Purification of a low-molecular-weight, mucin-type glycoprotein from human submandibular-sublingual saliva

Purified mucins in drug delivery research

One of the main challenges in the field of drug delivery remains the development of strategies to efficiently transport pharmaceuticals across mucus barriers, which regulate the passage and retention of molecules and particles in all luminal spaces of the body. A thorough understanding of the molecular mechanisms, which govern such selective permeability, is key for achieving efficient translocation of drugs and drug carriers. For this purpose, model systems based on purified mucins can contribute valuable information. In this review, we summarize advances that were made in the field of drug delivery research with such mucin-based model systems: First, we give an overview of mucin purification procedures and discuss the suitability of model systems reconstituted from purified mucins to mimic native mucus. Then, we summarize techniques to study mucin binding. Finally, we highlight approaches that made use of mucins as building blocks for drug delivery platforms or employ mucins as active compounds.

Absence of capsule reveals glycan-mediated binding and recognition of salivary mucin MUC7 by Streptococcus pneumoniae

Salivary proteins modulate bacterial colonization in the oral cavity and interact with systemic pathogens that pass through the oropharynx. An interesting example is the opportunistic respiratory pathogen Streptococcus pneumoniae that normally resides in the nasopharynx, but belongs to the greater Mitis group of streptococci, most of which colonize the oral cavity. Streptococcus pneumoniae also expresses a serine-rich repeat (SRR) adhesin, PsrP, which is a homologue to oral Mitis group SRR adhesins, such as Hsa of Streptococcus gordonii and SrpA of Streptococcus sanguinis. As the latter bind to salivary glycoproteins through recognition of terminal sialic acids, we wanted to determine whether S. pneumoniae also binds to salivary proteins through possibly the same mechanism. We found that only a capsule-free mutant of S. pneumoniae TIGR4 binds to salivary proteins, most prominently to mucin MUC7, but that this binding was not mediated through PsrP or recognition of sialic acid. We also found, however, that PsrP is involved in agglutination of human red blood cells (RBCs). After removal of PsrP, an additional previously masked lectin-like adhesin activity mediating agglutination of sialidase-treated RBCs becomes revealed. Using a custom-spotted glycoprotein and neoglycoprotein dot blot array, we identify candidate glycan motifs recognized by PsrP and by the putative S. pneumoniae adhesin that could perhaps be responsible for pneumococcal binding to salivary MUC7 and glycoproteins on RBCs.

Biopolymeric Mucin and Synthetic Polymer Analogs: Their Structure, Function and Role in Biomedical Applications

Mucin networks are viscoelastic fibrillar aggregates formed through the complex self-association of biopolymeric glycoprotein chains. The networks form a lubricious, hydrated protective shield along epithelial regions within the human body. The critical role played by mucin networks in impacting the transport properties of biofunctional molecules (e.g., biogenic molecules, probes, nanoparticles), and its effect on bioavailability are well described in the literature. An alternate perspective is provided in this paper, presenting mucin’s complex network structure, and its interdependent functional characteristics in human physiology. We highlight the recent advances that were achieved through the use of mucin in diverse areas of bioengineering applications (e.g., drug delivery, biomedical devices and tissue engineering). Mucin network formation is a highly complex process, driven by wide variety of molecular interactions, and the network possess structural and chemical variations, posing a great challenge to understand mucin’s bulk behavior. Through this review, the prospective potential of polymer based analogs to serve as mucin mimic is suggested. These analog systems, apart from functioning as an artificial model, reducing the current dependency on animal models, can aid in furthering our fundamental understanding of such complex structures.

Layer-by-Layers of Polymeric Micelles as a Biomimetic Drug-Releasing Network

Mucin networks are lubricous biofunctional coats formed through the continuous deposition of mucin glycoproteins. Previously, we demonstrated the synthesis of a mucin mimic using biotinylated-filomicelles crosslinked via streptavidin using a layer-by-layer approach. These networks recreate the fibrous nature of mucin and can serve as a drug-releasing network. In this work, the ability to vary the network properties by blending filomicelles with spherical micelles is demonstrated. In addition, the deposition of a dense polymer coating on the mucin network was shown to act as a barrier to control diffusion and improved the structural stability under simulated oral chemical conditions. These biomimetic coatings can be utilized as a delivery system, providing a tunable drug release for oral applications.

MUC7 polymorphisms are associated with a decreased risk of a diagnosis of asthma in an African American population

PURPOSE

Mucin glycoproteins contribute to lung pathophysiology in asthma. The protein backbone of mucin glycoproteins is encoded by specific MUC genes, which exhibit a high degree of polymorphisms that generate a variable number of tandem repeat (VNTR) domains. MUC7 typically encodes for 6 VNTRs, each with 23 amino acids. In a northern European cohort, a polymorphism encoding MUC7*5 (5-VNTR) is in 100% linkage disequilibrium with the single nucleotide polymorphism rs9982010 and associated with a decreased risk of being asthmatic and having better lung function. African Americans have a 5- to 10-fold increase in incidence of asthma relative to whites, who are believed to be partially associated with higher genetic susceptibility. Occurrence of the rs9982010 and MUC7 allelic frequencies was evaluated in inner-city African Americans to test their association with a diagnosis of asthma.

METHODS

Genomic DNA, collected from a cohort of African American asthmatic subjects, was used to detect the MUC7 VNTR polymorphisms and to analyze the rs9982010 single nucleotide polymorphism.

RESULTS

A logistic regression analysis showed that the MUC7*5-VNTR allele decreased the likelihood of a diagnosis of asthma (odds ratio, 0.173 [95% confidence interval, 0.041-0.737]; P < 0.018) and is not in a strong linkage disequilibrium with the rs9982010 (r = 0.03; odds ratio, 66; confidence interval, 5.913-736.72). A novel MUC7*4-VNTR polymorphism, identified in an African American nonasthmatic individual, was linked to a structural rearrangement of the VNTR domain.

CONCLUSIONS

These data extend the association of MUC7*5 allelic polymorphisms and asthma to inner-city African Americans.

Structure and function of the polymeric mucins in airways mucus

The airways mucus gel performs a critical function in defending the respiratory tract against pathogenic and environmental challenges. In normal physiology, the secreted mucins, in particular the polymeric mucins MUC5AC and MUC5B, provide the organizing framework of the airways mucus gel and are major contributors to its rheological properties. However, overproduction of mucins is an important factor in the morbidity and mortality of chronic airways disease (e.g., asthma, cystic fibrosis, and chronic obstructive pulmonary disease). The roles of these enormous, multifunctional, O-linked glycoproteins in health and disease are discussed.

Localization and expression of MUC5B and MUC7 mucins in pediatric sinus mucosa

OBJECTIVES

The purpose of this study was to analyze the secretory cell population and distribution of MUC5B and MUC7 mucins in the sinus mucosa of pediatric patients with and without chronic rhinosinusitis (CRS).

METHODS

Sinus mucosal specimens were collected at surgery in a pediatric tertiary care facility. Histologic, immunohistochemical, and morphometric analyses were performed on sinus mucosa of 20 children with CRS and 7 children without CRS.

RESULTS

A significant increase in the area of submucosal glands was evident in the sinus mucosa of children with CRS as compared to controls. MUC5B and MUC7 mucins were expressed in the submucosal glands, as well as in goblet cells, in the sinus mucosa of both populations. No differences in MUC5B or MUC7 expression were observed when mucin expression was normalized to glandular area.

CONCLUSIONS

Children with CRS have an increased number of submucosal glands, indicating that glandular mucins contribute to mucus overproduction in CRS. MUC5B and MUC7 mucins, which have previously been considered only glandular mucins, are also expressed in goblet cells in the sinus mucosa.

The salivary mucin MUC5B and lactoperoxidase can be used for layer-by-layer film formation

In situ ellipsometry was used to study layer-by-layer film formation on hydrophilic and hydrophobized silica surfaces by alternating sequential adsorption of human mucin MUC5B and cationic proteins lysozyme, lactoferrin, lactoperoxidase or histatin 5, respectively. The stability of the multilayers was investigated by addition of sodium dodecyl sulfate solution (SDS). Atomic force microscopy was employed to investigate morphological structures on the surfaces during the layer-by-layer film build-up. It was clearly shown that, on both hydrophilic and hydrophobized silica, only MUC5B and lactoperoxidase showed the ability for multilayer formation, resulting in an approximately linear increase in adsorbed amount and film thickness with each deposition cycle. The net increase in amounts per cycle was larger on the hydrophilic silica. Further, MUC5B needs to be adsorbed first on the hydrophilic substrates to obtain this fast build-up behavior. Generally, addition of SDS solution showed that a large fraction of the adsorbed film could be desorbed. However, films on the hydrophobized silica were more resistant to surfactant elution. In conclusion, MUC5B-cationic protein multilayers can be formed on hydrophilic and hydrophobized silica, depending on the choice of the cationic protein as well as in which order the build-up is started on hydrophilic silica. Additionally, SDS disrupts the layer-by-layer film formed by MUC5B and lactoperoxidase.

Relationship between the ability of oral streptococci to interact with platelet glycoprotein Ibalpha and with the salivary low-molecular-weight mucin, MG2

The oral streptococci Streptococcus sanguinis, Streptococcus gordonii and Streptococcus oralis are common aetiological agents of infective endocarditis, and their ability to adhere to and induce the aggregation of platelets is thought to be a virulence trait. The platelet glycoprotein GPIbalpha has been implicated as the adhesion receptor for S. sanguinis and S. gordonii, but it is not known if this is the case for S. oralis and other species. The aim of this study was to determine the GPIbalpha-interactive capability of a range of oral streptococci and to determine the relationship between this capability and their ability to interact with the salivary constituents that they would encounter in their normal habitat. All platelet-adhesive S. sanguinis strains and most S. gordonii strains adhered in a GPIbalpha-dependent manner, but strains of S. oralis, Streptococcus cristatus, Streptococcus parasanguinis and Streptococcus mitis had no direct affinity for platelets. Those strains that were able to bind GPIbalpha also bound to the low-molecular-weight submandibular salivary mucin, MG2, and this interaction was sialic acid-dependent. The data suggest that S. sanguinis and S. gordonii may be efficient colonizers of platelet vegetations because of their adaptation to recognize sialylated salivary mucins. In contrast, S. oralis does not interact with platelets and so is likely to colonize vegetations through an as yet unidentified mechanism.

Influences of animal mucins on lysozyme activity in solution and on hydroxyapatite surfaces

The purpose of this study was to investigate the influence of animal mucins on lysozyme activity in solution and on the surface of hydroxyapatite (HA) beads. The effects of animal mucins on lysozyme activity in solution were examined by incubating porcine gastric mucin (PGM) or bovine submaxillary mucin (BSM) with hen egg-white lysozyme (HEWL) or salivary samples. HA-immobilised animal mucins or lysozyme were used to determine the influence of animal mucins on lysozyme activity on HA surfaces. Lysozyme activity was determined by turbidity measurement of a Micrococcus lysodeikticus substrate suspension. Protein concentration was determined by ninhydrin assay. PGM inhibited the activity of HEWL and salivary lysozyme in solution. The amount of inhibition was dependent on mucin concentration, incubation time and temperature, and the structural integrity of the mucin. The inhibition of salivary lysozyme activity by PGM was greater in submandibular/sublingual saliva than in parotid saliva. The inhibition of lysozyme activity by PGM was markedly dependent on pH. However, BSM did not inhibit the in-solution lysozyme activities of HEWL and clarified saliva. Both PGM and BSM bound to HA surfaces, and HA-adsorbed animal mucins increased the subsequent adsorption of lysozyme. When HA beads were exposed to a mixture of HEWL and PGM or BSM, lysozyme activity on the HA surfaces was significantly increased. The results suggest that animal mucins affect lysozyme activity, and the effects are different on HA surfaces compared with in solution. Further research is needed to determine the effect of animal mucins on lysozyme activity in vivo.

Identification of N-linked glycoproteins in human saliva by glycoprotein capture and mass spectrometry

Glycoproteins make up a major and important part of the salivary proteome and play a vital role in maintaining the health of the oral cavity. Because changes in the physiological state of a person are reflected as changes in the glycoproteome composition, mapping the salivary glycoproteome will provide insights into various processes in the body. Salivary glycoproteins were identified by the hydrazide coupling and release method. In this approach, glycoproteins were coupled onto a hydrazide resin, the proteins were then digested and formerly N-glycosylated peptides were selectively released with the enzyme PNGase F and analyzed by LC-MS/MS. Employing this method, coupled with in-solution isoelectric focusing separation as an additional means for pre-fractionation, we identified 84 formerly N-glycosylated peptides from 45 unique N-glycoproteins. Of these, 16 glycoproteins have not been reported previously in saliva. In addition, we identified 44 new sites of N-linked glycosylation on the proteins.

[Expression of antimicrobial peptide MUC7 in kidneys with pyelonephritis]

BACKGROUND

Mucins are glycoproteins secreted by epithelial cells of various organ systems exerting multiple functions. MG2 as the protein transcript of the MUC7 gene has first been described as secreted by serous salivary glands in the oral cavity. We sought to explore changes of MUC7 expression in the kidney stimulated by bacterial infection of the upper urinary tract.

METHODS

We investigated the gene expression of MUC7 by reverse transcriptase-polymerase chain reaction in voided urine specimens from 15 patients with acute pyelonephritis compared to 15 healthy volunteers. Furthermore, the gene and protein expression of MUC7 was studied in 15 renal tissue samples with chronic bacterial pyelonephritis versus 10 normal human kidney samples taken from tumor-bearing organs.

RESULTS

MUC7 gene expression was detected in 5 of 15 voided urine samples of patients with pyelonephritis and in 2 samples from 15 healthy volunteers (Fisher's exact test p=0.39). MUC7 gene expression was detected in 7 of 15 tissue samples of kidneys with chronic pyelonephritis and in none of 10 normal renal tissue samples from tumor bearing organs (p=0.02). Immunohistochemical staining with the monoclonal antibody PANH3 revealed protein expression in 6 of the 15 tissue samples with chronic pyelonephritis, but not in normal tissue samples.

CONCLUSION

Upregulated MUC7 expression in the urinary tract particularly in renal tubular epithelium can occur under inflammatory conditions. This indicates a putative role of MUC7 as an antimicrobial host defense molecule within the urogenital tract.

Interactions of Streptococcus mutans glucosyltransferase B with lysozyme in solution and on the surface of hydroxyapatite

Several active enzymes have been identified as components of acquired enamel pellicle. In the present study, the interactions of Streptococcus mutans glucosyltransferase B (GtfB) with lysozyme in solution and on the surface of hydroxyapatite (HA) beads were studied. Experiments were also performed to investigate whether structural differences exist between glucans formed by GtfB enzyme in the presence or absence of lysozyme in solution and on the surface of HA. Hen egg-white lysozyme (HEWL) and saliva were used as the sources of lysozyme; lysozyme-depleted saliva was used as control. Lysozyme activity was significantly reduced when adsorbed onto HA beads compared with that in solution. The GtfB enzyme did not affect the activity of lysozyme in solution or that of adsorbed lysozyme onto HA. The presence of HEWL increased GtfB activity; bovine serum albumin had an even greater enhancing effect. Depletion of lysozyme from whole saliva increased GtfB activity in solution, but not on the surface of saliva-coated HA. The presence of lysozyme affected the amount of glucan formation by GtfB, but not the structure of glucans formed in solution and on the surface. Therefore, the interaction of lysozyme and GtfB enzymes on HA surface may modulate the formation of glucan and dental plaque.

The influence of product and oral characteristics on swallowing

The urge to swallow food could be triggered by a threshold level in both food particle size and lubrication of the food bolus. Thus, both oral physiology and product characteristics may influence the swallowing threshold. We quantified the swallowing threshold in a group of 266 healthy adult subjects (age 42 +/- 12 years) by counting the number of chewing cycles needed to prepare food for swallowing. The influence of oral physiology on the swallowing threshold was determined by measuring salivary flow rate, maximum bite force and masticatory performance. We used about 10 cm(3) of bread, toast, melba toast, breakfast cake, peanuts and cheese to determine the influence on the swallowing threshold of various food characteristics, e.g. hardness, moisture and fat. Furthermore, we tested the effect of buttering the bread, toast, melba toast and breakfast cake on the swallowing threshold. Salivary flow rates were significantly and negatively correlated with the number of chewing cycles of melba toast and breakfast cake. Hence, subjects with more saliva needed less chewing cycles for these dry products. Maximum bite force and masticatory performance had an influence on the swallowing threshold for the hard products only (carrot and peanut). Although significant, the correlation coefficients were less than 0.28. Thus, the oral physiology parameters explained less than 10% of the variance in the swallowing threshold. We found significantly different numbers of chewing cycles for the various foods, ranging from 17 for cake to 63 for carrot. Hard and dry products needed more chewing cycles until swallowing. Buttering the food significantly reduced the number of chewing cycles needed before swallowing. This was especially true for the dry products cake, melba toast and toast. Hard and dry products require more chewing cycles and longer time in mouth until swallowing for sufficient breakdown to take place and for enough saliva to be added to form a coherent bolus safe for swallowing. In spite of this, more saliva, higher maximum bite force and better masticatory performance were only weakly correlated with a smaller number of chewing cycles. Butter enhanced lubrication and bolus formation of dry products, thus reducing the number of chewing cycles until swallowing. In conclusion, product characteristics and to a lesser extent oral physiology significantly affect swallowing threshold.

The StcE protease contributes to intimate adherence of enterohemorrhagic Escherichia coli O157:H7 to host cells

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a diarrheal pathogen that causes attaching and effacing (A/E) lesions on intestinal epithelial cells. Strains of the O157 serogroup carry the large virulence plasmid pO157, which encodes the etp type II secretion system that secretes the genetically linked zinc metalloprotease StcE. The Ler regulator controls expression of many genes involved in A/E lesion formation, as well as StcE, suggesting StcE may be important at a similar time during colonization. Our laboratory has previously demonstrated that StcE cleaves C1-esterase inhibitor, a regulator of multiple inflammation pathways. Here we report two new substrates for StcE, mucin 7 and glycoprotein 340, and that purified StcE reduces the viscosity of human saliva. We tested the hypothesis that StcE contributes to intimate adherence of EHEC to host cells by cleavage of glycoproteins from the cell surface. The fluorescent actin stain (FAS) test was used to observe the intimate adherence represented by fluorescently stained bacteria colocalized with regions of bundled actin formed on HEp-2 cells. An E. coli O157:H7 strain with a stcE gene deletion was not affected in its ability to generally adhere to HEp-2 cells, but it did score threefold lower on the FAS test than wild-type or complemented strains. Addition of exogenous recombinant StcE increased intimate adherence of the mutant to wild-type levels. Thus, StcE may help block host clearance of E. coli O157:H7 by destruction of some classes of glycoproteins, and it contributes to intimate adherence of E. coli O157:H7 to the HEp-2 cell surface.

Adhesion of oral streptococci to experimental bracket pellicles from glandular saliva

The aim of this study was to evaluate the functions of bracket pellicles as the binding receptors for Streptococcus mutans and Streptococcus gordonii. Four different types of orthodontic brackets were used: stainless steel, monocrystalline sapphire, polycrystalline alumina, and plastic. The bracket pellicles were formed by incubating orthodontic brackets with fresh submandibular-sublingual saliva or parotid saliva for 2 hours. The pellicles were extracted, and their components were confirmed by gel electrophoresis, immunodetection, and amino acid composition analysis. The roles of the bracket pellicles in the adhesion of oral streptococci were evaluated by incubating tritium-labeled streptococci with pellicle-transfer blots. The results showed that the salivary components adhered selectively according to type of bracket and glandular saliva. The selective adsorption was also proven by the amino acid composition profiles. Among the several salivary proteins, MG2, alpha-amylase, and the acidic proline-rich proteins provided the binding sites for S gordonii. However, none of these proteins in the bracket pellicles contributed to the adhesion of S mutans. These findings suggest that numerous salivary proteins can adhere selectively to the orthodontic brackets, and some of them contribute to the binding of S gordonii.

Experimental salivary pellicles formed on the surface of self-curing resin

The aim of this study was to identify the salivary components present in the pellicles formed on self-curing resin and to investigate the qualitative variations in adsorbed salivary pellicle compositions according to different exposure time to saliva. Experimental pellicles were formed by the incubation of polymerized resin particles with fresh human parotid or submandibular-sublingual saliva for either 20 min or 2 h. Pellicles were extracted using formic acid and lyophilized, they were then subjected to sodium dodecyl sulphate-polyacrylamide gel electrophoresis and immunoblotting to identify the adsorbed salivary components. The amino acid profiles of the 2 h-pellicles were analysed and compared with those of fresh glandular salivas. There was a difference in the 2 h-pellicle components on the self-curing resin compared with those of other dental materials as well as tooth enamel. The amino acid profiles of the 2 h-pellicles were also different from those of fresh glandular salivas. In the case of submandibular-sublingual saliva, the components of the 2 h-pellicle showed a different pattern compared with those of the 20 min-pellicle. However, there was no significant difference between the components of the 2 h- and 20 min-pellicles in the case of parotid saliva. A distinct difference was found in the surface binding affinities of immunoglobulin (IgA) from different glandular salivas. The findings of this study provide information concerning the initial bacterial adhesion on the surfaces of self-curing resin.

Salivary biochemistry in Buffalo: the legacy of Michael J. Levine

The author pays tribute to the contributions of Michael J. Levine to the field of salivary biochemistry.

Electrophoretic analysis of whole saliva and prevalence of dental caries. A study in Mexican dental students

BACKGROUND

Variability in salivary proteins and their posttranslational modifications may play an important role in determining their protective features against dental caries. Knowledge of molecular content of saliva in different populations is important for a better understanding of protective properties of this biological fluid. Aims of this study were to analyze electrophoretic pattern and protein composition in resting human whole saliva (HWS) of a Mexican population and to correlate these data with decayed, missing, and filled teeth (DMFT) index in these subjects.

METHODS

Resting human whole saliva samples were collected from 120 healthy Mexican dental students. Salivary flow rate, protein concentration, and electrophoretic profile analyzed qualitatively by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) were correlated with DMFT index. Gels were successively triple-stained with Coomassie brilliant blue R250, periodic acid Schiff (PAS), silver stain, and salivary molecules were scored as absent (-), present (+/-), and high intensity and size (+).

RESULTS

These showed no substantial differences in number of bands between males and females; however, a slight correlation between total protein concentration and sex was found (p <or=0.05). With regard to salivary proteins and DMFT index, subjects with higher DMFT indices presented significant reduction or absence of high-molecular-weight mucin glycoprotein-1 (MG1), low-molecular-weight mucin glycoprotein-2 (MG2), and acidic proline-rich protein-1 (PRP-1), differing from subjects with lower DMFT indices (p <or=0.001).

CONCLUSIONS

This study concludes that genetic phenotypic polymorphism is present in the population studied and has correlations with oral health. We found specific characteristics and individual variability in number, intensity, and apparent molecular weight of band features in this Mexican population. These studies provide the initial step for creating an HWS database in this population.

Boundary lubrication by lubricin is mediated by O-linked beta(1-3)Gal-GalNAc oligosaccharides

Lubrication of mammalian joints is mediated by lubricin, a product of megakaryocyte stimulating factor gene (MSF; GenBank accession #U70136) expression. Lubricin (M(r) approximately 240 kDa) is a mucinous glycoprotein which is 50% (w/w) post-translationally modified with beta(1-3)Gal-GalNAc incompletely capped with NeuAc, and lubricates apposed cartilaginous surfaces in the boundary mode through an unknown mechanism. Both bovine and human lubricin were purified from synovial fluid and digested with recombinant glycosidases. Released oligosaccharides were identified and quantified by fluorophore assisted carbohydrate electrophoresis (FACE). Corresponding digests of human lubricin were also assayed in a friction apparatus oscillating latex rubber against polished glass at a pressure of 0.35 x 10(6) N/m(2) and the coefficient of friction (mu) was measured. Digestion with alpha2,3-neuraminidase decreased lubricating ability by 19.3%. Partial removal of beta(1-3)Gal-GalNAc moieties by endo-alpha-N-acetyl-D-galactosaminidase reduced lubricating ability by 77.2%. Human lubricin digested with combined alpha2,3-neuraminidase and beta1-3,6-galactosidase continued to lubricate at 52.2% of its nominal value. Both bovine and human lubricin released 48.6% and 54.4% of total beta(1-3)Gal-GalNAc sidechains following digestion with endo-alpha-N-acetyl-D-galactosaminidase. Biological boundary lubrication by synovial fluid in vitro is provided primarily by extensive O-linked beta(1-3)Gal-GalNAc.

Experimental salivary pellicles on the surface of orthodontic materials

The purpose of this study was to define the composition of salivary pellicles that form on the surfaces of orthodontic materials and to further investigate whether qualitative differences exist between the composition of adsorbed salivary pellicles that form on 3 different orthodontic materials: stainless steel bracket metal, elastomeric ligature ring, and bracket bonding resin. Experimental pellicles were formed by incubating these materials in fresh human parotid or submandibular-sublingual saliva for 2 hours. Pellicles were extracted with sodium dodecyl sulfate buffer and lyophilized. They were then subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting to identify the adsorbed salivary components. Remarkable differences in the profiles of pellicle components were found, dependent on the type of orthodontic materials. The pellicle components on the bracket metal were almost the same as those found on the elastomeric ligature ring. Salivary protein adsorption patterns to bonding resin showed different features. Distinct differences were also found between the surface-binding affinities of the same salivary proteins from different glandular salivas. These results may be explained on the basis that binding sites for specific proteins on the surfaces of the materials are covered by molecules of submandibular-sublingual saliva, probably mucins. The results of this study provide valuable information concerning initial bacterial adhesion to the surfaces of orthodontic materials, as well as information that could be used in the development of orthodontic materials with enhanced surface properties.

Heterogeneity of high-molecular-weight human salivary mucins

The existence of high-molecular-weight glycoproteins in saliva and salivary secretions has been recognized for nearly 30 years. These proteins, called mucins, are essential for oral health and perform many diverse functions in the oral cavity. Mucins have been intensively studied, and much has been learned about their biochemical properties and their interactions with oral micro-organisms and other salivary proteins. In the past several years, the major high-molecular-weight mucin in salivary secretions has been identified as MUC5B, one of a family of 11 human mucin gene products expressed in tissue-specific patterns in the gastrointestinal, respiratory, and reproductive tracts. MUC5B is one of four gel-forming mucins which exist as multimeric proteins with molecular weights greater than 20-40 million daltons. The heavily glycosylated mucin multimers form viscous layers which protect underlying epithelial surfaces from microbial, mechanical, and chemical assault. Another class of mucin molecules, the membrane-bound mucins, is structurally and functionally distinct from the gel-forming mucins. These proteins do not form multimers and can exist as both secreted and membrane-bound forms, with the latter anchored to epithelial cell membranes through a short membrane-spanning domain. In the present work, we show that two of the membrane-bound mucins, MUC1 and MUC4, are expressed in all major human salivary glands as well as in buccal epithelial cells. While the functions of these mucins in the oral environment are not understood, it is possible that they form a structural framework on the cell surface which not only is cytoprotective, but also may serve as a scaffold upon which MUC5B, and possibly other salivary proteins, assemble.

In vitro assessment of antifungal therapeutic potential of salivary histatin-5, two variants of histatin-5, and salivary mucin (MUC7) domain 1

Human salivary histatin-5 (Hsn-5) is a 24-residue peptide that possesses potent antifungal activity in vitro. The MUC7 gene encodes human salivary low-molecular-weight mucin (MG2). The candidacidal activity of MUC7 domain 1 (MUC7 D1, the N-terminal 51 amino acid residues of MUC7) in vitro has also been demonstrated. In this study, we have investigated the antifungal therapeutic potential of Hsn-5, its two variants, R12I/K17N and R12I/H21L, and MUC7 D1. First, these peptides were tested for activities against different clinically important fungi. We found them to possess broad-spectrum antifungal activities; specifically, most exhibited excellent in vitro activity against eight clinically important fungal strains tested, including Candida albicans and Candida glabrata and their azole-resistant counterparts and Cryptococcus neoformans and its amphotericin B-resistant counterpart. These findings also suggest that the mechanism of action of both Hsn-5 and MUC7 D1 for these fungi is different from that of amphotericin B or azole antifungal agents. Second, we examined the stability of these peptides in whole human saliva and human serum. In saliva, the Hsn-5 variants R12I/K17N and R12I/H21L and MUC7 D1 degraded at a lower rate than Hsn-5. In human serum, MUC7 D1 was also more stable than Hsn-5; both peptides were more stable in serum than in saliva. Third, we examined the cytotoxicity of these peptides using human erythrocytes and two human cell lines (KB and HSG). No (or very low) hemolytic activity was observed with any of the four peptides, even at the highest protein concentration tested (200 microM), while amphotericin B caused 100% hemolysis at only 12.5 microM. The toxic effects of Hsn-5 and MUC7 D1 toward KB and HSG cells were also much lower than that of amphotericin B as measured by trypan blue exclusion. Together, these findings indicate that the investigated peptides possess high antifungal therapeutic potential, in particular for the treatment of drug-resistant fungal strains associated with immunocompromised (particularly human immunodeficiency virus-infected) patients. The same peptides could also be used as components of artificial saliva for patients with salivary dysfunction.

Molecular mapping of statherin- and histatin-binding domains in human salivary mucin MG1 (MUC5B) by the yeast two-hybrid system

MGI is a high-molecular-weight mucin secreted by mucous acinar cells in human submandibular and sublingual glands. We have recently shown that the tracheobronchial mucin MUC5B is a major component of MG1. MUC5B is organized into cysteine-rich N- and C-terminal regions that flank a central tandem-repeat region containing cysteine-rich subdomains and imperfect 29-residue tandem repeats. In earlier work, we have shown that this mucin selectively forms heterotypic complexes with amylase, proline-rich proteins, statherin, and histatins in salivary secretions, and the aim of this study was to identify specific binding domains within MUC5B using the yeast two-hybrid system. Interactions of cysteine-rich domains in the tandem-repeat region (Cys1-Cys4) and C-terminal region (Cys8a, Cys8b, Cys8c) of MUC5B with statherin and histatins were investigated. These studies indicated that histatin 1 selectively bound to Cysl and Cys2, whereas statherin and histatin 1, 3, and 5 selectively bound to Cys8a. Analysis of the primary sequences of the identified binding domains suggests that these domains most probably can fold into globular-like structures in the native mucin. A ProDom blast search revealed that sequences in Cys1, Cys2, and Cys8a exhibit similarity to domains in evolutionarily diverse extracellular proteins known to participate in a wide variety of protein-protein interactions.

Salivary MUC5B-mediated adherence (ex vivo) of Helicobacter pylori during acute stress

OBJECTIVE

Biochemical host defenses at mucosal sites, such as the oral cavity, play a key role in the regulation of microbial ecology and the prevention of infectious disease. These biochemical factors have distinct features, some of which benefit the host and some that benefit bacteria. We investigated the effects of acute stress on the salivary levels of the carbohydrate structure sulfo-Lewis (sulfo-Le), which is linked to the mucosal glycoprotein MUC5B. Sulfo-Le was recently identified as an adhesion molecule for Helicobacter pylori; therefore, we also measured saliva-mediated adherence (ex vivo) of H. pylori. The oral cavity is suspected to be involved in the transmission of H. pylori.

METHODS

Saliva was collected from 17 undergraduates before (baseline), during (stress), and after (recovery) exposure to a video showing surgical procedures. In addition, blood pressure, an impedance cardiogram, and an electrocardiogram were recorded.

RESULTS

During stressor exposure, participants reported increased state anxiety. In addition, stroke volume increased and heart rate decreased. The stressor induced a strong increase in salivary sulfo-Le concentration (U/ml), sulfo-Le output (U/min), sulfo-Le/total protein ratio (U/mg protein), and saliva-mediated adherence (ex vivo) of H. pylori. As expected, sulfo-Le concentration correlated with the adherence of H. pylori (r = 0.72, p < .05). It was demonstrated that the observed adherence was induced by MUC5B and that the carbohydrate structure sulfo-Le contributed to this process.

CONCLUSIONS

Our study demonstrated a direct link between stress-mediated biochemical changes and altered host-microbe interactions in humans. Increased bacterial adherence may be a contributing factor in the observed relationship between stress and susceptibility to infectious disease.

Thickness of acquired salivary pellicle as a determinant of the sites of dental erosion

Dental erosion shows a typical distribution pattern within the dental arches. Tooth protection from erosion by salivary pellicle has been shown in vitro, but the hypothesis that pellicle may differ quantitatively at sites of erosion has not been investigated. This study aimed to determine the thickness of acquired salivary pellicle within the dental arches, investigate the possible relationship of this thickness to the distribution and severity of erosion within the arches, and confirm the protective effect of pellicle against dental erosion. Eight enamel blocks were produced from each of 5 bovine incisors assigned to five volunteers. Each block was further cut into 2 slabs, producing control and experimental slabs. Pellicle developed on experimental slabs located on 8 intra-oral sites after 1 hr of exposure was stained by "sheep anti-human IgGAM-FITC". Slabs were then visualized, and pellicle thickness measured, by confocal laser scanning microscopy. Eroded enamel lesions were produced in experimental and control slabs by means of pure orange juice. The degree of erosion was quantified by transverse microradiography. Pellicle thickness varied significantly within the dental arches and among individuals. An inverse relationship (r = -0.96, p<0.001) was observed between the degree of erosion and pellicle thickness. Significant differences in erosion were observed between slabs with and those without pellicle. This study has shown that the thickness of acquired salivary pellicle varies within the dental arches, which may be responsible for the site-specificity of dental erosion, and that pellicle does protect the teeth from erosion.

Isolation of human salivary mucin MG2 by a novel method and characterization of its interactions with oral bacteria

Human salivary mucin MG2 was purified from submandibular/sublingual gland secretion by ultrafiltration and sequential gel filtration chromatography on Sephadex G-200, Superose 6 (prepgrade), and Superose 6. This method differs from earlier procedures in that all steps are performed in the presence of 4 M guanidine hydrochloride and do not involve covalent modification of the mucin molecule. Electrophoretic analyses and Western blotting showed that purified MG2 did not contain detectable levels of other salivary proteins. Amino acid analysis showed that the composition of purified MG2 was in excellent agreement with the deduced sequence of MG2 apomucin encoded in the MUC7 gene. The yield of purified MG2 was 10-15 mg from 750 ml of salivary secretion. Binding of purified MG2 to Streptococcus mutans in vitro was not significantly affected by reductive methylation, but was nearly abolished by reduction and alkylation. These data identified a functional determinant for mucin-bacterial interactions in the N-terminal region where the only two cysteines (Cys45 and Cys50) in the MG2 apomucin occur. Additionally, purified MG2 bound to four strains of oral Streptococci, indicating that the binding is not dependent on complexing with other salivary proteins, such as secretory immunoglobulin A. The purification procedure described in this work will facilitate investigation of the role of MG2 in the oral environment.

MUC5B is a major gel-forming, oligomeric mucin from human salivary gland, respiratory tract and endocervix: identification of glycoforms and C-terminal cleavage

Mucins from human whole saliva, as well as from respiratory- and cervical-tract secretions, were subjected to density-gradient centrifugation in CsCl/0.5 M guanidinium chloride. A polydisperse population of MUC5B mucins was demonstrated in all samples using anti-peptide antisera (LUM5B-2, LUM5B-3 and LUM5B-4) raised against sequences within the MUC5B mucin. The sequences recognized by the LUM5B-2 and LUM5B-3 antisera are located within the domains flanking the highly glycosylated regions of MUC5B, and reduction increased the reactivity with these antibodies, suggesting that the epitopes are partially shielded and that these regions are folded and stabilized by disulphide bonds. Rate-zonal centrifugation before and after reduction showed MUC5B to be a large oligomeric mucin composed of disulphide-linked subunits. In saliva and respiratory-tract secretions, populations of MUC5B mucins with different charge densities were identified by ion-exchange HPLC, suggesting the presence of MUC5B 'glycoforms'. In trachea, the F2 monoclonal antibody against the sulpho-Lewis C structure reacted preferentially with the later-to-be-eluted populations. An antibody (LUM5B-4) recognizing a sequence in the C-terminal domain of MUC5B identified, after reduction, the mucin subunits as well as smaller fragments, suggesting that some of the MUC5B mucins are cleaved within the C-terminal domain. Immunohistochemistry revealed that MUC5B is produced by cells dispersed throughout the human submandibular and sublingual glands, in the airway submucosal glands as well as the goblet cells, and in the epithelium and glands of the endocervix. The F2 antibody stained a subpopulation of the MUC5B-producing cells in the airway submucosal glands, suggesting that different cells may produce different glycoforms of MUC5B in this tissue.

Isolation and physical characterization of the MUC7 (MG2) mucin from saliva: evidence for self-association

Saliva contains two major families of mucins (MG1 and MG2); the polypeptide of the smaller of these glycoproteins (MG2) has been assigned as the product of the MUC7 gene. In this study we have devised a rapid two-step procedure that recovers this glycoprotein essentially free of other components and in sufficient quantity to enable physical and self-interaction studies. Raw saliva was solubilized in 4 M guanidinium chloride and thereafter subjected to Sepharose CL-4B chromatography. The MG2-rich fraction was recovered free from the larger MG1 glycoproteins and also smaller proteins/glycoproteins (molecular mass less than 100 kDa). MG2 glycoproteins were finally purified by anion-exchange chromatography on Mono Q. The purity of the preparation was assessed by SDS/PAGE after radiolabelling of the molecules with [14C]acetic anhydride. Peptide mapping, N-terminal sequencing and amino acid analysis verified the polypeptide of the mucins as the MUC7 gene product. The isolated molecules were examined by electron microscopy and appeared as short flexible worm-like structures 30-120 nm in length. The distribution was heterogeneous, containing a major component with number-average and weight-average lengths of 52 and 55 nm respectively and a minor component with number-average and weight-average lengths of 94 and 98 nm respectively. We propose that the two differently sized populations represent monomeric and dimeric species of the mucins. Gel chromatography performed in 0.2 M NaCl indicated the presence of monomers, dimers and tetramers; an average molecular mass for the preparation was 192 kDa. However, in 4 M guanidinium chloride the molecular mass was 158 kDa and a similar molecular mass (155 kDa) was determined for the mucin preparation after reduction. These results suggest that the mucins might self-associate via a protein-mediated interaction. On the basis of the results a model is proposed for the self-association of the MUC7 mucin, which might be important for its biological function.

Bactericidal activity and poly-L-proline II conformation of the tandem repeat sequence of human salivary mucin glycoprotein (MG2)

The tandem repeat 23-residue sequence [TRS23 (145-167): T-T-A-A-P-P-T-P-S-A-T-T-P-A-P-P-S-S-S-A-P-P-E] of human salivary mucin glycoprotein MG2 was examined for its in vitro bactericidal activity against four oral microorganisms, Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Streptococcus gordonii, and Streptococcus mutans. The conformational features of the proline-rich peptide were determined by circular dichroism (CD) and 600 MHz two-dimensional (2D) nuclear magnetic resonance (NMR) in aqueous solution. The strains of P. gingivalis (W50 and 381), A. actinomycetemcomitans (Y4 and 67), S. gordonii (DL1), and S. mutans (GS5) are highly sensitive to this peptide at 1.5-3.0 microM concentrations, suggesting that the proline-rich repeat sequence is a potent bactericidal agent for oral pathogens. The assignment of backbone and side-chain proton resonances was accomplished by the combined analysis of 2D total correlated spectroscopy and nuclear Overhauser effect spectroscopy. The temperature dependence of amide NH chemical shifts and the 1H-2H exchange effect on amide NH resonances suggest the absence of intramolecularly hydrogen-bonded NH groups. The coupling constant (JNH-CalphaH) values, conformational restriction offered by the proline residues (phi = -60 degrees +/- 15 degrees), the set of medium- and short-range nuclear Overhauser effects observed for this sequence, and the results of restrained structure calculation using DIANA, the distance geometry algorithm for NMR applications, provide evidence for the existence of a significant population of poly-L-proline II-type helices in aqueous solution. The CD spectra of the peptide in phosphate buffer (pH 7.2) and in methanol are reminiscent of the CD spectrum of the poly-L-proline II helical conformation and are consistent with the NMR data. The bactericidal activity of the proline-rich repeat sequence suggests that bacterial colonization, facilitated by the adsorbed salivary mucins on tooth surface, could be partly controlled and cleared by proteolytically degraded proline-rich peptides of MG2 in saliva before the colonized organisms turn into pathogens. It appears that the poly-L-proline II helix is the biologically active backbone conformation for bactericidal activity of the tandem repeat sequences of salivary MG2.

MUC5B and MUC7 are differentially expressed in mucous and serous cells of submucosal glands in human bronchial airways

Mucins are high molecular-weight glycoproteins involved in the protection and lubrication of respiratory, gastrointestinal, and reproductive tracts. Hypersecretory diseases such as cystic fibrosis (CF), chronic bronchitis, and asthma result in dysregulated levels of mucin production stemming from increased abundance of mucin-secreting cell types in the surface airway epithelium and submucosal glands. The isolation of at least nine mucin genes has prompted studies to characterize the cellular expression patterns of these mucins in normal and diseased tissues. In the present study, in situ hybridization and immunocytochemical methods were used to determine the cellular distribution of MUC5B and MUC7 expression in CF and non-CF human bronchus. Our findings indicate that MUC5B and MUC7 have expression patterns in human bronchial airways that are limited exclusively to submucosal glands. Specifically, MUC5B expression was confined to all mucous tubules, whereas MUC7 expression was seen in a subset of lysozyme expressing serous tubules of submucosal glands. Interestingly, heterogeneity of MUC7 expression between glands of the same bronchus ranged from 0 to 93% of serous tubules, suggesting that functional diversity may exist between glands within the same bronchial sample. No remarkable differences were observed in the expression patterns of MUC5B or MUC7 between CF (n = 7) and non-CF (n = 10) bronchial samples. In conclusion, MUC5B and MUC7 expressions define different cellular compartments within submucosal glands of human bronchus and lend insight into the heterogeneity of mucin production in the lung.

Structural features of the human salivary mucin, MUC7

Human salivary mucin (MUC7) is characterized by a single polypeptide chain of 357 aa. Detailed analysis of the derived MUC7 peptide sequence reveals five distinct regions or domains: (1) an N-terminal basic, histatin-like domain which has a leucine-zipper segment, (2) a moderately glycosylated domain, (3) six heavily glycosylated tandem repeats each consisting of 23 aa, (4) another heavily glycosylated MUC1- and MUC2-like domain, and (5) a C-terminal leucine-zipper segment. Chemical analysis and semi-empirical prediction algorithms for O-glycosylation suggested that 86/105 (83%) Ser/Thr residues were O-glycosylated with the majority located in the tandem repeats. The high (approximately 25%) proline content of MUC7 including 19 diproline segments suggested the presence of polyproline type structures. CD studies of natural and synthetic diproline-rich peptides and glycopeptides indicated that polyproline type structures do play a significant role in the conformational dynamics of MUC7. In addition, crystal structure analysis of a synthetic diproline segment (Boc-Ala-Pro-OBzl) revealed a polyproline type II extended structure. Collectively, the data indicate that the polyproline type II structure, dispersed throughout the tandem repeats, may impart a stiffening of the backbone and could act in consort with the glycosylated segments to keep MUC7 in a semi-rigid, rod shaped conformation resembling a 'bottle-brush' model.

MUC7 gene expression and genetic polymorphism

This study examined differential expression of several mucin genes in the human submandibular gland and trachea, MUC7 tissue and species specificity, and MUC7 genetic polymorphism. Mucin gene expression examined by RT-PCR indicated that MUC1, MUC4 and MUC7 are expressed in the human submandibular gland, while MUC1, MUC2, MUC4, MUC5 and MUC7 are expressed in the human trachea. Northern blot analysis confirmed the expression of MUC7 in the human trachea and MUC4 in the human submandibular gland. Northern blot analysis also demonstrated that MUC7 is not expressed in the submandibular/sublingual gland complexes of hamster, mouse and rat. Southern blot analysis suggested the presence of a MUC7 homologue in monkey genomic DNA. Genetic polymorphism studies of MUC7 by PCR and Southern blot analysis revealed the presence of a limited variable number of tandem repeats (VNTR) polymorphism.

Human salivary mucin MG1 selectively forms heterotypic complexes with amylase, proline-rich proteins, statherin, and histatins

Heterotypic complexes between the high-molecular-weight mucin MG1 and other salivary proteins in human submandibular/sublingual secretion (HSMSL) could have a significant impact on the biological properties of these proteins in oral fluids in both health and disease. We describe a mild procedure for isolation and purification of native MG1 by gel filtration chromatography on Sepharose CL-2B which does not involve dialysis, lyophilization, use of denaturing agents, or covalent modification. Western blots of native MG1 probed with antibodies against 8 different salivary proteins showed that complexing occurs between MG1 and salivary amylase, proline-rich proteins (PRPs), statherins, and histatins but not MG1, sIgA, secretory component, or cystatins. When native MG1 was placed in 4 M guanidine hydrochloride and chromatographed on Sepharose CL-4B, ELISA measurement of column fractions showed that amylase, PRPs, statherins, and histatins were released. Interestingly, gel filtration resolved the material which eluted into 4 or 5 distinct peaks, suggesting that the released entities were heterotypic complexes. From these studies, the occurrence of at least three different types of complexes between MG1 and other salivary proteins has been identified. Type 1 complexes are dissociated by SDS-PAGE and in 4 M guanidine hydrochloride. Type II complexes are not dissociated under these conditions. Type III complexes are dissociated during SDS-PAGE and by 4 M guanidine hydrochloride, but the released proteins appear to be complexes containing amylase, PRPs, statherins, and histatins. The possible functional role of heterotypic complexes between MG1 and other salivary proteins as a physiologic delivery system, a mechanism for protection against proteolysis, a repository for precursors of the acquired enamel pellicle, and a vehicle for modulation of the viscoelastic and rheological properties of saliva is discussed.

Human oral microbial ecology and dental caries and periodontal diseases

In the human oral cavity, which is an open growth system, bacteria must first adhere to a surface in order to be able to colonize. Ability to colonize a non-shedding tooth surface is necessary prior to any odontopathic or periodontopathic process. Complex microbe-host relationships occur and must be studied before the commensal-to-pathogenic nature of the human indigenous oral flora can be understood. Medical pathogens, if present in the appropriate host, always produce specific disease. Caries and periodontal diseases are conditional diseases, requiring numbers of certain indigenous species at various sites, particularly the tooth surface. In the case of caries, the condition is related to sugar consumption. Periodontal disease/s may require certain host and environmental conditions, such as local environment or nutritional factors in gingival crevicular fluids. Nonetheless, critical numbers of certain indigenous species must be present in order for these diseases to occur. The aim of this review is to understand the acquisition of the indigenous oral flora and the development of human dental plaque. The role of the salivary pellicle and adherence of indigenous bacteria to it are critical first steps in plaque development. Bacterial interactions with saliva, nutritional factors, growth factors, and microbial physiologic processes are all involved in the overall process of microbial colonization.

Growth, incidence and activities of dissimilatory sulfate-reducing bacteria in the human oral cavity

Viable counts and activities of sulfate-reducing bacteria were determined in the oral cavities of 12 healthy volunteers. Of these, 10 harboured viable sulfate-reducing bacteria populations. Six separate sites were sampled: the posterior tongue, anterior tongue, mid buccal mucosa, vestibular mucosa, supragingival plaque and subgingival plaque. Sulfate-reducing bacteria occurred in all areas, with the highest incidence in supragingival plaque. Viable counts and sulfate-reducing activities in each of the regions varied from 0 to 10(8) cfu (g wet weight)-1 and from 0 to 50 nmol (g wet weight)-1 h-1, respectively. As sulfate-reducing bacteria can be detected in the oral cavity, they may potentially be involved in terminal oxidative processes carried out by the microflora of the mouth.

Binding of human high-molecular-weight salivary mucins (MG1) to Hemophilus parainfluenzae

In human saliva, two different mucin populations can be distinguished, viz., high-molecular-weight mucins (MG1, mol. wt > 1 x 10(6)) and low-molecular-weight mucins (MG2, mol. wt approximately 125 kD). The carbohydrate moiety of MG1 displays a wide spectrum of oligosaccharide structures, varying in composition, length, branching, and acidity. The biological significance of the heterogeneity in carbohydrate structures of mucins is unclear. The present investigation focused on the question whether MG1, because of its diverse carbohydrate side-chain population, can bind to a large variety of oral micro-organisms. A replica plate technique, in combination with immunochemical detection with monoclonal antibodies against MG1, was used to screen in vivo human oral microflora for the presence of micro-organisms which could bind the high-molecular-weight salivary mucin MG1. Binding to purified MG1 was established for Hemophilus (para)influenzae species, whereas other species, including Streptococcus and Staphylococcus, were negative. MG1 binding to Hemophilus parainfluenzae could be abolished by protease treatment of MG1. In contrast, periodate acid treatment, partial deglycosylation, or addition of monosaccharides did not affect MG1 binding to H. parainfluenzae, indicating that MG1 carbohydrate side-chains were not directly involved in the binding. The binding was pH-dependent, showing an increase when the pH was lowered from 8.0 to 4.0. These data indicate that MG1 can be bound in a selective manner by Hemophilus spp. and suggest that the 'naked' unglycosylated polypeptide moiety of MG1 is involved in its binding to Hemophilus parainfluenzae.

Saliva-bacterium interactions in oral microbial ecology

Saliva is thought to have a significant impact on the colonization of microorganisms in the oral cavity. Salivary components may participate in this process by one of four general mechanisms: binding to microorganisms to facilitate their clearance from the oral cavity, serving as receptors in oral pellicles for microbial adhesion to host surfaces, inhibiting microbial growth or mediating microbial killing, and serving as microbial nutritional substrates. This article reviews information pertinent to the molecular interaction of salivary components with bacteria (primarily the oral streptococci and Actinomyces) and explores the implications of these interactions for oral bacterial colonization and dental plaque formation. Knowledge of the molecular mechanisms controlling bacterial colonization of the oral cavity may suggest methods to prevent not only dental plaque formation but also serious medical infections that may follow microbial colonization of the oral cavity.

Analysis of Candida albicans adhesion to salivary mucin

Clearance of Candida albicans from the oral cavity is thought to be mediated via specific receptor-ligand interactions between salivary constituents and the fungus. Since surfaces in the oral cavity are normally coated with a saliva-derived pellicle, specific interactions between salivary constituents and C. albicans may also contribute to adhesion of C. albicans to the oral mucosa and dental prostheses. Therefore, the purpose of this study was to identify salivary constituents to which C. albicans is capable of binding. A solid-phase overlay assay was used in which electrophoretically separated rat and human salivary constituents bound to membrane filters were incubated with radiolabelled C. albicans cells. C. albicans adhered to a single salivary component from each host. Correlation of cell-binding activity with specific monoclonal antibody (MAb)-binding activity indicated that the constituent bound by C. albicans in human saliva was low-molecular-weight mucin (MG2) and that in rat saliva was rat submandibular gland (RSMG) mucin. Further studies showed an identical cell hybridization signal and MAb colocalization by using RSMG ductal saliva and an aqueous RSMG extract in the solid-phase overlay assay. Analysis of cell binding to the aqueous extract of RSMG fractionated by anion-exchange chromatography demonstrated that C. albicans binding was restricted to an acidic subfraction of the RSMG extract, which also bound the RSMG mucin-specific MAb. The Candida-binding fraction contained predominantly RSMG mucin glycoprotein and also a noncovalently associated, chloroform-extractable material. Furthermore, we identified two strains of C. albicans which differed severalfold in the ability to bind RSMG mucin in the overlay assay. These results suggest that C. albicans binds to only a specific subfraction of RSMG mucin and that the two C. albicans strains tested differ in the ability to bind RSMG mucin subfractions.

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

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