Structural studies of the capsular polysaccharide elaborated by Haemophilus influenza type d

Conformational comparisons of Pasteurella multocida types B and E and structurally related capsular polysaccharides

Pasteurella multocida, an encapsulated gram-negative bacterium, is a significant veterinary pathogen. The P. multocida is classified into 5 serogroups (A, B, D, E, and F) based on the bacterial capsular polysaccharide (CPS), which is important for virulence. Serogroups B and E are the primary causative agents of bovine hemorrhagic septicemia that is associated with significant yearly losses of livestock worldwide, primarily in low- and middle-income countries. The P. multocida disease is currently managed by whole-cell vaccination, albeit with limited efficacy. CPS is an attractive antigen target for an improved vaccine: CPS-based vaccines have proven highly effective against human bacterial diseases and could provide longer-term protection against P. multocida. The recently elucidated CPS repeat units of serogroups B and E both comprise a N-acetyl-β-D-mannosaminuronic acid/N-acetyl-β-D-glucosamine disaccharide backbone with β-D-fructofuranose (Fruf) side chain, but differ in their glycosidic linkages, and a glycine (Gly) side chain in serogroup B. Interestingly, the Haemophilus influenzae types e and d CPS have the same backbone residues. Here, comparative modeling of P. multocida serogroups B and E and H. influenzae types e and d CPS identifies a significant impact of small structural differences on both the chain conformation and the exposed potential antibody-binding epitopes (Ep). Further, Fruf and/or Gly side chains shield the immunogenic amino-sugar CPS backbone-a possible common strategy for immune evasion in both P. multocida and H. influenzae. As the lack of common epitopes suggests limited potential for cross-reactivity, a bivalent CPS-based vaccine may be necessary to provide adequate protection against P. multocida types B and E.

Effect of Side-Chain Functional Groups in the Immunogenicity of Bacterial Surface Glycans

Glycans on the surface of bacteria have diverse and essential biological functions and have widely been employed for treating various bacterial infectious diseases. Furthermore, these glycans comprise various functional groups, such as O-, N-, and carboxyl-modified, which significantly increase the diversity of glycan structures. These functional groups are not only crucial for glycans' structural identity but are also essential for their biological functions. Therefore, a clear understanding of the biological functions of these modified groups in corresponding bacterial glycans is crucial for their medical applications. Thus far, the activities of functional groups in some biomedical active carbohydrates have been elucidated. It has been shown that some functional groups are key constituents of biologically active bacterial glycans, while others are actually not essential and may even mask the functions of the glycans. This paper reviews the structures of naturally occurring side-chain functional groups in glycans located on the bacterial surface and their roles in immunological responses.

Cross-reactivity of Haemophilus influenzae type a and b polysaccharides: molecular modeling and conjugate immunogenicity studies

Haemophilus influenzae is a leading cause of meningitis disease and mortality, particularly in young children. Since the introduction of a licensed conjugate vaccine (targeting the outer capsular polysaccharide) against the most prevalent serotype, Haemophilus influenzae serotype b, the epidemiology of the disease has changed and Haemophilus influenzae serotype a is on the rise, especially in Indigenous North American populations. Here we apply molecular modeling to explore the preferred conformations of the serotype a and b capsular polysaccharides as well as a modified hydrolysis resistant serotype b polysaccharide. Although both serotype b and the modified serotype b have similar random coil behavior, our simulations reveal some differences in the polysaccharide conformations and surfaces which may impact antibody cross-reactivity between these two antigens. Importantly, we find significant conformational differences between the serotype a and b polysaccharides, indicating a potential lack of cross-reactivity that is corroborated by immunological data showing little recognition or killing between heterologous serotypes. These findings support the current development of a serotype a conjugate vaccine.

Sequence analysis of serotype-specific synthesis regions II of Haemophilus influenzae serotypes c and d: evidence for common ancestry of capsule synthesis in Pasteurellaceae and Neisseria meningitidis

Sequencing of yet unknown Haemophilus influenzae serotype c (Hic) and d (Hid) capsule synthesis regions II revealed four (ccs1-4) and five (dcs1-5) open reading frames, respectively. The inferred gene functions were in line with capsular polysaccharide structures. One or more proteins encoded by the Hic capsule synthesis region II showed similarity to Actinobacillus pleuropneumoniae serotype 1 and Actinobacillus suis K1 enzymes. Orthologues to the complete operon were observed in Actinobacillus minor strain 202, where even the gene order was conserved. Furthermore, Ccs4 was related to the capsule O-acetyltransferase of Neisseria meningitidis serogroup W-135. For the Hid locus, similarities to Hie, Mannheimia haemolytica A1 and N. meningitidis serogroup A were identified and the succession of genes was similar in the different species. The resemblance of genes and gene organization found for Hic and Hid with other species suggested horizontal gene transfer during capsule evolution across the bacterial classes.

Identification and characterization of the unique N-linked glycan common to the flagellins and S-layer glycoprotein of Methanococcus voltae

The flagellum of Methanococcus voltae is composed of four structural flagellin proteins FlaA, FlaB1, FlaB2, and FlaB3. These proteins possess a total of 15 potential N-linked sequons (NX(S/T)) and show a mass shift on an SDS-polyacrylamide gel indicating significant post-translational modification. We describe here the structural characterization of the flagellin glycan from M. voltae using mass spectrometry to examine the proteolytic digests of the flagellin proteins in combination with NMR analysis of the purified glycan using a sensitive, cryogenically cooled probe. Nano-liquid chromatography-tandem mass spectrometry analysis of the proteolytic digests of the flagellin proteins revealed that they are post-translationally modified with a novel N-linked trisaccharide of mass 779 Da that is composed of three sugar residues with masses of 318, 258, and 203 Da, respectively. In every instance the glycan is attached to the peptide through the asparagine residue of a typical N-linked sequon. The glycan modification has been observed on 14 of the 15 sequon sites present on the four flagellin structural proteins. The novel glycan structure elucidated by NMR analysis was shown to be a trisaccharide composed of beta-ManpNAcA6Thr-(1-4)-beta-Glc-pNAc3NAcA-(1-3)-beta-GlcpNAc linked to Asn. In addition, the same trisaccharide was identified on a tryptic peptide of the S-layer protein from this organism implicating a common N-linked glycosylation pathway.

Assembly of the K40 antigen in Escherichia coli: identification of a novel enzyme responsible for addition of L-serine residues to the glycan backbone and its requirement for K40 polymerization

Escherichia coli O8:K40 coexpresses two distinct lipopolysaccharide (LPS) structures on its surface. The O8 polysaccharide is a mannose homopolymer with a trisaccharide repeat unit and is synthesized by an ABC-2 transport-dependent pathway. The K40LPS backbone structure is composed of a trisaccharide repeating unit of N-acetylglucosamine (GlcNAc) and glucuronic acid (GlcA) and has an uncommon substitution, an L-serine moiety attached to glucuronic acid. The gene cluster responsible for synthesis of the K40 polysaccharide has previously been cloned and sequenced and was found to contain six open reading frames (ORFs) (P. A. Amor and C. Whitfield, Mol. Microbiol. 26:145-161, 1997). Here, we demonstrate that insertional inactivation of orf1 results in the accumulation of a semirough (SR)-K40LPS form which retains reactivity with specific polyclonal serum in Western immunoblots. Structural and compositional analysis of the SR-K40LPS reveals that it comprises a single K40 repeat unit attached to lipid A core. The lack of polymerization of the K40 polysaccharide indicates that orf1 encodes the K40 polymerase (Wzy) and that assembly of the K40 polysaccharide occurs via a Wzy-dependent pathway (in contrast to that of the O8 polysaccharide). Inactivation of orf3 also results in the accumulation of an SR-LPS form which fails to react with specific polyclonal K40 serum in Western immunoblots. Methylation linkage analysis and fast atom bombardment-mass spectrometry of this SR-LPS reveals that the biological repeat unit of the K40 polysaccharide is GlcNAc-GlcA-GlcNAc. Additionally, this structure lacks the L-serine substitution of GlcA. These results show that (i) orf3 encodes the enzyme responsible for the addition of the L-serine residue to the K40 backbone and (ii) substitution of individual K40 repeats with L-serine is essential for their recognition and polymerization into the K40 polysaccharide by Wzy.

Structure of a muramic acid containing capsular polysaccharide from the pathogenic strain of Vibrio vulnificus ATCC 27562

Vibrio vulnificus strains isolated from septicemia cases and from the environment show a wide variety of capsular types. In an attempt to find common structural features which can be correlated with pathogenicity and toxicity, we have determined structures of the capsular polysaccharides (CPS) from several pathogenic strains. We report the complete structure of the polysaccharide from the pathogenic V. vulnificus strain ATCC 27562 using a combination of homonuclear and heteronuclear one-dimensional and two dimensional NMR experiments. The 13C and 1H NMR spectra, including the exchangeable amide proton resonances, have been completely assigned. The amide linkage between Ser and C6 of GalA has been unambiguously determined by water-suppressed 2D NOESY. To verify the structure established by NMR, we have fragmented the polymer employing the Smith degradation procedure. The Smith product identified by NMR and matrix-assisted laser desorption mass spectrometry is consistent with the proposed structure for the CPS, which is composed of D-GlcNAc, MurNAc, D-GalA, L-Rha and is serine-linked as shown: [formula: see text]

Structural studies of the O-specific polysaccharide of Hafnia alvei strain PCM 1206 lipopolysaccharide containing D-allothreonine

The structure of the O-specific side-chain of the Hafnia alvei strain PCM 1206 lipopolysaccharide has been investigated. Methylation analysis, partial acid hydrolysis, FAB-MS/MS and 1H-NMR and 13C-NMR spectroscopy were the principal methods used. D-Allothreonine (D-aThr), amide-linked to the D-galacturonic acid, was identified as a constituent in the polysaccharide and the following structure of a pentasaccharide repeating unit was established: [structure: see text].

Occurrence of 2,4-dihydroxy-3,3,4-trimethylpyroglutamic acid as an N-acyl substituent in the O-polysaccharide chain of the lipopolysaccharide of Vibrio anguillarum V-123

A new and highly branched amino acid was found as an N-acyl substituent of the O-polysaccharide chain obtained from the lipopolysaccharide of Vibrio anguillarum V-123 (serogroup JO-2) and evidence is presented to support the structure as 2,4-dihydroxy-3,3,4-trimethylpyroglutamic acid. Acid hydrolysis of the O-polysaccharide gave the lactone of 2,4-dihydroxy-3,3,4-trimethylglutamic acid, together with 2-amino-2-deoxy-D-galacturonic acid, 2-amino-2,6-dideoxy-D-glucose (D-quinovosamine), and 4-amino-4,6-dideoxy-D-glucose (D-viosamine). Degradation of the O-polysaccharide with hydrogen fluoride yielded a fragment (H1) that was indicated by the 1H-NMR data to be 4-amino-4,6-dideoxy-D-glucose N-acetylated with 2,4-dihydroxy-3,3,4-trimethylpyroglutamic acid. The configuration of the amino acid was not determined.

Synthesis of carbohydrate-amino acid conjugates related to the capsular antigen K54 from Escherichia coli O6:K54:H10 and artificial antigens therefrom

The disaccharides alpha-L-Rhap-(1----3)-beta-D-GlcpA and beta-D-GlcpA-(1----3)-alpha-L-Rhap bearing amide-linked L-serine or L-threonine, which represent the repeating unit(s) of the capsular polysaccharide from E. coli O6:K54:H10, have been synthesised. O-tert-Butyl-protected amino acid tert-butyl esters were condensed with the corresponding biouronic acid as the 2-acrylamidoethyl or 2-azidoethyl glycosides. The azido function was replaced by the acrylamido group by catalytic hydrogenation followed by N-acryloylation. The tert-butyl groups were removed by treatment with trifluoroacetic acid to give the target monomers which were copolymerised with acrylamide to give neoglycoconjugates that are potentially useful for immunochemical studies.

Synthesis of an artificial antigen that corresponds to a disaccharide repeating unit of the capsular polysaccharide of Haemophilus influenzae type d. A facile synthesis of methyl 2-acetamido-2-deoxy-beta-D-mannopyranoside

The synthesis is described of p-nitrophenyl 2-acetamido-3-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-2-deoxy-beta -D- mannopyranosiduronic acid, corresponding to the disaccharide repeating unit of the capsular polysaccharide of Haemophilus influenzae type d, which, after conversion of the p-nitro- into a p-amino-phenyl residue, may be attached to a protein to make an artificial antigen for immunological studies. The synthesis incorporates a facile route to the 2-acetamido-2-deoxy-beta-D-mannopyranosyl unit.

Synthesis of glycuronamides of amino acids, constituents of microbial polysaccharides and their conversion into neoglycoconjugates of copolymer type

Glycopyranosiduronic acids, amidically linked to amino acids (alanine, serine, threonine, and lysine) were prepared. O-tert-Butyl and N epsilon-tert-butyloxycarbonyl protected amino acid tert-butyl esters were used in ethyl 2-ethoxy-1,2-dihydroquinoline-1-carboxylate promoted condensation with 2-azidoethyl glycosides of glucuronic and galacturonic acid. Reduction of the azido-function followed by N-acryloylation and removal of blocking groups with trifluoroacetic acid gave the target monomers. These were converted into neoglycoconjugates of copolymer type, potentially useful for immunochemical studies.

Structure of the amino acid-containing capsular polysaccharide from Escherichia coli O8:K49:H21

The structure of the capsular antigen of E. coli K49 and the oligosaccharides derived from it by partial acid hydrolysis were studied by 1D- and 2D-n.m.r. spectroscopy, g.l.c.-c.i.-mass spectrometry, and methylation analysis. The K49 polysaccharide consists of the repeating unit----4)-beta-D-GlcpA-(1----6)-beta-D-Galp-(1----6)-beta-D-Glcp- (1----3)-beta - D-GalpNAc-(1----. The glucuronic acid residues are substituted, in the apparent molar ratio of 4:1, with L-threonine and L-serine linked amidically to the carboxyl group.

Structural studies of acidic polymers produced by the O23 reference strain of Serratia marcescens: presence of amide-linked glutamic acid

The major fraction of an acidic galactoglucomannan present in lipopolysaccharide extracts from cell walls of the O23 reference strain of Serratia marcescens has the tetrasaccharide repeating-unit shown. In a minor fraction, L-glutamic acid was amide-linked to about half of the D-glucuronic acid residues. The possible contributions of the acidic polymers and a neutral polymer produced by the organism to cross-reactions with other serogroups are discussed.

Chemical characterization of enterobacterial common antigen isolated from Plesiomonas shigelloides ATCC 14029

Serologically characterized samples of enterobacterial common antigen (ECA) from Plesiomonas shigelloides, Salmonella montevideo and Shigella sonnei were investigated by chemical methods including methylation and NMR techniques. All showed the same sugar composition and contained a lipid moiety with palmitic acid as main fatty acid and with a phosphodiester group. Additional enzymatic studies, reported in the preceding paper, provided evidence that the lipid moiety is an L-glycerophosphatidyl residue attached via a phosphodiester linkage to C-1 of GlcNAc as the reducing end of the ECA sugar chain. ECA of P. shigelloides showed the best-resolved 13C-NMR spectra, especially after the removal of non-stoichiometric O-acetyl groups at C-6 of GlcNAc of the ECA repeating unit and of the lipid moiety by mild acid hydrolysis (0.01 M HCl, 100 degrees C, 10 min). Subsequent 13C-NMR studies were therefore carried out with the mild-acid-treated ECA of P. shigelloides which allowed a tentative assignment of all resonances of the ECA repeating unit. 13C-NMR spectra of Salmonella and Shigella ECA were essentially the same as those obtained with Plesiomonas ECA. The same trisaccharide repeating unit was encountered as demonstrated previously in the cyclic form of ECA isolated from S. sonnei by Dell et al. [Carbohydr. Res. 133, 95-104 (1984)]. Methylation analysis, however, afforded small amounts of terminal GlcNAc thus proving, in combination with the demonstration of the attached lipid moiety, an acyclic nature of ECA from P. shigelloides and from the two enterobacterial species. The question of whether the cyclic form co-exists in S. sonnei phase I and possibly in other enterobacterial species or, whether it had been formed during extraction as an artifact, has not yet been answered. The way in which ECA was isolated in our studies would preclude the presence of a non-amphiphilic (cyclic) polysaccharide. The finding that the sugar chain of ECA is attached to an L-glycerophosphatidyl residue is in full corroboration with serological, enzymatic and gel electrophoretic studies shown in the preceding paper and with the character of ECA as a surface antigen being anchored by hydrophobic interactions in the outer membrane of Enterobacteriaceae and P. shigelloides.

[Synthesis of trisaccharide determinants of enterobacterial common antigens]

In the presence of silver silicate, the reaction of 3,4,6-tri-O-acetyl-2-azido-2-deoxy-alpha-D-mannopyranosyl bromide with 1,6-anhydro-2-azido-3-O-benzyl-2-deoxy-beta-D-glucopyranose gave beta-glycosidically linked 1,6-anhydro-2-azido-3-O-benzyl-2-deoxy-4-O-(3,4,6- tri-O-acetyl-2-azido-2-deoxy-beta-D-mannopyranosyl)-beta-D- glucopyranose. After deacetylation and catalytic oxidation with oxygen and platinum, 1,6-anhydro-2-azido-4-O-[(2-azido-2-deoxy-beta-D-mannopyranosyl) uronic acid]-3-O-benzyl-2-deoxy-beta-D-glucopyranose was obtained. A series of intermediate steps led to the glycosyl donor 6-O-acetyl-2-azido-3-O-benzyl-4-O-[benzyl (3,4-di-O-acetyl-2-azido-2-deoxy-beta-D-mannopyranosyl)uronate]-2-deoxy- alpha, beta-glucopyranosyl chloride which was coupled with 8-methoxycarbonyloctyl 4-azido-2-O-benzyl-4,6-dideoxy-alpha-D-galactopyranoside to give 8-methoxycarbonyloctyl O-[benzyl (3,4-di-O-acetyl-2-azido-2-deoxy-beta-D-mannopyranosyl)uronate]- (1----4)-O-(6-O-acetyl-2-azido-3-O-benzyl-2-deoxy-alpha-D-glucopyranosyl )-(1----3)-4-azido-2-O-benzyl-4,6-dideoxy-alpha-D-galactopyranoside. Deblocking gave the spacer-linked repeating unit of the enterobacterial common antigen, beta-D-ManpNAcA-(1----4)-alpha-D-GlcpNAc-(1----3)-alpha- D-Fucp4NACO(CH2)8CO2CH3.

Structure of the serine-containing capsular polysaccharide K40 antigen from Escherichia coli O8:K40:H9

The structure of the K40 antigenic capsular polysaccharide (K40 antigen) of E. coli O8:K40:H9 was elucidated by determination of the composition, 1H- and 13C-n.m.r. spectroscopy, periodate oxidation and Smith degradation, and methylation analysis. The K40 polysaccharide consists of [(O-beta-D-glucopyranosyluronic acid)-(1----4)-O-(2-acetamido-2-deoxy-alpha-D-glucopyranosyl)-(1----6)-O -(2-acetamido-2-deoxy-alpha-D-glucopyranosyl)-(1----4)] repeating units. All of the glucuronic acid residues are substituted amidically with L-serine.

Structure of the capsular antigen of Neisseria meningitidis serogroup K

The capsular antigen isolated from the culture liquid of a Neisseria meningitidis serogroup K(1811) fermentation consists of the 2-acetamido-2-deoxymannuronic acid disaccharide repeating unit as follows: ----3)-beta-D-ManpNAcA-(1----4)-beta-D-ManpNAcA-(1---- The polysaccharide is O-acetylated at the non-glycosylated C-4. Structural evidence has been obtained from sugar analysis, methylation analysis, as well as 1H and 13C NMR spectroscopy.

Structure of the amino acid-containing capsular polysaccharide (K54 antigen) from Escherichia coli O6:K54:H10

The structure of the K54-antigenic polysaccharide (K54 antigen) of Escherichia coli O6:K54:H10 was elucidated by determination of the composition, 1H- and 13C-n.m.r. spectroscopy, periodate oxidation, and a study of the oligosaccharides obtained by partial hydrolysis with acid. The K54 polysaccharide consists of----3)-beta-D-glucosyluronic acid-(1----3)-alpha-L-rhamnosyl-(1----repeating-units. Of the glucuronic acid residues, approximately 85% are substituted in the ratio 9:1 with L-threonine and L-serine amidically linked to the carboxyl group. The K54 polysaccharide has a molecular weight of approximately 160,000, corresponding to approximately 380 repeating-units.

The structure of the polysaccharide moiety of Rhodopseudomonas sphaeroides ATCC 17023 lipopolysaccharide

The chemical structure of the polysaccharide moiety of the lipopolysaccharide Rhodopseudomonas sphaeroides ATCC 17023 was established. Mild acetic acid hydrolysis of isolated lipopolysaccharide, followed by preparative high-voltage paper electrophoresis afforded three oligosaccharides. They were characterized by chemical and physicochemical studies to be: GlcA(alpha 1----4)dOclA8P, Thr(6') GlcA(alpha 1----4)GlcA and GlcA(alpha 1----4)dOclA, where GlcA is D-glucuronic acid and dOc1A is 3-deoxy-D-manno-octulosonic acid. Carboxyl-reduction of the lipopolysaccharide followed by acid hydrolysis gave a trisaccharide: GlcA(alpha 1----4)Glc(alpha 1----4)Glc, showing the presence of three residues of glucuronic acids in the O-specific chain and indicating that only two of them are reducible by NaBH4. The linkage between the polysaccharide and lipid A was shown to be through a single 1,4-linked residue of dOc1A attached by a 2,6'-linkage to the lipid A moiety.

Cell-wall lipopolysaccharide of Escherichia coli 0114:H2. Structure of the polysaccharide chain

The O-specific polysaccharide of the 0114 antigen (lipopolysaccharide) of Escherichia coli 0114 and oligosaccharides obtained from it by Smith degradation and hydrogen fluoride solvolysis were analyzed, using proton and 13C nuclear magnetic resonance spectroscopy and methylation. The results indicated that the 0114 polysaccharide has the tetrasaccharide repeating unit alpha-N-acetylglucosamine(1 leads to 4) beta-3,6-dideoxy-3-(N-acetyl-L-seryl)aminoglucose(1 leads to 3) beta-ribofuranose(1 leads to 4)galactose. In the polysaccharide the repeating units are joined through beta 1 leads to 3-galactosyl linkages. This structure is compared with that of the serologically cross-reacting Shigella boydii 08 antigen and the serological similarity is discussed.

The lipopolysaccharide from Pseudomonas aeruginosa NCTC 8505. Structure of the O-specific polysaccharide

Structural studies have been carried out on the O-specific fraction from the lipopolysaccharide of Pseudomonas aeruginosa NCTC 8505, Habs serotype 03. The O-specific polysaccharide has a tetrasaccharide repeating-unit containing residues of L-rhamnose (Rha), 2-acetamido-2-deoxy-D-glucose (GlcNAc), 2-acetamido-2-deoxy-L-galacturonic acid (GalNAcA), and 2,4-diacetamido-2,4,6-trideoxy-D-glucose (BacNAc2). The following structure has been assigned to the repeating-unit: leads to 3)Rhap(beta 1 leads to 6)GlcpNAc(alpha 1 leads to 4)GalpNAcA(alpha 1 leads to 3)BacpNAc2(alpha 1 leads to. The parent lipopolysaccharide is a mixture of S, R, and SR species, and its high phosphorus content is partly due to the presence of triphosphate residues, as found for other lipopolysaccharides from P. aeruginosa. In addition to phosphorus, heptose, a 3-deoxyoctulosonic acid, and amide-bound alanine, the core oligosaccharide contains glucose, rhamnose, and galactosamine (molar proportions 3:1:1). The rhamnose and part of the glucose are present as unsubstituted pyranoside residues: other glucose residues are 6-substituted.

Structural and immunological studies of the Haemophilus influenzae type d capsular polysaccharide

Employing a combination of chemical and spectroscopic techniques, the structure of the Haemophilus influenzae type d capsular polysaccharide was found to be leads to 4)-beta-D-GlcNAc-(1 leads to 3)-beta-D-ManNAcA-(1 leads to. L-Alanine, L-serine, and L-threonine, in the molar ratios of approximately 1.0:1.0:0.3, were linked to C-6 of the D-mannosyluronic residue as amides; the (serine + alanine + threonine) to ManNAcA ratio was approximately 0.95:1.0. Removal of the amino acids by mild hydrolysis with sodium hydroxide resulted in a material that was cross-reactive with the native, type d polymer. The base-treated, type d polysaccharide was not observed to cross-react with either the H. influenzae type e or Escherichia coli K7 capsular polysaccharide, both of which are structurally similar to type d.