Genetic basis for expression of the major globotetraose-containing lipopolysaccharide from H. influenzae strain Rd (RM118)

A bifunctional Pasteurella multocida β1-3-galactosyl/N-acetylgalactosaminyltransferase (PmNatB) for the highly efficient chemoenzymatic synthesis of disaccharides

Glycosyltransferases are nature's key biocatalysts for the formation of glycosidic bonds. Discovery and characterization of new synthetically useful glycosyltransferases are critical for the development of efficient enzymatic and chemoenzymatic strategies for producing complex carbohydrates and glycoconjugates. Herein we report the identification of Pasteurella multocida PmNatB as a bifunctional single-catalytic-domain glycosyltransferase with both β1-3-galactosyltransferase and β1-3-N-acetylgalactosaminyltransferase activities. It is a novel glycosyltransferase for constructing structurally diverse GalNAcβ3Galα/βOR and Galβ3GalNAcα/βOR disaccharides in one-pot multienzyme systems with in situ generation of UDP-sugars.

Suppression of Alternative Lipooligosaccharide Glycosyltransferase Activity by UDP-Galactose Epimerase Enhances Murine Lung Infection and Evasion of Serum IgM

In pathogens that produce lipooligosaccharide (LOS), sugar residues within the surface-exposed LOS outer core mediate interactions with components of the host immune system, promoting bacterial infection. Many LOS structures are controlled by phase variation mediated by random slipped-strand base mispairing, which can reversibly switch gene expression on or off. Phase variation diversifies the LOS, however its adaptive role is not well-understood. Nontypeable Haemophilus influenzae (NTHi) is an important pathogen that causes a range of illnesses in the upper and lower respiratory tract. In NTHi a phase variable galactosyltransferase encoded by lic2A initiates galactose chain extension of the LOS outer core. The donor substrate for Lic2A, UDP-galactose, is generated from UDP-glucose by UDP-galactose epimerase encoded by galE. Our previous fitness profiling of H. influenzae mutants in a murine lung model showed that the galE mutant had a severe survival defect, while the lic2A mutant's defect was modest, leading us to postulate that unidentified factors act as suppressors of potential defects in a lic2A mutant. Herein we conducted a genome-wide genetic interaction screen to identify genes epistatic on lic2A for survival in the murine lung. An unexpected finding was that galE mutants exhibited restored virulence properties in a lic2A mutant background. We identified an alternative antibody epitope generated by Lic2A in the galE mutant that increased sensitivity to classical complement mediated killing in human serum. Deletion of lic2A or restoration of UDP-galactose synthesis alleviated the galE mutant's virulence defects. These studies indicate that when deprived of its galactosyl substrate, Lic2A acquires an alternative activity leading to increased recognition of NTHi by IgM and decreased survival in the lung model. Biofilm formation was increased by deletion of galE and by increased availability of UDP-GlcNAc precursors that can compete with UDP-galactose production. NTHi's ability to reversibly inactivate lic2A by phase-variation may influence survival in niches of infection in which UDP-Galactose levels are limiting.

Assay Methods for the Glycosyltransferases Involved in Synthesis of Bacterial Polysaccharides

Glycans play many important roles in bacterial biology and the complexity of the glycan structures requires biochemical assays in place to help characterize the biosynthetic pathways. Our focus has been on the use of enzymes from pathogens which make molecular mimics of host glycans. We have been examining glycosyltransferases that make strategic linkages in biologically active glycans which can be also exploited for potential therapeutic glycoconjugate synthesis. This chapter will provide details on assays for a variety of bacterial glycosyltransferases that we and others have used for the characterization of pathogen glycoconjugate biosynthetic pathways, and for the in vitro synthesis of human-like glycans produced by bacterial pathogens. The methods presented here should enable other assays to be developed for new pathway characterization.

Shielding of a lipooligosaccharide IgM epitope allows evasion of neutrophil-mediated killing of an invasive strain of nontypeable Haemophilus influenzae

Nontypeable Haemophilus influenzae is a frequent cause of noninvasive mucosal inflammatory diseases but may also cause invasive diseases, such as sepsis and meningitis, especially in children and the elderly. Infection by nontypeable Haemophilus influenzae is characterized by recruitment of neutrophilic granulocytes. Despite the presence of a large number of neutrophils, infections with nontypeable Haemophilus influenzae are often not cleared effectively by the antimicrobial activity of these immune cells. Herein, we examined how nontypeable Haemophilus influenzae evades neutrophil-mediated killing. Transposon sequencing (Tn-seq) was used on an isolate resistant to neutrophil-mediated killing to identify genes required for its survival in the presence of human neutrophils and serum, which provided a source of complement and antibodies. Results show that nontypeable Haemophilus influenzae prevents complement-dependent neutrophil-mediated killing by expression of surface galactose-containing oligosaccharide structures. These outer-core structures block recognition of an inner-core lipooligosaccharide epitope containing glucose attached to heptose HepIII-β1,2-Glc by replacement with galactose attached to HepIII or through shielding HepIII-β1,2-Glc by phase-variable attachment of oligosaccharide chain extensions. When the HepIII-β1,2-Glc-containing epitope is expressed and exposed, nontypeable Haemophilus influenzae is opsonized by naturally acquired IgM generally present in human serum and subsequently phagocytosed and killed by human neutrophils. Clinical nontypeable Haemophilus influenzae isolates containing galactose attached to HepIII that are not recognized by this IgM are more often found to cause invasive infections.

Neutrophils are white blood cells that specialize in killing pathogens and are recruited to sites of inflammation. However, despite the presence of large numbers of neutrophils in the middle ear cavity and lungs of patients with otitis media or chronic obstructive pulmonary disease, respectively, the bacterium nontypeable Haemophilus influenzae is often not effectively cleared from these locations by these immune cells. In order to understand how nontypeable Haemophilus influenzae is able to cause inflammatory diseases in the presence of neutrophils, we determined the mechanism that underlies resistance to neutrophil-mediated killing. We have shown that nontypeable Haemophilus influenzae prevents binding of antibodies of the IgM subtype through changes in their surface lipooligosaccharide structure, thereby preventing complement activation and clearance by human neutrophils.

Activation of innate immune responses by Haemophilus influenzae lipooligosaccharide

A Gram-negative pathogen Haemophilus influenzae has a truncated endotoxin known as lipooligosaccharide (LOS). Recent studies on H. influenzae LOS highlighted its structural and compositional implications for bacterial virulence; however, the role of LOS in the activation of innate and adaptive immunity is poorly understood. THP-1 monocytes were stimulated with either lipopolysaccharide (LPS) from Escherichia coli or LOS compounds derived from H. influenzae Eagan, Rd, and Rd lic1 lpsA strains. Cell surface expression of key antigen-presenting, costimulatory, and adhesion molecules, as well as gene expression of some cytokines and pattern recognition receptors, were studied. Eagan and Rd LOS had a lower capacity to induce the expression of ICAM-1, CD40, CD58, tumor necrosis factor alpha (TNF-α), and interleukin-1β (IL-1β) compared to LPS. In contrast, antigen-presenting (HLA-ABC or HLA-DR) and costimulatory (CD86) molecules and NOD2 were similarly upregulated in response to LOS and LPS. LOS from a mutant Rd strain (Rd lic1 lpsA) consistently induced higher expression of innate immune molecules than the wild-type LOS, suggesting the importance of phosphorylcholine and/or oligosaccharide extension in cellular responses to LOS. An LOS compound with a strong ability to upregulate antigen-presenting and costimulatory molecules combined with a low proinflammatory activity may be considered a vaccine candidate to immunize against H. influenzae.

Effective sugar nucleotide regeneration for the large-scale enzymatic synthesis of Globo H and SSEA4

We report here the development of chemoenzymatic methods for the large-scale synthesis of cancer-associated antigens globopentaose (Gb5), fucosyl-Gb5 (Globo H), and sialyl-Gb5 (SSEA4) by using overexpressed glycosyltransferases coupled with effective regeneration of sugar nucleotides, including UDP-Gal, UDP-GalNAc, GDP-Fuc, and CMP-Neu5Ac. The enzymes used in the synthesis were first identified from different species through comparative studies and then overexpressed in E. coli and isolated for synthesis. These methods provide multigram quantities of products in high yield with only two or three purification steps and are suitable for the evaluation and development of cancer vaccines and therapeutics.

Gene content and diversity of the loci encoding biosynthesis of capsular polysaccharides of the 15 serovar reference strains of Haemophilus parasuis

Haemophilus parasuis is the causative agent of Glässer's disease, a systemic disease of pigs, and is also associated with pneumonia. H. parasuis can be classified into 15 different serovars. Here we report, from the 15 serotyping reference strains, the DNA sequences of the loci containing genes for the biosynthesis of the group 1 capsular polysaccharides, which are potential virulence factors of this bacterium. We contend that these loci contain genes for polysaccharide capsule structures, and not a lipopolysaccharide O antigen, supported by the fact that they contain genes such as wza, wzb, and wzc, which are associated with the export of polysaccharide capsules in the current capsule classification system. A conserved region at the 3' end of the locus, containing the wza, ptp, wzs, and iscR genes, is consistent with the characteristic export region 1 of the model group 1 capsule locus. A potential serovar-specific region (region 2) has been found by comparing the predicted coding sequences (CDSs) in all 15 loci for synteny and homology. The region is unique to each reference strain with the exception of those in serovars 5 and 12, which are identical in terms of gene content. The identification and characterization of this locus among the 15 serovars is the first step in understanding the genetic, molecular, and structural bases of serovar specificity in this poorly studied but important pathogen and opens up the possibility of developing an improved molecular serotyping system, which would greatly assist diagnosis and control of Glässer's disease.

Evasion of killing by human antibody and complement through multiple variations in the surface oligosaccharide of Haemophilus influenzae

The lipopolysaccharide (LPS) of H. influenzae is highly variable. Much of the structural diversity is derived from phase variation, or high frequency on-off switching, of molecules attached during LPS biosynthesis. In this study, we examined the dynamics of LPS phase variation following exposure to human serum as a source of antibody and complement in multiple H. influenzae isolates. We show that lic2A, lgtC and lex2A switch from phase-off to phase-on following serial passage in human serum. These genes, which control attachment of a galα1-4gal di-galactoside structure (lic2A and lgtC phase-on) or an alternative glucose extension (lex2A phase-on) from the same hexose moiety, reduce binding of bactericidal antibody to conserved inner core LPS structures. The effects of the di-galactoside and alternative glucose extension were also examined in the context of the additional LPS phase variable structures phosphorylcholine (ChoP) and sialic acid. We found that di-galactoside, the alternative glucose extension, ChoP, and sialic acid each contribute independently to bacterial survival in the presence of human complement, and have an additive effect in combination. We propose that LPS phase variable extensions serve to shield conserved inner core structures from recognition by host immune components encountered during infection.

A novel branching pattern in the lipopolysaccharide expressed by non-typeable Haemophilus influenzae strain 1232

We report the novel branching pattern in lipopolysaccharide (LPS) expressed by non-typeable Haemophilus influenzae (NTHi) strain 1232. The strain expressed the β-d-Glcp-(1→4)-[α-d-Galp-(1→4)-β-d-Galp-(1→7)]-d-α-d-Hepp-(1→6)-β-d-Glcp chain linked to the proximal heptose (HepI) of the conserved triheptosyl inner-core moiety of NTHi LPS: l-α-d-HepIIIp-(1→2)-[PEtn→6]-l-α-d-HepIIp-(1→3)-l-α-d-HepIp-(1→5)-[PPEtn→4]-α-Kdop-(2→6)-lipid A. The structure has been elucidated using NMR spectroscopy, electrospray ionization mass spectrometry (ESI-MS) and capillary electrophoresis coupled to electrospray ionization tandem mass spectrometry (CE-ESI-MS(n)) on O-deacylated LPS and core oligosaccharide (OS) materials, as well as HPLC-ESI-MS(n) on permethylated, dephosphorylated OS. It was also found that a tetrasaccharide unit bearing sialic acid [α-Neu5Ac-(2→3)-β-d-Galp-(1→4)-β-d-GlcNAcp-(1→3)-β-d-Galp-(1→] could substitute O-4 of the β-d-Glcp linked to HepI. In addition, the distal heptose (HepIII) was substituted by PCho→6-β-d-Galp-(1→ at the O-2 position.

Haemophilus parainfluenzae has a limited core lipopolysaccharide repertoire with no phase variation

Cell surface lipopolysaccharide (LPS) is a well characterized virulence determinant for the human pathogen Haemophilus influenzae, so an investigation of LPS in the less pathogenic Haemophilus parainfluenzae could yield important insights. Using a panel of 18 commensal H. parainfluenzae isolates we demonstrate that the set of genes for inner core LPS biosynthesis largely resembles that of H. influenzae, with an additional heptosyltransferase I gene similar to waaC from Pasteurella multocida. Inner core LPS structure is therefore likely to be largely conserved across the two Haemophilus species. Outer core LPS biosynthetic genes are much less prevalent in H. parainfluenzae, although homologues of the H. influenzae LPS genes lpsB, non-phase variable lic2A and lgtC, and losA1, losB1 and lic2C are found in certain isolates. Immunoblotting using antibodies directed against selected LPS epitopes was consistent with these data. We found no evidence for tetranucleotide repeat-mediated phase variation in H. parainfluenzae. Phosphocholine, a phase variable H. influenzae LPS epitope that has been implicated in disease, was absent in H. parainfluenzae LPS as were the respective (lic1) biosynthetic genes. The introduction of the lic1 genes into H. parainfluenzae led to the phase variable incorporation of phosphocholine into its LPS. Differences in LPS structure between Haemophilus species could affect interactions at the bacterial-host interface and therefore the pathogenic potential of these bacteria.

Genome-scale approaches to identify genes essential for Haemophilus influenzae pathogenesis

Haemophilus influenzae is a Gram-negative bacterium that has no identified natural niche outside of the human host. It primarily colonizes the nasopharyngeal mucosa in an asymptomatic mode, but has the ability to disseminate to other anatomical sites to cause otitis media, upper, and lower respiratory tract infections, septicemia, and meningitis. To persist in diverse environments the bacterium must exploit and utilize the nutrients and other resources available in these sites for optimal growth/survival. Recent evidence suggests that regulatory factors that direct such adaptations also control virulence determinants required to resist and evade immune clearance mechanisms. In this review, we describe the recent application of whole-genome approaches that together provide insight into distinct survival mechanisms of H. influenzae in the context of different sites of pathogenesis.

Inactivation of Haemophilus influenzae lipopolysaccharide biosynthesis genes interferes with outer membrane localization of the hap autotransporter

Nontypeable Haemophilus influenzae is a major cause of localized respiratory tract disease and initiates infection by colonizing the nasopharynx. Colonization requires adherence to host epithelial cells, which is mediated by surface proteins such as the Hap adhesin. In this study, we identified a relationship between Hap levels in the outer membrane and lipopolysaccharide (LPS) biosynthesis enzymes. We found that mutation of the rfaF, pgmB, lgtC, kfiC, orfE, rfbP, lsgB, or lsgD genes, which are involved in the synthesis of the LPS oligosaccharide core in H. influenzae strain Rd/HapS243A, resulted in loss of Hap in the bacterial outer membrane and a decrease in hap transcript levels. In contrast, the same mutations had no effect on outer membrane localization of H. influenzae P5 or IgA1 protease or levels of p5 or iga1 transcripts, suggesting a Hap-specific effect. Elimination of the HtrA periplasmic protease resulted in a return of Hap to the outer membrane and restoration of hap transcript levels. Consistently, in lgtC phase-off bacteria, Hap was absent from the outer membrane, and hap transcript levels were reduced. Hap localization and hap transcript levels were not related to LPS size but to the functions of the LPS biosynthesis enzymes themselves. We speculate that the lack of certain LPS biosynthesis enzymes causes Hap to mislocalize and accumulate in the periplasm, where it is degraded by HtrA. This degradation then leads to a decrease in hap transcript levels. Together, these data highlight a novel interplay between Hap and LPS biosynthesis that can influence H. influenzae interactions with the host.

The role of lic2B in lipopolysaccharide biosynthesis in Haemophilus influenzae strain Eagan

Lipopolysaccharide (LPS) biosynthesis in Haemophilus influenzae involves genes from the lic2 locus that are required for chain extension from the middle heptose (HepII) of the conserved triheptosyl inner-core moiety. Lic2C initiates the process by attaching the first glucose to HepII, but the gene encoding for the enzyme adding the next β-D-Glcp- is uncharacterized. Lic2B is the candidate glucosyltransferase; however, in previous investigations, mutation of lic2B resulted in no hexose extension from HepII, likely due to a polar effect on the lic2C gene. In this study we complemented a lic2B knock-out mutant of H. influenzae strain Eagan with a functional lic2C gene and investigated its LPS by mass spectrometry and 2D NMR spectroscopy. Lic2B was found to encode a glucosyltransferase responsible for the linkage of β-D-Glcp-(1→4)-α-D-Glcp-(1→ extending from O-3 of the central heptose of the triheptosyl inner-core moiety, l-α-D-Hepp-(1→2)-[PEtn→6]-l-α-D-Hepp-(1→3)-l-α-D-Hepp-(1→5)-[PPEtn→4]-α-Kdo-(2→6)-lipid A.

ArcA-regulated glycosyltransferase lic2B promotes complement evasion and pathogenesis of nontypeable Haemophilus influenzae

Signaling mechanisms used by Haemophilus influenzae to adapt to conditions it encounters during stages of infection and pathogenesis are not well understood. The ArcAB two-component signal transduction system controls gene expression in response to respiratory conditions of growth and contributes to resistance to bactericidal effects of serum and to bloodstream infection by H. influenzae. We show that ArcA of nontypeable H. influenzae (NTHI) activates expression of a glycosyltransferase gene, lic2B. Structural comparison of the lipooligosaccharide (LOS) of a lic2B mutant to that of the wild-type strain NT127 revealed that lic2B is required for addition of a galactose residue to the LOS outer core. The lic2B gene was crucial for optimal survival of NTHI in a mouse model of bacteremia and for evasion of serum complement. The results demonstrate that ArcA, which controls cellular metabolism in response to environmental reduction and oxidation (redox) conditions, also coordinately controls genes that are critical for immune evasion, providing evidence that NTHI integrates redox signals to regulate specific countermeasures against host defense.

Genes required for the synthesis of heptose-containing oligosaccharide outer core extensions in Haemophilus influenzae lipopolysaccharide

Heptose-containing oligosaccharides (OSs) are found in the outer core of the lipopolysaccharide (LPS) of a subset of non-typable Haemophilus influenzae (NTHi) strains. Candidate genes for the addition of either l-glycero-d-manno-heptose (ld-Hep) or d-glycero-d-manno-heptose (dd-Hep) and subsequent hexose sugars to these OSs have been identified from the recently completed genome sequences available for NTHi strains. losA1/losB1 and losA2/losB2 are two sets of related genes in which losA has homology to genes encoding glycosyltransferases and losB to genes encoding heptosyltransferases. Each set of genes is variably present across NTHi strains and is located in a region of the genome with an alternative gene organization between strains that contributes to LPS heterogeneity. Dependent upon the strain background, the LPS phenotype, structure and serum resistance of strains mutated in these genes were altered when compared with the relevant parent strain. Our studies confirm that losB1 and losB2 usually encode dd-heptosyl- and ld-heptosyl transferases, respectively, and that losA1 and losA2 encode glycosyltransferases that play a role in OS extensions of NTHi LPS.

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.

Tracking insertion mutants within libraries by deep sequencing and a genome-wide screen for Haemophilus genes required in the lung

Rapid genome-wide identification of genes required for infection would expedite studies of bacterial pathogens. We developed genome-scale "negative selection" technology that combines high-density transposon mutagenesis and massively parallel sequencing of transposon/chromosome junctions in a mutant library to identify mutants lost from the library after exposure to a selective condition of interest. This approach was applied to comprehensively identify Haemophilus influenzae genes required to delay bacterial clearance in a murine pulmonary model. Mutations in 136 genes resulted in defects in vivo, and quantitative estimates of fitness generated by this technique were in agreement with independent validation experiments using individual mutant strains. Genes required in the lung included those with characterized functions in other models of H. influenzae pathogenesis and genes not previously implicated in infection. Genes implicated in vivo have reported or potential roles in survival during nutrient limitation, oxidative stress, and exposure to antimicrobial membrane perturbations, suggesting that these conditions are encountered by H. influenzae during pulmonary infection. The results demonstrate an efficient means to identify genes required for bacterial survival in experimental models of pathogenesis, and this approach should function similarly well in selections conducted in vitro and in vivo with any organism amenable to insertional mutagenesis.

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.

A dual role for the lex2 locus: identification of galactosyltransferase activity in non-typeable Haemophilus influenzae strains 1124 and 2019

Lipopolysaccharide (LPS) of Haemophilus influenzae 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-GlcIp-(1-->4)]-l-alpha-d-Hepp-(1-->5)-alpha-Kdop) to which addition of beta-d-Glcp to O-4 of GlcI in serotype b strains is controlled by the gene lex2B. In non-typeable H. influenzae strains 1124 and 2019, however, a beta-d-Galp is linked to O-4 of GlcI. In order to test the hypothesis that the lex2 locus is involved in the expression of beta-d-Galp-(1-->4-beta-d-Glcp-(1--> from HepI, lex2B was inactivated in strains 1124 and 2019, and LPS glycoform populations from the resulting mutant strains were investigated. Detailed structural analyses using NMR techniques and electrospray-ionisation mass spectrometry (ESIMS) on O-deacylated LPS and core oligosaccharide material (OS), as well as ESIMS(n) on permethylated dephosphorylated OS, indicated both lex2B mutant strains to express only beta-d-Glcp extensions from HepI. This provides strong evidence that Lex2B functions as a galactosyltransferase adding a beta-d-Galp to O-4 of GlcI in these strains, indicating that allelic polymorphisms in the lex2B sequence direct alternative functions of the gene product.

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.

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.

Synthesis of globopentaose using a novel β1,3-galactosyltransferase activity of theHaemophilus influenzaeβ1,3-N-acetylgalactosaminyltransferase LgtD

We have previously described a bacterial system for the conversion of globotriaose (Gb3) into globotetraose (Gb4) by a metabolically engineered Escherichia coli strain expressing the Haemophilus influenzae lgtD gene encoding beta1,3-N-acetylgalactosaminyltransferase [Antoine, T., Bosso, C., Heyraud, A. Samain, E. (2005) Large scale in vivo synthesis of globotriose and globotetraose by high cell density culture of metabolically engineered Escherichia coli. Biochimie 87, 197-203]. Here, we found that LgtD has an additional beta1,3-galactosyltransferase activity which allows our bacterial system to be extended to the synthesis of the carbohydrate portion of globopentaosylceramide (Galbeta-3GalNAcbeta-3Galalpha-4Galbeta-4Glc) which reacts with the monoclonal antibody defining the stage-specific embryonic antigen-3. In vitro assays confirmed that LgtD had both beta1,3-GalT and beta1,3-GalNAcT activities and showed that differences in the affinity for Gb3 and Gb4 explain the specific and exclusive formation of globopentaose.

Structural characterization of sialylated glycoforms of H. influenzae by electrospray mass spectrometry: fragmentation of protonated and sodiated O-deacylated lipopolysaccharides

Sialylated lipopolysaccharide (LPS) glycoforms from Haemophilus influenzae were characterized by tandem mass spectrometry using a new generation hyphenated mass spectrometer which combines a triple quadrupole and a linear ion trap (Q-Trap). The fragmentation of both protonated and sodiated molecular ions from O-deacylated LPS (LPS-OH) obtained in MS(2) experiments in the positive mode was studied. The MS(2) spectra of protonated ions provided unambiguous evidence for the presence and sequence of sialylated lactosamine present in lacto-N-neotetraose oligosaccharide extensions but not for sialyl-lactose structures whilst fragmentation of sodiated adducts, [M+Na](+), afforded information diagnostic of mono- and disialylated lactose extensions. To study this we used a highly sialylated LPS from a H. influenzae strain capable of sialyl-lactose expression only. We then applied the method to the H. influenzae genome strain, Rd, in which glycoforms containing both sialyl-lactose and sialyl-lacto-N-neotetraose were detected from diagnostic B-ions at m/z 638.2 ([Neu5Ac(1) Hex(2)+Na](+)) and 657.2 ([Neu5Ac(1) Hex(1) HexNAc(1)+H](+)). Unique fragmentation patterns provided the locations and sequences of these oligosaccharide extensions. This is the first time both sialylated lactose and sialylated lacto-N-neotetraose units have been detected and characterized by tandem mass spectrometry in the same molecule. This methodology is of general applicability for determination of common sialylated oligosaccharide extension in bacterial LPS.

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.

Synthesis of complex carbohydrates and glyconjugates: enzymatic synthesis of globotetraose using alpha-1,3-N-acetylgalactosaminyltransferase LgtD from Haemophilus infuenzae strain Rd

The lipopolysaccharide of capsule-deficient Haemophilus infuenzae strain Rd contains an N-acetylgalactosamine residue attached to the terminal globotriose moiety in the Hex5 glycoform. Genome analysis identified an open reading frame, HI1578, referred to as LgtD, whose amino acid sequence shows a significant level of similarity to those of a number of bacterial glycosyltransferases involved in lipopolysaccharide biosynthesis. To investigate its function, overexpression and biochemical characterization were performed. Most of the protein was obtained in a highly soluble and active form. Standard glycosyltransferase assay, high-performance liquid chromatography (HPLC), and liquid chromatography (LC)/mass spectrometry (MS) show that LgtD is an N-acetylgalactosaminyltransferase with high donor substrate specificity, and globotriose is a highly preferred acceptor substrate for the enzyme.

The role of Dam methylation in phase variation of Haemophilus influenzae genes involved in defence against phage infection

Haemophilus influenzae uses phase variation (PV) to modulate the activity of its defence systems against phage infection. The PV of the restriction–modification (R-M) system HindI, the main defence system against phage infection and incoming chromosomal and phage DNA in H. influenzae Rd, is driven by changes of the pentanucleotide repeat tract within the coding sequence of the hsdM gene and is influenced by lack of Dam methylation. Phase-variable resistance/sensitivity to phage infection correlates with changes in lipooligosaccharide (LOS) structure and occurs by slippage of tetranucleotide repeats within the gene lic2A, coding for a step in the biosynthesis of LOS. The lack of Dam activity destabilizes the tetranuclotide (5′-CAAT) repeat tract and increases the frequency of switching from sensitivity to resistance to phage infection more than in the opposite direction. The PV of the lgtC gene does not influence resistance or sensitivity to phage infection. Insertional inactivation of lic2A, but not lgtC or lgtF, leads to resistance to phage infection and to the same structure of the LOS as observed among phase-variable phage-resistant variants. This indicates that in the H. influenzae Rd LOS only the first two sugars (Glc-Gal) extending from the third heptose are part of bacterial phage receptors.

Genomic sequence of an otitis media isolate of nontypeable Haemophilus influenzae: comparative study with H. influenzae serotype d, strain KW20

In 1995, the Institute for Genomic Research completed the genome sequence of a rough derivative of Haemophilus influenzae serotype d, strain KW20. Although extremely useful in understanding the basic biology of H. influenzae, these data have not provided significant insight into disease caused by nontypeable H. influenzae, as serotype d strains are not pathogens. In contrast, strains of nontypeable H. influenzae are the primary pathogens of chronic and recurrent otitis media in children. In addition, these organisms have an important role in acute otitis media in children as well as other respiratory diseases. Such strains must therefore contain a gene repertoire that differs from that of strain Rd. Elucidation of the differences between these genomes will thus provide insight into the pathogenic mechanisms of nontypeable H. influenzae. The genome of a representative nontypeable H. influenzae strain, 86-028NP, isolated from a patient with chronic otitis media was therefore sequenced and annotated. Despite large regions of synteny with the strain Rd genome, there are large rearrangements in strain 86-028NP's genome architecture relative to the strain Rd genome. A genomic island similar to an island originally identified in H. influenzae type b is present in the strain 86-028NP genome, while the mu-like phage present in the strain Rd genome is absent from the strain 86-028NP genome. Two hundred eighty open reading frames were identified in the strain 86-028NP genome that were absent from the strain Rd genome. These data provide new insight that complements and extends the ongoing analysis of nontypeable H. influenzae virulence determinants.

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.

Characterization of a cluster of three glycosyltransferase enzymes essential for Moraxella catarrhalis lipooligosaccharide assembly

Moraxella catarrhalis isolates express lipooligosaccharide (LOS) molecules on their surface, which share epitopes similar to that of the Neisseria and Haemophilus species. These common LOS epitopes have been implicated in various steps of pathogenesis for the different organisms. In this study, a cluster of three LOS glycosyltransferase genes (lgt) were identified in M. catarrhalis 7169, a strain that produces a serotype B LOS. Mutants in these glycosyltransferase genes were constructed, and the resulting LOS phenotypes were consistent with varying degrees of truncation compared to wild-type LOS. The LOS structures of each lgt mutant were no longer detected by a monoclonal antibody (MAb 4G5) specific to a highly conserved terminal epitope nor by a monoclonal antibody (MAb 3F7) specific to the serotype B LOS side chain. Mass spectrometry of the LOS glycoforms assembled by two of these lgt mutants indicated that lgt1 encodes an alpha(1-2) glucosyltransferase and the lgt2 encodes a beta(1-4) galactosyltransferase. However, these structural studies could not delineate the function for lgt3. Therefore, M. catarrhalis lgt3 was introduced into a defined beta(1-4) glucosyltransferase Haemophilus ducreyi 35000glu- mutant in trans, and monoclonal antibody analysis confirmed that Lgt3 complemented the LOS defect. These data suggest that lgt3 encodes a glucosyltransferase involved in the addition of a beta(1-4)-linked glucose to the inner core. Furthermore, we conclude that this enzymatic step is essential for the assembly of the complete LOS glycoform expressed by M. catarrhalis 7169.

Large scale in vivo synthesis of globotriose and globotetraose by high cell density culture of metabolically engineered Escherichia coli

Large amounts of globotriose (Galalpha-4Galbeta-4Glc) are shown to be produced by the high cell density culture of an Escherichia coli strain over-expressing the Neisseria meningitidis lgtC gene for alpha-1,4-Gal transferase. The strain which was devoid of both alpha and beta galactosidase activity was fed with glycerol as the energy and carbon source and with lactose as precursor for globotriose synthesis. After complete exhaustion of lactose, globotriose could serve as an alternative acceptor for LgtC and the formation of a series of polygalactosylated compounds was observed. The system was extended to the synthesis of globotetraose (GalNAcbeta-3Galalpha-4Galbeta-4Glc) by overexpressing two additional genes: lgtD from Haemophilus influenzae Rd which encodes a beta-1,3-GalNAc transferase and wbpP from Pseudomonas aeruginosa which encodes a UDP-GalNAc C4 epimerase. Globotetraose could also be produced from exogenous globotriose which was shown to be actively taken up by the cells.

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.

Biosynthesis of cryptic lipopolysaccharide glycoforms in Haemophilus influenzae involves a mechanism similar to that required for O-antigen synthesis

It is generally thought that mucosal bacterial pathogens of the genera Haemophilus, Neisseria, and Moraxella elaborate lipopolysaccharide (LPS) that is fundamentally different from that of enteric organisms that express O-specific polysaccharide side chains. Haemophilus influenzae elaborates short-chain LPS that has a role in the pathogenesis of H. influenzae infections. We show that the synthesis of LPS in this organism can no longer be as clearly distinguished from that in other gram-negative bacteria that express an O antigen. We provide evidence that a region of the H. influenzae genome, the hmg locus, is involved in the synthesis of glycoforms in which tetrasaccharide units are added en bloc, not stepwise, to the normal core glycoforms, similar to the biosynthesis of an O-antigen.

lpt6, a gene required for addition of phosphoethanolamine to inner-core lipopolysaccharide of Neisseria meningitidis and Haemophilus influenzae

We previously described a gene, lpt3, required for the addition of phosphoethanolamine (PEtn) at the 3 position on the beta-chain heptose (HepII) of the inner-core Neisseria meningitidis lipopolysaccharide (LPS), but it has long been recognized that the inner-core LPS of some strains possesses PEtn at the 6 position (PEtn-6) on HepII. We have now identified a gene, lpt6 (NMA0408), that is required for the addition of PEtn-6 on HepII. The lpt6 gene is located in a region previously identified as Lgt-3 and is associated with other LPS biosynthetic genes. We screened 113 strains, representing all serogroups and including disease and carriage strains, for the lpt3 and lpt6 genes and showed that 36% contained both genes, while 50% possessed lpt3 only and 12% possessed lpt6 only. The translated amino acid sequence of lpt6 has a homologue (72.5% similarity) in a product of the Haemophilus influenzae Rd genome sequence. Previous structural studies have shown that all H. influenzae strains investigated have PEtn-6 on HepII. Consistent with this, we found that, among 70 strains representing all capsular serotypes and nonencapsulated H. influenzae strains, the lpt6 homologue was invariably present. Structural analysis of LPS from H. influenzae and N. meningitidis strains where lpt6 had been insertionally inactivated revealed that PEtn-6 on HepII could not be detected. The translated amino acid sequences from the N. meningitidis and H. influenzae lpt6 genes have conserved residues across their lengths and are part of a family of proven or putative PEtn transferases present in a wide range of gram-negative bacteria.

Three genes, lgtF, lic2C and lpsA, have a primary role in determining the pattern of oligosaccharide extension from the inner core of Haemophilus influenzae LPS

Lipopolysaccharide (LPS) is a virulence determinant of Haemophilus influenzae and exhibits substantial heterogeneity in structure within and between strains. Key factors contributing to this heterogeneity are the genes required to add the first glycose to each of the three heptose residues of the LPS inner core. In each case this addition can facilitate further oligosaccharide extension. lgtF is invariably present in strains and the product has a function in adding the glucose to the first heptose. lic2C is present in half the strains and was found to add a glucose to the second heptose. Insertion of lic2C into a strain that does not naturally contain it resulted in hexose incorporation from the second heptose of the LPS. The product of the lpsA gene can add a glucose or galactose to the third heptose. By allelic replacement of lpsA between strains it is shown that the sequence of the gene can be the sole determinant of this specificity. Thus, lgtF, lic2C and lpsA make significant but very distinct contributions to the conservation and variable patterns of oligosaccharide extensions seen in H. influenzae LPS.

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

Nontypeable Haemophilus influenzae (NTHi) is a common commensal of the human upper respiratory tract and is associated with otitis media in children. The structures of the oligosaccharide portions of NTHi lipopolysaccharide (LPS) from several otitis media isolates are now well characterized but it is not known whether there are structural differences in LPS from colonizing, nondisease associated strains. Structural analysis of LPS from nondisease associated NTHi strains 11 and 16 has been achieved by the application of high-field NMR techniques, ESI-MS, ESI-MSn, capillary electrophoresis coupled to ESI-MS, composition and linkage analyses on O-deacylated LPS and core oligosaccharide material. This is the first study to report structural details on LPS from strains taken from the nasopharynx from healthy individuals. Both strains express identical structures and contain the common element of H. influenzae LPS, 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-Kdop-(2-->6)-lipid A, in which each heptose is elongated by a single hexose residue with no further oligosaccharide extensions. In the major Hex3 glycoform, the terminal Hepp residue (HepIII) is substituted at the O-2 position by a beta-D-Galp residue and the central Hepp residue (HepII) is substituted at O-3 by a alpha-D-Glcp residue. Notably, the strains express two phosphocholine (PCho) substituents, one at the O-6 position of alpha-D-Glcp and the other at the O-6 position of beta-D-Galp. Major acetylation sites were identified at O-4 of Gal and O-3 of HepIII. Additionally, both strains express glycine, and strain 11 also expresses detectable amounts of N-acetylneuraminic acid.

Simple sequence repeats (microsatellites): mutational mechanisms and contributions to bacterial pathogenesis. A meeting review

This review summarises the presentations and discussions that took place during a European Science Foundation-funded workshop whose purpose was to gain current perspectives on the mutational mechanisms of simple sequence repeats and the contribution of localised hypermutation in such repeats to bacterial pathogenesis. In vitro biophysical and biochemical assays of mutational mechanisms were covered as well as genetic studies in various eukaryotic and prokaryotic organisms. Presentations on bacterial pathogenesis elaborated investigations of the use of repeats for typing of strains, epidemiological investigations of mutation rates and functions of loci whose expression is controlled by simple sequence repeats. This review tabulates current perspectives on the cis- and trans-acting factors for mutation of simple sequence repeats and the orientations of mononucleotide repeats in some bacterial species that utilise repeats for adaptation.

Structure and functional genomics of lipopolysaccharide expression in Haemophilus influenzae

The involvement of genes in the lic loci in H. influenzae LPS expression has been known for some time. However, it was not until recently that it was shown that the lic1 locus contains genes required for phase variable expression of phosphocholine substituents, while genes in the lic2 locus and lgtC are required for expression of the globoside trisaccharide, alpha-D-Galp-(1 --> 4)-beta-D-Galp-(1 --> 4)-beta-D-Glcp (i.e., the pK blood group epitope). The availability of the complete sequence of the H. influenzae strain Rd genome has facilitated significant progress in understanding the role of these and other genes in the expression and biosynthesis of LPS. We have employed a comparative structural fingerprinting strategy to establish the structural relationships among LPS from H. influenzae mutant strains in which putative biosynthesis genes were inactivated. Using this functional genomics approach, we have gained considerable insight into the genetic basis for intra-strain and strain-to-strain variation in epitope expression.

Structural profiling of lipopolysaccharide glycoforms expressed by non-typeable Haemophilus influenzae: phenotypic similarities between NTHi strain 162 and the genome strain Rd

Non-typeable Haemophilus influenzae (NTHi) is a significant cause of otitis media in children. We have employed single and multiple step electrospray ionization mass spectrometry (ESIMS) and NMR spectroscopy to profile and elucidate lipopolysaccharide (LPS) structural types expressed by NTHi strain 162, a strain obtained from an epidemiological study in Finland. ESIMS on O-deacylated LPS (LPS-OH) and core oligosaccharide (OS) samples of LPS provided information on the composition and relative abundance of glycoforms differing in the number of hexoses linked to the conserved inner-core element, L-alpha-D-Hepp-(1-->2)-[PEtn-->6]-L-alpha-D-Hepp-(1-->3)-L-alpha-D-Hepp-(1-->5)-[PPEtn-->4]-alpha-Kdop-(2-->6)-Lipid A of H. influenzae LPS. The strain examined was found to elaborate Hex2 to Hex5 LPS glycoform populations having structures identical to those observed for H. influenzae strain Rd [Risberg, A.; Masoud, H.; Martin, A.; Richards, J.C.; Moxon, E.R.; Schweda, E.K.H. Eur. J. Biochem. 1999, 261, 171-180], the strain for which the complete genome has been sequenced. In addition, sialyllactose-containing glycoforms previously identified in strain Rd as well as several NTHi strains, were identified as minor components. Multiple step tandem ESIMS (MS(n)) on dephosphorylated and permethylated OS provided information on the arrangement of glycoses within the major population of glycoforms and on the existence of additional isomeric glycoforms. Minor Hex1 and Hex6 glycoforms were detected and characterized where the Hex6 glycoform was comprised of a dihexosamine-containing pentasaccharide chain attached at the proximal heptose residue of the inner-core unit. LPS structural motifs present in the NTHi strain 162 are expressed by a genetically diverse set of disease causing isolates, providing the basis for a vaccine strategy against NTHi otitis media.

Structural analysis of lipopolysaccharides from Haemophilus influenzae serotype f. Structural diversity observed in three strains

Structural elucidation of the lipopolysaccharide (LPS) from three serotype f Haemophilus influenzae clinical isolates RM6255, RM7290 and RM6252 has been achieved using NMR spectroscopy techniques and ESI-MS on O-deacylated LPS and core oligosaccharide material (OS) as well as ESI-MSn on permethylated dephosphorylated OS. This is the first study to report structural details on LPS from serotype f strains. We found that the LPSs of all strains were highly heterogeneous mixtures of glycoforms expressing the common H. influenzae structural element 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 with variable length of OS chains linked to each of the heptoses. The terminal heptose (HepIII) in RM6255 is substituted at the O-3 position by a beta-d-Glcp residue whereas HepIII in strains RM7290 and RM6252 is substituted at O-2 by the globoside unit (alpha-d-Galp-(1-->4)-beta-d-Galp-(1-->4)-beta-d-Glc) or truncated versions thereof. The central heptose (HepII) is substituted by an alpha-d-Galp-(1-->4)-beta-d-Galp-(1-->4)-beta-d-Glcp-(1-->4)-alpha-d-Glcp unit in RM7290 and RM6252 or truncated versions thereof. Strain RM6255 does not express galactose in its LPS and only shows a cellobiose unit elongating from HepII (beta-d-Glcp-(1-->4)-alpha-d-Glcp). ESI-MSn on dephosphorylated and permethylated OS provided information on the existence of additional minor isomeric glycoforms.

Structural characterization of a novel branching pattern in the lipopolysaccharide from nontypeable Haemophilus influenzae

Structural analysis of the lipopolysaccharide (LPS) from nontypeable Haemophilus influenzae strain 981 has been achieved using NMR spectroscopy and ESI-MS on O-deacylated LPS and core oligosaccharide (OS) material as well as by ESI-MSn on permethylated dephosphorylated OS. A heterogeneous glycoform population was identified, resulting from the variable length of the OS branches attached to the glucose residue in the common structural element of H. influenzae LPS, l-alpha-d-Hepp-(1-->2)-[PEtn-->6]-l-alpha-d-Hepp-(1-->3)-[beta-d-Glcxp-(1-->4)]-l-alpha-d-Hepp-(1-->5)-[PPEtn-->4]-alpha-Kdop-(2-->6)-Lipid A. Notably, the O-6 position of the beta-d-Glcp residue was either substituted by PCho or the disaccharide branch beta-d-Galp-(1-->4)-d-alpha-d-Hepp, while the O-4 position was substituted by the globotetraose unit, beta-d-GalpNAc-(1-->3)-alpha-d-Galp-(1-->4)-beta-d-Galp-(1-->4)-beta-d-Glcp, or sequentially truncated versions thereof. This is the first time a branching sugar residue has been reported in the outer-core region of H. influenzae LPS. Additionally, a PEtn group was identified at O-3 of the distal heptose residue in the inner-core.

Structural diversity in lipopolysaccharide expression in nontypeable Haemophilus influenzae. Identification of L-glycerol-D-manno-heptose in the outer-core region in three clinical isolates

Structural elucidation of the lipopolysaccharide (LPS) from three nontypeable Haemophilus influenzae clinical isolates, 1209, 1207 and 1233 was achieved using NMR spectroscopy and ESI-MS on O-deacylated LPS and core oligosaccharide (OS) material as well as ESI-MS(n) on permethylated dephosphorylated OS. It was found that the organisms expressed a tremendous heterogeneous glycoform mixture resulting from the variable length of the OS chains attached to 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-Kdop-(2-->6)-Lipid A. Notably, the O-6 position of the beta-D-Glcp residue could either be occupied by PCho or L-glycero-D-manno-heptose (L,D-Hep), which is a location for L,D-Hep that has not been seen previously in H. influenzae LPS. The outer-core L,D-Hep residue was further chain elongated at the O-6 position by the structural element beta-D-GalpNAc-(1-->3)-alpha-D-Galp-(1-->4)-beta-D-Galp, or sequentially truncated versions thereof. The distal heptose residue in the inner-core was found to be chain elongated at O-2 by the globotetraose unit, beta-D-GalpNAc-(1-->3)-alpha-D-Galp-(1-->4)-beta-D-Galp-(1-->4)-beta-D-Glcp, or sequentially truncated versions thereof. Investigation of LPS from an lpsA mutant of isolate 1233 and a lic1 mutant of isolate 1209 was also performed, which aside from confirming the functions of the gene products, simplified elucidation of the OS extending from the proximal heptose (the lpsA mutant), and showed that the organism exclusively expresses LPS glycoforms comprising the outer-core l,d-Hep residue when PCho is not expressed (the lic1 mutant).

Donor substrate regeneration for efficient synthesis of globotetraose and isoglobotetraose

Here we describe the efficient synthesis of two oligosaccharide moieties of human glycosphingolipids, globotetraose (GalNAcbeta1-->3Galalpha1-->4Galbeta1-->4Glc) and isoglobotetraose (GalNAcbeta1-->3Galalpha1-->3Galbeta1-->4Glc), with in situ enzymatic regeneration of UDP-N-acetylgalactosamine (UDP-GalNAc). We demonstrate that the recombinant beta-1,3-N-acetylgalactosaminyltransferase from Haemophilus influenzae strain Rd can transfer N-acetylgalactosamine to a wide range of acceptor substrates with a terminal galactose residue. The donor substrate UDP-GalNAc can be regenerated by a six-enzyme reaction cycle consisting of phosphoglucosamine mutase, UDP-N-acetylglucosamine pyrophosphorylase, phosphate acetyltransferase, pyruvate kinase, and inorganic pyrophosphatase from Escherichia coli, as well as UDP-N-acetylglucosamine C4 epimerase from Plesiomonas shigelloides. All these enzymes were overexpressed in E. coli with six-histidine tags and were purified by one-step nickel-nitrilotriacetic acid affinity chromatography. Multiple-enzyme synthesis of globotetraose or isoglobotetraose with the purified enzymes was achieved with relatively high yields.

Identification and characterization of the N-acetylglucosamine glycosyltransferase gene of Haemophilus ducreyi

Haemophilus ducreyi is the causative agent of chancroid, a sexually transmitted ulcerative disease. In the present study, the Neisseria gonorrhoeae lgtA lipooligosaccharide glycosyltransferase gene was used to identify a homologue in the genome of H. ducreyi. The putative H. ducreyi glycosyltransferase gene (designated lgtA) was cloned and insertionally inactivated, and an isogenic mutant was constructed. Structural studies demonstrated that the lipooligosaccharide isolated from the mutant strain lacked N-acetylglucosamine and distal sugars found in the lipooligosaccharide produced by the parental strain. The isogenic mutant was transformed with a recombinant plasmid containing the putative glycosyltransferase gene. This strain produced the lipooligosaccharide glycoforms produced by the parental strain, confirming that the lgtA gene encodes the N-acetylglucosamine glycosyltransferase.

Identification and structural characterization of a sialylated lacto-N-neotetraose structure in the lipopolysaccharide of Haemophilus influenzae

A sialylated lacto-N-neotetraose (Sial-lNnT) structural unit was identified and structurally characterized in the lipopolysaccharide (LPS) from the genome-sequenced strain Rd [corrected] (RM118) of the human pathogen Haemophilus influenzae grown in the presence of sialic acid. A combination of molecular genetics, MS and NMR spectroscopy techniques showed that this structural unit extended from the proximal heptose residue of the inner core region of the LPS molecule. The structure of the Sial-lNnT unit was identical to that found in meningococcal LPS, but glycoforms containing truncations of the Sial-lNnT unit, comprising fewer residues than the complete oligosaccharide component, were not detected. The finding of sialylated glycoforms that were either fully extended or absent suggests a novel biosynthetic feature for adding the terminal tetrasaccharide unit of the Sial-lNnT to the glycose acceptor at the proximal inner core heptose.