Evidence of hydrophobic domains in human respiratory mucins. Effect of sodium chloride on hydrophobic binding properties

Mucin complexes of nanomaterials: first biochemical encounter

In recent years, the exposure of biological systems to various nanomaterials has become an issue of great public concern. Although living organisms have arrays of biological defense mechanisms against exposure to exogenous compounds, the biochemical mechanisms allowing various nanomaterials to enter the body are not well understood. A unique example of a typical mucosal glycoprotein capable of binding and solubilizing nanomaterials in physiological solution is provided, suggesting a possible route for entry into biological systems.

Barrier properties of mucus

Mucus is tenacious. It sticks to most particles, preventing their penetration to the epithelial surface. Multiple low-affinity hydrophobic interactions play a major role in these adhesive interactions. Mucus gel is also shear-thinning, making it an excellent lubricant that ensures an unstirred layer of mucus remains adherent to the epithelial surface. Thus nanoparticles (NP) must diffuse readily through the unstirred adherent layer if they are to contact epithelial cells efficiently. This article reviews some of the physiological and biochemical properties that form the mucus barrier. Capsid viruses can diffuse through mucus as rapidly as through water and thereby penetrate to the epithelium even though they have to diffuse 'upstream' through mucus that is being continuously secreted. These viruses are smaller than the mucus mesh spacing, and have surfaces that do not stick to mucus. They form a useful model for developing NP for mucosal drug delivery.

PMA stimulates MUC5B gene expression through an Sp1-based mechanism in airway epithelial cells

We previously showed that the MUC5B gene expression was elevated by phorbol 12-myristate 13-acetate (PMA) through an epidermal growth factor receptor-independent Ras/MEKK1/JNK and P38 signaling-based transcriptional mechanism. In the current study, we elucidated the molecular basis of this transcriptional regulation using promoter-reporter gene expression and chromatin immunoprecipitation (ChIP) assays with primary human bronchial epithelial cells that are cultured at the air-liquid interface. We have observed that PMA-induced MUC5B promoter activity is blocked by the Sp1-binding inhibitor, mithramycin A, in a dose-dependent manner. Deletion analysis with the MUC5B promoter construct demonstrated that both basal and PMA-induced promoter-reporter activities reside within the -222/-78 bp region relative to the transcriptional start site. NoShift transcriptional factor assays demonstrated that PMA stimulated Sp1 binding, but not STAT1 and c-Myc binding. Immunoprecipitation studies also verified the enhanced phosphorylation of Sp1 after PMA treatment. Site-directed mutagenesis and transfection studies demonstrated the involvement of Sp1-1 (-122/-114) and the Sp1-2 (-197/-186) cis elements in the basal and PMA-induced MUC5B promoter activity. The ChIP assay with anti-RNA polymerase II reconfirmed the PMA-induced MUC5B promoter activity by showing enhanced RNA polymerase II-DNA complex containing putative MUC5B Sp1-1, Sp1-2, or Sp1-3 sites. However, the ChIP assay using anti-Sp1 antibody demonstrated that the PMA-stimulated binding is only at Sp1-2. These results suggested an Sp1-based transcriptional mechanism with Sp1-1 as the regulator of basal MUC5B promoter activity and Sp1-2 as the regulator of PMA-induced MUC5B gene expression in the human airway epithelial cells.

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.

Self-association of mucin

Aggregation phenomena in aqueous solutions of purified human tracheobronchial mucin have been studied by rheological methods, steady-state fluorescence, quasielastic light scattering, and spin probe techniques. At temperatures below 30 degrees C and concentrations above 15 mg/mL and in the absence of chaotropic agents, mucin solutions are viscoelastic gels. A gel-sol transition is observed at temperatures above 30 degrees C that is manifested by the diminishing storage modulus and a loss tangent above unity throughout the studied frequency range of the oscillatory shear. No decline in the mucin molecular weight is observed by size-exclusion chromatography above 30 degrees C in the absence of redox agents or proteolytic enzymes. Aggregation of hydrophobic protein segments of the mucin chains at 37 degrees C is indicated by QELS experiments. The decreasing polarity of the microenvironment of pyrene solubilized into mucin solutions at temperatures above 30 degrees C, concomitant with the gel-sol transition, shows the hydrophobicity of the formed aggregates. ESR spectra of the fatty acid spin probe, 16-doxylstearic acid indicate that the aggregate-aqueous interface becomes more developed at elevated temperatures.

Purification and characterization of the MUC1 mucin-type glycoprotein, epitectin, from human urine: structures of the major oligosaccharide alditols

The MUC1 glycoprotein, epitectin, a component of the human bladder epithelium, was purified from human urine. Sedimentation equilibrium analysis and gel filtration using polysaccharide or protein standards revealed a polydisperse preparation with molecular weights ranging from about 0.9 to 1.3 x 10(6). This suggests that in the native state epitectin exists as aggregates of three or four monomer units of 350-400 kDa. Epitectin was found to have significant affinity to hexyl-, octyl- or phenyl agarose indicating that hydrophobic interactions and possibly carbohydrate-carbohydrate interactions may be responsible for the self-association. Chemical and enzymic deglycosylation of [125I]-labeled urine epitectin and metabolically labeled H.Ep.2 epitectin resulted in extremely polydisperse products. The buoyant densities of epitectin purified from urine and H.Ep.2 cells were found to be 1.39-1.40 g ml(-1), suggesting that the total carbohydrate content of these preparations is not significantly different. The O-linked saccharides of epitectin were fractionated by HPLC and analyzed by permethylation and FAB-MS. The neutral saccharides from both sources contain three common structures, namely Gal1 --> 3GalNAc, GlcNAc1 --> 6 (Gal1 --> 3) GalNAc and Gal1 --> 4GlcNAc --> 6 (Gal1 --> 3)GalNAc. The sialic acid of urine epitectin consisted entirely of N-acetylneuraminic acid. The two sources of epitectin, in vitro labeled on sialic acid, were found to have the same sialyl oligosaccharides but in different proportions. Metabolic labeling and N-glycanase susceptibility experiments firmly established the presence of N-linked saccharides in epitectin as minor components. The remarkable similarities in the total carbohydrate content, the carbohydrate composition and structures of saccharides between epitectin from urine, a non-malignant source, and H.Ep.2 cells is surprising in view of the prevailing view that MUC1 glycoproteins of cancer cells are underglycosylated compared to those produced by non-malignant cells.

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.

Biophysical characterization of mucin components HTM-1 and HTM-2 from tracheobronchial secretions of cystic fibrosis patients

Mucins present in the tracheobronchial secretions are responsible for the viscoelastic properties of the mucus. Any changes in the mucin structure may alter the physical properties of mucus and hence its function. Previous studies from this laboratory have reported the isolation and characterization of a major mucin component (HTM-1) and a minor, novel mucin component (HTM-2) from the tracheobronchial secretions of cystic fibrosis (CF) individuals. In the present study, the macromolecular properties of the CF mucin components HTM-1 and HTM-2 were further investigated using biophysical methods. Dynamic light scattering studies showed that CF HTM-1 and HTM-2 had a greater extended structure in buffer containing 0.10 and 0.15 M NaCl than that observed in the presence of 0.03 M NaCl. Also, CF HTM-1 had a compact configuration in the presence of 5 and 10 mM Ca2+, while under similar experimental conditions, the structure of CF HTM-2 was unaffected, indicating differences in the macromolecular properties of CF mucin components. Fluorescent probe binding studies revealed that CF HTM-1 had more hydrophobic probe binding domains than those observed for CF HTM-2. In summary, both biochemical and biophysical characterization suggests structural differences between the CF HTM-1 and HTM-2 components.

A novel human airway mucin cDNA encodes a protein with unique tandem-repeat organization

Highly specific affinity-purified polyclonal antibodies against deglycosylated human tracheobronchial mucin was used to select immunoreactive clones from a Uni-ZAP cDNA expression library prepared from normal human tracheal mRNA. The largest of three positive clones, designated pAM1, which reacted strongly with the polyclonal antibodies, was further characterized. Sequence analyses revealed a partial 941 bp cDNA that encoded a 313-amino-acid polypeptide. Bases 3-892 consisted of imperfect 41-nucleotide tandem repeats (CCAGGAGGGGACACCGGGTTCACGAGCTGCCCACGCCCTCT) that encoded a unique polypeptide with two types of consensus repeats, TSCPRPLQEGTRV and TSCPRPLQEGTPGSRAAHALSRRGHRVHELPTSSPGGDTGF. The overall composition of the deduced amino acid sequence matched that expected for a mucin protein core and is rich in serine, threonine, proline, glycine and alanine (approximately 51%). Northern blots probed with the mucin cDNA exhibited intense polydisperse hybridization bands with RNA isolated from normal human trachea and cystic-fibrosis bronchus. The data indicate that mucin encoded by clone pAM1 represents a unique type of peptide organization which has not been described in mucin cDNAs reported thus far.

Amiloride inhalation therapy in cystic fibrosis. Influence on ion content, hydration, and rheology of sputum

Amiloride inhalation as treatment for cystic fibrosis (CF) lung disease has been shown in independent studies to increase mucus clearance by ciliary and/or cough action and to retard the decline in lung function. It is hypothesized that amiloride therapy decreases the excess sodium and water absorption that is a characteristic of CF airway epithelium and that it leads to an improvement in the rheologic properties of mucus favoring airway mucus clearance. The aim of this study was to investigate whether amiloride treatment (5 x 10(-3) M amiloride in one-third normal saline four times a day) would change sputum electrolyte composition in patients with CF after 25 wk of therapy as compared with placebo (one-third normal saline), and whether appropriate changes in sputum water content and rheologic properties would accompany any changes in electrolyte composition. Sputum samples were obtained from six patients with CF undergoing amiloride therapy, using the dental cotton protection technique to avoid salivary contamination. The samples were stored at -80 degrees C until analyzed. For electrolyte analyses an aliquot of the sputum (minimum, 30 mg) was analyzed with ion-selective electrodes for sodium and potassium, and a chloride meter was used to measure chloride content. Chronic (25-wk) amiloride therapy increased significantly the sputum sodium (94.8 +/- 16.4 to 121.4 +/- 15.4 mmol/L, p = 0.001) and chloride (64.4 +/- 11.8 to 77.2 +/- 8.0 mmol/L, p = 0.10) content when compared with 25 wk of saline treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Suggestive evidence for two different mucin genes in rat intestine

In the present report we describe the isolation and sequence of a partial cDNA (M2-798) for a rat intestinal mucin designated M2. A rat intestinal lambda ZAP II cDNA library was screened using a polyclonal antiserum which was prepared against deglycosylated high-molecular-mass glycopeptides of the purified mucin. Mucin cDNA clones were found to contain tandem repeats of 18 nt which encoded a threonine- and proline-rich peptide having a consensus sequence of TTTPDV. This is the same sequence reported recently by Gum, Hicks, Lagace, Byrd, Toribara, Siddiki, Fearney, Lamport and Kim [(1991) J. Biol. Chem. 266, 22733-22738] for a rat intestinal cDNA called RMUC 176. A novel feature present in the cDNA M2-798 is a 246 nt unique region at the 3' end which encodes a hydrophobic sequence of 82 amino acids. RNA blots probed with M2-798 cDNA produced a single hybridization band between 7.5 and 9.0 kb in rat small intestine and colon. An identical hybridization pattern was obtained with a PCR-generated cDNA probe corresponding solely to the unique hydrophobic region of M2-798, demonstrating that this region is encoded by the authentic M2 mRNA. Our data suggest that the unique region of M2 has the potential to be either a transmembrane region, or a domain which mediates hydrophobic interactions of the mucin with other molecules. Since we have previously reported another rat intestinal cDNA which encodes the C-terminus of a mucin-like peptide (MLP) [Xu, Wang, Huan, Cutz, Forstner and Forstner (1992) Biochem. J. 286, 335-338], we wished to discover whether M2 was encoded by the same gene. RNA blotting experiments with probes specific for M2 and MLP showed different mRNAs for each. The message for M2 (7.5-8.5 kb) was smaller than that for MLP (> 9.5 kb) and, unlike MLP, gave no signal in human colonic LS174T cells. The results of DNA blots probed with M2-798 and an MLP-probe suggest that M2 and MLP are likely to be single-copy genes. It would appear therefore that normal rat intestine, like human intestine, may express two different mucin genes.

Degenerate 87-base-pair tandem repeats create hydrophilic/hydrophobic alternating domains in human mucin peptides mapped to 11p15

A human tracheobronchial lambda gt 11 cDNA library was screened using antiserum prepared against the deglycosylated protein backbone of human tracheobronchial mucins. Two cDNAs, designated JER 28 and 57, obtained from this immunoscreening, were used to isolate two other cDNA clones, JUL 7 and JUL 10, from a human tracheobronchial lambda gt 10 cDNA library. These four clones (561, 1830, 1631 and 991 bp), which mapped to chromosome 11p15, were all found to contain degenerate 87-base-pair tandem repeats which encode non-repetitive peptides. Numerous deletions or insertions in an otherwise virtually perfect 87-base-pair tandem repeat create many shifts in reading frame which completely destroy the repetitive peptide structure. The peptide is composed of alternate hydrophobic and hydrophilic domains which probably differ in the extent to which they are glycosylated. The mRNAs are expressed both in the respiratory and in the digestive tracts. These human mucin probes may be important in assessing the abnormal mucins associated with inflammatory diseases or carcinoma from human mucosae.

Adhesion of Yersinia enterocolitica to purified rabbit and human intestinal mucin

Interactions between Yersinia enterocolitica and purified intestinal mucins from rabbit and humans were investigated. Plasmid-bearing virulent organisms (but not plasmid-free nonvirulent bacteria) bound well to both mucins, suggesting that adherence was controlled by the virulence plasmid. Examination of binding to 14 different preparations of purified human intestinal mucin (8 preparations obtained from normal subjects and 6 samples from patients with cystic fibrosis) revealed no differences between normal and cystic fibrotic mucins in ability to serve as a binding substrate for virulent Y. enterocolitica. Analyses of binding curves suggested the presence of a single type of noninteracting receptor for Y. enterocolitica in both rabbit and human mucins with similar (but not necessarily identical) structures. Virulent bacteria bound to polystyrene through hydrophobic interactions that could be disrupted by treating the organisms with tetramethyl urea. In contrast, binding of plasmid-bearing Y. enterocolitica to intestinal mucin was not susceptible to tetramethyl urea and therefore does not appear to involve hydrophobic interactions. Prior incubation of organisms with mucin significantly inhibited binding to polystyrene, suggesting that mucin can mask hydrophobic adhesins on the bacterial surface. Hapten inhibition studies revealed that the monosaccharides galactose and N-acetylgalactosamine and the disaccharide lactose could markedly reduce (but not abolish) bacterial adherence to mucin but other monosaccharides and the RGD peptide had no effect on mucin binding. We conclude that virulent Y. enterocolitica is capable of interacting with the carbohydrate moiety of intestinal mucin. These interactions appear to be plasmid mediated and not hydrophobic.

Biophysical approaches to salivary mucin structure, conformation and dynamics

Our understanding of the origins of the physical and biochemical properties of mucous glycoproteins is incomplete and not with out controversy. Recent molecular biological and biophysical studies revealing the architecture and solution structure and dynamics of a series of salivary mucins, invaluable toward resolving many of these questions, are discussed. Mucins are very large, structurally heterogeneous, and highly expanded molecules with the carbohydrate playing a key role in maintaining the extended mucin conformation.

A heat-stable serine proteinase from the extreme thermophilic archaebacterium Sulfolobus solfataricus

A proteinase was purified to electrophoretic homogeneity from crude extracts of the thermoacidophilic archaebacterium Sulfolobus solfataricus. Molecular mass values assessed by SDS-PAGE and gel filtration were 54 and 118 kDa, respectively, which points to a dimeric structure of the molecule. An isoelectric point of 5.6 was also determined. The enzyme behaved as a chymotrypsin-like serine proteinase, as shown by the inhibitory effects exerted by phenylmethanesulfonyl fluoride, 3,4-dichloroisocoumarin, tosylphenylalaninechloromethyl ketone and chymostatin. Consistently with the inhibition pattern, the enzyme cleaved chromogenic substrates at the carboxyl side of aromatic or bulky aliphatic amino acids; however, it effectively attacked only a small number of such substrates, thus, displaying a specificity much narrower than and clearly different from that of chymotrypsin. This was confirmed by its inability to digest a set of natural substrate proteins, as well as insulin chains A and B; only after alkylation casein was degraded to some extent. Proteinase activity was significantly stimulated by Mn2+ which acted as a mixed-type nonessential activator. The enzyme also displayed a broad pH optimum in the range 6.5-8.0. Furthermore, it was completely stable up to 90 degrees C; above this temperature it underwent first-order thermal inactivation with half-lives ranging from 342 min (92 degrees C) to 7 min (101 degrees C). At 50 degrees C it could withstand 6 M urea and, to some extent, different organic solvents; however, at 95 degrees C it was extensively inactivated by all of these compounds. None of the chemical physical properties of the enzyme, including amino-acid analysis, provided evidence of a possible relation to other well-known microbial serine proteinases.

Evidence for secretion of high molecular weight mucins by canine tracheal epithelial cells in primary culture: effects of select secretagogues in mucin secretion

The purpose of this investigation was to provide evidence for the secretion of high molecular weight mucins, CTM-A and CTM-B, in primary culture of canine tracheal epithelial (CTE) cells. The cells were isolated from tracheas of mongrel dogs by pronase treatment. Primary cultures of the epithelial cells were established using ICN collagen inserts in Dulbecco's modified Eagle's/F12 medium supplemented with growth factors and could be maintained for up to 23 days. The evidence for the mucin secretion in culture medium and their localization in the cells was established by a) positive immunocytochemical staining using specific antibodies developed against purified native as well as deglycosylated CTM-A and CTM-B; b) incorporation of labeled amino acids, followed by electrophoresis and autoradiography detection of glycoconjugates purified from the culture medium; c) comparison of the amino acid compositions of mucin purified from canine tracheal pouch secretions and that purified from the culture medium; and d) Western blot analyses using specific polyclonal antibodies directed against deglycosylated CTM-A and CTM-B. Immunoaffinity purified secreted labeled glycoconjugates were resistant to hyaluronidase treatment. The effects of cyclic AMP (1 x 10(-5) M), dibutyryl cyclic AMP (1 x 10(-5) M), 8-bromocyclic AMP (1 x 10(-5) M), and prostaglandin E1 (1 x 10(-6) M) on mucin secretion by CTE cells were also investigated. Secretion of mucins by CTE cells in culture was considerably more enhanced by 8-bromocyclic AMP than that observed for other secretagogues used in this study.

Translation of messenger RNA from canine tracheal epithelial cells: identification of mucin core protein

A high-molecular-weight mucin (Mr approximately 11.0 x 10(6)) was purified from canine tracheal pouch secretions. The mucin was deglycosylated by treatment with trifluoromethane sulfonic acid for 8 h at 8 degrees C and subsequently with alpha-N-acetylgalactosaminidase. These treatments almost completely removed the carbohydrate moieties. The amino acid compositions of the deglycosylated and native mucins were similar, indicating that the deglycosylation procedure used did not cause notable degradation of the protein core. Antiserum specific for deglycosylated canine tracheal mucin was produced by immunization of rabbit with the antigen. RNA was isolated from fresh canine tracheal epithelial cells by extraction with guanidine isothiocyanate/hydrochloride and further fractionated by chromatography on oligo(dT)-cellulose to yield poly(A)+ RNA. The poly(A)+ RNA was translated in a rabbit reticulocyte cell-free translation system using [35S]methionine and [3H]leucine as radiolabels. The translation products were analyzed by gel electrophoresis and fluorography before and after immunoprecipitation with the antiserum to deglycosylated mucin. A labeled product of molecular weight 72,000 was present in the immunoprecipitate. When canine liver poly(A)+ RNA was used as control, no radioactivity above background was detected in the immunoprecipitate. It is concluded that the primary translation product of the canine tracheal epithelial cells is a 72,000-D protein and the monomer subunit of the mucin is about 167,000 D. Thus, in the native state, the canine tracheal mucin consists of several associating subunits.

Detection of distinct species in purified human respiratory mucin using monoclonal antibodies

The purpose of this investigation was to demonstrate the presence of different species (subpopulations) in the purified human tracheobronchial mucin (HTM-1). Mucin was highly purified from sputum specimens collected from a cystic fibrosis (CF) patient using a protocol involving sequential chromatography on Bio-Gel A-5m and hydroxylapatite columns. SDS-composite gel electrophoresis followed by periodic acid-Schiff's reagent staining was unable to detect mucin species. However, using enzyme-linked immunoelectrotransfer blot (EITB) method and polyclonal antibodies raised against HTM-1, at least four different migrating mucin species were detected. Further immunological characterization of these mucin species was carried out using a library of 16 monoclonal antibodies (MAbs) developed against the purified mucin. Nine MAbs belonged to the IgM class, two MAbs were IgG1, one IgG2a and remaining four were of the IgG3 subclass. Periodate oxidation of the mucin antigen was used to establish the nature of the mucin epitopes recognized by the MAbs. 11 MAbs recognized carbohydrate epitopes in the mucin molecule that were sensitive to periodate, while five MAbs reacted with periodate resistant carbohydrate epitopes or the protein portion of the mucin molecule. Enzyme-linked immunoelectrotransfer blot analysis of the MAbs against HTM-1 showed the presence of at least three distinct mucin species. Chromatography of the mucin on immunoaffinity columns (MAbs H(13.3), M(33.3) and CCK 061 conjugated to CNBr-activated Sepharose 4B), followed by ELISA and EITB analyses, established the mucin species recognized by the antibodies. These experiments further indicated that both unique and shared epitopes were present in the mucin species. These monoclonal antibodies may provide a promising approach to differentiate the secretory products of the tracheobronchial tree.

Macromolecular properties and polymeric structure of canine tracheal mucins

Two high-Mr mucus glycoproteins (mucins), CTM-A and CTM-B, were highly purified from canine tracheal pouch secretions, and their macromolecular properties as well as polymeric structure were investigated. On SDS/composite-gel electrophoresis, a diffuse band was observed for each mucin. Polyacrylamide-gel electrophoresis using 6% gels also showed the absence of low-Mr contaminants in the mucins. Comparison of chemical and amino acid compositions revealed significant differences between the two mucins. Using a static-laser-light-scattering technique, CTM-A and CTM-B were found to have weight-average Mr values of about 11.0 x 10(6) and 1.4 x 10(6) respectively. Both mucins showed concentration-dependent aggregation in buffer containing 6 M-guanidine hydrochloride. Under similar experimental conditions, reduced-alkylated CTM-A had an Mr of 5.48 x 10(6) and showed no concentration-dependent aggregation. Hydrophobic properties of the mucins, investigated by the fluorescent probe technique using mansylphenylalanine as the probe, showed the presence of a large number of low-affinity (KD approx. 10(5) M) binding sites. These sites appeared to be located on the non-glycosylated regions of the protein core, since Pronase digestion of the mucins almost completely eliminated probe binding. Reduction of disulphide bonds of CTM-A and CTM-B did not significantly alter the probe-binding properties. Also, addition of increasing NaCl concentrations (0.03-1.0 M) to the buffer caused only a small change in the hydrophobic properties of native and reduced-alkylated mucins. CTM-A was deglycosylated, without notable in the hydrophobic properties of native and reduced-alkylated mucins. CTM-A was deglycosylated, without notable degradation, using a combination of chemical and enzymic methods. On SDS/PAGE the protein core was estimated to have an Mr of approx. 60,000. On the basis of the protein and carbohydrate contents of the major mucin CTM-A, the mucin monomer was calculated to have an Mr of approx. 140,000. The high Mr (11 x 10(6] observed by physical methods is therefore due to self-association of the mucin monomer subunits.

Physicochemical characterization of a minor mucin component from cystic fibrosis tracheobronchial secretions

A minor mucin glycoprotein component (HTM-2) was purified from the tracheobronchial secretions of two cystic fibrosis patients using a protocol established in our laboratory. The secretions were solubilized in 0.1 M Tris-HCl buffer (pH 7.5) containing 0.22 M potassium thiocyanate and fractionated on a Bio-Gel A-5m column, followed by digestion with DNAase, rechromatography on the same column and chromatography on hydroxyapatite which resolved the major mucin (HTM-1) from the minor mucin component (HTM-2). The mucin component HTM-2 was further purified using Superose 6 chromatography. SDS-composite gel (2% polyacrylamide + 0.5% agarose) and 6% polyacrylamide gel electrophoresis showed that the purified HTM-2 was totally free of low-molecular-weight contaminants. Equilibrium density sedimentation centrifugation of purified HTM-2 using CsCl gradients also showed the absence of proteoglycans and other low-molecular-weight proteins. Comparison of carbohydrate and amino acid compositions of the two mucin components indicated that HTM-2 was quite different from the major mucin, HTM-1, reported earlier from our laboratory (Biochemistry, 24, 7334, 1985). This suggested that HTM-2 has a different polypeptide core and is perhaps a different gene product. The effects of 6 M guanidine-HCl and different concentrations of NaCl on the molecular size of HTM-2 and its ability to form aggregates was also investigated using the technique of static light scattering. In buffer containing 6 M guanidine-HCl, HTM-2 had a weight-average molecular weight of approximately 4.5 x 10(6). However, in the presence of buffer containing 0.03, 0.10 or 0.15 M NaCl, the molecular weight of HTM-2 was estimated to be approximately 11 x 10(6). These data suggest aggregation of HTM-2 in the presence of a range of NaCl concentrations. In contrast to HTM-1, which is a more anionic glycoprotein, the apparent molecular size of HTM-2 did not decrease at the higher NaCl concentration.

Production and characterization of monoclonal antibodies to purified deglycosylated cystic fibrosis respiratory mucin: evidence for the presence of four immunologically distinct epitopes

Respiratory mucus glycoproteins (mucins) were purified from the tracheobronchial secretions of three Cystic Fibrosis (CF) patients. The mucins were completely deglycosylated by treatment with trifluoromethanesulfonic acid and subsequent treatment with alpha-N-acetylgalactosaminidase. Over thirty hybrid clones secreting antibodies against the deglycosylated mucin (DGM) were obtained using standard hybridoma techniques. Hybrids with positive identification for CF-DGM were cloned twice using limiting dilution method to ensure the monoclonal nature of the antibodies. Eight stable clones (1a, 1b, 10a, 10c, 10d, 10e, 29d, and 30e) secreting monoclonal antibodies (MAbs) showing specificity of reaction to CF-DGM were obtained. Two clones, 29d and 30e, secreted antibodies of the IgM class while the other six clones secreted antibodies of the IgG1 subclass. Denaturation and reduction experiments suggested that MAbs 1b, 10e, 29d and 30e were directed against a given sequence of amino acids in the DGM while the other four MAbs, in addition to being sequence specific, were also conformation dependent. Further, competitive binding radioimmunoassays suggested that MAbs 1b, 10e, 29d and 30e recognize four distinct epitopes in the peptidic core of CF respiratory mucin. In summary, the MAbs may provide a promising approach to elucidate the structure of the polypeptide backbone of human respiratory mucins as well as for the screening of cDNA libraries for clones secreting mucin(s).