Structure determination of five sulfated oligosaccharides derived from tracheobronchial mucus glycoproteins

Computationally guided conversion of the specificity of E-selectin to mimic that of Siglec-8

Sulfated glycans have been found to be associated with various diseases and therefore have significant potential in molecular pathology as biomarkers. Although lectins are useful reagents for detecting glycans, there is a paucity of sulfate-recognizing lectins, and those that exist, such as from Maackia amurensis, display mixed specificities. Recombinant lectin engineering offers an emerging tool for creating novel glycan recognition by altering and/or enhancing endogenous specificities. The present study demonstrated the use of computational approaches in the engineering of a mutated form of E-selectin that displayed highly specific recognition of 6'-sulfo-sialyl Lewis X (6'-sulfo-sLe^x), with negligible binding to its endogenous nonsulfated ligand, sLe^x. This new specificity mimics that of the unrelated protein Siglec-8, for which 6'-sulfo-sLe^x is its preferred ligand. Molecular dynamics simulations and energy calculations predicted that two point mutations (E92A/E107A) would be required to stabilize binding to the sulfated oligosaccharide with E-selectin. In addition to eliminating putative repulsions between the negatively charged side chains and the sulfate moiety, the mutations also abolished favorable interactions with the endogenous ligand. Glycan microarray screening of the recombinantly expressed proteins confirmed the predicted specificity change but also identified the introduction of unexpected affinity for the unfucosylated form of 6'-sulfo-sLe^x (6'-sulfo-sLacNAc). Three key requirements were demonstrated in this case for engineering specificity for sulfated oligosaccharide: 1) removal of unfavorable interactions with the 6'-sulfate, 2) introduction of favorable interactions for the sulfate, and 3) removal of favorable interactions with the endogenous ligand.

Observations of, and Insights into, Cystic Fibrosis Mucus Heterogeneity in the Pre-Modulator Era: Sputum Characteristics, DNA and Glycoprotein Content, and Solubilization Time

Airway obstruction with chronic inflammation and infection are major contributors to the lung damage and mortality of cystic fibrosis (CF). A better understanding of the congested milieu of CF airways will aid in improving therapeutic strategies. This article retrospectively reports our observations, and discusses insights gained in the handling and analysis of CF sputa. CF and non-CF mucus samples were surveyed for morphological features by electron microscopy and analyzed for the macromolecular dry weight (MDW), total protein, lipid, carbohydrate, and DNA. Mucus character was investigated with chemical solubilization time as a comparative tool. CF mucus appeared distinctly thick, viscous, and heterogeneous, with neutrophils as the dominant immune cell. CF sputum DNA content varied markedly for and between individuals (~1–10% MDW), as did solubilization times (~1–20 h). CF Sputum DNA up to 7.1% MDW correlated positively with solubilization time, whereas DNA >7.1% MDW correlated negatively. 3D analysis of CF sputa DNA, GP, and solubilization times revealed a dynamic and predictive relationship. Reflecting on the heterogeneous content and character of CF mucus, and the possible interplay in space and time in the respiratory tract of polymeric DNA and mucous glycoproteins, we highlight it’s potential to affect infection-related airway pathologies and the success of therapeutic interventions.

Identification and characterization of sulfated glycoproteins from small cell lung carcinoma cells assisted by management of molecular charges

Proteins carrying sulfated glycans (i.e., sulfated glycoproteins) are known to be associated with diseases, such as cancer, cystic fibrosis, and osteoarthritis. Sulfated glycoproteins, however, have not been isolated or characterized from complex biological samples due to lack of appropriate tools for their enrichment. Here, we describe a method to identify and characterize sulfated glycoproteins that are involved in chemical modifications to control the molecular charge of the peptides. In this method, acetohydrazidation of carboxyl groups was performed to accentuate the negative charge of the sulfate group, and Girard's T modification of aspartic acid was performed to assist in protein identification by MS tagging. Using this approach, we identified and characterized the sulfated glycoproteins: Golgi membrane protein 1, insulin-like growth factor binding protein-like 1, and amyloid beta precursor-like protein 1 from H2171 cells, a small cell lung carcinoma cell line. These sulfated glycoproteins carry a complex-type N-glycan with a core fucose and 4'-O-sulfated LacdiNAc as the major glycan.

Identification of glycan structure alterations on cell membrane proteins in desoxyepothilone B resistant leukemia cells

Resistance to tubulin-binding agents used in cancer is often multifactorial and can include changes in drug accumulation and modified expression of tubulin isotypes. Glycans on cell membrane proteins play important roles in many cellular processes such as recognition and apoptosis, and this study investigated whether changes to the glycan structures on cell membrane proteins occur when cells become resistant to drugs. Specifically, we investigated the alteration of glycan structures on the cell membrane proteins of human T-cell acute lymphoblastic leukemia (CEM) cells that were selected for resistance to desoxyepothilone B (CEM/dEpoB). The glycan profile of the cell membrane glycoproteins was obtained by sequential release of N- and O-glycans from cell membrane fraction dotted onto polyvinylidene difluoride membrane with PNGase F and β-elimination respectively. The released glycan alditols were analyzed by liquid chromatography (graphitized carbon)-electrospray ionization tandem MS. The major N-glycan on CEM cell was the core fucosylated α2-6 monosialo-biantennary structure. Resistant CEM/dEpoB cells had a significant decrease of α2-6 linked sialic acid on N-glycans. The lower α2-6 sialylation was caused by a decrease in activity of β-galactoside α2-6 sialyltransferase (ST6Gal), and decreased expression of the mRNA. It is clear that the membrane glycosylation of leukemia cells changes during acquired resistance to dEpoB drugs and that this change occurs globally on all cell membrane glycoproteins. This is the first identification of a specific glycan modification on the surface of drug resistant cells and the mechanism of this downstream effect on microtubule targeting drugs may offer a route to new interventions to overcome drug resistance.

Enrichment method of sulfated glycopeptides by a sulfate emerging and ion exchange chromatography

Sulfated glycoproteins are of growing importance for biomarker discovery, as well as for investigating molecular recognition processes. Mass spectrometry (MS) has become a powerful technique for the characterization of glycans and glycoproteins. However, characterization and detection of sulfated glycopeptides by MS is difficult because of the low abundance and low ionization efficiency of these molecules. To overcome this problem, we developed a novel enrichment procedure for sulfated glycopeptides. The procedure consists of anion exchange chromatography and a sulfate emerging (SE) method which controls the net charge of peptides by utilizing limited proteolyzes and modification with acetohydrazide. Using this procedure, we are able to enrich and characterize the sulfated glycopeptides of bovine luteinizing hormone (bLH). Furthermore, we demonstrate the enrichment and detection of sulfated glycopeptides from a complex mixture comprising human serum spiked with bLH at a concentration of 0.1%.

Enabling techniques and strategic workflow for sulfoglycomics based on mass spectrometry mapping and sequencing of permethylated sulfated glycans

Sulfate modifications on terminal epitopes of N- and O-glycans have increasingly been implicated as critical determinants mediating a diverse range of biological recognition functions. To address these low abundance but important sulfated glycans, and the sulfoglycome in general, further development of enrichment strategies and enabling mass spectrometry (MS)-based mapping techniques are needed. In this report, we demonstrate that the sulfated glycans, with and without additional sialylation, can be successfully permethylated by the sodium hydroxide slurry method and be distinguished from phosphorylated glycans by virtue of this derivatization. In conjunction with simple microscale postderivatization fractionation steps, permethyl derivatives fully retaining the negatively charged sulfate moiety and separated from the nonsulfated ones, can be efficiently detected and sequenced de novo by advanced MS/MS in the positive-ion mode. In particular, we show that the highly sequence and linkage informative high energy collision induced dissociation (CID) MS/MS afforded by MALDI-TOF/TOF can be extended to sulfoglycomic applications. The sulfated parent ion selected for CID MS/MS was found to mostly retain the sulfate moiety and therefore allow efficient fragmentation via the usual array of glycosidic, cross ring, and concerted double cleavages. Collectively, the optimized strategy enables a high sensitivity detection and critical mapping of the sulfoglycome such as the one derived from lymph node tissues or cell lines in both negative and positive-ion modes. Novel sulfated epitopes were identified from a crude mouse lymph node preparation, which fully attested to the practical utility of the methodology developed.

Pseudomonas aeruginosa mucoid strain 8830 binds glycans containing the sialyl-Lewis x epitope

Pseudomonas aeruginosa infection of patients with cystic fibrosis (CF) is a leading cause of their morbidity and mortality. Pathogenesis is initiated in part by molecular interactions of P. aeruginosa with carbohydrate residues in airway mucins that accumulate in the lungs of patients with this disease. To explore the nature of the glycans recognized by a stable, mucoid, alginate-producing strain P. aeruginosa 8830 we generated a genetically modified Pa8830 expressing green fluorescent protein (Pa3380-GFP). We tested its binding to a panel of glycolipids and neoglycolipids in which selected glycans were covalently attached to dipalmitoyl phosphatidylethanolamine and analyzed on silica gel surfaces. Among all glycans tested, Pa8830-GFP bound best to sialyl-Le(x)-containing glycan NeuAc(alpha2-3)Gal(beta1-4)[Fuc(alpha1-3)]GlcNAc-R and bound weakly to H-type blood group Fucalpha1-2Galbeta1-4GlcNAc-R, sialyl-lactose, and Le(x), and exhibited little binding toward non-fucosylated derivatives. Interestingly, while Pa8830-GFP bound to the glycosphingolipid asialoGM1, it did not appear to bind to a wide variety of other glycosphingolipids including GM1, GM2, asialoGM2, and sulfatide. These results indicate that P. aeruginosa 8830 has preferential binding to sialyl-Le(x)-containing glycans and has weak recognition of related fucose- and sialic acid-containing glycans. The finding that Pa8830 binds sialyl-Le(x)-containing glycans, which occur at increased levels in mucins from CF patients, is consistent with studies of other strains of P. aeruginosa and further suggests that such glycans on CF mucins contribute to disease pathogenesis.

Exopolysaccharides produced by clinical strains belonging to the Burkholderia cepacia complex

BACKGROUND

In the frame of a research line dedicated to better clarify the role of exopolysaccharides (EPS) in bacterial virulence, EPS produced by species of the Burkholderia cepacia complex (Bcc), namely Burkholderia multivorans, Burkholderia cenocepacia, and a Bcc member of undetermined genomovar, all isolated at the Cystic Fibrosis Regional Centre of Florence (Italy), were investigated for they structural properties.

METHODS

Three strains of B. multivorans, three of B. cenocepacia and one of a Bcc member of undetermined genomovar were isolated from CF patients. The reference strains C1576 and J2315, for genomovar II and III, respectively, were included in the study. The bacteria were grown on solid media, the exopolysaccharides produced were purified, and their structures were determined. In addition, sugar analysis of sputum samples was accomplished to search for EPS produced in vivo.

RESULTS

Six strains out of seven produced the exopolysaccharide cepacian, while one strain of B. multivorans produced a completely different polymer, previously known in the literature as PS1. Two strains synthesised very small amounts of EPS. No definitive evidence for the presence of cepacian in sputum samples was found.

CONCLUSIONS

Most strains examined produced abundant amounts of polysaccharides. Cepacian was the most common EPS isolated and its production was not associated to a particular genomovar.

Respiratory tract mucin genes and mucin glycoproteins in health and disease

This review focuses on the role and regulation of mucin glycoproteins (mucins) in airway health and disease. Mucins are highly glycosylated macromolecules (> or =50% carbohydrate, wt/wt). MUC protein backbones are characterized by numerous tandem repeats that contain proline and are high in serine and/or threonine residues, the sites of O-glycosylation. Secretory and membrane-tethered mucins contribute to mucociliary defense, an innate immune defense system that protects the airways against pathogens and environmental toxins. Inflammatory/immune response mediators and the overproduction of mucus characterize chronic airway diseases: asthma, chronic obstructive pulmonary diseases (COPD), or cystic fibrosis (CF). Specific inflammatory/immune response mediators can activate mucin gene regulation and airway remodeling, including goblet cell hyperplasia (GCH). These processes sustain airway mucin overproduction and contribute to airway obstruction by mucus and therefore to the high morbidity and mortality associated with these diseases. Importantly, mucin overproduction and GCH, although linked, are not synonymous and may follow from different signaling and gene regulatory pathways. In section i, structure, expression, and localization of the 18 human MUC genes and MUC gene products having tandem repeat domains and the specificity and application of MUC-specific antibodies that identify mucin gene products in airway tissues, cells, and secretions are overviewed. Mucin overproduction in chronic airway diseases and secretory cell metaplasia in animal model systems are reviewed in section ii and addressed in disease-specific subsections on asthma, COPD, and CF. Information on regulation of mucin genes by inflammatory/immune response mediators is summarized in section iii. In section iv, deficiencies in understanding the functional roles of mucins at the molecular level are identified as areas for further investigations that will impact on airway health and disease. The underlying premise is that understanding the pathways and processes that lead to mucus overproduction in specific airway diseases will allow circumvention or amelioration of these processes.

Glycomics analyses of tear fluid for the diagnostic detection of ocular rosacea

A Glycomics approach to detect disease is illustrated in the analyses of human tear fluid for rosacea. The diagnosis of ocular rosacea is particularly challenging in a subgroup of patients that do not present with typical facial skin findings but have ocular signs and symptoms. Indeed, up to 90% of patients with ocular rosacea may have neither obvious roseatic skin changes nor a previous diagnosis of rosacea. Tear fluid was collected from 37 subjects (21 controls and 16 patients with ocular rosacea) after conjunctival stimulation with filter (Schirmer) paper. O-linked oligosaccharides were released from tear fluid by beta-elimination and then purified using solid-phase extraction. Mass spectra were recorded on an external source HiResMALDI with a 7.0 T magnet. Mass spectra were obtained in both the positive and negative modes. However, signals were stronger in the negative mode. Tear fluid samples from rosacea patients yielded distinctive clusters of peaks that extend to higher masses. Patients with rosacea presented several oligomeric series that were not found in the controls. To discriminate the ocular rosacea cases from the normal controls, the sum of absolute intensities of 13 series corresponding to nearly 50 identified mass spectrum peaks was used. Thirty-six out of the 37 samples were correctly classified. This yields a sensitivity of 100% (95% CI 79.5-100) and specificity of 95.2% (95% CI 76.2-99.9). The high abundance of oligosaccharides in the tear fluid of patients with rosacea may lead to an objective diagnostic marker for the disease.

Enzymatic synthesis of sulfated disaccharides using beta-D-galactosidase-catalyzed transglycosylation

We have established a unique enzymatic approach for obtaining sulfated disaccharides using Bacillus circulans beta-D-galactosidase-catalyzed 6-sulfo galactosylation. When 4-methyl umbelliferyl 6-sulfo beta-D-galactopyranoside (S6Gal beta-4MU) was used as a donor, the enzyme induced transfer of 6-sulfo galactosyl residue to GlcNAc acceptor. As a result, the desired compound 6'-sulfo N-acetyllactosamine (S6Gal beta1-4GlcNAc) and its positional isomer 6'-sulfo N-acetylisolactosamine (S6Gal beta1-6GlcNAc) were observed by HPAEC-PAD, in 49% total yield based on the donor added, and in a molar ratio of 1:3.5. With a glucose acceptor, the regioselectivity was substantially changed and S6Gal beta1-2Glc was mainly produced along with beta-(1-1)alpha, beta-(1-3), beta-(1-6) isomers in 74% total yield. When methyl alpha-D-glucopyranoside (Glc alpha-OMe) was an acceptor, the enzyme also formed mainly S6Gal beta1-2Glc alpha-OMe with its beta-(1-6)-linked isomer in 41% total yield based on the donor added. In both cases, it led to the predominant formation of beta-(1-2)-linked disaccharides. In contrast, with the corresponding methyl beta-D-glucopyranoside (Glc beta-OMe) acceptor, S6Gal beta1-3Glc beta-OMe and S6Gal beta1-6Glc beta-OMe were formed in a low total yield of 12%. These results indicate that the regioselectivity and efficiency on the beta-D-galactosidase-mediated transfer reaction significantly depend on the anomeric configuration in the glucosyl acceptors.

A remodeling system of the 3'-sulfo-Lewis a and 3'-sulfo-Lewis x epitopes

It has been reported that the chemically synthesized 3'-sulfo-Le(a) and 3'-sulfo-Le(x) epitopes have a high potential as a ligand for selectins. To elucidate the physiological functions of 3'-sulfated Lewis epitopes, a remodeling system was developed using a combination of a betaGal-3-O-sulfotransferase GP3ST, hitherto known alpha1,3/1,4-fucosyltransferases (FucT-III, IV, V, VI, VII, and IX) and arylsulfatase A. The pyridylaminated (PA) lacto-N-tetraose (Galbeta1-3GlcNAcbeta1-3Galbeta1-4Glc) was first converted to 3'-sulfolacto-N-fucopentaose II (sulfo-3Galbeta1-3(Fucalpha1-4)GlcNAcbeta1-3Galbeta1-4Glc)-PA by sequential reactions with GP3ST and FucT-III. The 3'-sulfolacto-N-fucopentaose III (sulfo-3Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-3Galbeta1-4Glc)-PA was then synthesized from lacto-N-neotetraose (Galbeta1-4GlcNAcbeta1-3Galbeta1-4Glc)-PA by GP3ST and FucT-III, -IV, -V, -VI, -VII, or -IX in a similar manner. The substrate specificity for the 3'-sulfated acceptor of the alpha1,3-fucosyltransferases was considerably different from that for the non-substituted and 3'-sialylated varieties. When the GP3ST gene was introduced into A549 and Chinese hamster ovary cells expressing FucT-III, they began to express 3'-sulfo-Le(a) and 3'-sulfo-Le(x) epitopes, respectively, suggesting that GP3ST is responsible for their biosynthesis in vivo. The expression of the 3'-sialyl-Le(x) epitope on Chinese hamster ovary cells was attenuated by the introduction of GP3ST gene, indicating that GP3ST and alpha2,3-sialyltransferase compete for the common Galbeta1-4GlcNAc-R oligosaccharides. Last, arylsulfatase A, which is a lysosomal hydrolase that catalyzes the desulfation of 3-O-sulfogalactosyl residues in glycolipids, was found to hydrolyze the sulfate ester bond on the 3'-sulfo-Le(x) (type 2 chain) but not that on the 3'-sulfo-Le(a) (type 1 chain). The present remodeling system might be of potential use as a tool for the study of the physiological roles of 3'-sulfated Lewis epitopes, including interaction with selectins.

Molecular cloning and characterization of a human beta-Gal-3'-sulfotransferase that acts on both type 1 and type 2 (Gal beta 1-3/1-4GlcNAc-R) oligosaccharides

A novel sulfotransferase gene (designated GP3ST) was identified on human chromosome 2q37.3 based on its similarity to the cerebroside 3'-sulfotransferase (CST) cDNA (Honke, K., Tsuda, M., Hirahara, Y., Ishii, A., Makita, A., and Wada, Y. (1997) J. Biol. Chem. 272, 4864-4868). A full-length cDNA was obtained by reverse transcription-polymerase chain reaction and 5'- and 3'-rapid amplification of cDNA ends analyses of human colon mRNA. The isolated cDNA clone predicts that the protein is a type II transmembrane protein composed of 398 amino acid residues. The amino acid sequence indicates 33% identity to the human CST sequence. A recombinant protein that is expressed in COS-1 cells showed no CST activity, but did show sulfotransferase activities toward oligosaccharides containing nonreducing beta-galactosides such as N-acetyllactosamine, lactose, lacto-N-tetraose (Lc4), lacto-N-neotetraose (nLc4), and Gal beta 1-3GalNAc alpha-benzyl (O-glycan core 1 oligosaccharide). To characterize the cloned sulfotransferase, a sulfotransferase assay method was developed that uses pyridylaminated (PA) Lc4 and nLc4 as enzyme substrates. The enzyme product using PA-Lc4 as an acceptor was identified as HSO(3)-3Gal beta 1-3GlcNAc beta 1-3Gal beta 1- 4Glc-PA by two-dimensional (1)H NMR. Kinetics studies suggested that GP3ST is able to act on both type 1 (Gal beta 1-3GlcNAc-R) and type 2 (Gal beta 1-4GlcNAc-R) chains with a similar efficiency. In situ hybridization demonstrated that the GP3ST gene is expressed in epithelial cells lining the lower to middle layer of the crypts in colonic mucosa, hepatocytes surrounding the central vein of the liver, extravillous cytotrophoblasts in the basal plate and septum of the placenta, renal tubules of the kidney, and neuronal cells of the cerebral cortex. The results of this study indicate the existence of a novel beta-Gal-3'-sulfotransferase gene family.

Prevotella enzymes involved in mucin oligosaccharide degradation and evidence for a small operon of genes expressed during growth on mucin

Mucin desulfation is believed to be a rate-limiting step in mucin degradation by colon bacteria. The activities of enzymes hydrolysing nine linkages found in mucin oligosaccharide chains were measured using model substrates, in extracts of two mucin-degrading bacteria, Prevotella strain RS2 and Bacteroides fragilis. Sulfatases desulfating N-acetylglucosamine-6-sulfate, galactose-6-sulfate and galactose-3-sulfate were found. The genomic DNA downstream from the gene encoding the mucin-desulfating sulfatase (N-acetylglucosamine-6-sulfatase) in Prevotella was sequenced, and two putative genes identified which are likely to be coexpressed with this sulfatase, though their activities are unknown. Northern and Western analyses showed that expression of this short operon of three genes is increased during growth on mucin.

Carbohydrate sulfation effects on growth of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a key player in the pathology and morbidity of cystic fibrosis. Chronic obstructive pulmonary disease, which results from the most common and severe mutations in this genetic disorder, typically includes chronic infection with P. aeruginosa which, even with rugged antibiotic and physical therapy regimens, is rarely eradicated. It is not known whether the increased oligosaccharide sulfation characteristic of cystic fibrosis tracheobronchial mucins plays a role in the survival of P. aeruginosa in the airway. In this study, sulfated monosaccharides were synthesized and tested for their effects on the growth of clinical isolates and laboratory strains of this organism when supplied as the sole carbon source in vitro. Carbohydrate sulfation was observed to reduce, but not prohibit, growth of P. aeruginosa on carbohydrates normally utilized in their nonsulfated form. The various sulfated sugars employed as the sole carbon source gave characteristic and consistent growth profiles and maximum growth values across the strains tested. P. aeruginosa isolates from patients with cystic fibrosis often express a mucoid phenotype, which is thought to contribute to their ability to survive in harsh conditions. Carbohydrate sulfation effects on growth did not differ significantly between mucoid and nonmucoid strains. These results suggest that the additional sulfation of tracheobronchial mucin documented in cystic fibrosis may in fact contribute to the mucin's resistance to utilization by P. aeruginosa and potentially other pathogens, providing an additional level of host protection, and limiting the available nutrient pool and thereby bacterial growth.

Expression of mucin-associated sulfo-Lea carbohydrate epitopes on human colon carcinoma cells

The level of sulfo-Lea (SO3-3Gal beta 1-3(Fuc alpha 1-4)GlcNAc) epitope recognized by monoclonal antibody (mAb) 91.9H in hepatic metastasis of colon carcinoma is known to be lower than at the primary sites. We examined 19 human colon carcinoma cell lines for their production of this epitope. Sixteen cell lines were found to produce high M(r) components that metabolically incorporated [35S]sulfate and were resistant to heparitinase I and chondroitinase ABC, and 8 of them were reactive with mAb 91.9H as shown by western blotting analysis. These were all of the 4 cell lines derived from well differentiated primary tumors (HCCP-2998, LS174T, GEO, and CBS), 2 of 10 cell lines (DLD-1 and HCT116) from moderately to poorly differentiated primary tumors, and 2 of 5 cell lines (SW480 and HCC-M1544) from metastases. Incubation of LS174T cells with benzyl-N-acetyl-alpha-D-galactosaminide abrogated the incorporation of [35S]sulfate and the reactivity of mAb 91.9H with high M(r) components in the cell lysates. Sodium chlorate, which inhibits the formation of 3'-phosphoadenosine 5'-phosphosulfate, also inhibited the [35S]sulfate incorporation and reactivity with mAb 91.9H. These treatments did not change the incorporation of [14C]threonine into high M(r) components. These results indicated that sulfo-Lea epitopes were expressed on O-linked carbohydrate chains in sulfomucins. Immunohistochemical studies of tumor tissues in nude mice indicated that sulfo-Lea was expressed at the site of orthotopic transplantation in the cecum. The expression appeared to be suppressed in liver metastatic foci in nude mice.

Sulfomucins in the human body

Mucins are widely distributed in mucous secretion fluids or are associated with plasma membranes. Up to now 9 genes of epithelial mucins have been identified, distributed over five chromosomes. Superposed on the genetic diversity, each type of mucin displays heterogeneity in oligosaccharide composition, including the terminal sugar residues. On top of that there is variation between individuals brought about by blood group antigens. Heterogeneity is further incited by the degree of sulfation. This tremendous structural heterogeneity endows mucin molecules with properties suggestive for a multifunctional role. The major biological function assigned to mucins is still the protection of tissues covered by the mucous gel. Current knowledge on the specific biological functions of the sulfate residues is fragmentary and periphrastic. Glycosylation including sulfation appears to be subject to modification under pathological conditions. There is evidence that sulfation rate-limits bacterial degradation of mucins. Moreover, accumulating data focus towards their involvement in recognition phenomena. Sulfate residues on blood group related structures provoke specific epitopes for selective interaction with microorganisms e.g. Helicobacter pylori. A distinct class of mucins acts as ligands for selectins, crucial in cellular recognition processes like cellular homing of lymphocytes. Whereas in earlier days mucins were only seen as water-binding molecules, protecting the underlying mucosa against harmful agents, the current picture of these molecules is characterized by the selective interaction with their environment, including epithelial-, and endothelial cells and microorganisms, thereby regulating a great number of biological processes. However, the specific role of sulfate remains to be further elucidated.

Disulfated oligosaccharides derived from tracheobronchial mucous glycoproteins of a patient suffering from cystic fibrosis

Twenty novel disulfated oligosaccharides were purified in nanomolar quantities from tracheo-bronchial mucous glycoproteins from a patient with cystic fibrosis via cleavage by alkaline borohydride treatment, followed by anion-exchange chromatography, size-exclusion chromatography, and high-performance liquid chromatography (HPLC). In addition to positive ion fast-atombombardment mass spectrometry (FABMS), proposed structures for the resulting purified disulfated oligosaccharides were also based on carbohydrate permethylation analyses, periodate oxidation, complete sequential exoglycosidase digestion, and parallel analysis of desulfated products. Sulfate esters were found to reside on C-3 or C-6 of terminal D-galactose and on C-6 of internal D-galactose or 2-acetamido-2-deoxy-D-glucose residues. For this group of oligosaccharides, ranging in size from tri- to undeca-saccharides and possessing linear, di- and tri-antennary forms, it was also observed that sulfate esters could be located on the same or on different branches and that branched oligosaccharides can possess sulfate esters on C-3 and C-6 of different terminal galactose residues within the same structure.

Oligosaccharide sequencing based on exo- and endoglycosidase digestion and liquid chromatographic analysis of the products

Exo- and endoglycosidases are used to sequence oligosaccharides and give valuable information on the monosaccharide sequence, together with the anomericity, the stereochemistry, and in some cases, the substitution pattern of the monosaccharides. Both sequential and parallel methods of oligosaccharide sequencing are discussed.

Characterization of a sulfotransferase from human airways responsible for the 3-O-sulfation of terminal galactose in N-acetyllactosamine-containing mucin carbohydrate chains

A galactose 3-O-sulfotransferase activity able to transfer a sulfate group from adenosine 3'-phosphate 5'-phosphosulfate to methyl galactosides or terminal N-acetyllactosamine-containing carbohydrate chains from human respiratory mucins was characterized in microsomal fractions prepared from human respiratory mucosa. The reaction products, methyl alpha- or beta-galactose 3-sulfate and three oligosaccharide alditols containing the sequence HSO3-3Gal beta 1-4GlcNAc beta 1-6GalNAc-itol were identified by high performance anion-exchange chromatography. Using methyl beta-galactoside as a substrate, the optimum activity was obtained with 0.1% Triton X-100, 30 mM NaF, 20 mM Mn2+, and 10 mM AMP in a 30 mM 2-(N-morpholino)ethanesulfonic acid buffer at pH 6.1. The apparent Km for methyl beta-galactoside and for adenosine 3'-phosphate 5'-phosphosulfate were observed at 0.69 x 10(-3) M and at 4 x 10(-6) M respectively. This sulfotransferase is different from that responsible for sulfatide synthesis.

Viscoelastic properties of human tracheobronchial mucin in aqueous solution

Human tracheobronchial mucin isolated from cystic fibrosis patients (CF HTBM) was purified using a combination of gel filtration and density gradient centrifugation. The resulting mucin was fractionated to reduce polydispersity and to facilitate studies of the molecular weight dependence of mucin viscoelasticity in concentrated solution. The viscoelastic properties of CF HTBM were examined in distilled water, 0.1M salt solutions and chaotropic solvents. In controlled strain experiments (strain > or = 5%) with increasing mucin concentration, a crossover from sol to gel behavior is observed. The gel strength, as measured by the magnitude of the storage modulus at comparable mucin concentrations, is greatest for distilled water, intermediate for 0.1M NaCl, and lowest for 6M GdnHCl. In distilled water, high molecular weight mucin undergoes a sol-gel transition at approximately 12 mg/mL, and shows evidence of a plateau modulus at higher concentrations. The storage and loss moduli of concentrated high molecular weight fractions in 6M GdnHCl exhibit a power law dependence on frequency typical of weak gels near the sol-gel transition at 20 mg/mL. Similar rheology is observed in 0.1M NaCl and 0.091M NaCl/3 mM CaCl2, but with evidence for additional weak associations at low frequency. The power law exponent in these systems is 0.70 +/- 0.02, in good agreement with prediction for networks formed by a percolation mechanism. Low molecular weight fractions in these solvents exhibit a fluid-like viscoelastic response. However, low molecular weight mucin in distilled water shows a strain-dependent increase in elasticity at low frequency indicative of weak intermolecular associations. Comparison of the rheological behavior of CF HTBM with our earlier studies of ovine submaxillary mucin lends support to the idea that carbohydrate side-chain interactions are important in the gelation mechanism of mucins.

Sulfated glycoconjugate receptors for the Bordetella pertussis adhesin filamentous hemagglutinin (FHA) and mapping of the heparin-binding domain on FHA

Filamentous hemagglutinin (FHA) is a major adhesin present on the surface of the gram-negative respiratory pathogen Bordetella pertussis. A number of binding mechanisms have been described for the interaction of FHA with eukaryotic cells. We have focused on its function as a sulfated polysaccharide-binding protein and on identifying potential receptors for FHA on the epithelial cell surface. Using a thin-layer overlay technique, we found that FHA binds specifically to sulfated glycolipids but not to gangliosides or other neutral glycolipids. These results suggest that epithelial cell surface sulfated glycolipids function as receptors for FHA. Further studies demonstrated that a Chinese hamster ovary (CHO) cell strain deficient in glycosaminoglycan expression exhibits greatly diminished attachment to FHA. By FHA-Affi-Gel chromatography, a putative receptor for FHA that has characteristics consistent with a heparan sulfate proteoglycan was isolated from epithelial cell extracts. In addition, by using recombinant FHA fusion proteins, a specific glycosaminoglycan-binding domain located near the N terminus of the FHA molecule was identified. Our results indicate that the B. pertussis adhesin FHA may utilize sulfated glycolipids and proteoglycans commonly found on the surface of human cells and tissues to initiate infection.

Colorectal mucin histochemistry in health and disease: a critical review

Neoplastic, inflammatory and regenerative processes affecting colorectal mucosa are associated with alterations in structure of epithelial mucin. This review collates mucin-, lectin-, and immuno-histochemical observations on colorectal mucins and introduces recent molecular genetic insights into the structure of the protein backbone of mucins. The numerous structural modifications uncovered by the various technical approaches have been reduced to a few manageable principles that are of relevance to both researcher and diagnostic pathologist. Particular attention is drawn to the need to appreciate the limited specificities of probes, the confounding influences of anatomical site and genetic factors (necessitating the use of appropriate positive and negative control tissues) and the precise location of secretory material. In the past, insufficient attention has been given to the effects of altered differentiation including metaplasia and differing lineage expression in epithelial disorders of growth. It is likely that certain changes loosely ascribed to goblet cell mucin, such as neo-expression of blood group antigens and anomalous expression of core carbohydrate structures, do not occur at all. Critical examination of available data point to only two consistent and unequivocal changes affecting goblet cell mucin in pathological processes: loss of O-acetyl substituents at sialic acid C4 and C7,8,9 and increased sialylation. Furthermore, there are no neoplasia-specific alterations in mucins documented to date. All neoplasia-associated changes have been described in non-neoplastic lesions also.

The role of airway mucus in pulmonary toxicology

Airway mucus is a complex airway secretion whose primary function as part of the mucociliary transport mechanism is to to serve as renewable and transportable barrier against inhaled particulates and toxic agents. The rheologic properties necessary for this function are imparted by glycoproteins, or mucins. Some respiratory disease states, e.g., asthma, cystic fibrosis, and bronchitis, are characterized by quantitative and qualitative changes in mucus biosynthesis that contribute to pulmonary pathology. Similar alterations in various aspects of mucin biochemistry and biophysics, leading to mucus hypersecretion and altered mucus rheology, result from inhalation of certain air pollutants, such as ozone, sulfur dioxide, nitrogen dioxide, and cigarette smoke. The consequences of these pollutant-induced alterations in mucus biology are discussed in the context of pulmonary pathophysiology and toxicology.

Structures of sulfated oligosaccharides in human trachea mucin glycoproteins

The structures of high molecular weight sulfated oligosaccharide chains in mucins purified from the sputum of a patient with cystic fibrosis and blood group H determinant were established. Reduced oligosaccharides released by treatment with alkaline borohydride were separated by ion exchange chromatography on DEAE-Agarose and a fraction containing multisulfated chains was further purified by lectin affinity chromatography to completely remove small amounts of sialylated chains. A major sulfated oligosaccharide fraction containing chains with an average of 160 to 200 sugar residues was isolated by gel filtration on BioGel P-10 columns and individual subfractions were characterized by methylation analysis, periodate oxidation and sequential glycosidase digestion before and after desulfation. Carbohydrate analysis yielded Fuc, Gal and GldNAc in a ratio of 1:2:2.1 and only one galactosaminitol residue for every 160- to 200 sugar residues. The average molecular weight of oligosaccharide chains in these fractions was between 27,000 and 40,000 daltons. Structural analysis showed that these high molecular weight chains contained varying amounts of the repeating unit shown in the following oligosaccharide. Only one in about every 10 repeating units contained sulfate esters. Several shorter chains which contain 2 to 3 sulfate esters were also isolated from this multisulfated oligosaccharide fraction. The structures proposed for these oligosaccharides indicate that they are lower molecular weight chains with the same general structure as those found in the high molecular weight sulfated oligosaccharides. Taken collectively, the results of these studies show that a major sulfated oligosaccharide fraction in respiratory mucin purified from the mucus of patients with cystic fibrosis contains high molecular weight branched chains that consist of a repeating oligosaccharide sequence with sulfate linked to the 6 positions of galactose and possibly GlcNAc residues in the side chains.

Clinical aspects of glycoprotein biosynthesis

Glycoproteins are widely distributed among species in soluble and membrane-bound forms, associated with many different functions. The heterogenous sugar moieties of glycoproteins are assembled in the endoplasmic reticulum and in the Golgi and are implicated in many roles that require further elucidation. Glycoprotein-bound oligosaccharides show significant changes in their structures and relative occurrences during growth, development, and differentiation. Diverse alterations of these carbohydrate chains occur in diseases such as cancer, metastasis, leukemia, inflammatory, and other diseases. Structural alterations may correlate with activities of glycosyltransferases that assemble glycans, but often the biochemical origin of these changes remains unclear. This suggests a multitude of biosynthetic control mechanisms that are functional in vivo but have not yet been unraveled by in vitro studies. The multitude of carbohydrate alterations observed in disease states may not be the primary cause but may reflect the growth and biochemical activity of the affected cell. However, knowledge of the control mechanisms in the biosynthesis of glycoprotein glycans may be helpful in understanding, diagnosing, and treating disease.

Sulfated sialyl-oligosaccharides derived from tracheobronchial mucous glycoproteins of a patient suffering from cystic fibrosis

Thirteen novel oligosaccharides, each possessing both a sulfate ester and a sialic acid residue, were isolated from tracheobronchial mucous glycoproteins from a patient with cystic fibrosis via cleavage by alkaline borohydride treatment, and by employing immobilized Limulus polyphemus lectin affinity chromatography, SynChroprep AX300 anion-exchange chromatography, Bio-Gel P-2 size-exclusion chromatography, and Hypersil 120A APS-2 high-performance liquid chromatography (HPLC). Proposed structures for the resulting purified sulfated sialyl-oligosaccharides were based on carbohydrate/permethylation analyses, periodate oxidation, complete sequential exoglycosidase digestion, analysis of desulfated products and, analysis by positive-ion fast-atom-bombardment mass spectrometry (FABMS). Sulfate esters on these sialyl-oligosaccharides resided on C-6 of a terminal or an internal D-galactose or 2-acetamido-2-deoxy-D-glucose residue or C-4 of a terminal D-galactose residue. The sialic acid residues were found to be either bound (2-->6)-alpha to 2-acetamido-2-deoxy-D-galactitol or (2-->3)-alpha or (2-->6)-alpha to a D-galactose residue occupying a nonreducing terminus. For this group of oligosaccharides, ranging in size from tri- to hepta-saccharides, it was also observed that a sialic acid residue and a sulfate ester did not residue on the same oligosaccharide branch when more than one branch existed. On linear unbranched sulfated sialyl-oligosaccharides, the sialic acid residue was bound to a D-galactose residue occupying a nonreducing terminus with the sulfate ester residing on an internal D-galactose or a 2-acetamido-2-deoxy-D-glucose residue. These results demonstrate that it is possible for sialic acid and a sulfate ester to exist on the same oligosaccharide and that this oligosaccharide can be as small as a trisaccharide.

Chloride channels, Golgi pH and cystic fibrosis

Cystic fibrosis (CF) is associated with a defect in a cAMP-activated chloride channel in secretory epithelia, which leads to decreased fluid secretion. In addition, many mucus glycoproteins show decreased sialylation but increased sulphation. We have recently shown that the pH of intracellular organelles is elevated in CF cells, due to defective chloride conductance in the vesicle membranes. We postulate that this may affect the activity of sialyl-, fucosyl- and sulphotransferases, and thus explain the abnormal glycosylation. Defects in sialylation of glycolipids might also generate receptors for Pseudomonas, which infects the respiratory tract of CF patients.

Structural analysis of monosulfated side-chain oligosaccharides isolated from human tracheobronchial mucous glycoproteins

To determine the location of some sulfate esters on respiratory mucins, an unambiguous sequencing strategy was developed for a crude, monosulfated oligosaccharide fraction derived from tracheobronchial mucous glycoproteins, isolated from sputum from a patient with cystic fibrosis, and which possessed Ricinus communis-I lectin affinity. Employing fractionation by Bio-Gel P-2 chromatography and high-voltage paper electrophoresis of the pool, eighteen branched and four straight-chained monosulfated oligosaccharides, each possessing at least one neutral D-galactose residue at a nonreducing terminus, were purified. Desulfated analogs of each sulfated oligosaccharide were then produced. Elucidation of their structures and sulfate ester locations was accomplished through a parallel comparative sequencing approach for the sulfated oligosaccharide and its desulfated analog. The method was based on their carbohydrate composition and parallel analysis by sequential exoglycosidase degradations, endoglycosidase digestion, permethylation analyses, and specific lectin affinities. Key to this approach was the inability for specific exoglycosidases and lectins to cleave or bind to, respectively, carbohydrates of their specificity which occupied nonreducing termini and possessed a sulfate ester. Herein we report the structures of twenty-two novel sulfated oligosaccharides. Oligosaccharides ranged from trisaccharides to heptasaccharides, were branched and unbranched, and each possessed a single sulfate ester on either C-6 of a terminal or an internal D-galactose residue or on C-6 of an internal residue of 2-acetamido-2-deoxy-D-glucose (N-acetyl-D-glucosamine).

Carbohydrate analysis of glycoproteins. A review

Many of the products prepared by biotechnological approaches, including recombinant genetic engineering, cell tissue culture, and monoclonal technologies, are glycoproteins. As little as five years ago, glycosylation was believed to play no significant role in the function of glycoproteins. Recent large scale testing of glycoprotein-based pharmaceuticals has indicated that both the extent and type of glycosylation can play a central role in glycoprotein activity. Although methods for compositional and sequence analysis of proteins and nucleic acids are generally available, similar methods have yet to be developed for carbohydrate oligomers and polymers. This review focuses on new, developing methods for the analysis and sequencing of the carbohydrate portion of glycoproteins. Included are: (1) the release of oligosaccharides and hydrolysis of carbohydrate chains using enzymatic and chemical methods; (2) fractionation by LPLC, electrophoresis, HPLC, and lectin affinity chromatography; (3) detection through the preparation of derivatives or by new electrochemical methods; (4) analysis by spectroscopic methods, including MS and high-field NMR; and (5) their sequencing through the use of multiple, well-integrated techniques. The ultimate goal of the analytical approaches discussed is to firmly establish structure and, thus, permit the study of structure-function relationships and eventually to allow the intelligent application of carbohydrate remodeling techniques in the preparation of new glycoproteins.

Characterization of oligosaccharides by lectin affinity high-performance liquid chromatography

Alterations of the oligosaccharide structures of glycoproteins are associated with differentiation, malignant transformation, and expression of the same protein in different cell types. The potential biological importance of oligosaccharides has resulted in a growing need for detailed structural information. When glycoproteins are available in limited quantities and/or bear highly heterogeneous oligosaccharides, characterization of their oligosaccharides is difficult. We have developed an efficient approach for obtaining detailed information about oligosaccharides by determining structural 'fingerprints' using lectin affinity high-performance liquid chromatography.

Complete 1H- and 13C-n.m.r. assignments for two sulphated oligosaccharide alditols of hen ovomucin

The complete 1H- and 13C-n.m.r. assignments for beta-D-Galp-(1----4)-beta-D-GlcpNAc-6-SO3H-(1----6)-[beta-D-Galp-(1----3 )]- D-GalNAcol and alpha-NeuAcp-(2----3)-beta-D-Galp-(1----3)-[beta-D-Galp-(1----4)-b eta-D- GlcpNAc-6-SO3H-(1----6)]-D-GalNAcol were made by a combination of 2-D correlation experiments (Relayed-Cosy; and 13C,1H Correlation-shift n.m.r. spectroscopy), and 1-D n.m.r. spectroscopy. The results illustrate the ability of these methods to locate sulphate and NeuAc groups in anionic mucinous glycoproteins.

Enzymatic sulfation of salivary mucins: structural features of 35S-labeled oligosaccharides

Sulfotransferase activity catalyzing the transfer of sulfate ester group from 3'-phosphoadenosine-5'-phosphosulfate to salivary mucins was found associated with Golgi-rich membrane fraction of rat submandibular salivary glands. Alkaline borohydride reductive cleavage of the synthesized 35S-labeled glycoprotein led to the liberation of the label into reduced acidic oligosaccharides. Most of the label was found incorporated in four oligosaccharides. These were identified as sulfated tri-, penta-, hepta- and nonasaccharides. The trisaccharide was characterized as SO3H,6GlcNAc beta 1,3Gal beta 1,3GalNac-o1, the pentasaccharide as SO3H,6GlcNAc beta 1,3Gal beta 1,4GlcNAc beta 1,3(NeuAc alpha 2,6) GalNAc-o1 and heptasaccharide as SO3H,6Gal beta 1,4GlcNAc beta 1,6(Fuc alpha 1) 2Gal beta 1,4GlcNAc beta 1,3Gal beta 1,3)GalNAc-o1.

The complexity of mucins

Mucins represent the main components of gel-like secretions, or mucus, secreted by mucosae or some exocrine glands. These high-molecular-weight glycoproteins are characterized by the large number of carbohydrate chains O-glycosidically linked to the peptide. The determination of mucin molecular weight and conformation has been controversial for several reasons: 1) the methods used to solubilize mucus and to purify mucins are different and 2) the molecules have a strong tendency to aggregate or to bind to other molecules (peptides or lipids). Recently, electron microscopy has shown the filamentous shape of most mucins and their polydisperse character which, in some secretions, might correspond to a polymorphism of the peptide part of these molecules. The recent development of high pressure liquid chromatography and high-resolution proton NMR spectroscopy has allowed major progress in the structural study of mucin carbohydrate chains. These chains may have from 1 to about 20 sugars and bear different antigenic determinants, such as A, B, H, I, i, X, Y or Cad antigens. In some mucins, such as human respiratory mucins, the carbohydrate chain diversity is remarkable, which raises many questions. Mucins are molecules located at the interface between mucosae and the external environment. The carbohydrate chain diversity might allow many interactions between mucins and microorganisms and play a major role in the colonization or the defense of mucosae.