Glycosphingolipid receptors for Pseudomonas aeruginosa

Chemical control over Asialo-GM1: A dual ligand for pili and Lectin A that activates swarming motility and facilitates adherence of Pseudomonas aeruginosa

Glycolipid, ganglio-N-tetraosylceramide (asialo-GM1), on the mammalian cells are known to be recognized by type IV pili of Pseudomonas aeruginosa. In this work, we show that asialo-GM1 can also be recognized by Lectin A (LecA), another adhesin protein of the P. aeruginosa, by a fluorescent polarization assay, a label-free bacterial motility enabled binding assay, and bacterial mutant studies. On hydrated semi-solid gel surfaces, asialo-GM1 enables swarming and twitching motilities, while on solid surfaces facilitates the bacterial adherence of P. aeruginosa. These results indicate that asialo-GM1 can modulate bioactivities, adherence, and motilities, that are controlled by opposite signaling pathways. We demonstrate that when a solution of pilin monomers or LecA proteins are spread on hydrated gel surfaces, the asialo-GM1 mediated swarming motility is inhibited. Treatment of artificial liposomes containing asialo-GM1 as a component of lipid bilayer with pilin monomers or LecA proteins caused transient leakage of encapsulated dye from liposomes. These results suggest that pili and LecA proteins not only bind to asialo-GM1 but can also cause asialo-GM1 mediated leakage. We also show that both pili and LecA mutants of P. aeruginosa adhere to asialo-GM1 coated solid surfaces, and that a class of synthetic ligands for pili and LecA inhibits both pili and LecA-mediated adherence of P. aeruginosa on asialo-GM1-coated surfaces.

Infection Transmission by Saliva and the Paradoxical Protective Role of Saliva

Saliva is produced by both major (parotid and submandibular and sublingual) and minor (located in the mouth) glands, with different constituents and properties between the two groups. In the mouth saliva is a colorless, odorless, tasteless, watery liquid containing 99% water and 1% organic and inorganic substances and dissolved gases, mainly oxygen and carbon dioxide. Salivary constituents can be grouped into proteins (e.g., amylase and lysozyme), organic molecules (e.g., urea, lipids, and glucose mainly), and electrolytes (e.g., sodium, calcium, chlorine, and phosphates). Cellular elements such as epithelial cells, leukocytes and various hormones, and vitamins have also been detected. The composition of saliva is modified, depending on factors such as secreted amount, circadian rhythm, duration and nature of stimuli, diet, and medication intake, among others.

NEU1 Sialidase Regulates Membrane-tethered Mucin (MUC1) Ectodomain Adhesiveness for Pseudomonas aeruginosa and Decoy Receptor Release

Airway epithelia express sialylated receptors that recognize exogenous danger signals. Regulation of receptor responsiveness to these signals remains incompletely defined. Here, we explore the mechanisms through which the human sialidase, neuraminidase-1 (NEU1), promotes the interaction between the sialoprotein, mucin 1 (MUC1), and the opportunistic pathogen, Pseudomonas aeruginosa. P. aeruginosa flagellin engaged the MUC1 ectodomain (ED), increasing NEU1 association with MUC1. The flagellin stimulus increased the association of MUC1-ED with both NEU1 and its chaperone/transport protein, protective protein/cathepsin A. Scatchard analysis demonstrated NEU1-dependent increased binding affinity of flagellin to MUC1-expressing epithelia. NEU1-driven MUC1-ED desialylation rapidly increased P. aeruginosa adhesion to and invasion of the airway epithelium. MUC1-ED desialylation also increased its shedding, and the shed MUC1-ED competitively blocked P. aeruginosa adhesion to cell-associated MUC1-ED. Levels of desialylated MUC1-ED were elevated in the bronchoalveolar lavage fluid of mechanically ventilated patients with P. aeruginosa airway colonization. Preincubation of P. aeruginosa with these same ex vivo fluids competitively inhibited bacterial adhesion to airway epithelia, and MUC1-ED immunodepletion completely abrogated their inhibitory activity. These data indicate that a prokaryote, P. aeruginosa, in a ligand-specific manner, mobilizes eukaryotic NEU1 to enhance bacterial pathogenicity, but the host retaliates by releasing MUC1-ED into the airway lumen as a hyperadhesive decoy receptor.

Glycolipid-Dependent, Protease Sensitive Internalization of Pseudomonas aeruginosa Into Cultured Human Respiratory Epithelial Cells

Internalization of PAK strain Pseudomonas aeruginosa into human respiratory epithelial cell lines and HeLa cervical cancer cells in vitro was readily demonstrable via a gentamycin protection assay. Depletion of target cell glycosphingolipids (GSLs) using a glucosyl ceramide synthase inhibitor, P4, completely prevented P. aeruginosa internalization. In contrast, P4 treatment had no effect on the internalization of Salmonella typhimurium into HeLa cells. Internalized P. aeruginosa were within membrane vacuoles, often containing microvesicles, between the bacterium and the limiting membrane. P. aeruginosa internalization was markedly enhanced by target cell pretreatment with the exogenous GSL, deacetyl gangliotetraosyl ceramide (Gg₄). Gg₄ binds the lipid raft marker, GM1 ganglioside. Target cell pretreatment with TLCK, but not other (serine) protease inhibitors, prevented both P. aeruginosa host cell binding and internalization. NFkB inhibition also prevented internalization. A GSL-containing lipid-raft model of P. aeruginosa host cell binding/internalization is proposed

Epithelial GM-CSF induction by Candida glabrata

The main cytokine induced by the interaction of oral epithelial cells with C. glabrata is granulocyte monocyte colony-stimulating factor (GM-CSF); however, the mechanisms regulating this response are unknown. Based on previously published information on the interactions of C. albicans with oral epithelial cells, we hypothesized that interaction with viable C. glabrata triggers GM-CSF synthesis via NF-kappaB activation. We found that C. glabrata-induced GM-CSF synthesis was adhesion-dependent, enhanced by endocytosis, and required fungal viability. NF-kappaB activation was noted during interaction of epithelial cells with C. glabrata, and pre-treatment with an NF-kappaB inhibitor partly inhibited GM-CSF synthesis. Blocking TLR4 with anti-TLR4 antibody did not inhibit GM-CSF production. In contrast, an anti-CDw17 antibody triggered significant inhibition of NF-kappaB activation and GM-CSF synthesis. beta-glucans did not stimulate GM-CSF synthesis, suggesting that the CDw17/NF-kappaB/GM-CSF pathway may be beta-glucan-independent. This study provides new insights into the mechanism of GM-CSF induction by C. glabrata.

The Multiple Carbohydrate Binding Specificities of Helicobacter pylori

Persistent colonization of the human stomach by Helicobacter pylori is a risk factor for the development of peptic ulcer disease and gastric cancer. Adhesion of microbes to the target tissue is an important determinant for successful initiation, establishment and maintenance of infection, and a variety of different candidate carbohydrate receptors for H. pylori have been identified. Here the different the binding specifities, and their potential role in adhesion to human gastric epithelium are described. Finally, recent findings on the roles of sialic acid binding SabA adhesin in interactions with human neutrophils and erythrocytes are discussed.

Laboratory and clinical Pseudomonas aeruginosa strains do not bind glycosphingolipids in vitro or during type IV pili-mediated initial host cell attachment

The glycosphingolipids (GSLs) gangliotriaosylceramide (Gg(3)) and gangliotetraosylceramide (Gg(4)) have been implicated as receptors for type IV pili (T4P)-mediated Pseudomonas aeruginosa epithelial cell attachment. Since P. aeruginosa T4P are divided into five groups, the authors determined whether GSLs in general, and Gg(3) and Gg(4) in particular, are specifically bound and required for host epithelial cell attachment of clinical and laboratory strains within these groups. An enterohaemorrhagic Escherichia coli strain, CL56, known to bind to both Gg(3) and Gg(4), provided a positive control. TLC overlay showed no binding of more than 12 P. aeruginosa strains to either Gg(3) or Gg(4) (or other GSLs), while CL56 Gg(3)/Gg(4) binding was readily detectable. GSL ELISA similarly demonstrated no significant P. aeruginosa binding to Gg(3) or Gg(4), compared with CL56. Using a selective chemical inhibitor, epithelial cell GSL synthesis was abrogated, and Gg(3) and Gg(4) expression deleted, but P. aeruginosa attachment was not impaired. Target cell attachment was mediated by T4P, since non-piliated, but flagellated, mutants were unable to bind to the target cells. CFTR (cystic fibrosis transmembrane conductance regulator) has also been implicated as a receptor; however, in this work, overexpression of CFTR had no effect on P. aeruginosa binding. It is concluded that neither Gg(3) nor Gg(4) are specifically recognized by P. aeruginosa, and that endogenous GSLs do not have a role in the attachment of live intact P. aeruginosa to cultured lung epithelial cells. In contrast to whole piliated P. aeruginosa, T4P sheared from such bacteria showed significant Gg(3) and Gg(4) binding, which may explain the results of other studies.

Sialidase fusion protein as a novel broad-spectrum inhibitor of influenza virus infection

Influenza is a highly infectious disease characterized by recurrent annual epidemics and unpredictable major worldwide pandemics. Rapid spread of the highly pathogenic avian H5N1 strain and escalating human infections by the virus have set off the alarm for a global pandemic. To provide an urgently needed alternative treatment modality for influenza, we have generated a recombinant fusion protein composed of a sialidase catalytic domain derived from Actinomyces viscosus fused with a cell surface-anchoring sequence. The sialidase fusion protein is to be applied topically as an inhalant to remove the influenza viral receptors, sialic acids, from the airway epithelium. We demonstrate that a sialidase fusion construct, DAS181, effectively cleaves sialic acid receptors used by both human and avian influenza viruses. The treatment provides long-lasting effect and is nontoxic to the cells. DAS181 demonstrated potent antiviral and cell protective efficacies against a panel of laboratory strains and clinical isolates of IFV A and IFV B, with virus replication inhibition 50% effective concentrations in the range of 0.04 to 0.9 nM. Mouse and ferret studies confirmed significant in vivo efficacy of the sialidase fusion in both prophylactic and treatment modes.

NontypeableHaemophilus influenzae-binding gangliosides of human respiratory (HEp-2) cells have a requisite lacto/neolacto core structure

Nontypeable Haemophilus influenzae (NTHI) are a major cause of human infections. We previously demonstrated high affinity and high specificity binding of NTHI to minor gangliosides of human respiratory (HEp-2) cells and macrophages, but not to brain gangliosides. We further identified the NTHI-binding ganglioside of human macrophages as alpha2,3-sialylosylparagloboside (IV3NeuAc-nLcOse4Cer, nLM1), which possesses a neolacto core structure that is absent in brain gangliosides. This supported a hypothesis that lacto/neolacto core carbohydrates are critical for NTHI-ganglioside binding. To investigate, we determined the core carbohydrate structure of NTHI-binding gangliosides of HEp-2 cells, through multiple approaches, including specific enzymatic degradation, mass spectral analysis and gas-liquid chromatography. Our analyses denote the following critical structural attributes of NTHI-binding gangliosides: (1) a conserved lacto/neolacto core structure; (2) requisite sialylation, which may be either internal or external, with alpha2,3 (human macrophages) or alpha2,6 (HEp-2 cells) anomeric linkages; (3) internalized galactose residues. Mass spectral and gas chromatographic analyses confirm that NTHI-binding gangliosides of HEp-2 cells possess lacto/neolacto carbohydrate cores and identify the structure of the major peak as NeuAcalpha2-6Galbeta1-4GlcNAcbeta1-3Galbeta1-4Glcbeta1-1Cer (alpha2,6-sialosylparagloboside, nLM1). Collectively, our studies denote NTHI-binding gangliosides as lacto/neolacto series structures.

Distribution of sialic acids in the milk of spanish mothers of full term infants during lactation

OBJECTIVES

The protective effect of human milk against infection is well known. Several non-immunologic components, including complex carbohydrates, have been described. The present study was undertaken to determine the sialic acid distribution in different milk fractions (complex carbohydrates).

METHODS

Milk samples from 12 Spanish women at three different lactational stages (colostrum, transitional milk and mature milk) were analyzed. Total and glycoprotein-bound, oligosaccharide-bound, casein-bound, and lipid-bound sialic acids were determined.

RESULTS

Sialic acids from human milk are mainly bound to oligosaccharides and only a small amount is present bound to glycoproteins or in the free form. All the fractions analyzed showed a similar trend: sialic acids decrease rapidly along lactation. Casein-bound sialic acid does not follow this trend. We detected the presence of an O-acetylated species of N-acetylneuraminic acid.

CONCLUSIONS

In human milk from Spanish women we observed slightly different values than those previously reported. This could be a result of population differences but nutritional or methodological aspects can not be discarded.

Synthetic peptide vaccine and antibody therapeutic development: prevention and treatment of Pseudomonas aeruginosa

Pseudomonas aeruginosa and Pseudomonas maltophilia account for 80% of opportunistic infections by pseudomonads. Pseudomonas aeruginosa is an opportunistic pathogen that causes urinary tract infections, respiratory system infections, dermatitis, soft tissue infections, bacteremia, and a variety of systemic infections, particularly in patients with severe burns, and in cancer and AIDS patients who are immunosuppressed. Pseudomonas aeruginosa is notable for its resistance to antibiotics, and is therefore a particularly dangerous pathogen. Only a few antibiotics are effective against Pseudomonas, including fluoroquinolones, gentamicin, and imipenem, and even these antibiotics are not effective against all strains. The difficulty treating Pseudomonas infections with antibiotics is most dramatically illustrated in cystic fibrosis patients, virtually all of whom eventually become infected with a strain that is so resistant that it cannot be treated. Since antibiotic therapy has proved so ineffective as a treatment, we embarked on a research program to investigate the development of a synthetic peptide consensus sequence vaccine for this pathogen. In this review article we will describe our work over the last 15 years to develop a synthetic peptide consensus sequence anti-adhesin vaccine and a related therapeutic monoclonal antibody (cross-reactive to multiple strains) to be used in the prevention and treatment of P. aeruginosa infections. Further, we describe the identification and isolation of a small peptide structural element found in P. aeruginosa strain K (PAK) bacterial pili, which has been proven to function as a host epithelial cell-surface receptor binding domain. Heterologous peptides are found in the pili of all strains of P. aeruginosa that have been sequenced to date. Several of these peptide sequences have been used in the development of an consensus sequence anti-adhesin vaccine targeted at the prevention of host cell attachment and further for the generation of a monoclonal antibody capable of prevention and treatment of existing infections.

Lactational changes in the fatty acid composition of human milk gangliosides

The objectives of this work were to study the FA composition of milk gangliosides, as well as to gain further insight into the characterization of human milk gangliosides. The potential capacity of human milk gangliosides to adhere to human enterotoxigenic Escherichia coli (ETEC-strains) was also studied. Human milk gangliosides were isolated and identified by high-performance TLC or immunoassay. The latter also was used to assay bacterial adhesion. The FA composition of gangliosides was studied by GC. The presence of O-acetyl GD3 (Neu5,9Ac2alpha2-8 NeuAcalpha2-3Galbeta1-4GlcCer) and trace amounts of GM1 [Galgamma1]3-3GalNAcgamma1,-3(Neualpha2-3)Galbeta1-4GlcCerl in human milk was confirmed. Medium-chain FA were almost absent in colostrum, whereas in the subsequent stages they rose to 20%. The levels of long-chain FA decreased after colostrum. With respect to the degree of saturation, gangliosides from colostrum were richer in monounsaturated FA than gangliosides synthesized during the rest of the lactation period, opposite to the pattern for PUFA. A human-ETEC colonization factor antigen II-expressing strain showed binding capacity to human milk GM3 (NeuAcalpha2-3Gal[1-4GlcCer). New data on human milk gangliosides have been gathered. A thorough knowledge of their composition is needed since they may have important biological implications in regard to newborns' defense against infection.

Receptor structure for F1C fimbriae of uropathogenic Escherichia coli

F1C fimbriae are correlated with uropathogenic Escherichia coli strains. Although F1C fimbriae mediate binding to kidney tubular cells, their receptor is not known. In this paper, we demonstrate for the first time specific carbohydrate residues as receptor structure for F1C-fimbria-expressing E. coli. The binding of the F1C fimbriated recombinant E. coli strain HB101(pPIL110-54) and purified F1C fimbriae to reference glycolipids of different carbohydrate compositions was evaluated by using thin-layer chromatography (TLC) overlay and solid-phase binding assays. TLC fimbrial overlay analysis revealed the binding ability of purified F1C fimbriae only to glucosylceramide (GlcCer), beta1-linked galactosylceramide 2 (GalCer2) with nonhydroxy fatty acids, lactosylceramide, globotriaosylceramide, paragloboside (nLc(4)Cer), lactotriaosylceramide, gangliotriaosylceramide (asialo-GM(2) [GgO(3)Cer]) and gangliotetraosylceramide (asialo-GM(1) [GgO(4)Cer]). The binding of purified F1C fimbriae as well as F1C fimbriated recombinant E. coli strain HB101(pPIL110-54) was optimal to microtiter plates coated with asialo-GM(2) (GgO(3)Cer). The bacterial interaction with asialo-GM(1) (GgO(4)Cer) and asialo-GM(2) (GgO(3)Cer) was strongly inhibited only by disaccharide GalNAcbeta1-4Galbeta linked to bovine serum albumin. We observed no binding to globotetraosylceramide or Forssman antigen (Gb(5)Cer) glycosphingolipids or to sialic-acid-containing gangliosides. It was demonstrated that the presence of a GalCer or GlcCer residue alone is not sufficient for optimal binding, and additional carbohydrate residues are required for high-affinity adherence. Indeed, the binding efficiency of F1C fimbriated recombinant bacteria increased by 19-fold when disaccharide sequence GalNAcbeta1-4Galbeta is linked to glucosylceramide as in asialo-GM(2) (GgO(3)Cer). Thus, it is suggested that the disaccharide sequence GalNAcbeta1-4Galbeta of asialo-GM(2) (GgO(3)Cer) which is positioned internally in asialo-GM(1) (GgO(4)Cer) is the high-affinity binding epitope for the F1C fimbriae of uropathogenic E. coli.

Pseudomonas aeruginosa binds to neoglycoconjugates bearing mucin carbohydrate determinants and predominantly to sialyl-Lewis x conjugates

Pseudomonas aeruginosa plays an important role in the colonization of the airways of patients suffering from cystic fibrosis. It binds to the carbohydrate part of respiratory and salivary mucins and its binding to cystic fibrosis mucins is even higher, suggesting that qualitative or/and quantitative modifications of the carbohydrate chains may be involved in this process. In order to find out the best carbohydrate receptors for P.aeruginosa, a flow cytometry technique using a panel of polyacrylamide based glycoconjugates labeled with fluorescein was developed. The neoglycoconjugates contained neutral, sialylated or sulfated chains analogous to carbohydrate determinants found at the periphery of respiratory mucins (Le(a), Le(y), Le(x), sialyl- and 3'-sulfo-Le(x), and blood group A determinants). We used also neoglycoconjugates containing Gal(alpha1-2)Galbeta and sialyl- N -acetyllactosamine determinants. The interaction of these glycoconjugates with the nonpiliated strain of P.aeruginosa, 1244-NP, was saturable except for the glycoconjugates containing blood group A or sialyl- N -acetyllactosamine epitopes. The measure of Kd indicated that strain 1244-NP had a higher affinity for the glycoconjugate bearing the sialyl-Le(x)determinant than for all the other glycoconjugates studied. The role of sialic acid was confirmed by competition assay using mainly sialylated mucin glycopeptides. In order to find out if this behavior was the same for pathological strains as for the 1244-NP mutant, four mucoid strains of P.aeruginosa isolated from cystic fibrosis patients were analyzed with the Le(x)neoglycoconjugate, its sialylated and its sulfated derivatives. Individual variations in the binding of these strains to the three glycoconjugates were observed. However, three strains out of four had a higher affinity for the sialyl-Le(x)than for the 3'-sulfo-Le(x)derivative.

Pili binding to asialo-GM1 on epithelial cells can mediate cytotoxicity or bacterial internalization by Pseudomonas aeruginosa

The interaction of Pseudomonas aeruginosa type IV pili and the glycosphingolipid asialo-GM1 (aGM1) can mediate bacterial adherence to epithelial cells, but the steps subsequent to this adherence have not been elucidated. To investigate the result of the interaction of pili and aGM1, we used polarized epithelial monolayers of Madin-Darby canine kidney (MDCK) cells in culture, which contained little detectable aGM1 on their apical surface but were able to incorporate exogenous aGM1. Compared to an untreated monolayer, P. aeruginosa PA103 displayed an eightfold increase in association with and fivefold more cytotoxicity toward MDCK cells pretreated with aGM1. Cytotoxicity of either carrier-treated or aGM1-treated monolayers required the type III secreted protein ExoU. Asialo-GM1 pretreatment of MDCK monolayers likewise augmented bacterial internalization of an isogenic invasive strain approximately fourfold. These increases were not seen in monolayers treated with GM1, the sialyated form of the glycolipid, and were inhibited by treatment with an antibody to aGM1. Also, the aGM1-mediated adhesion, cytotoxicity, and internalization required intact type IV pili since nonpiliated PA103 mutants were unaffected by aGM1 pretreatment of MDCK cells. These results demonstrate that epithelial cell injury and bacterial internalization can proceed from the same adhesin-receptor interaction, and they indicate that P. aeruginosa exoproducts solely determine the steps subsequent to adhesion.

Pilin C-terminal peptide binds asialo-GM1 in liposomes: a 2H-NMR study

Wideline 2H-NMR observations are described demonstrating the interaction of a synthetic peptide (PAK), representing residues 128-144 of the binding domain of pilin surface protein from Pseudomonas aeruginosa, with a complex glycosphingolipid thought to be its natural receptor. The receptor glycolipid (asialo-GM1) carried 2H probe nuclei on the terminal and next-to-terminal carbohydrate residues and was present as a minor component in fluid phosphatidylcholine liposomes. The peptide induced spectral changes that could be understood as arising from receptor motional changes, without receptor immobilization on the NMR time scale of 10(4) s-1. Spectral effects were reversed by reduction of the single peptide disulfide bond--a structural feature previously shown to be a determinant of PAK conformation (Campbell AP, McInnes C, Hodges RS, Sykes BD. 1995. Biochemistry 34:16255-16268). This is the first demonstration of PAK interaction with its epithelial cell receptor in liposomes.

Specific binding of Haemophilus influenzae to minor gangliosides of human respiratory epithelial cells

Gangliosides are sialylated glycosphingolipids that serve as receptors for various bacteria. To investigate endogenous gangliosides of human respiratory epithelial cells as potential receptors for Haemophilus influenzae, three strains, including nontypeable H. influenzae (NTHI) 1479, and isogenic fimbriated (f+) and nonfimbriated (f0) H. influenzae type b 770235, were 3H labeled and overlaid on two-dimensional thin-layer chromatography (TLC) plates containing either purified HEp-2 gangliosides or murine brain gangliosides. NTHI 1479 bound exclusively to two distinct minor ganglioside doublets, with mobilities near that of GM1. These minor gangliosides comprised only 14.2 and 9.4% of the total, respectively. NTHI 1479 also bound to a distinct ganglioside of human macrophages whose chromatographic mobilities closely resemble those of one of the NTHI-binding gangliosides of HEp-2 cells. H. influenzae type b 770235 f+ and f0 each bound to a different minor HEp-2 ganglioside doublet, with proportionately weaker affinity for a major ganglioside doublet. Remarkably, none of the three strains bound to any murine brain gangliosides. Moreover, when 80 to 90% of sialic acid residues were enzymatically removed from HEp-2 gangliosides, NTHI 1479 binding was proportionately impaired, compared with untreated controls. Our findings support a role for specific gangliosides of specific cells as receptors for H. influenzae strains. Our findings further demonstrate that individual minor gangliosides possess unique biological properties.

Interaction of the receptor binding domains of Pseudomonas aeruginosa pili strains PAK, PAO, KB7 and P1 to a cross-reactive antibody and receptor analog: implications for synthetic vaccine design

The four synthetic peptide antigens, PAK 128-144, PAO 128-144, KB7 128-144 and P1 126-148, correspond in amino acid sequence to the C-terminal receptor binding regions of four strains (PAK, PAO, KB7, P1) of Pseudomonas aeruginosa pilin. The NMR solution structures of the trans forms of the peptides show conserved beta-turns which have been implicated in antibody and receptor recognition. The interactions between these peptides and a cross-reactive monoclonal antibody, PAK-13, have been studied using two-dimensional (1)H NMR spectroscopy in order to map the antigenic determinants recognized by the antibody. Residues for which spectral changes were observed upon antibody binding differed from peptide to peptide but were mostly confined to one or both of the turn regions and to the hydrophobic pockets. Conformational changes in the beta-turns and hydrophobic pockets of these peptides upon antibody binding were also monitored by examination of the pattern of nuclear Overhauser effects (NOEs) versus transferred nuclear Overhauser effects (TRNOEs) for the free versus the bound peptides. Although TRNOEs developed strongly between side chain resonances in the hydrophobic pockets of the peptides, no additional backbone TRNOEs were observed in the presence of antibody, suggesting no major conformational changes in the secondary structures of the peptides upon binding. This implies a flexible antibody combining site, a feature which is discussed with respect to cross-reactivity, strain specificity, and the design of a synthetic peptide vaccine effective against a broad spectrum of P. aeruginosa strains. The binding of the PAK peptide to a disaccharide receptor analog, (beta GalNAc(1-4)beta Gal), was also studied using (1)H NMR in order to map the "adhesintope" recognized by the receptor. Spectral changes observed in the peptide spectrum with the binding of receptor were similar to those seen for the binding of antibody, suggesting that the epitope recognized by the antibody is structurally coincident with the adhesintope recognized by the receptor. The relevancy of this result is discussed with respect to immunogenicity versus pathogenicity, and the proper design of a vaccine which could prevent the mutational escape of the pathogen away from the host's defence systems.

Sialic acids in molecular and cellular interactions

Sialic acids (Sias) are terminal components of many glycoproteins and glycolipids especially of higher animals. In this exposed position they contribute significantly to the structural properties of these molecules, both in solution and on cell surfaces. Therefore, it is not surprising that Sias are important regulators of cellular and molecular interactions, in which they play a dual role. They can either mask recognition sites or serve as recognition determinants. Whereas the role of Sias in masking and in binding of pathogens to host cells has been documented over many years, their role in nonpathological cellular interaction has only been shown recently. The aim of this chapter is to summarize our knowledge about Sias in masking, for example, galactose residues, and to review the progress made during the past few years with respect to Sias as recognition determinants in the adhesion of pathogenic viruses, bacteria, and protozoa, and particularly as binding sites for endogenous cellular interaction molecules. Finally, perspectives for future research on these topics are discussed.

NMR solution structure of the receptor binding domain of Pseudomonas aeruginosa pilin strain P1. Identification of a beta-turn

The solution structure of the peptide antigen from the receptor binding domain of Pseudomonas aeruginosa strain P1 has been determined using two-dimensional 1H NMR techniques. Ensembles of solution conformations for the trans form of this 23-residue disulfide bridged peptide have been generated using a simulated annealing procedure in conjunction with distance and torsion angle restraints derived from NMR data. Comparison of the NMR-derived solution structures of the P1 peptide with those previously determined for the 17-residue PAK, PAO and KB7 strain peptides [McInnes, C., et al. (1993) Biochemistry 32, 13432-13440; Campbell, A.P., et al. (1995) Biochemistry 34, 16255-16268] reveals the common structural motif of a beta-turn, which may be the necessary structural requirement for recognition of a common cell surface receptor and a common cross-reactive antibody to which all four strains bind. The importance of this conserved beta-turn in the PAK, PAO, KB7 and P1 peptides is discussed with regard to the design of a synthetic peptide vaccine effective against multiple strains of Pseudomonas aeruginosa infections.

Interactions between glycoconjugates from human respiratory airways and Pseudomonas aeruginosa

Pseudomonas aeruginosa binds to different glycoconjugates in vitro. As six other bacteria, it binds to several glycolipids, mainly asialo GM1 and asialo GM2. Asialo GM1 has been reported to exist at the surface of cystic fibrosis cells. The binding of P. aeruginosa to asialo GM1 involves the pili, especially the C-terminal part of pilin that recognizes the GaINAc(beta 1,4) Gal sequence of asialo GM1.P. aeruginosa may also bind to sialylated membrane-bound glycoproteins. Human salivary and respiratory mucins are also recognized by P. aeruginosa. Mucins represent the main components of mucus. The peptide part (apomucin) of this broad family of secreted glycoproteins is encoded by several mucin genes. The apomucins are covered by a large number of carbohydrate chains that can be remarkably different and represent a mosaic of sites for attachment of microorganisms. The binding of P. aeruginosa to mucins involves outer membrane proteins and mucin carbohydrate chains that are structurally different from the carbohydrate recognized by pillin. Airway and salivary mucins secreted by patients suffering from cystic fibrosis (CF) show alterations in their carbohydrate moiety. The increased sulfation of airway mucins seems to correspond to a primary defect. Other abnormalities such as increased sialylation or fucosylation have also been detected. The binding of P. aeruginosa to airway or salivary mucins is increased in CF. However, the precise link between the carbohydrate alterations and the increased binding of P. aeruginosa to CF mucins remains to be elucidated.

Pathogenesis of corneal infection: binding of Pseudomonas aeruginosa to specific phospholipids

Clinical isolates of Pseudomonas aeruginosa were examined for binding interactions with phospholipids of corneal epithelium. Thin-layer chromatography (TLC) of lipids extracted from corneal epithelia followed by staining with an ammonium molybdate spray reagent revealed three phospholipid components, PL1, PL2, and PL3. The chromatographic mobility of PL1 was similar to that of the phospholipid standards phosphatidylinositol (PI) and phosphatidylserine (PS), which were not well resolved from one other; PL2 and PL3 comigrated with the standards phosphatidylcholine and phosphatidylethanolamine, respectively. By use of a TLC-bacterial overlay procedure, 35S-labeled P. aeruginosa organisms were shown to bind to PL1 but not to PL2 or PL3. P. aeruginosa binding to PL1 was concentration dependent. Alkaline methanolysis abolished the binding. PL1 was separated into two components, PL1-I and PL1-S, by chromatography on borate-treated TLC plates. Both PL1-I and PL1-S contained binding sites for P. aeruginosa. Mass spectral analysis identified PL1-I and PL1-S as PI and PS, respectively. Radiolabeled P. aeruginosa organisms were subsequently shown to bind to commercially available bovine PI and PS and synthetic dipalmitoyl-PS but not to other phospholipid standards, including bovine SM and PC or synthetic dioleoyl- and distearoyl-PC. A control Escherichia coli strain did not bind to either PS or PI. Tetramethylurea, a disrupter of hydrophobic associations, did not influence the binding of P. aeruginosa to PS or PI. P. aeruginosa bound to the monolayers of corneal epithelial cells. P. aeruginosa binding to the monolayer cultures as well as to rabbit corneas pretreated with exogenous PS and PI was significantly higher than that to those preincubated with PC or medium alone. The data suggest that phospholipids PS and PI present in mucus or on the cell surface may function as P. aeruginosa receptors and contribute to selective bacterium-host interactions responsible for initial colonization.

High-resolution thin-layer chromatography of gangliosides

In this review an updated overview of current improvements on thin-layer chromatography (TLC) of gangliosides over the past decade is provided. Basic general techniques and special advice is given for successful separation of glycosphingolipids. New approaches concerning continuous and multiple development, and several preparative TLC methods are also included. Emphasis is placed on TLC immunostaining and related techniques, i.e. practical applications of carbohydrate-specific antibodies, toxins and bacteria, viruses, lectins and eukaryotic cells. Thus, this review on ganglioside TLC summarizes its power as an analytical tool for a wide range of purposes.

Characterization of Pseudomonas aeruginosa fliO, a gene involved in flagellar biosynthesis and adherence

Pseudomonas aeruginosa binds to eukaryotic cells via both pilus and nonpilus adhesins, while binding of P. aeruginosa to mucin is pilus independent. To characterize genes involved in non-pilus-mediated adherence, transposon mutants of the nonpiliated strain P. aeruginosa PAK-NP that are unable to bind to cells or mucins were isolated. Two such mutants, P. aeruginosa B164 and P. aeruginosa RR18, were identified previously as deficient in binding to eukaryotic cells or mucins as well as nonmotile. The transposon insertion in each of these strains was mapped to the same gene. Sequence analysis of both DNA flanking the transposons and plasmids that could complement the mutations indicated that this open reading frame encodes a putative protein homolog of both Escherichia coli FliO and Erwinia carotovora subsp. atroseptica MopB. The transposons in both of these mutants are nonpolar, since the addition of the P. aeruginosa fliO gene in trans restored adherence to both cells and mucins to these mutants. The cloned fliO gene also complemented the motility defect of both B164 and RR18. A 1.6-kb KpnI fragment from the PAK chromosome that contained the fliO gene was sequenced. The fliO gene appears to be part of an operon with a complete open reading frame upstream of the FliO homolog encoding a putative protein homolog of FliN of both E. coli and Salmonella typhimurium. The partial open reading frame downstream of fliO encodes a putative homolog of both E. coli and S. typhimurium FliP. The fliN gene is flanked on its 5'-end by the 3'-end of a homolog of a fliM gene. The P. aeruginosa FliN protein was identified with a T7 expression system, while all attempts to identify the P. aeruginosa FliO protein were unsuccessful. Homologs of P. aeruginosa FliO are involved in the biosynthesis of flagella, but the function of FliO in this biosynthetic process remains unknown. Further study should reveal the precise role of P. aeruginosa FliO in non-pilus-mediated adherence, which could include regulation of expression or localization of a nonpilus adhesin.

Characterization of Pseudomonas aeruginosa-induced MDCK cell injury: glycosylation-defective host cells are resistant to bacterial killing

As a model for bacterium-induced epithelial cell injury, we have studied the interaction of Pseudomonas aeruginosa with polarized Madin-Darby canine kidney (MDCK) cells grown on filters. Following an initial period of bacterial adhesion, foci of injured host cells, which consisted of a central region of cell debris, surrounded by cells that were permeable and apparently necrotic, were formed. Host cell death was quantified by measuring the increased permeability of the monolayer to the macromolecular tracer [14C]inulin. Using this MDCK model system, we have identified bacterial and host cell factors necessary for the host cell damage. The ability of P. aeruginosa to cause MDCK cell damage was independent of elastase or exotoxin A production. In contrast, bacteria with a mutation in the regulatory locus exsA (which are deficient in exoenzyme S production) neither bound to nor caused host cell injury. MDCK cells with defects in cell surface glycosylation were resistant to cell injury, indicating that bacteria may require host cell glycolipids and/or glycoproteins as points of adhesion to cause subsequent host cell injury.

Blood group phenotype determines lectin-mediated adhesion of Pseudomonas aeruginosa to human outer ear canal epithelium

Pseudomonas aeruginosa is the most frequent bacterial pathogen causing acute diffuse otitis externa. In a recent prospective phase II study we demonstrated that lectin-mediated bacterial adhesion can be blocked by receptor-analogue carbohydrates in patients suffering from Pseudomonas aeruginosa-induced acute otitis externa. In this investigation, human ABO blood group antigens were analysed on outer ear canal epithelial cells with standard routine histological procedures by monoclonal antibodies for the blood groups A and B, and with Ulex europaeus I lectin for the blood group O, respectively. In all cases (n = 20) the blood groups could be shown immunohistologically. P. aeruginosa-specific adhesion and inhibition assays were performed in the presence of N-acetylgalactosamine (GalNAc), N-acetylglucosamine (GlcNAc), D-mannose and A-like substance. Outer ear canal tissue sections were incubated with P. aeruginosa (strain PA 60), presenting lectin-specificity for GalNAc. Sections from patients presenting with blood group A were closely settled with bacteria in the presence of non-specific GlcNAc, D-mannose and PBS however, GalNAc and A-like substance inhibited the microbial adhesion. Amongst others, P. aeruginosa present adhesion molecules (lectins) with specificity for GalNAc. Thus, the correlation between blood group A phenotype and P. aeruginosa-induced acute diffuse otitis externa was investigated. Statistical evaluation proved a highly significant association. These data support the hypothesis that P. aeruginosa lectins with GalNAc specificity apparently adhere to GalNAc moieties, representing the terminal blood group A-determinant and further indicate that patients presenting with blood group A may have a genetic disposition for this form of otitis externa.

Adherence of Pseudomonas aeruginosa and Candida albicans to glycosphingolipid (Asialo-GM1) receptors is achieved by a conserved receptor-binding domain present on their adhesins

Pseudomonas aeruginosa, a gram-negative bacterium, and Candida albicans, a dimorphic yeast, are evolutionarily distant microorganisms which can utilize filamentous structures termed pili and fimbriae, respectively, to mediate adherence to glycosphingolipids (asialoganglioside-GM1) receptors. The mechanism of adherence to glycosphingolipid receptors was investigated in these studies. By using monoclonal antibodies (MAbs) against purified pili of P. aeruginosa PAK (PK99H) and monospecific anti-peptide antibodies against the PAK pilin peptides [anti-PAK(128-144) and anti-PAK(134-140)], we demonstrated that these antibodies agglutinated C. albicans whole cells and cross-reacted with C. albicans fimbriae in immunoblots. A control MAb, PKL1, and anti-PAK(75-84) peptide antibodies failed to agglutinate C. albicans whole cells or cross-react with the fimbrial proteins. Conversely, the anti-C. albicans fimbrial MAb Fm16, but not Fm34, agglutinated P. aeruginosa PAK whole cells and Western blots (immunoblots). The interactions between PK99H and Fm16 and their respective homologous antigens were competitively inhibited by heterologous antigens; this demonstrated that the interactions between the antibodies and the heterologous antigens, i.e., PK99H with C. albicans fimbriae and Fm16 with P. aeruginosa pili, were highly specific and suggested that both adhesins share a common antigenic determinant. The immunological cross-reactivity between Fm16 and P. aeruginosa PAK pilin is localized onto the PAK(134-140) region as shown by a competitive enzyme-linked immunosorbent assay. The PAK(134-140) region of PAK pilin contains the epitope recognized by PK99H and also constitutes part of the receptor-binding domain of the pilus adhesin. Thus, the results from these studies suggest that common cell surface receptors are recognized by the P. aeruginosa and C. albicans adhesins because of a conserved receptor-binding domain on the adhesins.

Pili and lipopolysaccharide of Pseudomonas aeruginosa bind to the glycolipid asialo GM1

This study investigated which adhesins of Pseudomonas aeruginosa interact with the glycolipid asialo GM1, using solid-phase binding and thin-layer chromatography assays. Radioiodinated pili and flagella contaminated with lipopolysaccharide (LPS) bound to the glycolipid. When LPS was reduced to acceptable levels in pilus and flagellum samples, only pili specifically bound to the glycolipid. Commercial, radiolabeled LPS as well as whole bacteria of strain ATCC 19660 also bound to asialo GM1. Binding was specific, competitive, and saturable. Organ cultures of whole mouse eyes and scanning electron microscopy techniques were used also, and strain ATCC 19660 was inhibited from corneal binding by exogenous pili or commercial LPS and inhibition was concentration dependent for both. Binding of radiolabeled strain ATCC 19660 bacteria to neutral lipids extracted from bovine corneal epithelial tissue showed that the bacteria bound to a glycolipid which migrated at a position similar to that of an asialo GM1 standard and that the glycolipid stained positively with an antibody specific for asialo GM1. The data provide evidence that pili (reduced LPS) and LPS of P. aeruginosa bind to asialo GM1 glycolipid and that the glycolipid is not restricted to the mouse cornea.

PA-I and PA-II lectin interactions with the ABO(H) and P blood group glycosphingolipid antigens may contribute to the broad spectrum adherence of Pseudomonas aeruginosa to human tissues in secondary infections

Pseudomonas aeruginosa may cause serious infections in most human tissues/organs. Its adherence to them is mediated by a battery of adhesins including the PA-I and PA-II lectins, which are produced in this bacterium in high quantities. PA-I binds to the D-galactose of the erythrocyte glycosphingolipids exhibiting highest affinities for B and Pk (followed by P1) antigens, while PA-II preferentially binds to the L-fucose of H, A and B antigens. Intact P. aeruginosa cells also exhibit a clear Pk and P1 over p preference. Such affinities for the most common human ABH and P system antigens may underlie the widespread tissue infectivity and pathogenicity of this bacterium.

Binding of the galactose-specific Pseudomonas aeruginosa lectin, PA-I, to glycosphingolipids and other glycoconjugates

The carbohydrate-binding specificity of Pseudomonas aeruginosa lectin I (PA-I) in iodinated or biotinylated form was studied. A large number of glycosphingolipids, as well as some glycoproteins and neoglycoproteins were used as ligands. Also, inhibition by free saccharides of PA-I binding to glycosphingolipids was tested. It was found that the lectin binds most strongly to terminal and nonsubstituted Gal alpha 3Gal- or Gal alpha 4Gal-structures.

The pili of Pseudomonas aeruginosa strains PAK and PAO bind specifically to the carbohydrate sequence beta GalNAc(1-4)beta Gal found in glycosphingolipids asialo-GM1 and asialo-GM2

Pseudomonas aeruginosa employs pili to mediate adherence to epithelial cell surfaces. The pilus adhesin of P. aeruginosa strains PAK and PAO has been shown to bind to the glycolipid asialo-GM1 (Lee et al., 1994--accompanying article). PAK and PAO pili were examined for their abilities to bind to the synthetic beta GalNAc(1-4)beta Gal (a minimal structural carbohydrate receptor sequence of asialo-GM1 and asialo-GM2 proposed by Krivan et al., 1988a) using solid-phase binding assays. Both pili specifically bound to beta GalNAc(1-4)beta Gal. The binding of beta GalNAc(1-4)beta Gal-Biotin to the immobilized PAK and PAO pili was inhibited by corresponding free pili. The receptor binding domain of the PAK pilus resides in the C-terminal disulphide-looped region (residues 128-144) of the pilin structural subunit (Irvin et al., 1989). Biotinylated synthetic peptides corresponding the C-terminal residues 128-144 of P. aeruginosa PAK and PAO pilin molecules were shown to bind to the beta GalNAc(1-4)beta Gal-(bovine serum albumin (BSA)). The binding of biotinylated peptides to beta GalNAc(1-4)beta GAL-BSA was inhibited by PAK pili, Ac-KCTSDQDEQFIPKGCSK-OH (AcPAK(128-144)ox-OH) and Ac-ACKSTQDPMFTPKGCDN-OH (AcPAO(128-144)ox-OH) peptides. (In these peptides Ac denotes N alpha-acetylation of the N-terminus, -OH means a peptide with a free alpha-carboxyl group at the C-terminus and the 'ox' denotes the oxidation of the sulphhydryl groups of Cys-129 and Cys-142.) Both acetylated peptides were also able to inhibit the binding of beta GalNAc(1-4)beta Gal-biotin to the corresponding BSA-Peptide(128-144)ox-OH conjugates.(ABSTRACT TRUNCATED AT 250 WORDS)

The binding of Pseudomonas aeruginosa pili to glycosphingolipids is a tip-associated event involving the C-terminal region of the structural pilin subunit

Pili are one of the adhesins of Pseudomonas aeruginosa that mediate adherence to epithelial cell-surface receptors. The pili of P. aeruginosa strains PAK and PAO were examined and found to bind gangliotetraosyl ceramide (asialo-GM1) and, to a lesser extend, II3N-acetylneuraminosylgangliotetraosyl ceramide (GM1) in solid-phase binding assays. Asialo-GM1, but not GM1, inhibited both PAK and PAO pili binding to immobilized asialo-GM1 on the microtitre plate. PAO pili competitively inhibited PAK pili binding to asialo-GM1, suggesting the presence of a structurally similar receptor-binding domain in both pilus types. The interaction between asialo-GM1 and pili occurs at the pilus tip as asialo-GM1 coated colloidal gold only decorates the tip of purified pili. Three sets of evidence suggest that the C-terminal disulphide-bonded region of the Pseudomonas pilin is exposed at the tip of the pilus: (i) immunocytochemical studies indicate that P. aeruginosa pili have a basal-tip structural differentiation where the monoclonal antibody (mAb) PK3B recognizes an antigenic epitope displayed only on the basal ends of pili (produced by shearing) while the mAb PK99H, whose antigenic epitope resides in residues 134-140 (Wong et al., 1992), binds only to the tip of PAK pili; (ii) synthetic peptides, PAK(128-144)ox-OH and PAO(128-144)ox-OH, which correspond to the C-terminal disulphide-bonded region of Pseudomonas pilin are able to bind to asialo-GM1 and inhibit the binding of pili to the glycolipid; (iii) PK99H was shown to block PAK pilus binding to asialo-GM1.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of lipid-linked oligosaccharides (neoglycolipids) in the identification of carbohydrate receptors for microbial pathogens

Specific oligosaccharide chains on the host cell surface act as receptors for many microbial pathogens. Identification of receptor structures is an important step in the understanding of the pathogenesis of infection. Glycolipid receptors have been identified by direct binding assays. However, technical difficulties have prevented demonstration of bacterial binding to the oligosaccharides of glycoproteins; these have been identified mainly by inhibition assays. By a novel technique developed in our laboratory, oligosaccharides released from glycoproteins are linked to lipids to form neoglycolipids. These can be used in bacterial binding assays. The feasibility of this approach has been demonstrated using type 1 fimbriated Escherichia coli binding specifically to neoglycolipids rich in mannose residues. The application of the method has resulted in a demonstration of a new type of adhesive specificity for E. coli and differences in the binding specificities of E coli and Pseudomonas aeruginosa. Further application of this technique by generating oligosaccharides purified from mucus glycoproteins from patients with cystic fibrosis to use in binding assays with P aeruginosa is currently being undertaken. The basic knowledge gained by this approach may in time see the development of novel therapy in the form of receptor blocking agents.

Evidence for asialo GM1 as a corneal glycolipid receptor for Pseudomonas aeruginosa adhesion

Anti-gangliotetraosylceramide (anti-asialo GM1) and antiparagloboside monoclonal antibodies (MAbs) were used in immunofluorescence, immunoelectron-microscopic, and in vitro binding inhibition assays to determine whether either of the glycolipids was detectable in the normal cornea, whether levels changed following corneal scarification and either trypsin treatment or incubation in vitro with Pseudomonas aeruginosa, and whether either of the MAbs could competitively inhibit P. aeruginosa binding to cornea. No immunostaining above background for either glycolipid was observed in frozen, unfixed sections or in lightly fixed, K4M-embedded antibody-gold-labeled thin sections of normal cornea. In frozen sections of organ-cultured scarified cornea, no increased immunostaining for anti-asialo GM1 or antiparagloboside reactivity was noted immediately or 60 min after corneal scarification. However, at 60 min after scarification and in vitro incubation of the eye with either trypsin or P. aeruginosa, enhanced immunostaining for both glycolipids was associated with cells within or immediately adjacent to the wound site. Trypsin increased immunoreactivity in the wound site more markedly compared with incubation with P. aeruginosa, but immunostaining was similarly localized with either treatment. No staining above background was seen in control sections. Similarly, with immunoelectron microscopy, increased immunogold-MAb staining for both glycolipids was seen on the plasma membranes of the wound-site cells of eyes incubated with either trypsin or P. aeruginosa compared with controls that were similarly immunostained but with the primary antibody either omitted or substituted with a nonspecific MAb. Competitive binding inhibition assays, in which the bacterial inoculum or the eye in organ culture was incubated with anti-asialo GM1 MAb prior to topical ocular application of the bacteria, showed significantly decreased P. aeruginosa adhesion compared with preparations similarly treated with phosphate-buffered saline or antiparagloboside MAb. These data provide evidence to support the hypothesis that asialo GM1, not paragloboside, serves as a receptor for P. aeruginosa binding to the scarified cornea of the adult mouse and spatially localizes both glycolipids in the wound site.

Pseudomonas aeruginosa pili bind to asialoGM1 which is increased on the surface of cystic fibrosis epithelial cells

The basis for the unique association of Pseudomonas aeruginosa and the cystic fibrosis (CF) lung has remained obscure despite major advances in the understanding of the molecular genetic cause of this disease. There is evidence to suggest that abnormalities in CF transmembrane conductance regulator function result in alterations in the glycosylation of epithelial components. The number of asialoGM1 residues, as representative of a class of glycolipids which contain a GalNAc beta 1-4Gal sequence for P. aeruginosa attachment, was quantified by flow cytometric studies of respiratory epithelial cells in primary culture from both CF patients and normal subjects. Superficial asialoGM1 was detected on 12% of the CF cells as compared with 2.9% of the cells from normal control subjects (P = 0.03, chi 2 = 4.73), and more asialoGM1 residues were exposed on CF cells after modification by P. aeruginosa exoproducts. AsialoGM1, but not the sialylated glycolipid GM1, was demonstrated to be a receptor for 125I-labeled P. aeruginosa pilin, a major adhesin for this organism, and exogenous asialoGM1 was found to competitively inhibit P. aeruginosa adherence to epithelial cells, thus, confirming the biological role of the asialoGM1 receptor. Quantitative and qualitative differences in the sialylation of superficial glycolipids in CF epithelial cells may directly contribute to the colonization of the CF lung by P. aeruginosa.

Altered carbohydrate composition of salivary mucins from patients with cystic fibrosis and the adhesion of Pseudomonas aeruginosa

We compared the chemical composition of salivary mucin glycopeptides from cystic fibrosis (CF) and from non-CF subjects and the adhesion of Pseudomonas aeruginosa to these different salivary glycopeptides. Three pools of CF saliva, four pools of non-CF saliva, one individual CF saliva, and one individual non-CF saliva were studied. The soluble fraction of the saliva was treated with pronase, and gel filtration was performed to obtain high and low molecular mass salivary mucin glycopeptides. The yield of total glycopeptides was significantly higher from CF than from non-CF saliva. Furthermore, the chemical composition revealed a significantly higher sialic acid content in CF than in non-CF mucin glycopeptides, and higher sulfate and fucose content in CF than in non-CF high molecular mass glycopeptides. We studied the adhesion of a nonmucoid strain of P. aeruginosa (1244), its nonpiliated isogenic derivative, and a mucoid strain (M35) to salivary mucin glycopeptides from patients with CF and from non-CF subjects. The three strains bound significantly more to the CF salivary glycopeptides than to the corresponding non-CF salivary glycopeptides. The nonpiliated isogenic mutant of P. aeruginosa 1244 also bound to CF salivary glycopeptides, suggesting that the adhesion of P. aeruginosa could involve nonpilus adhesions. Furthermore, neuraminidase treatment of CF glycopeptides decreased the adhesion of P. aeruginosa 1244. Altogether these results suggested that differences in mucins may in part explain the specificity of P. aeruginosa for CF.

Adhesins and receptors of Pseudomonas aeruginosa associated with infection of the respiratory tract

Substantial progress has been made in defining a number of Pseudomonas adhesins which may be involved in the pathogenesis of respiratory infection. As yet, it is unclear which of these adhesins are primarily responsible for initiating infection in CF. The findings that CF epithelial cells have increased numbers of receptors for P. aeruginosa attachment and that CF epithelia are less highly sialylated than normal epithelial cells is consistent with a role for Pseudomonas pili in the initial recognition of asialoganglioside receptors on epithelial cells. In addition, there is ample evidence supporting the presence of several classes of non-pilus adhesins. Adherence properties of P. aeruginosa clearly vary from strain to strain and it appears likely that all potential adhesions are not equally expressed. More importantly, the regulation of the expression of these adhesins is unlikely to be constitutive. Some may be expressed only when triggered by the appropriate environmental conditions as found in vivo. In reviewing the pathogenesis of Pseudomonas infection in the CF lung, several classes of receptors must be considered. Pseudomonas infection is limited to the bronchi in CF. The organisms do not invade the bronchial tissue, but remain in the airways forming a biofilm with associated microcolonies. Thus, it would seem reasonable to expect Pseudomonas receptors within respiratory mucin. However, to date, there is little confirmatory data to support the presence of specific receptors in mucin. Alternatively, it is possible that the failure of bacterial binding to mucin components may contribute to colonization as organisms which are not efficiently cleared by muco-ciliary function may persist in the airways long enough to find or expose cryptic epithelial binding sites. This hypothesis is supported by binding studies which demonstrate decreased Pseudomonas attachment to CF as compared with normal respiratory mucins. Based on the available data, there appears to be a hierarchy of adhesin expression. Multiple ligand-receptor interactions may occur in the respiratory tract and it may be difficult to analyze the effect of secondary adhesins in the presence of what appears to be the dominant ligand, i.e. pilin. Thus, the failure to find the expected sialylated receptor for Pseudomonas attachment may be due to methodologic problems such as studying strains under conditions in which pili are well expressed and affinities for asialylated receptors predominate. This may not be the situation in vivo after the initial contact of the infecting organisms with the epithelial surface. Not only must the organism attach initially, but it must then be able to persist within the lung. Further studies, based on genetically defined mutants should help define which P. aeruginosa gene products and which components of the CF but not the normal epithelium are responsible for this unique but ultimately fatal host/bacterium interaction.

Low-molecular-mass human salivary mucin, MG2: structure and binding of Pseudomonas aeruginosa

Low-molecular-mass human salivary mucin, MG2, was isolated from human submandibular-sublingual saliva (HSMSL) employing citraconylation, gel filtration, and ion-exchange chromatography. Following proteolysis with trypsin, two glycopeptides were purified. The higher molecular weight glycopeptide was highly glycosylated with O-linked units. The lower molecular weight glycopeptide was less glycosylated and contained most of the N-linked units. Interaction between components of HSMSL and pili of Pseudomonas aeruginosa was examined by an overlay binding assay. Pili were found to bind to MG2. Preliminary studies indicated that the binding may involve a protein to protein interaction.

Differences in the binding specificities of Pseudomonas aeruginosa M35 and Escherichia coli C600 for lipid-linked oligosaccharides with lactose-related core regions

Membrane glycolipids contain the lactose sequence (galactose linked to glucose), and the oligosaccharide is variously extended such that there is a cell-type-specific repertoire. In this study, binding of Pseudomonas aeruginosa M35 to lipid-linked lactose (Gal beta 1-4Glc [structure 1]), lacto-N-neotetraose (Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc [structure 2]), lacto-N-tetraose (Gal beta 1-3GlcNAc beta 1-3Gal beta 1-4Glc [structure 3]), and asialo GM1 (Gal beta 1-3GalNAc beta 1-4Gal beta 1-4Glc [structure 4]) was evaluated and compared with binding of Escherichia coli C600 to these compounds. Oligosaccharides were linked to the lipid phosphatidylethanolamine dipalmitoate, and the resulting neoglycolipids were resolved on thin-layer chromatograms or coated onto plastic microtiter wells. Lipid-linked structures 1 to 4 were bound by P. aeruginosa and E. coli in the chromatogram assay, but only structure 4 was bound in the microtiter well assay. As shown previously for E. coli binding to lipid-linked structures 1 to 3, binding to lipid-linked structure 4 was not inhibited with oligosaccharide, indicating a requirement for lipid and oligosaccharide. With few exceptions, sialylation and fucosylation of structures 1 to 4 resulted in impaired or abolished binding. Comparisons of binding intensities in the chromatogram assay indicated that recognition by P. aeruginosa and recognition by E. coli are not identical. Presence of the additional disaccharide unit, as in structure 2, resulted in enhanced binding of P. aeruginosa but diminished binding of E. coli relative to lactose binding; fucosylation at galactose of lactose resulted in markedly diminished binding of P. aeruginosa only. In the microtiter well assay, binding of E. coli to asialo GM1 was much weaker than P. aeruginosa binding. The saccharide-plus-lipid-dependent adhesion may be an important factor in increased susceptibility to infection of epithelia already damaged by microbial and chemical agents; the differing strengths of adhesion to the structural variants may relate to tissue tropism.