[Study of the fibrillar structures of human bronchial secretion]

Chemical aspects of tracheal glycoproteins

The chemical characteristics of tracheal mucus obtained directly from the epithelial surface of the trachea indicate that the mucus from each animal source consists of a group of sulphated sialic acid-containing glycoproteins. Fractionation of the native glycoprotein from the cat by gel chromatography in the presence of urea and dithiothreitol suggests a value of about 3 X 10(6) for the molecular weights. The chief monosaccharide constituents are N-acetylneuraminic acid, N-acetylglucosamine, N-acetylgalactosamine, fucose and galactose. In the goose tracheal mucin, mannose is present (serum proteins being absent). Doubly labelled cat mucus, obtained by giving Na235SO4 and [3H]glucose simultaneously into the lumen of the trachea, is massively released by parasympathetic agents, e.g. pilocarpine. The resulting mucus has a high content of 35S and is derived largely from submucosal gland cells. Subsequent exposure to an irritant, ammonia, releases a low sulphation fraction, highly labelled with 3H, arising from goblet cells. Evidence supports the view that the overall mucus is composed of mixed secretions, chemically distinct, from different cellular synthesizing sites. Differential nervous stimulation of the various sites may cause far-reaching changes in the chemical and physical properties of the mucus by selective action on the secretion of one or more of the contributing glycoproteins.

Chondroitin sulfate in sputum from patients with cystic fibrosis and chronic bronchitis

In order to ascertain whether or not the presence of glycosaminoglycans in sputa of patients suffering from chronic bronchial disorders was related to tracheobronchial infection, an electrophoretic procedure was set up. The different acidic macromolecular components of sputum, namely nucleic acids, glycosaminoglycans, and bronchial glycopeptides could be identified in proteolyzed sputum using agarose electrophoresis before and after the action of different enzymes: nucleases, chondroitinases, hyaluronidase and heparinase. This procedure was used to analyze 13 sputum samples from patients suffering from cystic fibrosis (CF) and 12 sputum samples from patients suffering from chronic bronchitis. Chondroitin sulfate was identified in 11 infected sputum samples from patients with CF and also in the noninfected sputum from a patient with chronic bronchitis. These data suggest a relationship between the presence of chondroitin sulfate proteoglycans in sputum and severe tracheobronchial infection in CF.

Sulfated O-glycoproteins secreted by guinea pig trachea in organ culture

Organ culture of guinea pig trachea was performed in the presence of [35S]sulfate in order to characterize the sulfated glycoproteins released from the respiratory epithelium and mucosa. The sulfated macromolecules that were synthesized during a 6-h incorporation were separated by CsBr density-gradient centrifugation and gel-filtration chromatography successively. Most of the sulfated secreted macromolecules corresponded to a population of glycoproteins sensitive to reductive beta-elimination but resistant to both chondroitinase ABC and heparinase. These glycoproteins had different buoyant densities (ranging from 1.48 g/ml to 1.16 g/ml) and could be subfractionated according to molecular mass. A major part of the radioactivity was incorporated into high-molecular-mass mucins that were excluded from a Sepharose CL-2B column and did not penetrate into polyacrylamide gel in PAGE. However, a mixture of sulfated O-glycoproteins of much lower molecular mass was also characterized in addition to low amounts of chondroitin sulfate. Epithelial goblet cells are the predominant mucin-containing cells of the respiratory guinea pig trachea. Our results suggest that a wide range of sulfated O-glycoproteins are secreted by the guinea pig tracheal mucosa.

Pericellular glycoconjugates of cultured fibroblasts from control and cystic fibrosis patients

1. Labeled glycoconjugates released by trypsin from cell surfaces of control and cystic fibrosis (CF) skin fibroblasts were purified and fractionated by column chromatography on Sephadex G-50 and Concanavalin A Sepharose. Based on chemical analysis and specific enzymatic digestions: (1) Glycoconjugates were characterized as O-linked glycopeptides consisting predominantly of glycosaminoglycan type and N-linked glycopeptides with glycans of complex type. Their relative proportions were similar between the two groups. (2) The N-linked glycopeptides exhibited an increased molar ratio of fucose to galactose in CF fibroblasts. (3) When pericellular glycoconjugates were metabolically labeled with [14C]glucosamine and [3H]fucose, incorporation and degradation kinetics were similar between the two groups.

Tracheobronchial mucin receptor for Pseudomonas aeruginosa: predominance of amino sugars in binding sites

Pseudomonas aeruginosa, a common respiratory tract colonizer and pathogen, adheres to injured tracheal cells and to tracheobronchial mucin. These phenomena suggest that there are specific receptors for this organism in the respiratory tract. The receptor on injured tracheal cells contains n-acetylneuraminic acid as the principal sugar, but the structure of the receptor in mucin has not been described. Using a microtiter plate assay to study bacterial adherence to mucin, we have partially characterized the mucin receptor for P. aeruginosa. The receptor for both nonmucoid and mucoid strains is sensitive to periodate oxidation, suggesting that it is carbohydrate in nature, and the amino sugars n-acetylglucosamine and n-acetylneuraminic acid inhibited the adherence of both types of strains. Nonmucoid strains were more sensitive to inhibition by n-acetylneuraminic acid than to inhibition by n-acetylglucosamine, but the mucoid strains varied in their sensitivities to inhibition by each amino sugar. Preincubation of mucin with heat-inactivated influenza A virus (which binds to neuraminic acid) significantly reduced the adherence of P. aeruginosa. Treatment of mucin with Clostridium perfringens neuraminidase also reduced bacterial adherence significantly. Treatment of mucin with pronase did not affect adherence. Our results suggest that n-acetylglucosamine and n-acetylneuraminic acid are important constituents of the binding sites for P. aeruginosa on human tracheobronchial mucin.

Complex structure of human bronchial mucus glycoprotein

Human bronchial mucus glycoproteins or mucins were isolated from the sputum of two patients by a method avoiding reducing agents and involving water extraction and gel filtration on Sepharose CL-2B in 6 M guanidinium chloride. The chemical analysis indicated approximately 25-40% lipid. The amino acid and carbohydrate analysis differ quantitatively from that of mucins purified after prior reduction of mucus. These fractions also have a higher proportion of aspartic and glutamic acids than that of the mucins from reduced sputum. These mucins are still contaminated by small amounts of peptides but do not seem to contain disulfide-attached cross-linking protein. Human bronchial mucins have a strong tendency to form aggregates except in 6 M guanidinium chloride. Electron microscopy performed with various procedures indicates the presence of both micelles and flexible threads measuring 200-1000 nm. Delipidation removes most of the micellar forms. Thereafter mucins appear mainly as polydisperse flexible extended threads and also as aggregates. These features of bronchial mucins do not fit with the generally accepted idea of mucin subunits linked by disulfide bridges (unless they are linked end to end) and alternatively favour a model where mucin molecules behave like filaments that could easily aggregate according to the solvent system (mucin concentration, absence of dissociating conditions).

Primary-structure determination of fourteen neutral oligosaccharides derived from bronchial-mucus glycoproteins of patients suffering from cystic fibrosis, employing 500-MHz 1H-NMR spectroscopy

The structure of carbohydrate units of bronchial-mucus glycoproteins obtained from cystic fibrosis patients was investigated by 500-MHz 1H-NMR spectroscopy and methylation analysis. To that purpose, the mucin was subjected to alkaline borohydride degradation. Neutral oligosaccharide-alditols, ranging in size from disaccharides to pentasaccharides, were isolated. Eight compounds could be purified to homogeneity; furthermore, three fractions were obtained consisting mainly of two components. For all 14 compounds the primary structure could be elucidated. 500-MHz 1H-NMR spectroscopy was found to be effective in detecting heterogeneity and to be invaluable for the determination of structures in mixtures of oligosaccharide-alditols. The structures can be divided into two groups depending on the core disaccharide. One group contains Gal(beta 1 leads to 3)GalNAc-ol as common structural element, the other GlcNAc(beta 1 leads to 3)GalNAc-ol. Both disaccharides were identified as such; the other compounds can be conceived as extensions thereof. The most complex representatives of the two groups are: (formula; see text) The italicized structural elements, comprising the SSEA-1 determinant and the type-1 blood-group-H determinant, are novel sequences in oligosaccharide chains of mucin-type glycoproteins.

Physicochemical properties of avian tracheal mucus

Dual-radiolabelled avian tracheal secretions were obtained by giving Na235SO4 and D-[1-3H]glucosamine simultaneously into the lumen of the trachea in preparations in vitro. These secretions comprised fibrillar, gelatinous and soluble-phase mucins. These were eluted as single components in the non-retarded fractions from Bio-Gel A-15m. Although no evidence of the presence of subunit structure was found, chemical and radiolabelling analyses showed a high degree of internal inhomogeneity among the three types of mucins. The differences among these mucins could be attributed to the chemical nature of their constituent glycoproteins. Glycoprotein fractions separated by ion-exchange chromatography were found to contain sulphate and N-acetylneuraminic acid residues in differing amounts. The overall acidic properties appeared to be correlated with ester sulphate content. A close similarity in the carbohydrate composition and a reciprocal relationship between the total ester sulphate residue contents and 35S- and 3H-labelling suggested that, in addition to stepwise glycosylation and sulphation, some pre-existing sulphated oligosaccharides might have been utilized for the synthesis of acidic glycoproteins.

Characterization of mucin isolated from rat tracheal transplants

Subcutaneous rat tracheal grafts yield several milligrams of secretions from which a homogeneous mucin fraction was isolated and purified. Histological evidence demonstrated that a normal mucociliary epithelium and mucous secretion were maintained for the 4-6 weeks of the experiment. The collected secretions were initially characterized by column chromatography on Sepharose CL-6B which separated the excluded high molecular weight mucins (unpurified mucin fraction) from most of the serum-type glycoproteins and proteins, including albumin. A reductive alkylation treatment of the unpurified mucin fraction followed by Sepharose CL-4B chromatography removed contaminating protein and most of the mannose-containing material from the mucin fraction. The void volume material from this column produced a single high molecular weight band upon sodium dodecyl sulfate agarose/acrylamide gel electrophoresis. The purified mucin fraction contained 16.5% protein and primarily galactose, N-acetylglucosamine, N-acetylgalactosamine, and sialic acid. This fraction also underwent beta-elimination in the presence of alkaline borohydride, demonstrating the presence of O-glycosidic linkages.

The separation and characterization of bronchial glycoproteins by density-gradient methods

1. Sputum samples from a total of 18 asthmatic and chronic bronchitic patients were examined by analytical density-gradient ultracentrifugation. CsBr was used as the dispersal agent and dense electrolyte. 2. The patterns show two main groups of components, banding at about 1.3g/ml and 1.5g/ml; in addition, a few samples showed a further zone at approx. 1.65g/ml. These components were identified as protein, secretory glycoprotein and DNA respectively. The glycoprotein zone was frequently hypersharp, and usually contained two or more partially resolved bands; it was always well resolved from the protein. 3. The glycoprotein components were isolated from nine representative sputum samples by density-gradient ultracentrifugation on a preparative scale. Analytical density-gradient ultracentrifugation was used to monitor the efficiency of the separations. 4. Some sputum samples separated cleanly under these conditions, the glycoprotein being essentially devoid of free protein; in others, separation was apparently incomplete, although computer simulation indicated that the conditions were adequate to ensure separation. Further density-gradient separations in CsCl were necessary with several samples before satisfactory products were obtained; mixtures of CsCl with guanidinium chloride were no more effective than CsCl alone. The reluctance to separate indicates a very strong, but non-covalent, interaction between protein and glycoprotein, probably associated with the gelatinous character of the secretion. 5. The purified glycoprotein components were characterized analytically and physicochemically. They contained N-acetylgalactosamine, N-acetylglucosamine, galactose, fucose and N-acetylneuraminic acid, and had an amino acid composition in which serine, threonine and proline predominated; however, aspartic acid, glutamic acid and cystine were also appreciable. The glycoproteins were of very high molecular weight, and usually showed more than one component in sedimentation velocity; their distribution in a density gradient indicated a substantial, but largely monotonic, density heterogeneity. 6. Thiol reduction decreased the molecular weight very substantially, but the products were relatively more homogeneous than the native materials. The amino acid composition was changed significantly and a small and variable proportion of protein or peptide was liberated. It is concluded that the native materials are disulphide-linked aggregates, probably through a cross-linking peptide, in confirmation of earlier studies.

Comparison of structural glycoproteins from mucus of different sources

The main structural glycoprotein derived from three mammalian mucociliary epithelial secretions (bovine cervical, human lung and human middle ear mucus) were compared. The glycoprotein was purified on a cesium chloride density gradient after prior cleavage of disulphide bonds. Marked similarities were seen for the glycoproteins in their sugar and amino acid composition, in electrophoretic mobility, in sedimentation rate and in their banding densities in a cesium chloride density gradient. The molecular weight of these materials was approximately 0.6-10(6). The similarity noted for these materials occurred despite two of them (lung and middle ear) being derived from pathological sources. The glycoprotein derived from an amphibian mucociliary epithelial secretion (frog palatal mucus) was different; it banded at a lower buoyant density and had a lower sugar content. These findings are discussed in terms of the rheological properties and physiological transport role of mucus on ciliated epithelia. It is suggested that reported differences in the properties of mammalian secretions from different sources is due to differences in the extent of crosslinking between glycoprotein units rather than to chemical or structural differences. In the case of the frog its very different composition may be in keeping with its rather different rheological properties.

[Rheological properties of human bronchial secretions: demonstration of proline-rich polypeptides and their role (author's transl)]

Human bronchial secretions were examined for chemical components and rheological properties. Proline-rich polypeptides (PRP) obtained by ultrasonic treatment and by contact with a cationic resin (AG 50WX2) were purified by gel-filtration chromatography and high-voltage electrophoresis. The chemical composition of these components allowed a classification according to their proline, glycine, glutamic acid and lysine contents. Rheological experiments suggest a biological role for the PRP in the fibrillar structure of sputum.

[Identification and characterization of proteins from human bronchial secretion (author's transl)]

An analysis of bronchial mucus proteins was carried out by crossed immunoelectrophoresis. Before electrophoretic migration, sputum was treated with Ecteola-cellulose, which retains acid mucins. The proteins were then extracted by a phosphate/saline buffer pH 7.5. Crossed immunoelectrophoresis of the "bronchial extracts" was carried out with an anti-human serum: fifteen proteins were detected. Among them, IgA and protease inhibitiors play an important role in bronchial pathology. Bronchial extracts were also studied with immune serums against milk proteins, whole saliva and proteins of bronchial mucus. Bronchotransferrin, amylase and two esterases were characterized. Four other proteins were also detected with immune serums against bronchial mucus-proteins: their biological role is still unknown.

[Purification and chemical study of a Collocalia glycoprotein]

A glycoprotein was purified from the aqueous extract of "edible bird's nest" (Collocalia) using free flow preparative electrophoresis and represented the main fraction of Collocalia glycoproteins. This glycoprotein is homogeneous upon agarose electrophoresis and slightly polydisperse upon ultracentrifugation (S So 20w = 3,0). The carbohydrate moiety contains galactose, mannose, glucosamine, galactosamine and sialic acid, which is completely released by Clostridium perfringens or Diplococcus pneumoniae neuraminidases and has the same chromatographic behaviour as N-acetyl-neuraminic acid. The peptide part of the glycoprotein is rich in serine, threonine and proline. About 40 p. cent of the hydroxyaminoacids are involved in carbohydrate-peptide linkages.

Effect of disodium cromoglycate (Intal) on sputum protein composition

The protein content in the sputum of nine patients with asthma was compared with that in 11 non-asthmatic patients by a method of gel electrophoresis. It was found that the albumin content was significantly higher in the sputum of the asthmatics than of the non-asthmatics (P<0·01). A further 11 asthmatic patients who were taking disodium cromoglycate (Intal) as part of their treatment had sputum albumin levels indistinguishable from the non-asthmatics. When patients with asthma were then studied serially, before and after disodium cromoglycate therapy, the albumin content returned to non-asthmatic levels within two days of starting treatment. It is suggested that disodium cromoglycate has a previously unrecognized action in altering sputum proteins.