Characterization of novel structural features in the lipopolysaccharide of nondisease associated nontypeable Haemophilus influenzae

The Eukaryotic Elongation Factor 1 Alpha (eEF1α) from the Parasite Leishmania infantum Is Modified with the Immunomodulatory Substituent Phosphorylcholine (PC)

Proteins and glycolipids have been found to be decorated with phosphorylcholine (PC) both in protozoa and nematodes that parasitize humans and animals. PC epitopes can provoke various effects on immune cells leading to an immunomodulation of the host’s immune system that allows long-term persistence of the parasites. So far, only a limited number of PC-modified proteins, mainly from nematodes, have been identified. Infections caused by Leishmania spp. (e.g., L. infantum in southern Europe) affect about 12 million people worldwide and are characterized by a wide spectrum of clinical forms in humans, ranging from cutaneous to fatal visceral leishmaniasis. To establish and maintain the infection, these protozoa are dependent on the secretion of effector molecules into the host for modulating their immune system. In this project, we analyzed the PC modification of L. infantum promastigotes by 2D-gel based proteomics. Western blot analysis with the PC-specific antibody TEPC-15 revealed one PC-substituted protein in this organism, identified as eEF1α. We could demonstrate that the binding of eEF1α to one of its downstream effectors is dependent on its PC-modification. In this study we provide evidence that in this parasite the modification of eEF1α with PC may be essential for its function as an important virulence factor.

Structural characterization of bacterial lipopolysaccharides with mass spectrometry and on- and off-line separation techniques

The focus of this review is the application of mass spectrometry to the structural characterization of bacterial lipopolysaccharides (LPSs), also referred to as "endotoxins," because they elicit the strong immune response in infected organisms. Recently, a wide variety of MS-based applications have been implemented to the structure elucidation of LPS. Methodological improvements, as well as on- and off-line separation procedures, proved the versatility of mass spectrometry to study complex LPS mixtures. Special attention is given in the review to the tandem mass spectrometric methods and protocols for the analyses of lipid A, the endotoxic principle of LPS. We compare and evaluate the different ionization techniques (MALDI, ESI) in view of their use in intact R- and S-type LPS and lipid A studies. Methods for sample preparation of LPS prior to mass spectrometric analysis are also described. The direct identification of intrinsic heterogeneities of most intact LPS and lipid A preparations is a particular challenge, for which separation techniques (e.g., TLC, slab-PAGE, CE, GC, HPLC) combined with mass spectrometry are often necessary. A brief summary of these combined methodologies to profile LPS molecular species is provided.

Profiling LPS glycoforms of non-typeable Haemophilus influenzae by multiple-stage tandem mass spectrometry

Non-typeable (acapsular) Haemophilus influenzae (NTHi) is a major cause of otitis media accounting for 25-30% of all cases of the disease. Lipopolysaccharide (LPS) is an essential and exposed component of the H. influenzae cell wall. A characteristic feature of H. influenzae LPS is the extensive inter-strain and intra-strain heterogeneity of glycoform structure which is key to the role of the molecule in both commensal and disease-causing behavior of the bacterium. However, to characterize LPS structure unambiguously is a major challenge due to the extreme heterogeneity of glycoforms that certain strains express. A powerful tool for obtaining sequence and branching information is multiple-stage tandem ESI-MS (ESI-MS( n )) performed on dephosphorylated and permethylated oligosaccharide material using an ESI-quadrupole ion trap mass spectrometer. In general, permethylation increases the MS response by several orders of magnitude and sequence information is readily obtained since methyl tagging allows the distinction between fragment ions generated by cleavage of a single glycosidic bond and inner fragments resulting from the rupture of two glycosidic linkages. Using this approach we are now able to identify all isomeric glycoforms in very heterogeneous LPS preparations.

Immunomodulation by phosphocholine--biosynthesis, structures and immunological implications of parasitic PC-epitopes

Phosphocholine (PC) as a small haptenic molecule present on antigens of parasites can provoke various effects on immune cells leading to immunomodulation of the host's immune system. This immunomodulation not only allows long-term persistence but also prevents severe pathology due to down-regulation of cellular immune responses. Additionally, PC plays an important role for development and fertility of the parasites. To fully understand the mechanisms of immunomodulation the detailed knowledge of the biosynthesis of the PC-epitopes, their molecular structure and biological function has to be elucidated. The implication of parasite-specific transferases in the biosynthesis of the PC-epitopes and the sensitivity of parasites towards disruption of the choline metabolism offers new perspectives for the development of anti-parasitic drugs and therapies. Furthermore, the immunomodulation provoked by PC-epitopes preventing inflammatory reactions may be useful in the treatment of inflammatory diseases. This review summarizes the current knowledge on the biosynthesis of PC-epitopes, their structures and immunological implications.

Profiling structural elements of short-chain lipopolysaccharide of non-typeable Haemophilus influenzae

Lipopolysaccharide (LPS) is a major virulence determinant of the human bacterial pathogen Haemophilus influenzae. A characteristic feature of H. influenzae LPS is the extensive intra- and inter-strain heterogeneity of glycoform structure which is key to the role of the molecule in both commensal and disease-causing behaviour of the bacterium. The chemical composition of non-typeable Haemophilus influenzae (NTHi) LPS is highly diverse. It contains a number of different monosaccharides (Neu5Ac, L-glycero-D-manno heptose, D-glycero-D-manno heptose, Kdo, D-Glc, D-Gal, D-GlcNAc, D-GalNAc) and non-carbohydrate substituents. Prominent non-carbohydrate components are O-acetyl groups, glycine and phosphates. We now know that sialic acid (N-acetylneuraminic acid or Neu5Ac) and certain oligosaccharide extensions are important in the pathogenesis of NTHi; however, the biological implications for many of the various features are still unknown. Electrospray ionization mass spectrometry in combination with separation techniques like CE and HPLC is an indispensable tool in profiling glycoform populations in heterogeneous LPS samples. Mass spectrometry is characterized by its extreme sensitivity. Trace amounts of glycoforms expressing important virulence determinants can be detected and characterized on minute amounts of material. The present review focuses on LPS structures and mass spectrometric methods which enable us to profile these in complex mixtures.

Capillary electrophoresis-based methods for the determination of lipids--a review

Capillary electrophoresis (CE) is a high-resolution technique for the separation of complex biological and chemical mixtures. CE continues to emerge as a powerful tool in the determination of lipids. Here we review the analytical potential of CE for the determination of a wide range of lipids. The different classes of lipids are introduced, and the different modes of CE and optimization methods for the separation of lipids are described. The advantages and disadvantages of the different modes of CE compared to traditional methods like gas chromatography (GC) and liquid chromatography (LC) in the determination of lipids are discussed. Finally, the potential of CE in the determination of lipids in the future is illustrated.

Application of capillary electrophoresis mass spectrometry and liquid chromatography multiple-step tandem electrospray mass spectrometry to profile glycoform expression during Haemophilus influenzae pathogenesis in the chinchilla model of experimental otitis media

Otitis media caused by nontypeable Haemophilus influenzae (NTHi) is a common and recurrent bacterial infection of childhood. The structural variability and diversity of H. influenzae lipopolysaccharide (LPS) glycoforms are known to play a significant role in the commensal and disease-causing behavior of this pathogen. In this study, we determined LPS glycoform populations from NTHi strain 1003 during the course of experimental otitis media in the chinchilla model of infection by mass spectrometric techniques. Building on an established structural model of the major LPS glycoforms expressed by this NTHi strain in vitro (M. Månsson, W. Hood, J. Li, J. C. Richards, E. R. Moxon, and E. K. Schweda, Eur. J. Biochem. 269:808-818, 2002), minor isomeric glycoform populations were determined by liquid chromatography multiple-step tandem electrospray mass spectrometry (LC-ESI-MS(n)). Using capillary electrophoresis ESI-MS (CE-ESI-MS), we determined glycoform profiles for bacteria from direct middle ear fluid (MEF) samples. The LPS glycan profiles were essentially the same when the MEF samples of 7 of 10 animals were passaged on solid medium (chocolate agar). LC-ESI-MS(n) provided a sensitive method for determining the isomeric distribution of LPS glycoforms in MEF and passaged specimens. To investigate changes in LPS glycoform distribution during the course of infection, MEF samples were analyzed at 2, 5, and 9 days postinfection by CE-ESI-MS following minimal passage on chocolate agar. As previously observed, sialic acid-containing glycoforms were detected during the early stages of infection, but a trend toward more-truncated and less-complex LPS glycoforms that lacked sialic acid was found as disease progressed.

Structural elucidation of lipopolysaccharide core oligosaccharides from lic1 and lic1/lic2 mutants of Haemophilus influenzae type b strain Eagan

The structures of lipopolysaccharides (LPSs) of lic1 and lic1/lic2 mutants from Haemophilus influenzae type b strain Eagan (RM153) were investigated using methylation analysis, electrospray ionization - mass spectrometry, and nuclear magnetic resonance spectroscopy on O-deacylated, O- and N-deacylated core oligosaccharide (OS); and deacylated, dephosphorylated, and terminally reduced samples. The backbone OS derived from the major LPS glycoforms were determined to consist of the inner-core triheptosyl unit, L-alpha-D-Hepp-(1-2)-L-alpha-D-Hepp-(1-3)-L-alpha-D-Hepp-(1-, common to all H. influenzae strains investigated to date that is linked to the lipid A region of the molecule via a Kdo residue to which beta-D-Glcp and beta-D-Galp residues are attached in 1,4 and 1,2 linkages to the proximal (HepI) and distal (HepIII) heptose residues, respectively. It was found that the lic1 mutant predominately elaborates the Hex4 LPS glycoforms previously identified in the parent strain where a beta-D-Glcp-(1-4)-alpha-D-Glcp unit is linked in a 1,3 linkage to the central heptose (HepII) of the triheptosyl moiety. The lic1 locus consists of 4 genes (lic1A to lic1D) in a single transcriptional unit that directs phase variable expression of phosphocholine. The lic1A gene is phased off in the RM153 isolate of strain Eagan. LPS from the double mutant, lic1/lic2 had a similar structure to that of lic1 mutant except that there was no chain extension from the central heptose in the inner core (HepII). The lic2 locus consists of 4 genes (lic2A to lic2D). Our structural data were consistent with the proposed function of lic2C, providing the first definitive evidence for its role as the glycosyltransferase required for chain initiation from HepII. The presence of an O-acetyl group at O-3 of the distal heptose (HepIII) was elucidated by 1H NMR on the mild acid liberated core OS samples.

Duplicate copies of lic1 direct the addition of multiple phosphocholine residues in the lipopolysaccharide of Haemophilus influenzae

The genes of the lic1 operon (lic1A to lic1D) are responsible for incorporation of phosphocholine (PCho) into the lipopolysaccharide (LPS) of Haemophilus influenzae. PCho plays a multifaceted role in the commensal and pathogenic lifestyles of a range of mucosal pathogens, including H. influenzae. Structural studies of the LPS of nontypeable H. influenzae (NTHI) have revealed that PCho can be linked to a hexose on any one of the oligosaccharide chain extensions from the conserved inner core triheptosyl backbone. In a collection of NTHI strains we found several strains in which there were two distinct but variant lic1D DNA sequences, genes predicted to encode the transferase responsible for directing the addition of PCho to LPS. The same isolates were also found to express concomitantly two PCho residues at distinct positions in their LPS. In one such NTHI isolate, isolate 1158, structural analysis of LPS from lic1 mutants confirmed that each of the two copies of lic1D directs the addition of PCho to a distinct location on the LPS. One position for PCho addition is a novel heptose, which is part of the oligosaccharide extension from the proximal heptose of the LPS inner core. Modification of the LPS by addition of two PCho residues resulted in increased binding of C-reactive protein and had consequential effects on the resistance of the organism to the killing effects of normal human serum compared to the effects of glycoforms containing one or no PCho. When bound, C-reactive protein leads to complement-mediated killing, indicating the potential biological significance of multiple PCho residues.

Novel globoside-like oligosaccharide expression patterns in nontypeable Haemophilus influenzae lipopolysaccharide

We report the novel pattern of lipopolysaccharide (LPS) expressed by two disease-associated nontypeable Haemophilus influenzae strains, 1268 and 1200. The strains express the common structural motifs of H. influenzae; globotetraose [beta-d-GalpNAc-(1-->3)-alpha-d-Galp-(1-->4)-beta-d-Galp-(1-->4)-beta-d-Glcp] and its truncated versions globoside [alpha-d-Galp-(1-->4)-beta-d-Galp-(1-->4)-beta-d-Glcp] and lactose [beta-d-Galp-(1-->4)-beta-d-Glcp] linked to the terminal heptose (HepIII) and the corresponding structures with an alpha-d-Glcp as the reducing sugar linked to the middle heptose (HepII) in the same LPS molecule. Previously these motifs had been found linked only to either the proximal heptose (HepI) or HepIII of the triheptosyl inner-core moiety l-alpha-d-Hepp-(1-->2)-[PEtn-->6]-l-alpha-d-Hepp-(1-->3)-l-alpha-d-Hepp-(1-->5)-[PPEtn-->4]-alpha-Kdo-(2-->6)-lipid A. This novel finding was obtained by structural studies of LPS using NMR techniques and ESI-MS on O-deacylated LPS and core oligosaccharide material, as well as electrospray ionization-multiple-step tandem mass spectrometry on permethylated dephosphorylated oligosaccharide material. A lpsA mutant of strain 1268 expressed LPS of reduced complexity that facilitated unambiguous structural determination. Using capillary electrophoresis-ESI-MS/MS we identified sialylated glycoforms that included sialyllactose as an extension from HepII, this is a further novel finding for H. influenzae LPS. In addition, each LPS was found to carry phosphocholine and O-linked glycine. Nontypeable H. influenzae strain 1200 expressed identical LPS structures to 1268 with the difference that strain 1200 LPS had acetates substituting HepIII, whereas strain 1268 LPS has glycine at the same position.

Application of capillary electrophoresis mass spectrometry to the characterization of bacterial lipopolysaccharides

Capillary electrophoresis (CE) is a high-resolution technique for the separation of complex biological mixtures and has been widely applied to biological analyses. The coupling of capillary electrophoresis with mass spectrometry (MS) provides a powerful approach for rapid identification of target analytes present at trace levels in biological matrices, and for structural characterization of complex biomolecules. Here we review the analytical potential of combined capillary electrophoresis electrospray mass spectrometry (CE-MS) for the analysis of bacterial lipopolysaccharides (LPS). This hyphened methodology facilitates the determination of closely related LPS glycoform and isoform families by exploiting differences in their unique molecular conformations and ionic charge distributions by electrophoretic separation. On-line CE-MS also provides an additional avenue to improve detection limits, which has been successfully applied to directly probe oligosaccharide LPS glycoform populations of bacteria isolated from infected animal models without the need for further passage.

Biofilm growth increases phosphorylcholine content and decreases potency of nontypeable Haemophilus influenzae endotoxins

Nontypeable Haemophilus influenzae (NTHI) is a common respiratory commensal and opportunistic pathogen. NTHI is normally contained within the airways by host innate defenses that include recognition of bacterial endotoxins by Toll-like receptor 4 (TLR4). NTHI produces lipooligosaccharide (LOS) endotoxins which lack polymeric O side chains and which may contain host glycolipids. We recently showed that NTHI biofilms contain variants with sialylated LOS glycoforms that are essential to biofilm formation. In this study, we show that NTHI forms biofilms on epithelial cell layers. Confocal analysis revealed that sialylated variants were distributed throughout the biofilm, while variants expressing phosphorylcholine (PCho) were found within the biofilm. Consistent with this observation, PCho content of LOS purified from NTHI biofilms was increased compared to LOS from planktonic cultures. Hypothesizing that the observed changes in endotoxin composition could affect bioactivity, we compared inflammatory responses to NTHI LOS purified from biofilm and planktonic cultures. Our results show that endotoxins from biofilms induced weaker host innate responses. While we observed a minimal effect of sialylation on LOS bioactivity, there was a significant decrease in bioactivity associated with PCho substitutions. We thus conclude that biofilm growth increases the proportion of PCho+ variants in an NTHI population, resulting in a net decrease in LOS bioactivity. Thus, in addition to their well-documented resistance phenotypes, our data show that biofilm communities of NTHI bacteria contain variants that evoke less potent host responses.

Complex O-acetylation in non-typeable Haemophilus influenzae lipopolysaccharide: evidence for a novel site of O-acetylation

The structure of the lipopolysaccharide (LPS) of non-typeable Haemophilus influenzae strain 723 has been elucidated using NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS) on O-deacylated LPS and core oligosaccharide material (OS), as well as ESI-MSn on permethylated dephosphorylated OS. It was found that the LPS contains the common structural element of H. influenzae, l-alpha-D-Hepp-(1-->2)-[PEtn-->6]-l-alpha-D-Hepp-(1-->3)-[beta-D-Glcp-(1-->4)]-l-alpha-D-Hepp-(1-->5)-[PPEtn-->4]-alpha-Kdo-(2-->6)-Lipid A, in which the beta-D-Glcp residue (GlcI) is substituted by phosphocholine at O-6 and the distal heptose residue (HepIII) by PEtn at O-3, respectively. In a subpopulation of glycoforms O-2 of HepIII was substituted by beta-D-Galp-(1-->4)-beta-D-Glcp-(1--> or beta-D-Glcp-(1-->. Considerable heterogeneity of the LPS was due to the extent of substitution by O-acetyl groups (Ac) and ester-linked glycine of the core oligosaccharide. The location for glycine was found to be at Kdo. Prominent acetylation sites were found to be at GlcI, HepIII, and the proximal heptose (HepI) residue of the triheptosyl moiety. Moreover, GlcI was acetylated at O-3 and/or O-4 and HepI was acetylated at O-2 as evidenced by capillary electrophoresis ESI-MSn in combination with NMR analyses. This is the first study to show that an acetyl group can substitute HepI of the inner-core region of H. influenzae LPS.

Structural investigation of lipopolysaccharides from nontypeable Haemophilus influenzae: investigation of inner-core phosphoethanolamine addition in NTHi strain 981

LPS of NTHi comprises a conserved tri-l-glycero-D-manno-heptosyl inner-core moiety (l-alpha-D-Hepp-(1-->2)-[PEtn-->6]-l-alpha-D-Hepp-(1-->3)-[beta-D-Glcp-(1-->4)]-l-alpha-D-Hepp-(1-->5)-alpha-Kdop) in which addition of PEtn to the central heptose (HepII) in strain Rd is controlled by the gene lpt6. It was recently shown that NTHi strain 981 contains an additional PEtn linked to O-3 of the terminal heptose of the inner-core moiety (HepIII). In order to establish whether lpt6 is also involved in adding PEtn to HepIII, lpt6 in strain 981 was inactivated. The structure of the LPS of the resulting mutant strain 98llpt6 was investigated by MS and NMR techniques by which it was confirmed that the lpt6 gene product is responsible for addition of PEtn to O-6 of HepII in strain 981. However, it is not responsible for adding PEtn to O-3 of HepIII since the 981lpt6 mutant still had full substitution with PEtn at HepIII.

Structural analysis of the lipopolysaccharide of Pasteurella multocida strain VP161: identification of both Kdo-P and Kdo-Kdo species in the lipopolysaccharide

The structure of the lipopolysaccharide from the Pasteurella multocida strain VP161 was elucidated. The lipopolysaccharide was subjected to a variety of degradative procedures. The structures of the purified products were established by monosaccharide and methylation analyses, NMR spectroscopy and mass spectrometry. The following structures for the lipopolysaccharides were determined on the basis of the combined data from these experiments. [structure: see text]. Based on the NMR data, all sugars were found in pyranose ring forms, and Kdo is 2-keto-3-deoxy-octulosonic acid, L-alpha-D-Hep is L-glycero-D-manno-heptose, PPEtn is pyrophosphoethanolamine and PCho is phosphocholine. Intriguingly, when the O- and fully deacylated LPS was examined, it was evident that there was variability in the arrangement of the Kdo region of the molecule. Glycoforms were found with a Kdo-P moiety, as well as glycoforms elaborating a Kdo-Kdo group. Furthermore the Glc II residue was not attached to Hep I when two Kdo residues were present, but it was attached when the Kdo-P arrangement was elaborated, suggesting a biosynthetic incompatibility due to either steric hindrance or an inappropriate acceptor conformation. This variation in the Kdo region of the LPS was also observed in several other Pasteurella multocida strains investigated including the genome strain Pm70.

An Alternate Pattern for Globoside Oligosaccharide Expression in Haemophilus influenzae Lipopolysaccharide: Structural Diversity in Nontypeable Strain 1124

Common structural motifs of Haemophilus influenzae lipopolysaccharide (LPS) are globotetraose [beta-d-GalpNAc-(1-->3)-alpha-d-Galp-(1-->4)-beta-d-Galp-(1-->4)-beta-d-Glcp] and its truncated versions globoside [alpha-d-Galp-(1-->4)-beta-d-Galp-(1-->4)-beta-d-Glcp] and lactose [beta-d-Galp-(1-->4)-beta-d-Glcp] linked to the terminal heptose (HepIII) of the triheptosyl inner-core moiety l-alpha-d-Hepp-(1-->2)-[PEA-->6]-l-alpha-d-Hepp-(1-->3)-l-alpha-d-Hepp-(1-->5)-[PPEA-->4]-alpha-Kdo-(2-->6)-lipid A. We report here structural studies of LPS from nontypeable H. influenzae strain 1124 expressing these motifs linked to both the proximal heptose (HepI) and HepIII at the same time. This novel finding was obtained by structural studies of LPS using NMR techniques and electrospray ionization mass spectrometry (ESI-MS) on O-deacylated LPS and core oligosaccharide material (OS) as well as ESI-MS(n)() on permethylated dephosphorylated OS. The use of defined mutants allowed us to confirm structures unambiguously and understand better the biosynthesis of each of the globotetraose units. We found that lgtC is involved in the expression of alpha-d-Galp-(1-->4)-beta-d-Galp in both extensions, whereas lic2A directs only the expression of beta-d-Galp-(1-->4)-beta-d-Glcp when linked to HepIII. The LPS of NTHi strain 1124 contained sialylated glycoforms that were identified by CE-ESI-MS/MS. A common sialylated structure in H. influenzae LPS is sialyllactose linked to HepIII. This structure exists in strain 1124. However, results for the lpsA mutant indicate that sialyllactose extends from HepI as well, a molecular environment for sialyllactose in H. influenzae that has not been reported previously. In addition, the LPS was found to carry phosphorylcholine, O-linked glycine, and a third PEA group which was linked to O3 of HepIII.

Electrophoretic and mass spectrometric strategies for profiling bacterial lipopolysaccharides

Capillary electrophoresis (CE) is a high-resolution separation technique that has been widely used for trace analysis in biological samples. On-line capillary electrophoresis-electrospray mass spectrometry (CE-MS) was developed for the analysis of lipopolysaccharide (LPS) glycoforms from the gram-negative bacteria, Haemophilus influenzae. In this paper, we report on the application of CE-MS to characterize structural differences in O-deacylated LPS samples from H. influenzae strains Rd 11.7 and 375.1. The resolution capability of on-line CE-MS was first demonstrated by analysis of a complex LPS mixture from H. influenzae strain Rd 11.7. This strain contains a mixture of isomeric glycoforms differing in the number and positions of hexose moieties. Sialic acid containing glycoforms were also determined. Structural features of LPS from a lic1 mutant of H. influenzae strain 375 (375.1) were studied using on-line CE-MS/MS. With the separation provided by CE, two isomeric glycoforms differing in the location of phosphoethanolamine substituents were characterized by tandem mass spectrometry.

Mapping Bacterial Glycolipid Complexity Using Capillary Electrophoresis and Electrospray Mass Spectrometry

This chapter presents the application of capillary electrophoresis coupled to electrospray mass spectrometry (CE-ES-MS) for the analysis of complex bacterial lipopolysaccharides (LPS) from pathogenic strains of Haemophilus influenzae and Neisseria meningitidis. A discussion is included of the development of electrophoretic conditions conducive to trace-level enrichment and separation of closely related glycoforms and isoforms, which provided sensitive detection of glycolipids from as little as five bacterial colonies. The chapter also describes the use of mixed MS scanning functions to aid the identification of specific functionalities and immunodeterminants of LPS, such as pyrophosphoethanolamine, phosphocholine, and N-acetyl neuraminic acid (Neu5Ac), which represent less than 2% of the overall LPS population. The combination of high-resolution capillary electrophoresis with sensitive tandem mass spectrometry (MS/MS) provides a unique analytical tool to probe the subtle structural changes resulting from oligosaccharide branching and location of substituted LPS isoforms. The ability to detect a diverse LPS population over a wide dynamic range of expression using CE-MS enables the correlation of structural changes between bacterial strains and isogenic mutants to assign functional gene relationship.