Synthesis and Immunogenicity of a Methyl Rhamnan Pentasaccharide Conjugate from Pseudomonas aeruginosa A-Band Polysaccharide.

Pseudomonas aeruginosa was added to the World Health Organization's priority pathogen list for research and development of new antibiotics in 2017. Alongside the development of new antibiotics to fight antimicrobial-resistant P. aeruginosa, vaccines would be an appealing addition to the toolbox health professionals have against this bacteria, which causes life-threatening respiratory infections. Recently, the structure of a novel immunogenic terminal carbohydrate moiety on the cell surface of P. aeruginosa was elucidated, consisting of a 3-O-methyl (1→4)-α-d-rhamnan pentasaccharide. As isolating this oligosaccharide from P. aeruginosa in sufficient amounts for producing a conjugate vaccine is challenging, herein we describe the synthesis of 3-O-methyl d-rhamnose oligosaccharide. We also report the conjugation of the synthetic pentasaccharide to human serum albumin and its resulting immunogenicity.

Structural Characterization and Evaluation of an Epitope at the Tip of the A-Band Rhamnan Polysaccharide of Pseudomonas aeruginosa.

Pseudomonas aeruginosa produces a variety of cell surface glycans. Previous studies identified a common polysaccharide (PS) antigen often termed A-band PS that was composed of a neutral d-rhamnan trisaccharide repeating unit as a relatively conserved cell surface carbohydrate. However, nuclear magnetic resonance (NMR) spectra and chemical analysis of A-PS preparations showed the presence of several additional components. Here, we report the characterization of the carbohydrate component responsible for these signals. The carbohydrate antigen consists of an immunogenic methylated rhamnan oligosaccharide at the nonreducing end of the A-band PS. Initial studies performed with the isolated antigen permitted the production of conjugates that were used to immunize mice and rabbits and generate monoclonal and polyclonal antibodies. The polyclonal antibodies were able to recognize the majority of P. aeruginosa strains in our collection, and three monoclonal antibodies were generated, one of which was able to recognize and facilitate opsonophagocytic killing of a majority of P. aeruginosa strains. This monoclonal antibody was able to recognize all P. aeruginosa strains in our collection that includes clinical and serotype strains. Synthetic oligosaccharides (mono- to pentasaccharides) representing the terminal 3-O-methyl d-rhamnan were prepared, and the trisaccharide was identified as the antigenic determinant required to effectively mimic the natural antigen recognized by the broadly cross-reactive monoclonal antibody. These data suggest that there is considerable promise in this antigen as a vaccine or therapeutic target.

The capsular polysaccharides of Pasteurella multocida serotypes B and E: Structural, genetic and serological comparisons.

We describe the structural characterization of the capsular polysaccharides (CPSs) of Pasteurella multocida serotypes B and E. CPS was isolated following organic solvent precipitation of the supernatant from flask grown cells. Structural analysis utilizing nuclear magnetic resonance spectroscopy enabled the determination of the CPS structures and revealed significant structural similarities between the two serotypes, but also provided an explanation for the serological distinction. This observation was extended by the development of polyclonal sera to the glycoconjugate of serotype B CPS that corroborated the structural likenesses and differences. Finally, identification of these structures enabled a more comprehensive interrogation of the genetic loci and prediction of roles for some of the encoded proteins in repeat unit biosynthesis.

Structural analysis of the lipopolysaccharide O-antigen from Fusobacterium nucleatum strain CC 7/3 JVN3 C1 and development of a mouse monoclonal antibody specific to the O-antigen.

Fusobacterium nucleatum is becoming increasingly recognised as an emerging pathogen, gaining attention as a potential factor for exacerbating colorectal cancer and is strongly linked with pregnancy complications including pre-term and still births. Little is known about the virulence factors of this organism; thus, we have initiated studies to examine the bacterium's surface glycochemistry. In an effort to characterise the surface carbohydrates of F. nucleatum, the aims of this study were to investigate the structure of the lipopolysaccharide (LPS) O-antigen of the cancer-associated isolate F. nucleatum strain CC 7/3 JVN3 C1 (hereafter C1) and to develop monoclonal antibodies (mAbs) to the LPS O-antigen that may be beneficial to the growing field of F. nucleatum research. In this study, we combined several technologies, including nuclear magnetic resonance (NMR) spectroscopy, to elucidate the structure of the LPS O-antigen repeat unit as -[-4-ß-Gal-3-α-FucNAc4N-4-α-NeuNAc-]-. We have previously identified this structure as the LPS O-antigen repeat unit from strain 10953. In this present study, we developed a mAb to the C1 LPS O-antigen and confirmed the mAbs cross-reactivity to the 10953 strain, thus confirming the structural identity.

Utilizing CMP-Sialic Acid Analogs to Unravel Neisseria gonorrhoeae Lipooligosaccharide-Mediated Complement Resistance and Design Novel Therapeutics.

Neisseria gonorrhoeae deploys a novel immune evasion strategy wherein the lacto-N-neotetraose (LNnT) structure of lipooligosaccharide (LOS) is capped by the bacterial sialyltransferase, using host cytidine-5'-monophosphate (CMP)-activated forms of the nine-carbon nonulosonate (NulO) sugar N-acetyl-neuraminic acid (Neu5Ac), a sialic acid (Sia) abundant in humans. This allows evasion of complement-mediated killing by recruiting factor H (FH), an inhibitor of the alternative complement pathway, and by limiting classical pathway activation ("serum-resistance"). We utilized CMP salts of six additional natural or synthetic NulOs, Neu5Gc, Neu5Gc8Me, Neu5Ac9Ac, Neu5Ac9Az, legionaminic acid (Leg5Ac7Ac) and pseudaminic acid (Pse5Ac7Ac), to define structural requirements of Sia-mediated serum-resistance. While all NulOs except Pse5Ac7Ac were incorporated into the LNnT-LOS, only Neu5Gc incorporation yielded high-level serum-resistance and FH binding that was comparable to Neu5Ac, whereas Neu5Ac9Az and Leg5Ac7Ac incorporation left bacteria fully serum-sensitive and did not enhance FH binding. Neu5Ac9Ac and Neu5Gc8Me rendered bacteria resistant only to low serum concentrations. While serum-resistance mediated by Neu5Ac was associated with classical pathway inhibition (decreased IgG binding and C4 deposition), Leg5Ac7Ac and Neu5Ac9Az incorporation did not inhibit the classical pathway. Remarkably, CMP-Neu5Ac9Az and CMP-Leg5Ac7Ac each prevented serum-resistance despite a 100-fold molar excess of CMP-Neu5Ac in growth media. The concomitant presence of Leg5Ac7Ac and Neu5Ac on LOS resulted in uninhibited classical pathway activation. Surprisingly, despite near-maximal FH binding in this instance, the alternative pathway was not regulated and factor Bb remained associated with bacteria. Intravaginal administration of CMP-Leg5Ac7Ac to BALB/c mice infected with gonorrhea (including a multidrug-resistant isolate) reduced clearance times and infection burden. Bacteria recovered from CMP-Leg5Ac7Ac-treated mice were sensitive to human complement ex vivo, simulating in vitro findings. These data reveal critical roles for the Sia exocyclic side-chain in gonococcal serum-resistance. Such CMP-NulO analogs may provide a novel therapeutic strategy against the global threat of multidrug-resistant gonorrhea.

Characterization of a trifunctional glucosyltransferase essential for Moraxella catarrhalis lipooligosaccharide assembly.

The human respiratory tract pathogen Moraxella catarrhalis expresses lipooligosaccharides (LOS), glycolipid surface moieties that are associated with enhanced colonization and virulence. Recent studies have delineated the major steps required for the biosynthesis and assembly of the M. catarrhalis LOS molecule. We previously demonstrated that the glucosyltransferase enzyme Lgt3 is responsible for the addition of at least one glucose (Glc) molecule, at the ß-(1-4) position, to the inner core of the LOS molecule. Our data further suggested a potential multifunctional role for Lgt3 in LOS biosynthesis. The studies reported here demonstrate that the Lgt3 enzyme possesses two glycosyltransferase domains (A1 and A2) similar to that of other bifunctional glycosyltransferase enzymes involved in surface polysaccharide biosynthesis in Escherichia coli, Pasteurella multocida and Streptococcus pyogenes. Each Lgt3 domain contains a conserved DXD motif, shown to be involved in the catalytic activity of other glycosyltransferases. To determine the function of each domain, A1 (N-terminal), A2 (C-terminal) and double A1A2 site-directed DAD to AAA mutants were constructed and the resulting LOS phenotypes of these modified strains were analyzed. Our studies indicate that the Lgt3 N-terminal A1 catalytic domain is responsible for the addition of the first ß-(1-3) Glc to the first Glc on the inner core. The C-terminal catalytic domain A2 then adds the ß-(1-4) Glc and the ß-(1-6) Glc, confirming the bifunctional nature of this domain. The results from these experiments demonstrate that Lgt3 is a novel, multifunctional transferase responsible for the addition of three Glcs with differing linkages onto the inner core of M. catarrhalis LOS.

Requirement of the lipopolysaccharide O-chain biosynthesis gene wxocB for type III secretion and virulence of Xanthomonas oryzae pv. Oryzicola.

Xanthomonas oryzae pv. oryzicola causes bacterial leaf streak of rice. A mutant disrupted in wxocB, predicted to encode an enzyme for lipopolysaccharide (LPS) synthesis, was previously shown to suffer reduced virulence. Here, we confirm a role for wxocB in virulence and demonstrate its requirement for LPS O-chain assembly. Structure analysis indicated that wild-type LPS contains a polyrhamnose O chain with irregular, variant residues and a core oligosaccharide identical to that of other Xanthomonas spp. and that the wxocB mutant lacks the O chain. The mutant also showed moderate impairment in exopolysaccharide (EPS) production, but comparison with an EPS-deficient mutant demonstrated that this impairment could not account entirely for the reduced virulence. The wxocB mutant was not detectably different from the wild type in its induction of pathogenesis-related rice genes, type II secretion competence, flagellar motility, or resistance to two phytoalexins or resveratrol, and it was more, not less, resistant to oxidative stress and a third phytoalexin, indicating that none of these properties is involved. The mutant was more sensitive to SDS and to novobiocin, so increased sensitivity to some host-derived antimicrobials cannot be ruled out. However, the mutant showed a marked decrease in type III secretion into plant cells. This was not associated with any change in expression of genes for type III secretion or the ability to attach to plant cells in suspension. Thus, virulence of the wxocB mutant is likely reduced due primarily to a direct, possibly structural, effect of the loss of the O chain on type III delivery of effector proteins.

The K1 capsular polysaccharide from Acinetobacter baumannii is a potential therapeutic target via passive immunization.

The emergence of extremely resistant and panresistant Gram-negative bacilli, such as Acinetobacter baumannii, requires consideration of nonantimicrobial therapeutic approaches. The goal of this report was to evaluate the K1 capsular polysaccharide from A. baumannii as a passive immunization target. Its structure was determined by a combination of mass spectrometric and nuclear magnetic resonance (NMR) techniques. Molecular mimics that might raise the concern for autoimmune disease were not identified. Immunization of CD1 mice demonstrated that the K1 capsule is immunogenic. The monoclonal antibody (MAb) 13D6, which is directed against the K1 capsule from A. baumannii, was used to determine the seroprevalence of the K1 capsule in a collection of 100 A. baumannii strains. Thirteen percent of the A. baumannii isolates from this collection were seroreactive to MAb 13D6. Opsonization of K1-positive strains, but not K1-negative strains, with MAb 13D6 significantly increased neutrophil-mediated bactericidal activity in vitro (P < 0.05). Lastly, treatment with MAb 13D6 3 and 24 h after bacterial challenge in a rat soft tissue infection model resulted in a significant decrease in the growth/survival of a K1-positive strain compared to that of a K1-negative strain or to treatment with a vehicle control (P < 0.0001). These data support the proof of principle that the K1 capsule is a potential therapeutic target via passive immunization. Other serotypes require assessment, and pragmatic challenges exist, such as the need to serotype infecting strains and utilize serotype-specific therapy. Nonetheless, this approach may become an important therapeutic option with increasing antimicrobial resistance and a diminishing number of active antimicrobials.

Identification and characterization of a glycosyltransferase involved in Acinetobacter baumannii lipopolysaccharide core biosynthesis.

Although Acinetobacter baumannii has emerged as a significant cause of nosocomial infections worldwide, there have been few investigations describing the factors important for A. baumannii persistence and pathogenesis. This paper describes the first reported identification of a glycosyltransferase, LpsB, involved in lipopolysaccharide (LPS) biosynthesis in A. baumannii. Mutational, structural, and complementation analyses indicated that LpsB is a core oligosaccharide glycosyl transferase. Using a genetic approach, lpsB was compared with the lpsB homologues of several A. baumannii strains. These analyses indicated that LpsB is highly conserved among A. baumannii isolates. Furthermore, we developed a monoclonal antibody, monoclonal antibody 13C11, which reacts to an LPS core epitope expressed by approximately one-third of the A. baumannii clinical isolates evaluated to date. Previous studies describing the heterogeneity of A. baumannii LPS were limited primarily to structural analyses; therefore, studies evaluating the correlation between these surface glycolipids and pathogenesis were warranted. Our data from an evaluation of LpsB mutant 307::TN17, which expresses a deeply truncated LPS glycoform consisting of only two 3-deoxy-d-manno-octulosonic acid residues and lipid A, suggest that A. baumannii LPS is important for resistance to normal human serum and confers a competitive advantage for survival in vivo. These results have important implications for the role of LPS in A. baumannii infections.

Application of electrospray ionization with Fourier transform ion cyclotron resonance mass spectrometry for structural screening of core oligosaccharides from lipopolysaccharides of the bacteria Proteus.

Electrospray ionization with Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) was used for screening and structural elucidation of core oligosaccharides isolated from lipopolysaccharides of bacteria of the genus Proteus. Mass spectra allowed the determination of the molecular masses with high accuracy and the estimation of the chemical heterogeneity of the samples. They did not, however, provide sufficient information to identify structural details of the branched oligosaccharides. Therefore, various fragmentation techniques for determining such details were examined. Infrared multiphoton dissociation tandem mass spectrometry (IRMPD-MS/MS) experiments in negative ion mode resulted in cleavage between the structurally conserved inner core region and the variable outer core region. Positive ion capillary skimmer dissociation mass spectra showed numerous fragment ion peaks, including those corresponding to the subsequent cleavage of the glycosidic linkages starting from the non-reducing end of the oligosaccharide. Despite their complexity, these mass spectrometric studies allowed confirmation of previously determined Proteus lipopolysaccharide core structures, and identification of new related structures in other strains of these bacteria.

Temperature-dependent variations and intraspecies diversity of the structure of the lipopolysaccharide of Yersinia pestis.

Yersinia pestis spread throughout the Americas in the early 20th century, and it occurs predominantly as a single clone within this part of the world. However, within Eurasia and parts of Africa there is significant diversity among Y. pestis strains, which can be classified into different biovars (bv.) and/or subspecies (ssp.), with bv. orientalis/ssp. pestis most closely related to the American clone. To determine one aspect of the relatedness of these different Y. pestis isolates, the structure of the lipopolysaccharide (LPS) of four wild-type and one LPS-mutant Eurasian/African strains of Y. pestis was determined, evaluating effects of growth at mammalian (37 degrees C) or flea (25 degrees C) temperatures on the structure and composition of the core oligosaccharide and lipid A. In the wild-type clones of ssp. pestis, a single major core glycoform was synthesized at 37 degrees C whereas multiple core oligosaccharide glycoforms were produced at 25 degrees C. Structural differences occurred primarily in the terminal monosaccharides. Only tetraacyl lipid A was made at 37 degrees C, whereas at 25 degrees C additional pentaacyl and hexaacyl lipid A structures were produced. 4-Amino-4-deoxyarabinose levels in lipid A increased with lower growth temperatures or when bacteria were cultured in the presence of polymyxin B. In Y. pestis ssp. caucasica, the LPS core lacked D-glycero-D-manno-heptose and the content of 4-amino-4-deoxyarabinose showed no dependence on growth temperature, whereas the degree of acylation of the lipid A and the structure of the oligosaccharide core were temperature dependent. A spontaneous deep-rough LPS mutant strain possessed only a disaccharide core and a slightly variant lipid A. The diversity and differences in the structure of the Y. pestis LPS suggest important contributions of these variations to the pathogenesis of this organism, potentially related to innate and acquired immune recognition of Y. pestis and epidemiologic means to detect, classify, control and respond to Y. pestis infections.

Structural and serological characterisation of the O-antigenic polysaccharide of the lipopolysaccharide from Acinetobacter baumannii strain 24.

Extraction of dry bacteria of Acinetobacter baumannii strain 24 by phenol-water yielded a lipopolysaccharide (LPS) that was studied by serological methods and fatty acid analysis. After immunisation of BALB/c mice with this strain, monoclonal antibody S48-3-13 (IgG(3) isotype) was obtained, which reacted with the LPS in western blot and characterized it as S-form LPS. Degradation of the LPS in aqueous 1% acetic acid followed by GPC gave the O-antigenic polysaccharide, whose structure was determined by compositional analyses and NMR spectroscopy of the polysaccharide and O-deacylated polysaccharide as [carbohydrate structure: see text] where QuiN4N is 2,4-diamino-2,4,6-trideoxyglucose and GalNAcA 2-acetamido-2-deoxygalacturonic acid. The amino group at C-4 of the QuipN4N residues is acetylated in about 2/3 of LPS molecules and (S)-3-hydroxybutyrylated in the rest.

Role of the complement-lectin pathway in anaphylactoid reaction induced with lipopolysaccharide in mice.

We show that Proteus vulgaris O25 (PO25) lipopolysaccharide (LPS) induced an anaphylactoid reaction not only in wild-type and in lipid A non-responding mice but also in recombinase-activating gene-2-deficient (RAG-2(-/-)) and in mast cell-deficient (W/Wv) animals. Western blot analysis indicated that PO25 LPS bound to Ra-reactive factor (RaRF), the complex of mannan-binding lectins (MBL) and MBL-associated serine proteases. Binding of RaRF to PO25 LPS led to the activation of C4 component without participation of either C1 or Ig, via the lectin pathway. Relative concentration of RaRF and hemolytic activity in mouse serum decreased rapidly during the process of anaphylactoid reaction. A significant drop of MBL-A, but not MBL-C level was observed. Administrationwith antiserum to RaRF prevented animals from death as a consequence of the inhibition of interaction of RaRF with the carbohydrate target and complement activation. These results indicate that complement-lectin pathway activation is responsible for the anaphylactoid reaction induced with LPS in muramyldipeptide-primed mice. RaRF also activated fibrinogen in vitro suggesting the involvement of the coagulation system in the process investigated.

Structural investigation of the O-specific polysaccharides of Morganella morganii consisting of two higher sugars.

The lipopolysaccharide of the bacterium Morganella morganii (strain KF 1676, RK 4222) yielded two polysaccharides, PS1 and PS2, when subjected to mild acid degradation followed by GPC. The polysaccharides were studied by 1H and 13C NMR spectroscopy, including two-dimensional COSY, TOCSY, NOESY, 1H,(13)C HMQC, and HMBC experiments. Each polysaccharide was found to contain a disaccharide repeating unit consisting of two higher sugars, 5-acetamidino-7-acetamido-3,5,7,9-tetradeoxy-L-glycero-D-galacto-non-2-ulosonic acid (a derivative of 8-epilegionaminic acid, 8eLeg5Am7Ac) and 2-acetamido-4-C-(3'-carboxamide-2',2'-dihydroxypropyl)-2,6-dideoxy-D-galactose (shewanellose, She). The two polysaccharides differ only in the ring size of shewanellose and have the following structures:Shewanellose has been previously identified in a phenol-soluble polysaccharide from Shewanella putrefaciens A6, which shows a close structural similarity to PS2.

The core structure of the lipopolysaccharide from the causative agent of plague, Yersinia pestis.

The rough-type lipopolysaccharide (LPS) of the plague pathogen, Yersinia pestis, was studied after mild-acid and strong-alkaline degradations by chemical analyses, NMR spectroscopy and electrospray-ionization mass spectrometry, and the following structure of the core region was determined:where L-alpha-D-Hep stands for L-glycero-alpha-D-manno-heptose, Sug1 for either 3-deoxy-alpha-D-manno-oct-2-ulosonic acid (alpha-Kdo) or D-glycero-alpha-D-talo-oct-2-ulosonic acid (alpha-Ko), and Sug2 for either beta-D-galactose or D-glycero-alpha-D-manno-heptose. A minority of the LPS molecules lacks GlcNAc.

The structure of the carbohydrate backbone of the lipopolysaccharide from Acinetobacter baumannii strain ATCC 19606.

The chemical structure of the phosphorylated carbohydrate backbone of the lipopolysaccharide (LPS) from Acinetobacter baumannii strain ATCC 19606 was investigated by chemical analysis and NMR spectroscopy of oligosaccharides obtained after deacylation or mild acid hydrolysis. From the combined information the following carbohydrate backbones can be deduced: where R1 = H and R2 = alpha-Glcp-(1-->2)-beta-Glcp-(1-->4)-beta-Glcp-(1-->4)-beta-Glcp-(1 as major and R1 = Ac and R2 = H as minor products. All monosaccharides are d-configured. Also, smaller oligosaccharide phosphates were identified that are thought to represent degradation products of the above structures.