Host epithelial glycoconjugates and pathogenic bacteria

Uroplakin Ia is the urothelial receptor for uropathogenicEscherichia coli: evidence from in vitro FimH binding

The binding of uropathogenic Escherichia coli to the urothelial surface is a crucial initial event for establishing urinary tract infection because it allows the bacteria to gain a foothold on the urothelial surface, thus preventing them from being removed by micturition. In addition, it triggers bacterial invasion as well as host urothelial defense. This binding is mediated by the FimH adhesin located at the tip of the bacterial type 1-fimbrium, a filamentous attachment apparatus, and its urothelial receptor. We have prepared a biotinylated, recombinant FimH-FimC adhesin:chaperone complex and used it to identify its mouse urothelial receptor. The FimH-FimC complex binds specifically to a single 24 kDa major mouse urothelial plaque protein, which we identified as uroplakin Ia by mass spectrometry, cDNA cloning and immunoreactivity. The terminal mannosyl moieties on Asn-169 of uroplakin Ia are responsible for FimH as well as concanavalin A binding. Although FimH binds to uroplakin Ia with only moderate strength (Kd ∼100 nM between pH 4 and 9), the binding between multiple fimbriae of a bacterium and the crystalline array of polymerized uroplakin receptors should achieve high avidity and stable bacterial attachment. The FimH-FimC complex binds preferentially to the mouse urothelial umbrella cells in a pattern similar to uroplakin staining. Our results indicate that the structurally related uroplakins Ia and Ib are glycosylated differently, that uroplakin Ia serves as the urothelial receptor for the type 1-fimbriated E. coli, and that the binding of uropathogenic bacteria to uroplakin Ia may play a key role in mediating the urothelial responses to bacterial attachment.

Agglutinin and acidic proline-rich protein receptor patterns may modulate bacterial adherence and colonization on tooth surfaces

Bacterial binding to salivary proteins may in part account for individual differences in the colonization of tooth surfaces. High-molecular-weight glycoproteins, agglutinins, mediate S. mutans adherence, whereas acidic proline-rich proteins mediate adherence of other early-colonizing streptococci and Actinomyces. The aim of the present study was to examine the composition of adherence-related salivary proteins and dental plaque micro-organisms in three individuals with a low, moderate, and high capacity to mediate S. mutans adherence. The S. mutans (strain Ingbritt) binding activity resided with a 300-kDa agglutinin which was six-fold more prevalent in the high S. mutans binding saliva compared with the low one. Binding to all three salivas was completely blocked by a monoclonal anti-agglutinin antibody. The moderate S. mutans binding saliva was found to contain adherence-inhibiting components. Furthermore, the low and moderate S. mutans binding salivas mediated binding of A. naeslundii strain LY7 to a greater extent than the saliva with high S. mutans binding. The A. naeslundii binding activity resided with the acidic proline-rich proteins (APRPs) and paralleled the relative content of 106- and 150-residue APRPs. Low A. naeslundii binding coincided with an almost two-fold higher ratio of 106/150 APRPs compared with the high A. naeslundii binding saliva. During conventional gel filtration, a degradation of the acidic, basic, and glycosylated proline-rich proteins was evident in the saliva with high S. mutans and low A. naeslundii binding. This saliva donor had a comparably high rate of dental plaque formation, high counts of S. mutans, and low counts of other streptococci and Actinomyces.

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.

Adherence to lipids and intestinal mucin by a recently recognized human pathogen, Campylobacter upsaliensis

Campylobacter upsaliensis is a recently recognized human enteric pathogen associated with enteritis, colitis, bacteremia, and sepsis. Very little is known about the mechanisms of pathogenesis of this organism. The goals of this study were to determine whether C. upsaliensis binds to epithelial cells and whether there are specific lipid molecules that might serve as cell membrane receptors. In addition, we also explored C. upsaliensis binding to purified human small-intestinal mucin, since the mucus gel overlying the epithelium provides an initial contact surface for the bacteria and must be penetrated for the organisms to reach their cell receptors. Binding of C. upsaliensis to model epithelial cells was shown by microscopy adhesion assays, and binding to lipids was detected by thin-layer chromatography-overlay assays. Bacteria bound to phosphatidylethanolamine (PE), gangliotetraosylceramide (Gg4), and, more weakly, to phosphatidylserine (PS). There was no binding to ceramide, cholesterol, phosphatidylcholine, and globosides. Using receptor-based microtiter well immunoassays, we observed binding to be equal, specific, and saturable for PE and Gg 4 but low and nonspecific for PS. At least five bacterial surface proteins (50 to 90 kDa) capable of PE binding were identified by a lipid-silica affinity column technique. In slot blot overlay assays, biotin-labeled C. upsaliensis also bound in a concentration-dependent fashion to purified human small-intestinal mucin, implying that these microorganisms also express an adhesin(s) recognizing a specific mucin epitope(s). We speculate that binding to mucins may influence access of the bacteria to cell membrane receptors and thereby influence host resistance to infection.

Protein glycosylation. Structural and functional aspects

During the last decade, there have been enormous advances in our knowledge of glycoproteins and the stage has been set for the biotechnological production of many of them for therapeutic use. These advances are reviewed, with special emphasis on the structure and function of the glycoproteins (excluding the proteoglycans). Current methods for structural analysis of glycoproteins are surveyed, as are novel carbohydrate-peptide linking groups, and mono- and oligo-saccharide constituents found in these macromolecules. The possible roles of the carbohydrate units in modulating the physicochemical and biological properties of the parent proteins are discussed, and evidence is presented on their roles as recognition determinants between molecules and cells, or cell and cells. Finally, examples are given of changes that occur in the carbohydrates of soluble and cell-surface glycoproteins during differentiation, growth and malignancy, which further highlight the important role of these substances in health and disease.

Role of a 22-kilodalton pilin protein in binding of Pseudomonas cepacia to buccal epithelial cells

Previously we have shown that many isolates of Pseudomonas cepacia obtained from the sputum of patients with cystic fibrosis exhibit specific binding to purified mucins. The binding was mediated by a 22-kDa protein located on peritrichous pili of the bacteria. Nonpiliated bacteria did not bind to mucin. In the present study we found that both piliated and nonpiliated P. cepacia bind to buccal epithelial cells (BECs) obtained from health human volunteers. Scatchard plot analyses of binding data with the LIGAND computer program suggest the presence of at least two classes of cell receptors (A and B) for piliated P. cepacia (isolates PC 5 and PC 7) and a single class of receptors (A) for nonpiliated P. cepacia (isolates PC 45 and PC 61). The affinity constants for receptor A varied from 1.7 x 10(-9) to 4.7 x 10(-8) ml/CFU. Receptor B had a lower affinity constant (2.5 x 10(-10) to 1.2 x 10(-9) ml/CFU) but a greater saturation capacity. Receptor B was similar in affinity to the mucin receptor for piliated P. cepacia (3.3 x 10(-10) to 1.3 x 10(-9) ml/CFU). Purified mucin partially inhibited the binding of piliated bacteria to BECs by competing with BEC receptor site B. The purified 22-kDa pilin adhesin and an antiadhesin antibody also caused partial inhibition. One BEC receptor for piliated isolates of P. cepacia was identified as a 55-kDa protein as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of BEC homogenate supernatants, Western blotting (immunoblotting), and bacterial overlay assays. Preincubation of piliated bacteria with either mucin or the antiadhesin antibody abolished binding to the 55-kDa BEC receptor. In summary, our results indicate that piliated P. cepacia interacts with BECs by using at least two different adhesin-receptor systems. One adhesin (not examined) is common to piliated and nonpiliated P. cepacia, but the other system is the pilus-localized 22-kDa mucin-binding adhesin and its 55-kDa BEC receptor protein. Because it mediates adherence to both mucin and epithelial cells, the 22-kDa adhesin may be an important virulence determinant in cystic fibrosis lung infections in which mucins are abnormally adhesive on mucosal surfaces.

Swine and cattle enterotoxigenic Escherichia coli-mediated diarrhea. Development of therapies based on inhibition of bacteria-host interactions

Enterotoxigenic Escherichia coli (ETEC) frequently occurs in diarrheal disease afflicting domestic animals. In this paper is summarized the research carried out over the last decade on the two important determinants of virulence that plays a role in the development of the infection, namely the colonizing ability of the small intestine mediated by specific fimbrial adhesins acting as lectins and the production of enterotoxins. Recent progress in knowledge of the phenomenon led to alternative strategies of prevention and cure of enteric infection. Since bacterial recognition of mucosa surface receptors in an initial event in colonization, several approaches based on the competitive inhibition of ETEC adhesion have been developed. This review examines the following approaches: competitive colonization with non pathogenic strains, design of adhesin or toxin vaccines, receptor analog therapy and methods for in vivo suppression of virulence factors.

Fimbrial types among respiratory isolates belonging to the family Enterobacteriaceae

Bacterial attachment is believed to be an early step in gram-negative nosocomial pneumonia. The frequency of fimbria-associated adhesins among respiratory pathogens has not been studied in detail. In this study isolates belonging to the family Enterobacteriaceae, prospectively obtained from intensive care unit patients who were suspected of having nosocomial pneumonia, were examined for fimbria-associated adhesins. Type 3, P, type 1, and other fimbrial phenotypes were identified by specific hemagglutination and electron microscopy. The Klebsiella type 3 fimbrial phenotype was further characterized by using a monoclonal antibody. Also, both type 3 and Escherichia coli P fimbrial genotypes were detected by using DNA colony blot assays. The frequencies of genera or species isolated were as follows: Enterobacter (38.6%), Klebsiella (26.8%), Serratia (17.7%), E. coli (13%), and Proteus (5.2%). Isolates of Klebsiella oxytoca, K. pneumoniae, and Enterobacter cloacae most commonly possessed the type 3 fimbrial phenotype and genotype. The phenotype and genotype for E. coli P fimbriae (46.2 and 50%, respectively), a known pathogenic determinant in the urinary tract, were detected more frequently than expected. In addition, a previously unspecified hemagglutinin that was specific for porcine erythrocytes was almost uniformly expressed among isolates of Enterobacter aerogenes. Finally, the expression of the type 1 fimbrial phenotype was widely detected among the isolates tested but notably absent among K. oxytoca and Proteus mirabilis isolates. The frequency of the various fimbrial types identified suggests a role for these bacterial organelles in adherence to respiratory epithelia.