Masticatory lubrication. The role of carbohydrate in the lubricating property of a salivary glycoprotein-albumin complex

Separate oligosaccharide determinants mediate interactions of the low-molecular-weight salivary mucin with neutrophils and bacteria

The low-molecular-weight human salivary mucin (MG2) coats oral surfaces, where it is in a prime location for governing cell adhesion. Since oligosaccharides form many of the interactive facets on mucin molecules, we examined MG2 glycosylation as it relates to the molecule's adhesive functions. Our previous study of MG2 oligosaccharide structures showed that the termini predominantly carry T, sialyl-T, Lewisx (Lex), sialyl Lex (sLex), lactosamine, and sialyl lactosamine determinants [Prakobphol, A., et al. (1998) Biochemistry 37, 4916-4927]. In addition, we showed that sLex determinants confer L-selectin ligand activity to this molecule. Here we studied adhesive interactions between MG2 and cells that traffic in the oral cavity: neutrophils and bacteria. Under flow conditions, neutrophils tethered to MG2-coated surfaces at forces between 1.25 and 2 dyn/cm2, i.e., comparable to the shear stress generated at the tooth surface by salivary flow ( approximately 0.8 dyn/cm2). MG2 was also found in association with neutrophils isolated from the oral cavity, evidence that the cells interact with this mucin in vivo. Since MG2 serves as an adhesion receptor for bacteria, the MG2 saccharides that serve this function were also identified. Seven of 18 oral bacteria strains that were tested adhered to MG2. Importantly, six of these seven strains adhered via T antigen, sialyl-T antigen, and/or lactosamine sequences. No adherence to Lex and sLex epitopes was detected in all the strains that were tested. Together, these results suggest that distinct subsets of MG2 saccharides function as ligands for neutrophil L-selectin and receptors for bacterial adhesion, a finding with interesting implications for both oral health and mucin function.

Interactions of grape seed tannins with salivary proteins

To evaluate the amount and type of condensed tannins binding salivary proteins, which are supposed to be involved in astringent sensation, model systems allowing further analyses of proteins and condensed tannins were developed. The precipitates formed after addition of grape seed tannins to salivary proteins indicate that a binding interaction occurs. Dissociation of insoluble complexes was achieved by sodium dodecyl sulfate treatment. Thiolysis reaction allowed the quantification and characterization of proanthocyanidins on both the resulting pellet and the supernatant. Binding proteins were investigated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The higher polymerized tannins predominantly precipitated together with the salivary proteins. The condensed tannins remaining in solution were low molecular weight polymers.

Encoding of human basic and glycosylated proline-rich proteins by the PRB gene complex and proteolytic processing of their precursor proteins

Proline-rich proteins (PRPs) constitute a family of about 20 members in human saliva that are encoded by six genes. Assignment of genomic DNA coding regions is complicated because of the occurrence of many alleles and the great similarity of amino acid sequences of PRPs. To overcome these problems, the nucleotide sequences of the genes encoding basic and glycosylated PRPs from one person were determined and then aligned with her previously determined protein sequences. This, together with additional protein data, has also resolved various discrepancies between corresponding protein and DNA sequences. For the first time in one person it is now possible to account for all the regions in the PRB genes encoding basic and glycosylated PRPs, and the primary structures of all secreted basic and glycosylated PRPs have been determined. Each gene encodes a precursor protein that subsequently undergoes proteolytic cleavage, thereby giving rise to the secreted proteins. The results have allowed identification of all the proteolytic cleavage sites in the precursor proteins, which all conform to a consensus cleavage site for furin. To evaluate if furin is responsible for the precursor protein cleavages, a recombinant precursor protein was synthesized by in vitro transcription translation of a PRB1 allele. The protein was shown to be correctly cleaved by furin, giving rise to the expected secreted proteins.

Interaction of tannin with human salivary proline-rich proteins

Tannins are polyphenolic compounds, widely distributed in plant-based foods, which have harmful effects on animals including humans. Salivary proline-rich proteins (PRPs) may act as a defence against tannins by forming complexes with them and thereby preventing their interaction with other biological compounds and absorption from the intestinal canal. The aim here was to compare the ability of members of the family of human PRPs to form insoluble complexes with tannin and to assess the stability of such complexes under conditions similar to those in the alimentary tract. Basic PRPs (BPRPs), which have no other known biological functions, were very effective in forming insoluble complexes with both condensed tannin and tannic acid. Practically no tannin bound to acidic PRPs (APRPs) and glycosylated PRPs (GPRPs), suggesting that tannin in the diet would not affect their biological activities. There were only small differences in the tannin-precipitating ability of various BPRPs of different sizes or sequences, indicating that, although there is considerable phenotypic variation of PRPs, it is not likely to cause marked individual variation in tannin-binding ability. Tryptic digestion of an APRP led to a marked increase in tannin binding to the resulting proline-rich peptides, supporting observations in other studies that there may be an interaction between the proline-poor N-terminal and the proline-rich C-terminal regions in native APRPs, which inhibits the biological activities of the proteins. Deglycosylation of a GPRP also led to a dramatic increase in tannin-binding ability, showing that the carbohydrate side-chains prevent binding of tannin. Most of the condensed tannin-PRP complexes remained insoluble under conditions similar to those in the stomach and small intestine, supporting the proposal that PRPs act as a defence against tannin.

Human low-molecular-weight salivary mucin expresses the sialyl lewisx determinant and has L-selectin ligand activity

Previously we showed that the low-molecular-weight mucin (MG2, encoded by MUC7), a major component of human submandibular/sublingual saliva, is a bacterial receptor that coats the tooth surface. Here we tested the hypothesis that the structure of its carbohydrate residues contains important information about its function. Purified MG2 (Mr 120 000) was digested with trypsin, and the resulting Mr 90 000 fragment, which carried primarily O-linked oligosaccharides, was subjected to reductive beta-elimination. The released oligosaccharides were characterized by using nuclear magnetic resonance spectroscopy and mass spectrometry. Of the 41 different structures we detected, the most prominent included NeuAcalpha2-->3Galbeta1-->3GalNAc-ol (sialyl-T antigen), Galbeta1-->4(Fucalpha1-->3)GlcNAcbeta1-->6(Galbeta1 -->3)GalNAc-ol [type 2 core with Lewisx (Lex) determinant], and NeuAcalpha2-->3Galbeta1-->4(Fucalpha1-->3)GlcNAcbet a1-->6(Galbeta1--> 3) GalNAc-ol [type 2 core with sialyl Lex (sLex) determinant]. We also detected di-, tri-, and pentasaccharides with one sulfate group. Lex, sLex, and related sulfated structures are ligands for selectins, adhesion molecules that mediate leukocyte trafficking. Therefore, we investigated whether MG2 was a selectin ligand. In an enzyme-linked immunosorbent assay, L-selectin chimeras interacted with immobilized MG2 in a Ca2+-dependent manner. L-Selectin chimeras also bound to MG2 immobilized on nitrocellulose. Together, these results suggest that the saccharides that MG2 carries could specify some of its important functions, which may include mediating leukocyte interactions in the oral cavity.

Asparagine-linked carbohydrate chains of inducible rat parotid proline-rich glycoprotein contain terminal beta-linked N-acetylgalactosamine

Rats treated with daily injection of DL-isoproterenol for 10 consecutive days (25 mg kg(-1) body weight) showed marked induction of a proline-rich glycoprotein (GPRP) of 220 kDa. Proteinase K digestion of GPRP produced a homogeneous glycopeptide with an average chemical composition as follows (residues per mol): Pro4, Glx3, Asx2, Gly1, His1, Thr1, Arg1, GlcNAc5, GalNac1, Man3, Gal2-3, and Fuc1. The structural analysis of the asparagine-linked carbohydrate unit was performed by methylation, periodate oxidation and enzymatic degradation. Methylation studies indicated that the three mannosyl residues were substituted at 1,2-, 1,2,4-, and 1,3,6-positions. Fucose, N-acetylgalactosamine, 1.5 residues of galactose and 0.35 residues of N-acetylglucosamine were terminally located and one galactose residue was 1,4-substituted. Approximately four of the 5 N-acetylglucosamine residues were substituted at 1,4-position and approximately 1 residue of N-acetylglucosamine was substituted at 1,4,6-positions. Periodate oxidation studies and exoglycosidase results were consistent with the methylation data. Based on the results of Smith degradation, methylation and sequential exoglycosidase digestions a triantennary oligosaccharide structure having terminal N-acetylgalactosamine in one of the branches is proposed for the major Asn-linked carbohydrate moiety of GPRP.

Quantification of human myeloperoxidase in oral fluids

Peroxidase activity in human whole saliva is derived from salivary peroxidase and myeloperoxidase. Present spectrophotometric assays are relatively non-specific and influenced by ions present in salivary secretions, resulting in an over and/or underestimation of peroxidase activities. Specific polyclonal or monoclonal antibodies would greatly simplify the identification of salivary peroxidase and myeloperoxidase in human saliva and determine the relative contribution of each enzyme to the total peroxidase activity in human saliva. In the present study, a highly purified preparation of myeloperoxidase was used to raise polyclonal antibodies against the antigen. The antibodies were purified and extensively characterized in terms of their ability to interact with the antigen, with other mammalian peroxidases, and with other proteins present in salivary fluids. The antibodies recognized only myeloperoxidase and did not cross-react with any of the substances tested, showing that these antibodies can be used to detect and differentiate myeloperoxidase from other peroxidases in saliva. We have also developed and tested a sandwich ELISA which can be used in a clinical setting to quantify myeloperoxidase in whole saliva and gingival crevicular fluid.

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.

Evaluation of major parotid glycoproteins in patients with burning mouth syndrome

OBJECTIVE

This study was to investigate the potential role of salivary glycoproteins in burning mouth syndrome.

STUDY DESIGN

This study compared major parotid glycoproteins in a group of patients with burning mouth syndrome and age-, sex-, race-matched healthy controls.

RESULTS

By use of a glycoprotein detection kit, saliva from both patients and controls exhibited three major parotid glycoprotein banding patterns consisting of either one or two bands, molecular weights 58 kDa and 77 kDa. The strong lectin reactivity of major parotid glycoproteins with Ricinus communis agglutinin suggests that galactose is the most prevalent terminal sugar. In addition, major parotid glycoproteins were shown to express blood group antigen H. On the basis of metachromatic characteristics and immunologic reactivity, major parotid glycoproteins appear to be members of the proline rich protein multigene family, proline rich glycoprotein, genetic polymorphism G1. No qualitative difference was observed in major parotid glycoprotein banding patterns between patients and controls.

CONCLUSION

These findings do not support a role for major parotid glycoproteins in burning mouth syndrome.

Lubrication of human and bovine enamel compared in an artificial mouth

Bovine enamel has been a good model for human enamel across a broad range of studies. The present work sought to consider if bovine enamel would be a suitable substitute for human enamel in experiments on simulated oral lubrication. Enamel samples of the same size were prepared from bovine and human teeth for use as maxillary and mandibular elements in a miniature artificial mouth. Sliding speeds from 1.99 to 7.84 mm/s and occlusal forces of 3.8-19.5 N were used. Water and four solutions consisting of a mucin-rich fraction, a statherin-rich fraction, 3[(3-cholamidopropyl)-dimethylammonio]-1-propanesulphonate and sodium dodecyl sulphate were evaluated. The high correlations between widely different lubricants on the two enamel substrates gives confidence in the use of bovine enamel as a model for human enamel in salivary lubrication studies. Knoop hardness indentations on enamel samples were combined with friction data and calculations of the true contact area to give a method for the indirect determination of surface shear. The calculated surface shear value was compared with published values obtained by punch shear testing.

Purification and characterization of rat parotid glycosylated, basic and acidic proline-rich proteins

A unique family of proline-rich proteins (PRPs) is induced in rats following prolonged isoproterenol treatment. PRPs can be divided into glycosylated (GPRP), basic (BPRP) and acidic (APRP) proline-rich proteins based on their physicochemical characteristics. Inducible rat parotid PRPs were isolated from aqueous extracts of parotid glands of isoproterenol-treated animals by sequential chromatography on columns of DEAE-Sepharose CL-6B, Sephadex G-100 and FPLC on Suprose-12 column. The GPRP showed a single homogeneous band on sodium dodecylpolyacrylamide gel electrophoresis with an estimated molecular weight of approximately 220,000. Compositional analysis of GPRP revealed that this protein contained 19.7% glutamic acid/glutamine, 28.2% proline and 9.5% glycine, and 44% carbohydrate, consisting of fucose (2.81g/100g), mannose (9.78g/100g), galactose (9.29g/100g), N-acetylglucosamine (18.03g/100g) and N-acetylgalactosamine (3.90g/100g). Basic PRPs consisted of a family of proteins with estimated molecular masses ranging from 14-45 kDa. These proteins contained 42.6% proline, 20.65% glutamic acid/glutamine and 21.33% glycine. Acidic PRPs also comprised of a family of metachromatically stained ladder of 40-60 kDa containing 29.1% proline, 21.5% glutamic acid/glutamine and 17.8% glycine. APRP were heavily glycosylated containing N-acetylglucosamine (6.34g/100g), N-acetylgalactosamine (19.04g/100g) and glucuronic acid (38.08g/100g).

Biochemical composition of human saliva in relation to other mucosal fluids

This paper describes several salivary components and their distribution in other mucosal secretions. Histatins are polypeptides which possess exceptional anti-fungal and anti-bacterial activities, but are nevertheless present only in saliva. Proline-rich proteins (PRPs) are members of a closely related family, of which the acidic PRPs are found solely in saliva, whereas the basic PRPs are also found in other secretions. Mucins are a group of glycoproteins that contribute to the visco-elastic character of the mucosal secretions. Despite the similarities in their structure and behavior, mucins have distinct tissue distributions and amino acid sequences. Other salivary proteins are present in one or more mucosal secretions. Lysozyme is an example of a component belonging to an ancient self-defense system, whereas secretory immunoglobulin A (sIgA) is the secreted part of a sophisticated adaptive immune system. Cystatins are closely related proteins which belong to a multigene family. Alpha-Amylase is a component that is believed to play a specific role in digestion, but is nevertheless present in several body fluids. Kallikrein and albumin are components of blood plasma. But whereas albumin diffuses into the different mucosal secretions, kallikrein is secreted specifically by the mucosal glands. The presence of these proteins specifically in saliva, or their distribution in other mucosal secretions as well, may provide important clues with respect to the physiology of those proteins in the oral cavity.

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.

Structure, biosynthesis, and function of salivary mucins

The glandular secretions of the oral cavity lining the underlying buccal mucosa are highly specialized fluids which provide lubrication, prevent mechanical damage, protect efficiently against viral and bacterial infections, and promote the clearance of external pollutants. This mucus blanket contains large glycoproteins termed mucins which contribute greatly to the viscoelastic nature of saliva and affect its complex physiological activity. The protein core of mucins consists of repetitive sequences, rich in O-glycosylated serine and threonine, and containing many helix-breaking proline residues. These features account for the extended, somewhat rigid structure of the molecule, a high hydrodynamic volume, its high buoyant density, and high viscosity. The oligosaccharide moiety of salivary mucins accounts for up to 85% of their weight. The oligosaccharide side chains exhibit an astonishing structural diversity. The isolation, composition, structure, molecular characteristics, and functional relevance of salivary mucins and their constituents is discussed in relation to recent advancements in biochemistry and molecular biology.

Bacterial-protein interactions in the oral cavity

Bacteria in the oral cavity must interact with salivary proteins if they are to survive. Such interactions can take several forms, either providing nutrients, a means of adhesion to surfaces, or resulting in aggregation or killing and, therefore, clearance of organisms. Recent work has provided an insight into the mechanisms of some of these bacterial-protein interactions, revealing complexity and diversity. For example, the interaction between a putative Streptococcus mutans adhesin, P1 (B, I/II, etc.), and a parotid glycoprotein results in adhesion when it occurs at a surface or aggregation when in solution, and different domains of P1 appear to be involved in the two processes. An alternative strategy is employed by Actinomyces viscosus, which interacts, via its type-1 fimbriae, with a proline-rich salivary protein; however, this interaction occurs only when the PRP is adsorbed to a surface. A. viscosus takes advantage of a conformational change in the PRP when it becomes surface-bound, which exposes a cryptic part of the molecule. A third, and intriguing, type of interaction is seen between various streptococci and salivary amylase. This does not result in either adherence or aggregation but provides organisms with the ability to utilize starch breakdown products for metabolism. An understanding of the mechanisms involved in bacterial-protein interactions could conceivably lead to novel methods for controlling specific pathogens, but the systems operating in the mouth are numerous, complex, and diverse.

Solution and solid-state circular dichroism analyses of a human salivary proline-rich glycoprotein repeating domain and its subfragments

Solution- and solid-state c.d. spectra, as well as surface energetics values, were collected for a series of peptides derived from human salivary proline-rich glycoprotein (PRG). The acronyms and sequences for these peptides are as follows: PRG9-2 = NH2-G(1)-P(2)-CONH2, PRG9-3 = NH2-G(1)-P(2)-P(3)-CONH2, PRG9-4 = NH2-G(1)-P(2)-P(3)-P(4)-CONH2, PRG9-5 = NH2-G(1)-P(2)-P(3)-P(4)-H(5)-CONH2, PRG9-6 = NH2-G(1)-P(2)-P(3)-P(4)-H(5)-P(6)-CONH2, PRG9-7 = NH2-G(1)-P(2)-P(3)-P(4)-H(5)-P(6)-G(7)-CONH2, PRG9-8 = NH2-G(1)-P(2)-P(3)-P(4)-H(5)-P(6)-G(7)-K(8)-CONH2, and PRG9-9 = NH2-G(1)-P(2)-P(3)-P(4)-H(5)-P(6)-G(7)-K(8)-P(9)-CONH2. The presence of stable poly-L-proline II-like 'mini' helices in the solution state was found to be dependent on peptide chain length, pH, salt, and organic solvent type. Other conformational features such as kinks and beta-/gamma-turns were also found in the larger peptides. Solid-state peptide conformations were not necessarily related to their solution-state counterparts. Poly-L-proline II-like 'mini' helices, kinks, and beta-/gamma-turns were similarly found in the various substrate-bound PRG9 peptides. Surface energetics parameters suggested specific orientations for PRG9 peptides and their constituent acids and homopolymers.

Macaque salivary proline-rich protein: structure, evolution, and expression

Proline-rich proteins are a family of proteins that exhibit unique features including an unusual high proline content and salivary-specificity. As a major constituent in the salivary secretion of higher primates, proline-rich proteins may have biological roles in oral lubrication and protection. In this article, the genomic structure and regulation by cAMP of one of the macaque salivary proline-rich protein genes, MnP4, is reviewed. The evolution of this multigene family of proteins is also discussed.

Alignment of amino acid and DNA sequences of human proline-rich proteins

Human proline-rich proteins (PRPs) constitute a complex family of salivary proteins that are encoded by a small number of genes. The primary gene product is cleaved by proteases, thereby giving rise to about 20 secreted proteins. To determine the genes for the secreted PRPs, therefore, it is necessary to obtain sequences of both the secreted proteins and the DNA encoding these proteins. We have sequenced most PRPs from one donor (D.K.) and aligned the protein sequences with available DNA sequences from unrelated individuals. Partial sequence data have now been obtained for an additional PRP from D.K. named II-1. This protein was purified from parotid saliva by gel filtration and ion-exchange chromatography. Peptides were obtained by cleavage with trypsin, clostripain, and N-bromosuccinimide, followed by column chromatography. The peptides were sequenced on a gas-phase protein sequenator. Overlapping peptide sequences were obtained for most of II-1 and aligned with translated DNA sequences. The best fit was obtained with clones containing sequences for the allele PRB4M (Lyons et al., 1988). However, there was not complete identity of the protein amino acid sequence and the DNA-derived sequences, indicating that II-1 is not encoded by PRB4M. Other PRPs isolated from D.K. also fail to conform to any DNA structure so far reported. This shows the need to obtain amino acid sequences and corresponding DNA sequences from the same person to assign genes for the PRPs and to determine the location of the postribosomal cleavage points in the primary translation product.

The structure and evolution of the human salivary proline-rich protein gene family

We present the nucleotide sequences of four members of the six-member human salivary proline-rich protein (PRP) gene family. The four genes are PRB1 and PRB2, which encode basic PRPs, and PRB3 and PRB4, which encode glycosylated PRPs. Each PRB gene is approximately 4.0 kb in length and contains four exons, the third of which is entirely composed of 63-bp tandem repeats and encodes the proline-rich portion of the protein products. Exon 3 contains different numbers of tandem repeats in the different PRB genes. Variation in the numbers of these repeats is also responsible for length variations in different alleles of the PRB genes. We have determined a probable evolutionary history of the human PRP gene family by comparing the nucleotide sequences of the six PRP genes. The present-day six PRP loci probably evolved from a single ancestral gene by four sequential gene duplications, leading to six genes that fall into three subsets, each consisting of two genes. During this evolutionary process, multiple rearrangements and gene conversion occurred mainly in the region from the 3' end of IVS2 and the 3' end of exon 3.

Purification and characterization of a glycosylated proline-rich protein from human parotid saliva

1. A glycosylated proline-rich protein (GPRP) was purified to homogeneity by subjecting parotid saliva to immunoaffinity, cation exchange, affinity and hydrophobic chromatography. 2. The purified GPRP had a molecular weight of 78 kDa as analyzed by SDS-PAGE. 3. The amino acid analysis revealed a preponderance of proline, glycine and glutamic acid/glutamine, which accounted for 77% of the total amino acids. 4. Cysteine, tyrosine or phenylalanine residues were not detected. 5. The glycoprotein contained 34% neutral sugars and the oligosaccharides were rich in mannose and N-acetylglucosamine, indicating that N-linked oligosaccharides were the predominant type of oligosaccharides in the molecule. 6. These observations were confirmed by treatment of the purified glycoprotein with specific N-glycosidase which removed the N-linked oligosaccharides leaving a core protein with an apparent molecular weight of 51 kDa. 7. The isoelectric point of GPRP was approx 7.0 and the molecule was not affected by reduction with 2-mercaptoethanol, indicating that no disulfide linkages were present. 8. The GPRP bound to hydroxyapatite and this binding could be partially inhibited by preincubation of the hydroxyapatite with parotid or submandibular saliva. 9. The purified GPRP also bound to a protein with an apparent molecular weight of 95 kDa present in submandibular saliva.

Formation of salivary-mucosal pellicle: the role of transglutaminase

The present investigation was carried out to identify salivary components of mucosal pellicles in vivo and explore further the mechanism of interaction between salivary molecules and buccal epithelial cells. By using specific antisera and immunoprotein blotting, high-(MG1) and low-(MG2) molecular-mass salivary mucins, amylase, salivary cystatins and proline-rich proteins were detected within mucosal pellicle in vivo. In addition, the data indicated that the mucins and proline-rich proteins could be cleaved into lower-molecular-mass products, whereas the proline-rich proteins could also be cross-linked into higher-molecular-mass complexes. The role of buccal epithelial cell transglutaminase in these interactions was further studied by utilizing purified iodinated amylase, neutral cystatin SN and acidic proline-rich proteins 1 and 3 (APRP1 and 3). After incubation with buccal epithelial cells in vitro 125I-labelled APRPs appeared to undergo a greater degree of cross-linking than 125I-labelled cystatin SN, as determined by SDS/PAGE/autoradiography. Amylase did not appear to be cross-linked at all. Recovery of 125I-labelled APRPs and 125I-labelled cystatin SN with epithelial cell envelopes after repeated extraction suggested that both molecules were cross-linked to envelope proteins, but that 125I-labelled APRPs were cross-linked to a greater degree than 125I-labelled cystatin SN. Cross-linking in buccal epithelial cell preparations was inhibited by an excess of methylamine hydrochloride, a transglutaminase substrate. In a further assessment of amylase, cystatin and APRPs as transglutaminase substrates, only APRP3 and a partially purified preparation of APRPs acted as an amine acceptor for the cross-linking of [14C]methylamine by purified transglutaminase, as determined by SDS/PAGE/fluorography. This reaction was completely inhibited by excess EDTA. The combined data from this study suggest that during mucosal pellicle formation multiple components of saliva adsorb to buccal epithelial cell surfaces, and that, within this group, selected components are enzymically cross-linked by an epithelial transglutaminase and/or proteolytically cleaved into smaller fragments.

Comparative analysis of lysosomal hydrolases and natural glycoprotein substrates in the rat major salivary glands

1. The activities of some lysosomal hydrolases and the concentrations of their natural substrates were studied in the submandibular and sublingual glands of male and female rats using biochemical procedures. 2. In sublingual gland enzyme activities and substrate concentrations show the highest values. 3. The enzyme activities appear, in general, lower and the natural substrate concentrations higher in the females with respect to males. 4. In both glands beta-galactosidase shows the highest activity and beta-glucosidase the lowest. 5. These findings suggest that metabolic turnover of glycoproteins is slower in females than in males, probably because the oestrogens control the activity of lysosomal hydrolases.

Large-scale purification and characterization of the major phosphoproteins and mucins of human submandibular-sublingual saliva

The major components of human submandibular-sublingual saliva (HSMSL) are mucins, amylases, cystatins, proline-rich proteins and statherin. Structure-function studies of these molecules have been hampered by the small amounts of purified materials that can be isolated from human secretions. The present study describes an integrated purification protocol for the large-scale preparation of many of these molecules. To dissociate partially heterotypic complexes among salivary molecules, HSMSL was initially fractionated into four pools by gel filtration with 6 M-guanidine hydrochloride. Subsequent fractionation of these four pools by gel-filtration and ion-exchange chromatography resulted in the purification of high- and low-Mr mucins, neutral and acidic cystatins, acidic and basic proline-rich proteins and statherin. Many variants or isoforms of these salivary molecules have been identified and biochemically characterized. Biochemical studies indicated that the low-Mr mucin exists as two isoforms which vary in their sialic acid to fucose ratios. Three isoforms of acidic cystatin S were characterized which differ in their phosphate content. Two isoforms of a basic proline-rich peptide were identified; the smaller peptide was a truncated form missing the first seven amino acids.

Investigation of cis/trans proline isomerism in a multiply occurring peptide fragment from human salivary proline-rich glycoprotein

The solution-state conformations of eight proline-containing peptide fragments found in human salivary proline-rich glycoprotein (PRG) were investigated in 2 x distilled water (treated with metal ion chelating resin) using 13C-nuclear magnetic resonance (NMR) and circular dichroism (CD) spectroscopy. The peptide sequences and acronyms were as follows: PRG9-2 = NH2-G(1)-P(2)-CONH2, PRG9-3 = NH2-G(1)P(2)-P(3)-CONH2, PRG9-4 = NH2-G(1)-P(2)-P(3)-P(4)-CONH2, PRG9-5 = NH2-G(1)-P(2)-P(3)-P(4)-H(5)-CONH2, PRG9-6 = NH2-G(1)-P(2)-P(3)-P(4)-H(5)-P(6)-CONH2, PRG9-7 = NH2-G(1)-P(2)-P(3)-P(4)-H(5)-P(6)-G(7)-CONH2, PRG9-8 = NH2-G(1)-P(2)-P(3)-P(4)-H(5)-P(6)-G(7)-K(8)-CONH2 and PRG9-9 = NH2-G(1)-P(2)-P(3)-P(4)-H(5)-P(6)-G(7)-K(8)-P(9)-CONH2. Sequence-specific resonance assignments from the 13C-NMR spectra indicated that the trans proline isomer dominated the conformations of the peptides. CD results clearly showed the presence of the poly-L-proline II helix as the major conformation in PRG9-3----PRG9-5, supplemented by beta- and/or gamma-turns in PRG9-6----PRG9-9. These data suggest that in "metal free" water, native PRG could contain several small poly-L-proline II helices along with beta- and/or gamma-turns. Since proline is the major amino acid present in native PRG, these localized conformations may contribute to PRG's global conformation and act as a primary force in determining its biological activities.

Statherin: a major boundary lubricant of human saliva

The lubricating properties of human submandibular-sublingual salivary fractions were examined using a servohydraulic model of mandibular movement. Fractions containing statherin exhibited a strong tendency to boundary lubrication. The lubricity of purified statherin was confirmed and compared to the amphipathic molecules gramacidin S and sodium dodecyl sulfate. Contact angle measurements of statherin paralleled the other amphipathic molecules. The helical content of statherin increased in trifluoroethanol indicating the presence of amphipathic helical regions. CD studies and hydrophobic moment calculations indicated that statherin adopts an amphipathic helical conformation at the N-terminus. An energy-minimized model of the polar N-terminal residues 1-15 suggested that this domain could be positioned in space to interact with a hydroxyapatite substrate. These data imply that under appropriate conditions statherin may display an amphipathic nature which enables it to function as a boundary lubricant on enamel.

Interaction of a salivary mucin-secretory immunoglobulin A complex with mucosal pathogens

This study examined the interaction of a human salivary low-molecular-weight mucin (MG2) with Staphylococcus aureus and Pseudomonas aeruginosa by using both solution-phase and solid-phase assays. In solution phase, MG2 in human submandibular-sublingual saliva (HSMSL) bound to the bacterial surface; however, the highly purified mucin isoforms (MG2a and MG2b) did not. Mucin binding appeared to be dependent on heterotypic complexing between MG2 and secretory immunoglobulin A (IgA), although other salivary molecules may also be involved. In contrast, in a solid-phase assay in which HSMSL, MG2-containing fractions with secretory IgA, and purified MG2 were immobilized onto a solid surface, there was minimal adherence of S. aureus. The collective results suggest that mucin binding to S. aureus and P. aeruginosa may be predicated on the formation of an MG2-secretory IgA complex. Such interactions may facilitate microbial clearance from the oral cavity and play an important role in preventing colonization of the oral cavity and the respiratory tract by potential pathogens.

Analysis of possible factors influencing the occurrence of occlusal tooth wear in a young Saudi population

The purpose of this study was to attempt to correlate possible etiologic factors with the occurrence of occlusal tooth wear in a young Saudi population. The material comprised 90 individuals with a mean age of 22 years within a range of 19-25 years. A dentition wear index, in addition to anterior and posterior wear subindices were derived from tooth-by-tooth evaluations of casts. Factors found to correlate significantly with increased occlusal wear were bruxism, biting habits such as pen- and nail-biting, use of an indigenous chewing-stick called miswak, and high intake of fruit juices. There was no correlation between subjects from differing geographic and/or climatic habitats and the severity of tooth wear. The common element of a harsh desert terrain may constitute the dominant passive abrasive etiologic factor in the present sample.

Basic proline-rich proteins from human parotid saliva: relationships of the covalent structures of ten proteins from a single individual

Eleven basic proline-rich proteins were purified from the parotid saliva of a single individual. The complete amino acid sequences of six of these were determined by conventional protein sequence methodology, bringing to nine the number of known primary structures of nonglycosylated basic proline-rich proteins from the same individual. The partial sequence of one additional protein is also reported. All of the basic proline-rich proteins studied contain segments with identical or very similar sequences, but with two possible exceptions, none of the proteins is derived from another secreted proline-rich protein. The amino acid sequences of nine nonglycosylated basic proline-rich proteins were compared with primary structures deduced from published nucleotide sequences of DNA coding for human parotid proline-rich proteins. The sequences align well, in general, but differences also exist pointing to the complexity of the genetics of these proteins. Seven secretory basic proline-rich proteins appear to be formed from three larger precursors by selective posttranslational proteolyses of arginyl bonds. One of the basic proline-rich proteins appears to derive from human acidic proline-rich proteins. The remaining two proteins studied do not conform to any DNA structure as yet reported. Two of the basic proline-rich proteins studied are phosphoproteins and exhibit abilities to inhibit hydroxyapatite formation in vitro.

A new assessment in vitro of human salivary lubrication using a compliant substrate

The lubrication effect of salivary secretions was assessed in terms of separating a rigid object from a compliant substrate. There was little difference among the various secretions of a single donor. The viscosity of salivas increased as a function of time. Neither the friction testing nor viscometry provided an adequate model of the tissue-coating function ascribed to saliva.

The role of saliva in maintaining oral homeostasis

Dental practitioners are becoming more cognizant of the importance of saliva as they treat a greater number of older patients, especially those with medical problems requiring a variety of medications that have xerostomia as a side effect. This article discusses salivary composition and function in a broad perspective, relating them to clinical concerns and current research. Understanding the role of saliva in maintaining health, as well as its relation to oral disease, is vital to the competent dental practitioner.

Oral mucosal pellicle. Adsorption and transpeptidation of salivary components to buccal epithelial cells

The present investigation was carried out to examine the mechanism(s) whereby salivary molecules interact with human buccal epithelial cells. By utilizing antiserum against human parotid saliva, selected salivary components were detected by electrophoretic-transfer analysis of 1.5% SDS extracts of epithelial cells. Incubation of the cells and their aqueous cell-free extracts with 125I-labelled parotid saliva resulted in the formation of an iodinated high-molecular-mass complex which was not present in 125I-labelled saline alone. Formation of this complex was time-dependent and was inhibited by treating the buccal epithelial cells or their cell-free extracts with EGTA, iodoacetamide, N-ethylmaleimide or by heating at 100 degrees C for 15 min. The epithelial cells also promoted incorporation of [14C]putrescine into high-molecular-mass complexes whose formation was inhibited by iodoacetamide, unlabelled putrescine and EGTA. Cell extracts mediated cross-linking of monodansylcadaverine into alpha-casein, and this interaction was inhibited by iodoacetamide. Significant amounts of radioactivity were recovered with the epithelial-cell envelopes after exhaustive extraction of 125I-saliva- or [14C]putrescine-treated epithelial cells with 4% (w/v) SDS/10% (v/v) beta-mercaptoethanol. The incorporation of radioactivity into epithelial-cell envelopes was inhibited by pretreatment of the cells with putrescine, EGTA, iodoacetamide, or heating at 100 degrees C for 15 min. These data suggest that: (1) oral mucosal pellicle is formed by the selective adsorption of saliva to the epithelial-cell plasma membrane and its associated cytoskeleton; and (2) the adsorbed salivary components may be cross-linked to each other or the epithelial cytoskeleton by epithelial transglutaminases.

Lubrication of selected salivary molecules and artificial salivas

The lubrication regime displayed by human salivas (parotid and submandibular-sublingual), purified salivary molecules (the mucins MG1 and MG2 and alpha-amylases), and selected artificial salivas (Oracare D, Saliva Substitute, and Orthana) was assessed in vitro using a friction-testing device. Thin-film (boundary) lubrication was observed for all of the salivary samples and two of the artificial salivas examined. Oracare D, a glycerol-based artificial saliva, was the exception since it lubricated by a thick-film (hydrodynamic) regime. On a molar basis, the best lubricants of the purified salivary molecules were MG1 greater than MG2 approximately nonglycosylated alpha-amylases approximately glycosylated alpha-amylases.

Enzymatic sulfation of mucus glycoprotein in rat submandibular salivary gland

1. The enzymic activity which catalyzes transfer of sulfate ester group from 3'-phosphoadenosine-5'-phosphosulfate to mucus glycoprotein was found associated with Golgi-rich membrane fraction of rat submandibular salivary gland. 2. Optimum enzyme activity was obtained with 0.5% Triton X-100, 4 mM MgCl2 and 25 mM NaF at a pH of 6.8 using desulfated submandibular salivary mucus glycoprotein. The apparent Km of the enzyme for mucus glycoprotein was 11.1 mg/ml. 3. Alkaline borohydride reductive cleavage of the synthesized 35S-labeled glycoprotein led to the liberation of the label into reduced oligosaccharides. A 75.4% of the label was found incorporated in four oligosaccharides. These were identified in order of abundance as sulfated penta-, tri-, hepta- and nonsaccharides. 4. Based on the results of chemical and enzymatic analyses of the intact and desulfated compounds the pentasaccharide was characterized as SO3H----GlcNAc beta----Gal beta----GlcNAc(NeuAc alpha----)GalNAc-ol and the trisaccharide as SO3H----GlcNAc beta----Gal beta----GalNAc-ol.

Physico-chemical characteristics of mucus glycoproteins and lipids of the human oral mucosal mucus coat in relation to caries susceptibility

Mucus coat was isolated from oral epithelial surfaces of caries-resistant and caries-susceptible subjects, analysed for content and composition of lipids and mucus glycoproteins, and evaluated for physico-chemical characteristics. The mucus coat from caries-resistant subjects had a protein content similar to that of the caries-susceptible group but a higher content of carbohydrate and a lower content of lipids and covalently bound fatty acid. The carbohydrate component was mainly mucus glycoprotein, which accounted for 28.4% of the dry weight of caries-resistant mucus and 25.3% of caries-susceptible mucus. By chromatographic analysis on Bio-Gel A-50, both types of preparations had high (Mr approximately 2000 kdalton) and low (Mr approximately 300 kdalton) molecular-weight mucus glycoproteins. In the caries-susceptible mucus coat these two glycoproteins were in similar proportions, whereas the low molecular-weight glycoprotein predominated in caries-resistant mucus. In both preparations, the high molecular-weight glycoprotein was characterized by a high content of carbohydrates, associated lipids and covalently bound fatty acids, whereas the low molecular-weight glycoprotein was richer in protein and contained lesser amounts of associated and covalently bound lipids. Although the low molecular-weight glycoprotein showed only minor compositional differences with caries status, the high molecular-weight glycoprotein of the caries-resistant group had a 2.5 times lower content of covalently bound fatty acid, a 1.3 times lower content of associated lipids and contained 1.2 times more sulphate and sialic acid then that of the caries-susceptible group.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro characterization of human salivary lubrication

The friction coefficients for parotid and submandibular-sublingual salivas of 7 subjects were measured. At the load and speeds used, the lubricatory properties of the secretions followed the McKee-Petroff's curve. The friction coefficients for both secretions approximated those reported for boundary and thin film lubrication.

Isolation and characterization of six proteins from rabbit parotid saliva belonging to a unique family of proline-rich proteins

Proline-rich proteins are major components of salivary secretion from humans non-human primates, rats, hamsters and rabbits. They are also synthesized in mice in response to chronic stimulation by beta agonists. This study to provide an understanding of the structural and genetic relationships within these families of proteins to determine the possible function of the proline-rich proteins. Rabbit parotid saliva was collected and proline-rich proteins were affinity purified using goat antibodies to human proline-rich proteins. Purification was achieved by repeated cation exchange chromatography on a Mono S column a Fast Protein Liquid Chromatography system. Six basic proline-rich proteins were purified. The apparent molecular weights were between 75,000 and 125,000, based on their mobilities in sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Glycine, glutamine (and glutamate) and proline accounted for 79-87% of total amino acids in all proteins, but proline was present in smaller amounts (17-21%) than in proline-rich proteins from other species. All proteins were glycosylated but not phosphorylated. Circular dichroism of two proline-rich proteins, MS7A and MS5B, indicated the absence of secondary structure. The N-terminal sequences of three proteins electro-eluted after preparative gel electrophoresis were determined. A high degree of similarity was found in various regions of mouse, rat, monkey and human proline-rich proteins. Rabbits thus synthesize constitutively a family of proteins that are immununologically and structurally related to proline-rich proteins other species.

Effect of ethanol on the in vitro sulfation of salivary mucin

In vitro sulfation of mucus glycoprotein by sulfotransferase from rat submandibular salivary gland and the effect of ethanol on this enzyme activity was investigated. Subcellular fractionation studies revealed that the enzyme which catalyzes the transfer of sulfate ester group from 3'-phosphoadenosine-5'-phosphosulfate to submandibular gland mucus glycoprotein is associated with Golgi-rich membrane fraction. The sulfotransferase enzyme exhibited optimum activity at pH 6.8 in the presence of 0.5% Triton X-100, 4 mM MgCl2, and 25 mM NaF. The enzyme was equally capable of sulfation of the desulfated intact as well as proteolytically degraded desulfated glycoprotein preparations, whereas the acceptor capacity of the intact mucus glycoprotein was 70% lower. The submandibular gland sulfotransferase activity was inhibited by ethanol. The rate of inhibition of mucus glycoprotein sulfation was proportional to the concentration of ethanol up to 0.4 M, at which concentration a 39% reduction in the sulfotransferase activity occurred. The apparent Km value of the enzyme for salivary mucus glycoprotein was 11.1 microM, and the Kl in the presence of ethanol was 0.93 M. The synthesized 35S-labeled glycoprotein gave on CsCl equilibrium density gradient centrifugation 35S-labeled peak which coincided with that of the glycoprotein. Alkaline borohydride treatment of this glycoprotein led to the liberation of the label into the acidic oligosaccharide alditol fraction. As the inhibition by ethanol of sulfotransferase enzyme occurred below its isosmotic concentration to plasma, the observed effect could also be detrimental to salivary mucus glycoprotein sulfation in vivo.

Sulfation in vitro of mucus glycoprotein by submandibular salivary gland: effects of prostaglandin and acetylsalicylic acid

Enzymatic sulfation of mucus glycoprotein by rat submandibular salivary gland and the effect of prostaglandin and acetylsalicylic acid on this process were investigated in vitro. The sulfotransferase enzyme which catalyzes the transfer of sulfate ester group from 3'-phosphoadenosine-5'-phosphosulfate to submandibular gland mucus glycoprotein has been located in the detergent extracts of Golgi-rich membrane fraction of the gland. Optimum enzyme activity was obtained at pH 6.8 with 0.5% Triton X-100, 25 mM NaF and 4 mM MgCl2, using the desulfated glycoprotein. The enzyme was also capable of sulfation of the intact mucus glycoprotein, but the acceptor capacity of such glycoprotein was 68% lower. The apparent Km of the submandibular gland sulfotransferase for salivary mucus glycoprotein was 11.1 microM. The 35S-labeled glycoprotein product of the enzyme reaction gave in CsCl density gradient a 35S-labeled peak which coincided with that of the glycoprotein. This glycoprotein upon reductive beta-elimination yielded several acidic 35S-labeled oligosaccharide alditols which accounted for 75% of the 35S-labeled glycoprotein label. Based on the analytical data, the two most abundant oligosaccharides were identified as sulfated tri- and pentasaccharides. The submandibular gland sulfotransferase activity was stimulated by 16,16-dimethyl prostaglandin E2 and inhibited by acetylsalicylic acid. The rate of enhancement of the glycoprotein sulfation was proportional to the concentration of prostaglandin up to 2.10(-5) M, at which point a 31% increase in sulfation was attained. The inhibition of the glycoprotein sulfation by acetylsalicylic acid was proportional to the drug concentration up to 2.5.10(-4) M at which concentration a 48% reduction in the sulfotransferase activity occurred. The apparent Ki value for sulfation of salivary mucus glycoprotein in presence of acetylsalicylic acid was 58.9 microM. The results suggest that prostaglandins may play a role in salivary mucin sulfation and that this process is sensitive to such nonsteroidal anti-inflammatory agents as acetylsalicylic acid.

N.m.r. analyses of the histidine microenvironments in a human salivary proline-rich glycoprotein

The pKa's of the three histidine residues in a proline-rich glycoprotein from human parotid saliva (PRG) were determined by 360 MHz proton n.m.r. spectroscopy. The addition of calcium (0.64 mM) caused drops in the pKa's of all three histidines by approximately 0.25 units. When imidazole and cyclo)L-histidine-L-proline) were used as model compounds, corresponding concentrations of calcium had no effect on their pKa's. Also, the model compounds gave absolute pKa values in good agreement with similar chemical species reported in the literature. Exchange lifetime data and previously reported hydrogen----deuterium exchange experiments suggest that the PRG histidine N tau H protons are not involved in hydrogen-bonds. Collectively, these data imply that changes in PRG conformation occur upon the addition of calcium.

Role of associated and covalently bound lipids in salivary mucin hydrophobicity: effect of proteolysis and disulfide bridge reduction

The hydrophobic properties of salivary mucus glycoprotein were investigated by fluorescence spectroscopy using bis(8-anilino-1-naphthalene-sulfonate). The mucin, purified from rat submandibular salivary gland, was subjected to removal of associated and covalently bound lipids, degradation with pronase, and reduction with beta-mercaptoethanol, and titrated with the probe. Analyses of fluorescence data revealed the presence of 49 +/- 5 hydrophobic binding sites in the intact mucin molecule, a 69% increase in the number of binding sites occurred following extraction of associated lipids, while the removal of covalently bound fatty acids caused a 25% decrease in the binding sites. Proteolytic destruction of the nonglycosylated regions of the glycoprotein essentially abolished the probe binding, whereas reduction produced glycoprotein subunits whose combined number of hydrophobic binding sites was 2.4 times greater than that of mucus glycoprotein polymer. The results suggest that associated and covalently bound lipids contribute to hydrophobic characteristics of salivary mucin and that the hydrophobic binding sites reside on the nonglycosylated regions of this glycoprotein buried within its core.

Biochemistry and lectin binding properties of mammalian salivary mucous glycoproteins

The molecules responsible for the highly viscous properties of mucus are secretory glycoproteins referred to as mucins. Salivary mucins are characterized by a high sugar to protein ratio and are of a broad range of molecular weight from 7 x 10(4) to millions. With a few exceptions, they contain up to 30% of hexosamine (galactosamine and glucosamine), 8-33% of sialic acid, trace to 15% of galactose or fucose and little or no mannose. The size of carbohydrate side chains of these glycoproteins ranges from one to about fifteen units of sugar. These carbohydrate side chains are usually O-glycosidically linked through N-acetylgalactosamine to a peptidyl serine or threonine. In some instances, ester sulfate groups, mainly on N-acetylglucosamine, are also a structural feature. In many of these glycoproteins, the saccharide sequence is the same as that which determines the specificity of blood groups. Carbohydrate sequence analysis shows that salivary mucins exhibit considerable polydispersity, great diversity and remarkable structural flexibility not only among animal species but also within the same mucin molecule. Based on their lectin-binding ability, they can be used for purification of lectins, and lectins coupled to resin may be useful for the isolation of mucin-type glycoproteins. The epithelial mucous secretions modulate oral microbial flora; many secretory components serve as lectin-receptors for the attachment of microbes. The judicious use of lectins with widely differing binding characteristics has already been valuable in the in situ localization of salivary glycoproteins, in elucidating structural details, recording sugar density within a given tissue section, and defining host-parasite interactions. It is hoped that their use, together with monoclonal antibody (158) and tissue culture techniques (159, 160) will further clarify the roles of individual secretory mucous glycoproteins in health and disease.

Enzymatic sulphation of mucus glycoprotein in rat sublingual salivary gland

Sulphotransferase activity catalysing the transfer of sulphate ester group from 3'-phosphoadenosine-5'-phosphosulphate to salivary mucus glycoprotein was located in detergent extracts of the Golgi-rich membrane fraction of rat sublingual salivary glands. Optimum enzyme activity was obtained with 0.5 per cent Triton X-100, 20 mM NaF and 2 mM MgCl2, at pH 6.8, using desulphated sublingual salivary mucus glycoprotein. The enzyme was equally capable of sulphation of the proteolytically degraded and desulphated glycoprotein, whereas the acceptor capacity of intact salivary mucus glycoprotein was about four times lower. The Golgi enzyme preparation also catalysed the sulphation of galactosylceramide. However, the sulphation of mucus glycoprotein was not affected by the presence of this glycolipid, suggesting that the sulphotransferase involved in mucin sulphation is different from that responsible for the synthesis of galactosylceramide sulphate. The apparent Km of the sublingual-gland mucus glycoprotein sulphotransferase for salivary mucin was 7.7 microM. The 35S-labelled glycoprotein product of the enzyme reaction gave, in CsCl density gradient, a band in which the 35S label coincided with the glycoprotein. Alkaline borohydride reductive cleavage of this glycoprotein released the label into the reduced acidic oligosaccharide fraction. Upon thin-layer chromatography, two [35S]-oligosaccharides were detected. These were identified as penta- and heptasaccharides, each bearing a labelled sulphate ester group on the terminal N-acetylglucosamine residue. Based on the results of chemical and enzymatic analyses of the intact and desulphated compounds the following structures for these oligosaccharides are suggested: SO3----GlcNAc beta----Gal beta----GlcNAc beta----Gal beta----GlcNAc beta----(NeuAc----)GalNAc-ol and SO3----GlcNAc beta----Gal beta----GlcNAc beta----(NeuAc----)GalNAc-ol.

Human submandibular gland statherin and basic histidine-rich peptide are encoded by highly abundant mRNA's derived from a common ancestral sequence

The molecular cloning of sequences encoding human submandibular gland (SMG) statherin and a basic histidine-rich peptide is described. The corresponding mRNA's were highly abundant in the human and the Rhesus monkey (Macaca mulatta) SMG, but no homologous message was detectable in the murine SMG. Sequence analysis revealed strong homology between the statherin and basic histidine-rich mRNA's, suggesting their evolution from a common ancestral sequence.

Lubrication and viscosity features of human saliva and commercially available saliva substitutes

The lubricating features and viscosity of human saliva and five commercially available saliva substitutes were compared. The results indicate that little correlation exists between these parameters. Saliva substitutes based on carboxymethylcellulose do not appear to lubricate biocompatible hard interfaces well and, therefore, might not protect against the rapid attrition observed in xerostomic individuals. In contrast, a mucin-based substitute proved to be a better lubricant with values comparable to whole human saliva.