this strain and that of Fp 950106-1/1, which belongs to a different O-serotype, are identical except for wzy, which encodes the putative polymerase that links trisaccharide repeats into O-PS chains. We have now found from results of glycosyl composition analysis and high-resolution nuclear magnetic resonance, that the linkage of D-Qui2NAc4NR to L-Rha, which is α1-2 for Fp CSF259-93 versus ß1-3 for Fp 950106-1/1, is the only structural difference between O-PS from these strains. The corresponding difference in O-serotype specificity was established from the reactions of rabbit and trout anti-F. psychrophilum antibody with purified O-PS and LPS. Moreover, LPS-based differences in antigenicity were noted between strains with O-PS loci identical to those of Fp CSF259-93 or Fp 950106-1/1, except for the genes predicted to direct synthesis of different R-groups in Qui2NAc4NR. The findings provide a framework for defining the genetic basis of O-PS structure and antigenicity and suggest that the repertoire of F. psychrophilum O-serotypes extends beyond what is presently recognized from serological studies of this important fish pathogen.

WciG O-Acetyltransferase Functionality Differentiates Pneumococcal Serotypes 35C and 42.

Streptococcus pneumoniae expresses capsular polysaccharides (CPSs) to protect itself from opsonophagocytic killing. The genes responsible for capsules synthesized by the Wzy-dependent mechanism, which accounts for 96 of the 98 known pneumococcal capsule types, are in a chromosomal region known as the cps locus. The nucleotide sequence in this region has been determined for all serotypes. In contrast, not all CPS structures have been defined. The structure of the serotype 35C polysaccharide was recently reported, but the presence of O-acetyltransferase genes in the serotype 35C cps locus suggested that it could be incomplete, as the reported structure contains no O-acetylation. In addition, the genetic distinction of serotype 35C from the closely related serotype 42 was unclear, as their reported cps loci are nearly identical. To clarify these discrepancies, we obtained serotype 35C and 42 clinical and reference isolates and studied their serological and genetic properties, as well as the structures of CPSs purified from reference isolates. We demonstrated that the O-acetyltransferase WciG was functional in serotype 35C but nonfunctional in serotype 42 due to a deletion in wciG Serotype 35C was O-acetylated at the 5- and 6-positions of 3-ß-galactofuranose, as well as the 2-position of 6-ß-galactofuranose. However, serotype 42 has only O-acetylation at 3-ß-galactofuranose, an observation consistent with its loss of WciG functionality, which is associated with O-acetylation at the 2-position and subsequent reaction with typing antiserum 35a. These findings provide a comprehensive view of the genetic, biochemical structural, and serological bases of serotypes 35C and 42.

Structures of Capsular Polysaccharide Serotypes 35F and 35C of Streptococcus pneumoniae Determined by Nuclear Magnetic Resonance and Their Relation to Other Cross-Reactive Serotypes.

UNLABELLED: The structures of Streptococcus pneumoniae capsular polysaccharides (CPSs) are essential for defining the antigenic as well as genetic relationships between CPS serotypes. The four serotypes that comprise CPS serogroup 35 (i.e., types 35F, 35A, 35B, and 35C) are known to cross-react with genetically related type 20, 29, 34, 42, or 47F. While the structures of CPS serotype 35A (CPS35A) and CPS35B are known, those of CPS35F and CPS35C are not. In the present study, the serotypes of CPS35F and CPS35C were characterized by high-resolution heteronuclear magnetic resonance (NMR) spectroscopy and glycosyl composition analyses to reveal the following repeat unit structures: [Formula: see text] where OAc indicates O-acetylated. Importantly, CPS35F, the immunizing serotype for the production of group 35 serum, more closely resembles CPS34 and CPS47F than other members of serogroup 35. Moreover, CPS35C is distinct from either CPS35F or CPS35B but closely related to CPS35A and identical to de-O-acetylated CPS42. The findings provide a comprehensive view of the structural and genetic relations that exist between the members of CPS serogroup 35 and other cross-reactive serotypes. IMPORTANCE: Cross-reactions of diagnostic rabbit antisera with Streptococcus pneumoniae capsular polysaccharide serotypes are generally limited to members of the same serogroup. Exceptions do, however, occur, most notably among a group of nonvaccine serotypes that includes the members of serogroup 35 (i.e., types 35F, 35A, 35B, and 35C) and other genetically related types. The presently determined structures of S. pneumoniae serotypes 35F and 35C complete the structural characterization of serogroup 35 and thereby provide the first comprehensive description of how different members of this serogroup are related to each other and to types 29, 34, 42, and 47F. The structural and genetic features of these serotypes suggest the existence of three distinct capsular polysaccharide subgroups that presumably emerged by immune selection in the human host.

Chemical structures of Streptococcus pneumoniae capsular polysaccharide type 39 (CPS39), CPS47F, and CPS34 characterized by nuclear magnetic resonance spectroscopy and their relation to CPS10A.

Structural characterization of Streptococcus pneumoniae capsular polysaccharides (CPS) is a prerequisite for unraveling both antigenic and genetic relationships that exist between different serotypes. In the current study, comparative structural studies of S. pneumoniae CPS serogroup 10 (CPS10) were extended to include genetically related S. pneumoniae CPS34, CPS39, and CPS47F. High-resolution heteronuclear nuclear magnetic resonance (NMR) spectroscopy confirmed the published structure of CPS34 and, in conjunction with glycosyl composition analyses, revealed the following repeat unit structures of the other serotypes, which have not been previously characterized: [structure: see text] Common and unique structural features of these polysaccharides, including different positions of O-acetylation, were unambiguously associated with specific genes in each corresponding cps locus. The only exception involved the gene designated wcrC, which is associated with the α1-2 transfer of Gal pyranoside (Galp) to ribitol-5-phosphate in the synthesis of CPS10A, CPS47F, and CPS34 but with α1-1 transfer of Gal to ribitol-5-phosphate in the synthesis of CPS39. The corresponding gene in the cps39 locus, although related to wcrC, more closely resembled a previously identified gene (i.e., wefM) of Streptococcus oralis that is associated with α1-1 transfer of Galp to ribitol-5-phosphate. These and other recent findings identify linkages from α-Galp to ribitol-5-phosphate and from this residue to adjacent Gal furanoside (Galf) as important sites of CPS structural and genetic diversity.

The conformation of a ribose derivative in aqueous solution: a neutron-scattering and molecular dynamics study.

The structure of aqueous solutions of methyl ß-D-ribofuranoside was investigated by coupling molecular dynamics (MD) simulations and neutron scattering measurements with isotopic substitution. Using a sample of the sugar isotopically-labeled at a single unique position, neutron scattering structure factors and radial distribution functions can be compared with MD simulations constrained to different conformations to determine which conformer best fits the experimental results. Three different simulations were performed with the methyl ether group of the sugar unconstrained and constrained in each of its staggered orientations. The results of the unconstrained simulation showed that the methyl ester group occupied predominantly the 300° position, which is in agreement with the diffraction experimental results. This result suggests that the molecular mechanics force field used in the simulation adequately describes the conformation of the 1-methyl ether group in the methyl ß-D-ribofuranoside.

Comparative structural and molecular characterization of Streptococcus pneumoniae capsular polysaccharide serogroup 10.

Streptococcus pneumoniae serogroup 10 includes four cross-reactive capsular polysaccharide (CPS) serotypes (10F, 10A, 10B, and 10C). In the present study, the structures of CPS10B and CPS10C were determined by chemical and high resolution NMR methods to define the features of each serotype. Both CPS10C and CPS10F had ß1-6-linked Galf branches formed from the termini of linear repeating units by wzy-dependent polymerization through the 4-OH of subterminal GalNAc. The only difference between these polysaccharides was the wcrC-dependent α1-2 or wcrF-dependent α1-4 linkages between Gal and ribitol-5-phosphate. The presence of one linkage or the other also distinguished the repeating units of CPS10B and CPS10A. However, whereas these polysaccharides both had ß1-3-linked Galf branches linked to GalNAc, only CPS10A had additional ß1-6-linked Galp branches. These Galp branches and the reaction of a CPS10A-specific monoclonal antibody were eliminated by deletion of wcrG from the cps10A locus. In contrast, deletion of this gene from the cps10B locus had no effect on the structure of CPS10B, thereby identifying wcrG as a pseudogene in this serotype. The ß1-3-linked Galf branches of CPS10A and CPS10B were eliminated by deletion of wcrD from each corresponding cps locus. Deletion of this gene also eliminated wcrG-dependent ß1-6-linked Galp branches from CPS10A, thereby identifying WcrG as a branching enzyme that acts on the product of WcrD. These findings provide a complete view of the molecular, structural, and antigenic features of CPS serogroup 10, as well as insight into the possible emergence of new serotypes.

Structure of type 3Gn coaggregation receptor polysaccharide from Streptococcus cristatus LS4.

The presence of a novel coaggregation receptor polysaccharide (RPS) on the dental plaque isolate Streptococcus cristatus LS4 was suggested by this strain's antigenic and coaggregation properties. Examination of RPS isolated from strain LS4 by a combination of 2-dimensional and pseudo 3-dimensional single quantum heteronuclear NMR methods that included detection of (13)C chemical shifts at high resolution revealed the following repeat unit structure: →6)-ß-d-Galf-(1→6)-ß-d-GalpNAc-(1→3)-α-d-Galp-(1→P→6)-α-d-Galp-(1→3)-ß-L-Rhap-(1→4)-ß-d-Glcp-(1→. The identification of this polysaccharide as RPS3Gn, a new structural type, was established by the α-d-Galp-containing epitope of RPS serotype 3 and Gn recognition motif (i.e., ß-d-GalpNAc (1→3)-α-d-Galp) for coaggregation with other bacteria.

Measuring the magnitude of internal motion in a complex hexasaccharide.

For the development of a scheme for quantitative experimental estimation of internal motion in the complex human milk hexasaccharide lacto-N-di-fuco hexose I (LNDFH I), we measured a large number of experimental residual dipolar couplings in liquid crystal orienting media. We present a total of 40 (13)C--(1)H and (1)H--(1)H dipolar coupling values, each representing distinct directions of internuclear vectors. The NMR data were interpreted with established methods for analysis of rigid subdomains of the oligosaccharide as well as a novel method in which dipolar couplings were calculated over an ensemble of conformers from a solvent Molecular Dynamics trajectory using multiple linear regression analysis. The Lewis(b) epitope region of LNDFH I assumed a single unique conformation with internal motion described by fluctuations of 5-10° in glycosidic dihedral angles consistent with previous studies. Greater flexibility was observed for the remaining GlcNAc1→3-ß-D-Gal and ß-D-Gal1→4Glc linkages, with the former glycosidic linkage existing in a conformational exchange among three states. The results were also supported by similar results of calculations carried out with conformers obtained from a simple Monte Carlo simulation without explicit solvent.

Structure and molecular characterization of Streptococcus pneumoniae capsular polysaccharide 10F by carbohydrate engineering in Streptococcus oralis.

Although closely related at the molecular level, the capsular polysaccharide (CPS) of serotype 10F Streptococcus pneumoniae and coaggregation receptor polysaccharide (RPS) of Streptococcus oralis C104 have distinct ecological roles. CPS prevents phagocytosis of pathogenic S. pneumoniae, whereas RPS of commensal S. oralis functions as a receptor for lectin-like adhesins on other members of the dental plaque biofilm community. Results from high resolution NMR identified the recognition region of S. oralis RPS (i.e. Galfbeta1-6GalNAcbeta1-3Galalpha) in the hexasaccharide repeat of S. pneumoniae CPS10F. The failure of this polysaccharide to support fimbriae-mediated adhesion of Actinomyces naeslundii was explained by the position of Galf, which occurred as a branch in CPS10F rather than within the linear polysaccharide chain, as in RPS. Carbohydrate engineering of S. oralis RPS with wzy from S. pneumoniae attributed formation of the Galf branch in CPS10F to the linkage of adjacent repeating units through sub terminal GalNAc in Galfbeta1-6GalNAcbeta1-3Galalpha rather than through terminal Galf, as in RPS. A gene (wcrD) from serotype 10A S. pneumoniae was then used to engineer a linear surface polysaccharide in S. oralis that was identical to RPS except for the presence of a beta1-3 linkage between Galf and GalNAcbeta1-3Galalpha. This polysaccharide also failed to support adhesion of A. naeslundii, thereby establishing the essential role of beta1-6-linked Galf in recognition of adjacent GalNAcbeta1-3Galalpha in wild-type RPS. These findings, which illustrate a molecular approach for relating bacterial polysaccharide structure to function, provide insight into the possible evolution of S. oralis RPS from S. pneumoniae CPS.

Comparative structural and molecular characterization of ribitol-5-phosphate-containing Streptococcus oralis coaggregation receptor polysaccharides.

The antigenically related coaggregation receptor polysaccharides (RPS) of Streptococcus oralis strains C104 and SK144 mediate recognition of these bacteria by other members of the dental plaque biofilm community. In the present study, the structure of strain SK144 RPS was established by high resolution NMR spectroscopy as [6Galfbeta1-6GalNAcbeta1-3Galalpha1-2ribitol-5-PO(4)(-)-6Galfbeta1-3Galbeta1](n), thereby indicating that this polysaccharide and the previously characterized RPS of strain C104 are identical, except for the linkage between Gal and ribitol-5-phosphate, which is alpha1-2 in strain SK144 versus alpha1-1 in strain C104. Studies to define the molecular basis of RPS structure revealed comparable genes for six putative transferases and a polymerase in the rps loci of these streptococci. Cell surface RPS production was abolished by disrupting the gene for the first transferase of strain C104 with a nonpolar erm cassette. It was restored in the resulting mutant by plasmid-based expression of either wcjG, the corresponding gene of S. pneumoniae for serotype 10A capsular polysaccharide (CPS) biosynthesis or wbaP for the transferase of Salmonella enterica that initiates O-polysaccharide biosynthesis. Thus, WcjG, like WbaP, appears to initiate polysaccharide biosynthesis by transferring galactose-1-phosphate to a lipid carrier. In further studies, the structure of strain C104 RPS was converted to that of strain SK144 by replacing the gene (wefM) for the fourth transferase in the rps locus of strain C104 with the corresponding gene (wcrC) of strain SK144 or Streptococcus pneumoniae serotype 10A. These findings identify genetic markers for the different ribitol-5-phosphate-containing types of RPS present in S. oralis and establish a close relationship between these polysaccharides and serogroup 10 CPSs of S. pneumoniae.

Molecular and antigenic characterization of a Streptococcus oralis coaggregation receptor polysaccharide by carbohydrate engineering in Streptococcus gordonii.

The coaggregation receptor polysaccharides (RPS) of Streptococcus oralis and related species are recognized by lectin-like adhesins on other members of the oral biofilm community and by RPS-specific antibodies. The former interactions involve beta-GalNAc or beta-Gal containing host-like motifs in the oligosaccharide repeating units of these polysaccharides, whereas the latter involves features of these molecules that are immunogenic. In the present investigation, the molecular and corresponding structural basis for the serotype specificity of S. oralis ATCC 10557 RPS was determined by engineering the production of this polysaccharide in transformable Streptococcus gordonii 38. This involved the systematic replacement of genes in the rps cluster of strain 38 with different but related genes from S. oralis 10557 and structural characterization of the resulting polysaccharides. The results identify four unique genes in the rps cluster of strain 10557. These include wefI for an alpha-Gal transferase, wefJ for a GalNAc-1-phosphotransferase that has a unique acceptor specificity, wefK for an acetyl transferase that acts at two positions in the hexasaccharide repeating unit, and a novel wzy associated with the beta1-3 linkage between these units. The serotype specificity of engineered polysaccharides correlated with the wefI-dependent presence of alpha-Gal in these molecules rather than with partial O-acetylation or with the linkage between repeating units. The findings illustrate a direct approach for defining the molecular basis of polysaccharide structure and antigenicity.

Molecular basis of L-rhamnose branch formation in streptococcal coaggregation receptor polysaccharides.

The presence of L-rhamnose (Rha) branches in the coaggregation receptor polysaccharides (RPS) of Streptococcus gordonii 38 and Streptococcus oralis J22 was eliminated by replacement of wefB with ermAM in these strains. The expression of this gene in S. oralis 34 did not, however, result in the addition of Rha branches to the linear RPS of this strain, which is identical to that produced by the wefB-deficient mutant of S. gordonii 38. This paradoxical finding was explained by a subtle difference in acceptor specificity of the galactose-1-phosphotransferases encoded by downstream wefC in S. gordonii 38 and wefH in S. oralis 34. These genes were distinguished by the unique ability of WefC to act on the branched acceptor formed by the action of WefB.

Two different O-polysaccharides from Escherichia coli O86 are produced by different polymerization of the same O-repeating unit.

The structure of a new O-polysaccharide from Escherichia coli O86:K62:B7 was determined using NMR and methylation analysis. The structure is as follows: [carbohydrate: see text]. Comparison with the previously published structure from E. coli O86:K2:H2 revealed that the O-polysaccharides from these two E. coli O86 serotypes share the same branched pentasaccharide repeating unit. However, they differ in the anomeric configuration of the linkage, the linkage position, and the identity of the residue through which polymerization occurs. The immunochemical activity of these two forms of LPS toward anti-B antibody was studied and compared. The results showed that LPS from E. coli O86:K2:H2 strain possesses higher blood group B reactivity. The immunoreactivity difference was explained by modeling of the O-repeating unit tetrasaccharide fragments. This finding provides a good system for the further study of O-polysaccharide biosynthesis especially the repeating unit polymerization mechanism.

Carbohydrate engineering of the recognition motifs in streptococcal co-aggregation receptor polysaccharides.

The cell wall polysaccharides of certain oral streptococci function as receptors for the lectin-like surface adhesins on other members of the oral biofilm community. Recognition of these receptor polysaccharides (RPS) depends on the presence of a host-like motif, either GalNAcbeta1-3Gal (Gn) or Galbeta1-3GalNAc (G), within the oligosaccharide repeating units of different RPS structural types. Type 2Gn RPS of Streptococcus gordonii 38 and type 2G RPS of Streptococcus oralis J22 are composed of heptasaccharide repeats that are identical except for their host-like motifs. In the current investigation, the genes for the glycosyltransferases that synthesize these motifs were identified by high-resolution nuclear magnetic resonance (NMR) analysis of genetically altered polysaccharides. RPS production was switched from type 2Gn to 2G by replacing wefC and wefD in the type 2Gn gene cluster of S. gordonii 38 with wefF and wefG from the type 2G cluster of S. oralis J22. Disruption of either wefC or wefF abolished cell surface RPS production. In contrast, disruption of wefD in the type 2Gn cluster or wefG in the type 2G cluster eliminated beta-GalNAc from the Gn motif or beta-Gal from the G motif, resulting in mutant polysaccharides with hexa- rather than heptasaccharide subunits. The mutant polysaccharides reacted like wild-type RPS with rabbit antibodies against type 2Gn or 2G RPS but were inactive as co-aggregation receptors. Additional mutant polysaccharides with GalNAcbeta1-3GalNAc or Galbeta1-3Gal recognition motifs were engineered by replacing wefC in the type 2Gn cluster with wefF or wefF in the type 2G cluster with wefC respectively. The reactions of these genetically modified polysaccharides as antigens and receptors provide further insight into the structural basis of RPS function.

Escherichia coli O86 O-antigen biosynthetic gene cluster and stepwise enzymatic synthesis of human blood group B antigen tetrasaccharide.

Previous study showed that some Gram-negative bacteria possess human blood group activity. Among them, Escherichia coli O86 has high blood group B activity and weak blood group A activity. This is due to the cell surface O-antigen structure, which resembles that of human blood group B antigen. In this study, we sequenced the entire E. coli O86 antigen gene cluster and identified all the genes responsible for O-antigen biosynthesis by sequence comparative analysis. The blood group B-like antigen in E. coli O86 O-polysaccharide was synthesized by sequentially employing three glycosyltransferases identified in the gene cluster. More importantly, we identified a new bacterial glycosyltransferase (WbnI) equivalent to human blood group transferase B (GTB). The enzyme substrate specificity and stepwise enzymatic synthesis of blood group B-like antigen revealed that the biosynthetic pathway of B antigen is essentially the same in E. coli O86 as in humans. This new finding provides a model to study the specificity and structure relationship of blood group transferases and supports the hypothesis of anti-blood group antibody production by bacterial stimulation.

Conformation of the hexasaccharide repeating subunit from the Vibrio cholerae O139 capsular polysaccharide.

In the past decade, several outbreaks of cholera have been reported to be caused by Vibrio cholerae O139, a strain which differs from the more common O1 strain in that the former is encapsulated. The hexasaccharide repeating subunit has been isolated from the V. cholerae O139 capsular polysaccharide by digestion with a recently discovered polysaccharide lyase derived from a bacteriophage specific for this serogroup. It specifically cleaves at a single position of the 4-linked galacturonic acid producing an unsaturated sugar product in quantities for conformational studies by (1)H and (13)C NMR spectroscopy. We report conformational studies on this oligosaccharide by molecular modeling and NMR spectroscopy including nuclear Overhauser effects and residual dipolar coupling of a sample weakly oriented in liquid crystalline solution. The structure contains a tetrasaccharide epitope homologous to the human Lewis(b) blood group antigen, which adopts a relatively well-defined single conformation. Comparison of these results with those of a previously published study of the intact capsular polysaccharide indicates that the conformations of the epitope in the two cases are identical or at least closely similar. Thus, this epitope, which may be essential for the pathogenicity of this V. cholerae strain, is not a "conformational epitope" requiring a certain critical size for antigenicity as has been reported for several other bacterial capsular antigens.

Conformational studies of blood group A and blood group B oligosaccharides using NMR residual dipolar couplings.

The conformations of two synthetic trisaccharides of blood group A and B (alpha-L-Fucp-(1-->2)-[alpha-D-GalpNAc-(1-->3)]-alpha-D-Galp and alpha-L-Fucp-(1-->2)-[alpha-D-Galp-(1-->3)]-alpha-D-Galp, respectively) and of a type A tetrasaccharide alditol, Fucp-(1-->2)-[alpha-D-GalpNAc-(1-->3)]-beta-D-Galp-(1-->3)-GalNAc-ol, were studied by NMR measurements of one-bond C-H residual dipolar couplings in partially oriented liquid crystal solutions. The conformations of the three oligosaccharides were analyzed by generating thousands of structures using a Monte-Carlo method. Two different strategies were applied to calculate theoretical dipolar couplings for these structures. In the first method, the orientation of the molecule was calculated from the optimal fit of the molecular model to the experimental data, while in the second method the orientation tensor was calculated directly from the moment of inertia of the molecular model. Both methods of analysis give similar results but with slightly better agreement with experiment for the former one. The analysis of the results implies a single unique conformation for both blood group epitopes in solution in disagreement with theoretical models suggesting the existence of two conformers in solution.

Carbohydrate analysis of bacterial polysaccharides by high-pH anion-exchange chromatography and online polarimetric determination of absolute configuration.

A significant problem in structure determination of complex carbohydrates, especially for bacterial polysaccharides, is determination of the absolute configuration of the component monosaccharides. A number of analytical methods have been used for this purpose but, as a result of the wide variety of chemical properties of sugars found in complex polysaccharides, no single method is universally applicable. High-resolution gas chromatography of volatile derivatives with chiral reagents is the most widely used method. Optical activity, although direct and simple, lacks sensitivity generally requiring a large quantity of pure monosaccharide. We report a combination of high-performance anion-exchange chromatography (HPAEC) with combined electrochemical pulsed amperometric detection and in-line detection of optical rotation with an in-line laser polarimeter for analysis of a number of sugars found in complex polysaccharides. We show that application of the method for analysis of capsular polysaccharides of several gram-positive and gram-negative pathogenic bacteria provides useful information simultaneously on carbohydrate composition and the enantiomeric configuration of component sugars.