Genetics of human salivary proteins

Solid-state NMR studies of biomineralization peptides and proteins

Nature has evolved sophisticated strategies for engineering hard tissues through the interaction of proteins, and ultimately cells, with inorganic mineral phases. This process, called biomineralization, is how living organisms transform inorganic materials such as hydroxyapatite, calcite, and silica into highly intricate and organized structures. The remarkable material properties of shell, bone, and teeth come from the activities of proteins that function at the organic-inorganic interface. A better understanding of the biomolecular mechanisms used to promote or retard the formation of mineral-based structures could provide important design principles for the development of calcification inhibitors and promoters in orthopedics, cardiology, urology, and dentistry. With the knowledge of the structural basis for control of hard tissue growth by proteins, scientists could potentially develop materials using biomimetic principles with applications in catalysis, biosensors, electronic devices, and chromatographic separations, to name a few. Additionally, biomineralization also has potential applications in electronics, catalysis, magnetism, sensory devices, and mechanical design. Where man-made hard materials require the use of extreme temperatures, high pressure, and pH, biological organisms can accomplish these feats at ambient temperature and at physiological pH. Despite the fact that many researchers want to identify and control the structure of proteins at material and biomineral interfaces, there is a decided lack of molecular-level structure information available for proteins at biomaterial interfaces in general. In particular, this holds for mammalian proteins that directly control calcification processes in hard tissue. The most fundamental questions regarding the secondary and tertiary structures of proteins adsorbed to material surfaces, how proteins catalyze the formation of biomineral composites, or how proteins interact at biomaterial interfaces remain unanswered. This is largely due to a lack of methods capable of providing high-resolution structural information for proteins adsorbed to material surfaces under physiologically relevant conditions. In this Account, we highlight recent work that is providing insight into the structure and crystal recognition mechanisms of a salivary protein model system, as well as the structure and interactions of a peptide that catalyzes the formation of biosilica composites. To develop a better understanding of the structure and interactions of proteins in biomaterials, we have used solid-state NMR techniques to determine the molecular structure and dynamics of proteins and peptides adsorbed onto inorganic crystal surfaces and embedded within biomineral composites. This work adds to the understanding of the structure and crystal recognition mechanisms of an acidic human salivary phosphoprotein, statherin.

Reactivity of polymeric proanthocyanidins toward salivary proteins and their contribution to young red wine astringency

Recent studies have indicated the presence of significant amount of highly polymerized and soluble proanthocyanidins in red wine and such compounds interacted readily with proteins, suggesting that they might be particularly astringent. Thus, the objective of this work was to verify the astringency of polymeric proanthocyanidins and their contribution to red wine astringency. The precipitation reactions of the purified oligomeric procyanidins (degree of polymerization ranging from 2 to 12-15) and polymeric procyanidins (degree of polymerization ranging from 12-15 to 32-34) with human salivary proteins were studied; salivary proteins composition changes before and after the reaction was verified by SDS-PAGE and procyanidins composition changes by spectrometric, direct HPLC and thiolysis-HPLC methods. The astringency intensity of these two procyanidin fractions was evaluated by a sensory analysis panel. For verifying the correlation between polymeric proanthocyanidins and young red wine astringency, the levels of total oligomeric and total polymeric proanthocyanidins and other phenolic composition in various young red wines were quantified and the astringency intensities of these wines were evaluated by a sensory panel. The results showed that polymeric proanthocyanidins had much higher reactivity toward human salivary proteins and higher astringency intensity than the oligomeric ones. Furthermore, young red wine astringency intensities were highly correlated to levels of polymeric proanthocyanidins, particularly at low concentration range (correlation coefficient r = 0.9840) but not significant correlated to total polyphenols (r = 0.2343) or other individual phenolic compounds (generally r < 0.3). These results indicate the important contribution of polymeric proanthocyanidins to red wine astringency and the levels of polymeric polyphenols in red wines may be used as an indicator for its astringency.

Discovery of putative salivary biomarkers for Sjögren's syndrome using high resolution mass spectrometry and bioinformatics

The purpose of the current study was to determine if saliva contains biomarkers that can be used as diagnostic tools for Sjögren's syndrome (SjS). Twenty seven SjS patients and 27 age-matched healthy controls were recruited for these studies. Unstimulated glandular saliva was collected from the Wharton's duct using a suction device. Two µl of salvia were processed for mass spectrometry analyses on a prOTOF 2000 matrix-assisted laser desorption/ionization orthogonal time of flight (MALDI O-TOF) mass spectrometer. Raw data were analyzed using bioinformatic tools to identify biomarkers. MALDI O-TOF MS analyses of saliva samples were highly reproducible and the mass spectra generated were very rich in peptides and peptide fragments in the 750-7,500 Da range. Data analysis using bioinformatic tools resulted in several classification models being built and several biomarkers identified. One model based on 7 putative biomarkers yielded a sensitivity of 97.5%, specificity of 97.8% and an accuracy of 97.6%. One biomarker was present only in SjS samples and was identified as a proteolytic peptide originating from human basic salivary proline-rich protein 3 precursor. We conclude that salivary biomarkers detected by high-resolution mass spectrometry coupled with powerful bioinformatic tools offer the potential to serve as diagnostic/prognostic tools for SjS.

Total protein of whole saliva as a biomarker of anaerobic threshold

Saliva provides a convenient and noninvasive matrix for assessing specific physiological parameters, including some biomarkers of exercise. We investigated whether the total protein concentration of whole saliva (TPWS) would reflect the anaerobic threshold during an incremental exercise test. After a warm-up period, 13 nonsmoking men performed a maximum incremental exercise on a cycle ergometer. Blood and stimulated saliva were collected during the test. The TPWS anaerobic threshold (PAT) was determined using the Dmax method. The PAT was correlated with the blood lactate anaerobic threshold (AT; r = .93, p < .05). No significant difference (p = .16) was observed between PAT and AT. Thus, TPWS provides a convenient and noninvasive matrix for determining the anaerobic threshold during incremental exercise tests.

Interaction of copper and human salivary proteins

Interaction of taste molecules with saliva is the first step in the flavor perception process. Saliva is assumed to influence copper-induced sensation by controlling the copper solubility or causing astringency via binding of proteins with copper. This study was performed to identify the nature of copper-protein interactions in relation to the sensory perception of copper. Saliva was treated with CuSO4 x 5H2O at levels of 0, 2.5, 5, 10, 20, or 40 mg/L, and changes in salivary proteins were analyzed using high performance liquid chromatography (HPLC) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Protein peaks that showed changes in HPLC were characterized with SDS-PAGE. HPLC analysis revealed that copper treatment up to 40 mg/L decreased several proteins, including the dominant peak, by 70%. This peak was composed of alpha-amylase, a secretory component, and basic proline-rich proteins. SDS-PAGE results showed that salivary proteins of molecular weight 29 kDa and 33 kDa precipitated when copper was added at concentrations > or =10 mg/L. This study provides biochemical information for understanding perception mechanisms of copper sensation.

Fluoride ingestion from toothpaste and diet in 1- to 3-year-old Brazilian children

OBJECTIVE

This study estimated the total daily fluoride intake of 1- to 3-year-old children from diet and dentifrice. The constituents of the diet were divided into solids, water, milk, and other beverages, which were analyzed separately. The correlation between fingernail fluoride concentrations and the total daily fluoride intake by children was also investigated.

METHODS

Thirty-three children, living in a fluoridated area, participated in the study. Fluoride intake from diet was monitored by the 'duplicate plate' method, investigating the different constituents of the diet. Fluoride ingested from dentifrice was determined by subtracting the amount of fluoride recovered after brushing from the amount originally placed onto the child's toothbrush. Fingernails were clipped and collected on three occasions. Fluoride was analyzed with the ion-specific electrode, after hexamethyldisiloxane-facilitated diffusion. Data were tested by anova and Tukey's post hoc tests, Student's t-tests and linear regression (P < 0.05).

RESULTS

Mean (+/-SD) fluoride intake from diet and dentifrice was 0.025 +/- 0.013 and 0.106 +/- 0.085 mg/kg body weight/day, respectively, totaling 0.130 mg/kg body weight/day. A strong positive correlation (r = 0.971, P < 0.0001) was seen between the amount of dentifrice loaded onto the brush (0.49 +/- 0.30 g) and the amount of fluoride ingested during each tooth brushing (0.59 +/- 0.45 mg). Among the constituents of the diet, water and milk had a significantly higher contribution to the fluoride intake (0.18 +/- 0.11 mg/day, P < 0.0001), when compared with solids (0.07 +/- 0.05 mg/day) and other beverages (0.07 +/- 0.04 mg/day). Mean (+/-SD) fingernail fluoride concentration on the three dates of collection was 3.11 +/- 1.14, 2.22 +/- 1.47 and 3.53 +/- 1.40 mug F/g. There was no significant correlation between fingernail fluoride concentration and the total fluoride intake.

CONCLUSIONS

Most of the children are exposed to a daily fluoride intake above the suggested threshold for dental fluorosis. The dentifrice alone is responsible for an average of 81.5% of the daily fluoride intake, while among the constituents of the diet, water and milk are the most important contributors. In addition, small variations in daily fluoride intake cannot be detected in fingernails.

Human minor and major gland saliva proteins and ability to mediate Actinomyces naeslundii adherence

Bacteria-binding components and the ability to mediate bacterial adhesion to the tooth surface have been thoroughly studied in major salivary gland secretions. Our knowledge on the bacteria binding activity in minor gland saliva is, however, limited. In this study, proteins were examined in parallel in minor (palatal, buccal and labial) and major (parotid and submandibular/sublingual) salivary gland secretions in one subject using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. The adherence of early colonizing Actinomyces naeslundii to pellicles formed from the secretions on hydroxyapatite beads was also examined. Amylase, IgA, proline-rich proteins and the high-molecular-weight glycoproteins, agglutinins, were detected in all saliva tested. Carbohydrate-reactive antibodies recognized the low-molecular weight mucin, MUC 7 in submandibular/sublingual saliva only. A. naeslundii strain 12104 adhered to all pellicles and especially to the buccal gland saliva pellicles. Strain LY7 adhered in highest numbers to the submandibular/sublingual saliva pellicles. It also bound in considerable numbers to parotid and palatal saliva pellicles but not to the ones formed from buccal and labial gland saliva. Our findings indicate that several bacteria-binding components are secreted in both minor and major gland saliva. The adherence-promoting ability of the various gland secretions differs, however.

New method for evaluating astringency in red wine

Astringency is an important sensory attribute of red wine. It is usually estimated by tasting and is subject to a certain subjectivity. It can also be estimated by using the gelatin index. This procedure is not very reproducible because there are many gelatins on the market with a heterogeneous composition. Furthermore, the gelatin index determines procyanidin concentration by acid hydrolysis that gives only an approximate result. This paper proposes a new and reproducible method that determines astringency by using ovalbumin as the precipitation agent and tannic acid solutions as standards. Statistical analysis of the results indicates that this method is more reproducible (RSD = 5%) than the gelatin index (RSD = 12%) and correlates better with sensorial analysis.

Interaction of plant polyphenols with salivary proteins

Tannins are polyphenols that occur widespread in plant-based food. They are considered to be part of the plant defense system against environmental stressors. Tannins have a number of effects on animals, including growth-rate depression and inhibition of digestive enzymes. Tannins also have an effect on humans: They are, for example, the cause of byssinosis, a condition that is due to exposure to airborne tannin. Their biological effect is related to the great efficiency by which tannins precipitate proteins, an interaction that occurs by hydrophobic forces and hydrogen bonding. Two groups of salivary proteins, proline-rich proteins and histatins, are highly effective precipitators of tannin, and there is evidence that at least proline-rich proteins act as a first line of defense against tannins, perhaps by precipitating tannins in food and preventing their absorption from the alimentary canal. Proline plays an important role in the interaction of proline-rich proteins with tannins. In contrast, it is primarily basic residues that are responsible for the binding of histatins to tannin. The high concentration of tannin-binding proteins in human saliva may be related to the fruit and vegetable diet of human ancestors.

The BSP30 salivary proteins from cattle, LUNX/PLUNC and von Ebner's minor salivary gland protein are members of the PSP/LBP superfamily of proteins

Saliva influences rumen function in cattle, yet the biochemical role for most of the bovine salivary proteins (BSPs) has yet to be established. Two cDNAs (BSP30a and BSP30b) from bovine parotid salivary gland were cloned and sequenced, each coding for alternate forms of a prominent protein in bovine saliva. The BSP30 cDNAs share 96% sequence identity with each other at the DNA level and 83% at the amino acid level, and appear to arise from separate genes. The predicted BSP30a and BSP30b proteins share 26-36% amino acid identity with parotid secretory protein (PSP) from mouse, rat and human. BSP30 and PSP are in turn more distantly related to a wider group of proteins that includes lung-specific X protein, also known as palate, lung, and nasal epithelium clone (LUNX/PLUNC), von Ebner's minor salivary gland protein (VEMSGP), bactericidal permeability increasing protein (BPI), lipopolysaccharide binding protein (LBP), cholesteryl ester transfer protein (CETP), and the putative olfactory ligand-binding proteins RYA3 and RY2G5. Bovine cDNAs encoding homologs of LUNX/PLUNC and VEMSGP were isolated and sequenced. Northern blot analysis showed that LUNX/PLUNC, BSP30 and VEMSGP are expressed in bovine salivary tissue and airways, and that they have non-identical patterns of expression in these tissues. The expression of both BSP30a and BSP30b is restricted to salivary tissue, but within this tissue they have distinct patterns of expression. The proximity of the human genes coding for the PSP/LBP superfamily on HSA20q11.2, their similar amino acid sequence, and common exon segmentation strongly suggest that these genes evolved from a common ancestral gene. Furthermore, they imply that the BSP30a and BSP30b proteins may have a function in common with other members of this gene family.

Role of saliva in the maintenance of taste sensitivity

Saliva is the principal fluid component of the external environment of the taste receptor cells and, as such, could play a role in taste sensitivity. Its main role includes transport of taste substances to and protection of the taste receptor. In the initial process of taste perception, saliva acts as a solvent for taste substances; salivary water dissolves taste substances, and the latter diffuse to the taste receptor sites. During this process, some salivary constituents chemically interact with taste substances. For example, salivary buffers (e.g., bicarbonate ions) decrease the concentration of free hydrogen ions (sour taste), and there are some salivary proteins which may bind with bitter taste substances. Another effect of saliva on taste transduction is that some salivary constituents can continuously stimulate the taste receptor, resulting in an alteration of taste sensitivity. For example, the taste detection threshold for NaCl is slightly above the salivary sodium concentrations with which the taste receptor is continuously stimulated. In contrast, saliva protects the taste receptor from damage brought about by dryness and bacterial infection, and from disuse atrophy via a decrease in transport of taste stimuli to the receptor sites. This is a long-term effect of saliva that may be related to taste disorders. These various effects of saliva on the taste perception differ depending on the anatomical relationship between the taste buds and oral openings of the ducts of the salivary glands. Many taste buds are localized in the trenches of the foliate and circumvallate papillae, where the lingual minor salivary glands (von Ebner's glands) secrete saliva. Taste buds situated at the surface of the anterior part of the tongue and soft palate are bathed with the mixed saliva secreted mainly by the three major salivary glands.

Proteolytic processing of a human salivary proline-rich protein precursor by proprotein convertases

Salivary proline-rich proteins (PRPs) are synthesized as precursors that are cleaved before secretion giving rise to glycosylated PRPs which have lubricating function and basic PRPs which are potent precipitators of dietary tannins. The putative cleavage sites in the precursors for basic and glycosylated PRPs all conform to the sequence RSXR downward arrowS (X can be A, S or P) in agreement with the recognition sequence (RXXR downward arrow) for various proprotein convertases. PRB4S, a proprotein giving rise to a basic PRP (IB-5) as well as a glycosylated PRP (II-1) was synthesized by in vitro transcription-translation. It was cleaved by furin at RSAR downward arrowS(173-178) giving rise to two proteins II-1 and IB-5. Similarly another precursor with the sequence RSAR downward arrowS(173-178) was also cleaved by furin. This together with previous results show that in vitro furin can cleave all RSXR downward arrowS sequences in the proproteins that give rise to glycosylated and basic PRPs. To demonstrate cellular cleavage, a human submandibular cell line (HSG) was transfected with a vector encoding PRB4S. This resulted in secretion of II-1 and IB-5. The degree of cleavage was enhanced by coexpressing furin and PRB4S. No cleavage occurred if the cells expressed a mutant PRB4S, R177Q, where the furin cleavage site had been destroyed. Cleavage was also inhibited if a furin inhibitor was coexpressed with PRB4S. Incubating the cells at 20 degrees C which blocks exit of proteins from the trans-Golgi network demonstrated that cleavage occurs before exit of the proteins from this network. These results show that furin may be responsible for in vivo cleavage of PRP precursors. Transfecting furin-deficient RPE.40 cells with a vector encoding PRB4S also led to secretion of II-1 and IB-5 showing that convertases other than furin can also cleave PRB4S in tissue culture.

Determination of the human salivary peptides histatins 1, 3, 5 and statherin by high-performance liquid chromatography and by diode-array detection

A reversed-phase high-performance liquid chromatography (HPLC) method with diode-array detection for the quantification of several human salivary peptides is described. Sample pretreatment consisted of the acidification of whole saliva by phosphate buffer. This treatment produced precipitation of mucins, alpha-amylases and other high-molecular-mass salivary proteins, simultaneous inhibition of intrinsic protease activities and reduction of sample viscosity. Direct HPLC analysis by diode-array detection of the resulting acidic sample allowed one to quantify histatin 1, histatin 3, histatin 5, statherin, as well as uric acid, in normal subjects. Moreover, the groups of peaks pertaining to proline-rich proteins and cystatins were tentatively identified. The method can be useful in assessing the concentration of salivary peptides from normal subjects and from patients suffering oral and/or periodontal diseases.

Structure of human salivary histatin 5 in aqueous and nonaqueous solutions

The solution structure of human salivary histatin 5 (D-S-H-A-K-R-H-H-G-Y-K-R-K-F-H-E-K-H-H-S-H-R-G-Y) was examined in water (pH 3.8) and dimethyl sulfoxide solutions using 500 MHz homo- and heteronuclear two-dimensional (2D) nmr. The resonance assignment of peptide backbone and side-chain protons was accomplished by 2D total correlated spectroscopy and nuclear Overhauser effect (NOE) spectroscopy. The high JNH-C alpha H values (> or = 7.4 Hz), absence of any characteristic NH-NH (i, i + 1) or C alpha H-C beta H (i, i + 3) NOE connectivities, high d delta/dT values (> or = 0.004 ppm K-1) and the fast 1H/2H amide exchange suggest that histatin 5 molecules remain unstructured in aqueous solution at pH 3.8. In contrast, histatin 5 prefers largely alpha-helical conformation in dimethyl sulfoxide solution as evident from the JNH-C alpha H values (< or = 6.4 Hz), slow 1H/2H exchange, low d delta/dT values (< or = 0.003 ppm K-1) observed for amide resonances of residues 6-24, and the characteristic NH-NH (i, i + 1) and C alpha H-C beta H (i, i + 3) NOE connectivities. All backbone amide 15N-1H connectivities fall within 6 ppm on the 15N scale in the 2D heteronuclear single quantum correlated spectrum, and the restrained structure calculations using DIANA suggest the prevalence of alpha-helical conformations stabilized by 19 (5-->1) intramolecular backbone amide hydrogen bonds in polar aprotic medium such as dimethyl sulfoxide. The interside-chain hydrogen bonding and salt-bridge type interactions that normally stabilize the helical structure of linear peptides in aqueous solutions are not observed. Histatin 5, unlike other naturally occurring antimicrobial polypeptides such as magainins, defensins, and tachyplesins, does not adopt amphiphilic structure, precluding its insertion into microbial membranes and formation of ion channels across membranes. Electrostatic (ionic type) and hydrogen bonding interactions of the positively charged and polar residues with the head groups of microbial membranes or with a membrane-bound receptor could be the initial step involved in the mechanism of antimicrobial activity of histatins.

Expression and characterization of human salivary statherin from Escherichia coli using two different fusion constructs

Saliva is a supersaturated solution with respect to hydroxyapatite, the main inorganic component of tooth enamel. Several acidic phosphoproteins are present in saliva which allow the supersaturated state to be maintained without random crystallization occurring. Statherin is the only salivary protein currently known to inhibit both the primary and secondary precipitation of hydroxyapatite in the supersaturated environment of saliva. To identify the residues of statherin that are necessary to control biomineralization, a recombinant form of human statherin was produced from Escherichia coli using a yeast intein fusion construct. The primary structure of the recombinant statherin was characterized by SDS-PAGE, N-terminus sequencing, MALDI mass spectrometry, and amino acid analysis and found to have the expected values relative to human-derived statherin. The secondary structure of the recombinant statherin was investigated by circular dichroism spectroscopy, which revealed the predominant presence of random coil in phosphate-buffered saline solution, with a higher propensity toward alpha helicity in 100% TFE. This increase in helicity in 100% TFE was also found in statherin that was synthesized by solid-phase synthesis. These results demonstrate that human statherin can be produced in a recombinant form which behaves comparably to the natural form.

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.

Characterization of the rat salivary-gland B1-immunoreactive proteins

The B1-immunoreactive proteins (B1-IPs) are major secretory products of rat submandibular gland acinar-cell progenitors, and are also produced by neonatal and adult rat sublingual and parotid glands. In order to characterize the B1-IPs, we have previously isolated cDNA clones encoding rat parotid secretory protein (PSP; the predominant parotid B1-IP) and the related clone ZZ3, which is developmentally regulated in the neonatal submandibular gland. The remainder of the B1-IPs were uncharacterized. This report demonstrates that all of the B1-IPs are derived from the PSP and ZZ3 transcripts. Molecular cloning and Western-blot analyses using PSP- and ZZ3-specific antisera show that, of the B1-IPs, only PSP and neonatal submandibular gland protein A (SMGA) are products of the Psp gene. This finding corrects our previous assertion that SMGA is derived from ZZ3. Neonatal submandibular gland proteins B1 and B2, as well as apparent Mr 26000-28000 and Mr 18000-20000 forms in submandibular, sublingual and parotid glands, are derived from the gene encoding ZZ3 by differential N-glycosylation and by proteolytic cleavage. The apparent Mr 18000-20000 proteolytic products are significant in secretion product collected in vitro, but rare in gland homogenate and submandibular/sublingual saliva. The gene encoding ZZ3 has been named Smgb. Psp and Smgb are regulated similarly in the developing submandibular gland, but differently in the sublingual and parotid glands. The expression pattern of Psp is conserved between rat and mouse. However, no evidence for proteins derived from an Smgb-like gene was observed in neonatal mouse submandibular or sublingual glands.

Delmopinol hydrochloride- and chlorhexidine digluconate-induced precipitation of salivary proteins of different molecular weights

Gel electrophoresis was used to analyze precipitates formed of delmopinol hydrochloride or chlorhexidine digluconate mixed with unstimulated whole saliva samples from five test subjects. Final concentrations of delmopinol (6.4 mM) or chlorhexidine (6.4 mM, 2.2 mM) mixed with whole saliva were incubated for 10 min at 37 degrees C. The precipitates were pelleted by centrifugation and resuspended to a similar protein density. The protein patterns in the pellets were analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis, using 12.3% gels. The amount of pellet protein was determined by densitometry in four molecular weight ranges (10-21.5, 21.5-26, 26-45, and 45-300). The results indicated that high molecular weight (45-300) proteins dominated in the precipitate and that 2.2 mM chlorlhexidine precipitated more salivary protein than 6.4 mM. At equimolar concentration (6.4 mM) delmopinol precipitated more high molecular weight salivary proteins than chlorhexidine.

Candidacidal activity of recombinant human salivary histatin-5 and variants

Human salivary histatins possess fungicidal and bactericidal activities. The current investigation evaluates the structure-function relationship of histatins with regard to their candidacidal activity by using recombinant histatin-5 and its variants produced in Escherichia coli. The purified recombinant histatins were examined for their candidacidal activity and secondary structure. The m21 (with Lys-13 replaced by Thr [Lys-13-->Thr]) and m71 (Lys-13-->Glu) variants are significantly less effective than recombinant histatin-5 in killing Candida albicans, suggesting that Lys-13 is critical for candidacidal activity. The m68 (Lys-13-->Glu and Arg-22-->Gly) variant is significantly less potent than the recombinant histatin-5 as well as m71, indicating that Arg-22 is crucial for the cidal activity. The candidacidal activities of m1 (Arg-12-->Ile), m2 (Arg-12-->Ile and Lys-17-->Asp), m12 (Arg-12-->Lys and His-21-->Leu), and m70 (His-19-->Pro and His-21-->Arg) variants, however, are comparable to that of recombinant histatin-5, indicating that Arg-12, Lys-17, His-19, and His-21 are not functionally important. The conformational preferences of histatin-5 and variants were determined by circular dichroism. The results indicate that all proteins have a strong tendency to adopt alpha-helical conformation in trifluoroethanol. Previously, we have shown that the alpha-helical conformation is one of the important structural requirements for eliciting appreciable candidacidal activity. Collectively, the data suggest that in addition to the helical conformation, specific residues such as Lys-13 and Arg-22 in the sequence of histatin-5 are, indeed, important for candidacidal activity.

Sodium dodecyl sulphate-polyacrylamide gel electrophoresis of human whole saliva

The purpose of this study was to characterize the electrophoretic patterns of human resting and stimulated whole saliva. Pooled and individual, uncentrifuged, unprocessed whole saliva from 20 healthy, unmedicated individuals was run on sodium dodecyl sulphate-polyacrylamide gel electrophoresis and stained with Coomassie blue R-250. Similar and characteristic patterns for whole saliva were observed for all samples, consisting of over 34 blue- and pink-violet-staining bands. Individual differences were usually in the size (or density) of the bands, not in the number. Repeat sampling of stimulated whole saliva over a period of weeks from the same individuals revealed a striking consistency of protein patterns, indicating a profound physiological stability of whole saliva. These results provide baseline data for whole saliva and suggest its use for future studies.

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).

The influence of histatin-5 fragments on the mineralization of hydroxyapatite

The adsorption of histatin 5 on hydroxyapatite (HAP) was determined and compared to that of several fragments of histatin 5, such as residues 1-16 (N16), 7-16 (M10), 9-24 (C16), 11-24 (C14), 13-24 (C12), 15-24 (C10). The influence of the adsorbed peptides on the seeded crystal growth of HAP was investigated with the constant composition method. The adsorption affinity of the peptides as well as their ability to inhibit mineralization was influenced by the length of the peptide chain. Histatin 5 showed the highest affinity, as determined by a Langmuir model, whereas the smaller C10 and C12 displayed the lowest equilibrium uptake. The smaller C10 and C12 peptides were, on the other hand, more effective as crystal growth inhibitors, indicating a more efficient coverage of surface active sites. Electrophoretic mobility data indicated an increase in the positive charge at the HAP surface in the presence of these peptides, which were efficient HAP crystallite dispersants.

PRB3 null mutations result in absence of the proline-rich glycoprotein Gl and abolish Fusobacterium nucleatum interactions with saliva in vitro

The glycosylated proline-rich glycoprotein (Gl or PRG), a product of the PRB3 gene, is a major constituent of human parotid saliva. Important functions proposed for Gl include acting as a bacterial receptor. The Gl proteins of several subjects were typed by two polyacrylamide gel electrophoresis (PAGE) systems: acid-lactate PAGE followed by staining with the periodic acid-Schiff reagent and sodium dodecyl sulfate-PAGE followed by electrophoretic transfer and staining with amido black or concanavalin A. The results showed one subject who apparently lacked Gl. The four exons, including splice junctions, for both PRB3 alleles of this subject were completely sequenced. Unexpressed (null) mutations were detected with an identical C nucleotide insertion in the same coding region of exon 3 of both alleles. This C nucleotide insertion leads to a frameshift with a premature termination codon that probably results in markedly reduced or absent PRB3 gene expression. We then used a nitrocellulose blot overlay assay to assay the bacterial receptor activity of parotid saliva from the PRB3null subject. No interactions with Fusobacterium nucleatum, shown previously to interact selectively with Gl, were detected. Together, these results suggest that this subject does not express the PRB3 gene and that one of the consequences is an altered ability to interact with a bacterium known to colonize the oral cavity.

Salivary macromolecules. A structure/function synopsis

The status of our structure/function studies is at a crossroad. Further studies are needed to understand events on a molecular level, particularly how saliva is made and processed. Animal models as well as tissue and cell culture systems are being developed to address these issues. Nevertheless, enough information is now available to begin enhancing the natural defense properties of salivary secretions through clinical modalities such as the development of (1) diagnostic reagents and tests for local and systemic disease, (2) artificial salivas for the treatment of salivary dysfunction, and (3) topical vaccines to combat against oral diseases.

Salivary proline-rich proteins: biochemistry, molecular biology, and regulation of expression

The proline-rich proteins (PRPs) in mammalian salivary glands are encoded by tissue-specific multigene families whose members have diverged with respect to structure and regulation of expression. PRPs are expressed constitutively in humans, and comprise about [70%] of the total salivary proteins. Families of similar proteins are dramatically increased or induced in parotid and submandibular glands of rats, mice and hamsters by treatment with the [beta-] agonist isoproterenol. Feeding tannins to rats and mice mimics the effects of isoproterenol on the parotid glands. Salivary PRPs may constitute a defense mechanism against tannins and other polyhydroxylated phenols ingested. Putative transcriptional regulatory sequences have been identified in mouse PRP genes.

Development of artificial salivas

Salivary research is at a critical crossroads regarding the clinical application of basic knowledge. Studies by numerous salivary researchers over the last 5 years using advanced technologies (e.g., protein chemistry, molecular biology, and biophysics) have demonstrated that the structural requirements for salivary function are quite complex. Nevertheless, several patterns or principles have evolved. First, the majority if not all salivary molecules are multifunctional. Second, the conformation of a molecule is an important factor in biological activity. Third, many molecules have overlapping functions (e.g., mucins and amylase interact with viridans streptococci; statherin and proline-rich proteins are involved in mineralization). Thus, saliva has "built-in" compensatory or redundant properties. Nevertheless, it must be determined which molecule is more potent or effective with respect to a particular function. Fourth, salivary molecules may be "amphifunctional". In other words, the different functions of a single molecule may be protective or potentially harmful depending on the intraoral site of action. Examples of amphifunctional molecules are amylase and statherin. Fifth, functional relationships may exist between different salivary components. The principles mentioned above can provide experimental strategies for the design and synthesis of a first generation of salivary substitutes that can be topically applied to oral surfaces. These molecules should be used to combat microbial mediated diseases and occlusal disharmony in subjects with normal salivary flow as well as those with xerostomia. In general, these substitutes should be long-lasting, biocompatible, biodegradable, and provide specific protective qualities that can be targeted to selected intraoral sites.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Genetics of salivary protein polymorphisms

Human salivary PRPs are determined by six closely linked genes on chromosome 12p13.2. The many PRPs show complex electrophoretic patterns that differ between individuals and reflect numerous genetic polymorphisms. Frequent length and null polymorphisms are common among PRPs. Common themes emerge as a background for these PRP polymorphisms. First, posttranslational proteolysis occurs with double-banded patterns among acidic PRPs and the generation of numerous basic PRPs derived from precursor proteins. Specific mutations may interfere with proteolysis, preventing generation of double-banded acidic PRPs (as with the Pa protein) or of small basic PRPs from precursor proteins (as with Pm proteins). Second, single cysteine substitutions in PRPs (Pa from PRH1 and G1 8 from PRB3) may lead to disulfide bonded homodimers as well as heterodimers with salivary peroxidase. Third, frequent homologous and unequal crossing-over within the PRP gene cluster leads to frequent protein size-variants (intragenic events as with the G1 protein variants) and the generation of the PRB2/1 fusion gene (intergenic event) with deletion of the PRB1 coding region and absence of multiple PRB1 coded proteins (Ps, Pm, Pe) in PRB2/1 homozygotes. Fourth, null mutations may also be produced (as with PsO and G1 0) by single nucleotide changes.

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.

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.

Sodium dodecyl sulphate-polyacrylamide gel electrophoresis of human parotid salivary proteins

The proteins in human parotid saliva have been separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis into 20 or more well resolved species. The Coomassie Brilliant Blue (CBB) R-250 and silver staining procedures have been modified to overcome the problems encountered with staining of proline-rich proteins. By means of the CBB R-250 procedure which stains proline-rich proteins pink-violet, immunoblotting, concanavalin A binding, periodate-Schiff staining and zinc binding, all of the major proteins have been characterised. Substantial individual-to-individual differences were observed in the protein patterns formed. Comparison of parotid, submandibular, and whole saliva from a single individual indicated that fewer proline-rich proteins are expressed in submandibular saliva than in parotid, but whole saliva contains much lower levels than either duct secretion. The results will form a useful base for future research into the functions of salivary proteins.

Clinical applications of electrophoresis of human salivary proteins

Human salivary proteins have been studied by electrophoresis in denaturing and non-denaturing polyacrylamide gel electrophoresis (PAGE) as well as by isoelectric focusing (IEF) and two-dimensional procedures, and the clinical applications of this have been reviewed. Whilst non-denaturing PAGE is useful in studying polymorphisms, sodium dodecylsulphate PAGE appears to be otherwise preferable. Immobilized pH gradients containing carrier ampholytes (CAs) give better resolution than CA-based IEF and overcome the problems of cathode drift and loss of basic material. Proline-rich proteins stain poorly with conventional procedures and special techniques are necessary. In clinical studies, findings must be viewed over and above the large number of polymorphisms which occur normally. Studies relating salivary protein and peptide profiles to dental caries susceptibility are encouraging. Specific protein abnormalities have been associated with connective tissue disorders and could form the basis of new non-invasive diagnostic procedures. Protein differences associated with cystic fibrosis and diabetes mellitus, however, merit reinvestigation with the new procedures now available. Detection of HIV antigens in saliva is a new area of research. In the light of new techniques available and new information which has arisen from DNA studies, future prospects for the clinical applications of electrophoresis of saliva look good.

Two-dimensional electrophoresis of human parotid salivary proteins from normal and connective tissue disorder subjects using immobilised pH gradients

Two-dimensional electrophoretic analysis of human salivary proteins using immobilised pH gradients in the first dimension, thin-layer gradient horizontal sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the second, and modified staining procedures has resulted in a substantial improvement in their resolution. Unlike carrier ampholyte-based techniques, immobilised pH gradients prevent the loss of proteins of pI greater than 8; accordingly, basic components, including basic proline-rich proteins, can now be resolved. A two-dimensional map showing the locations and identities of most of the major proteins has been constructed. Narrow-range pH gradients can be constructed to give increased resolution of proteins of particular interest. By means of a pH 3.5-5.0 gradient, the abnormal salivary proteins associated with connective tissue disorders were found to be a highly heterogeneous group of pI approximately 3.75-4.75 and Mr approximately 32,000; although low levels occurred in some normal individuals, there was less heterogeneity (pI approximately 3.75-4.25). The technique should form a base for future structural, functional, and clinical studies on human salivary proteins.

Accumulation and localization of two adult acinar cell secretory proteins during development of the rat submandibular gland

The seromucous acinar cells of the adult rat submandibular gland secrete a characteristic mucin glycoprotein and a family of unusual glutamine/glutamic acid-rich proteins (GRP). Monoclonal antibodies to the mucin and GRP localized in a very few Type III cells in glands of newborn and 1 day-old rats, using light and electron microscopic immunocytochemistry. Both mucin and GRP reactivities were present in the polymorphic Type IIIP granules during the 1st postnatal week. By 9 days after birth, the granules contained both mucin and GRP and were mucous-like in appearance. At earlier stages, however, cells containing only GRP or mucin could be found, indicating that the initiation of GRP and mucin biosynthesis may not be coordinately regulated. No reactivity was seen in the neonatal Type I cells or in duct cells at any age. Northern and Western blot analysis showed GRP mRNA and protein levels to be barely detectable at birth, with marked increases during the first 2 postnatal weeks. In contrast, Western blots of B1-immunoreactive proteins (B1-IP) showed levels highest in the 1st week and markedly decreased in the adult. Immunocytochemical colocalization, using gold particles of different sizes, showed that the B1-IP, mucin, and GRP colocalized in the granules. These results strengthen the hypothesis that the adult acinar cells develop from the neonatal Type III cells. No evidence was obtained for the involvement of Type I cells in the pathway of acinar cell development.

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.

Multiple forms of statherin in human salivary secretions

Sequential chromatography of hydroxyapatite-adsorbed salivary proteins from submandibular/sublingual secretions on Sephadex G-50 and reversed-phase HPLC resulted in the purification of statherin and several statherin variants. Amino acid analysis, Edman degradation and carboxypeptidase digestion of the obtained protein fractions led to the determination of the complete primary structures of statherin SV1, statherin SV2, and statherin SV3. SV1 is identical to statherin but lacks the carboxyl-terminal phenylalanine residue. SV2, lacking residues 6-15, is otherwise identical to statherin. SV3 is identical to SV2 but lacks the carboxyl-terminal phenylalanine. These results provide the first evidence for multiple forms of statherin which are probably derived both by post-translational modification and alternative splicing of the statherin gene.

Purification and characterization of a rabbit salivary protein, a potent inhibitor of crystal growth of calcium phosphate salts

Human saliva is supersaturated with respect to basic calcium phosphate salts but is stabilized by specific macromolecules that inhibit calcium phosphate precipitation. One of the families of inhibitory proteins in human and monkey saliva is the acidic proline-rich proteins. The purpose of this study was to isolate and characterize inhibitors of calcium phosphate precipitation from rabbit parotid saliva. Saliva was fractionated by immunoaffinity chromatography and anion exchange chromatography. Individual fractions were assayed for their ability to inhibit calcium phosphate crystal growth and the fraction associated with the inhibition was purified by repeated anion exchange chromatography, preparative gel electrophoresis and electroelution. A major (APRP) and two minor proteins (AM1, AM2) that were inhibitory were purified. APRP is an acidic proline-rich phospho-glycoprotein and a very potent inhibitor of secondary crystal growth of calcium phosphate as it was active at a concentration of 2 x 10(-8) M in a standard assay. The N-terminal sequence of one APRP was EYENLDGSLAATQNDDD?Q and a clostripain fragment of APRP had the following N-terminal sequence PQHRPPRPGGH-????SPPP?GN???PPP. Although the N-terminal segment of APRP does not resemble that of proline-rich proteins, alignment of the clostripain fragment with the repeat region of such proteins from rat, mouse, monkey and man revealed a high degree of similarity, indicating a structural relationship with the proline-rich protein family.

Primary structure and anticandidal activity of the major histatin from parotid secretion of the subhuman primate, Macaca fascicularis

A major macaque histatin (M-histatin 1) from the parotid secretion of the subhuman primate, Macaca fascicularis, was isolated by gel filtration on Bio-Gel P-2 and purified to homogeneity by reversed-phase high-performance liquid chromatography on a TSK-ODS C18 column. The complete amino acid sequence of M-histatin 1, determined by automated Edman degradation, is: (formula; see text) M-histatin 1 contains 38 amino acid residues, a phosphoserine at residue 2, has a molecular weight of 4881.8, a calculated pI of 8.5, and histidine forms 26.3% of the mass. The hydropathicity plot of M-histatin 1 predicts that the molecule is entirely hydrophilic, and Chou-Fasman secondary prediction indicates that the polypeptide is devoid of alpha-helix and beta-sheet conformation in aqueous solutions but contains a series of beta turns. M-histatin 1 includes a six-amino-acid insert (residue 10-15) not present in human histatins and, with the introduction of gaps to maximize homology, it displays 89% and 91% sequence similarity with human histatins 1 and 3, respectively. M-histatin 1 exhibited fungicidal and fungistatic effects against the dimorphic pathogen, Candida albicans, in three separate bioassays. Its anticandidal effects were comparable with or greater than those of human histatins 1, 3, and 5. M-histatins 2, 3, and 4 were not sequenced directly because insufficient materials were available, but the amino acid composition of M-histatin 3 was nearly identical to that of the N-terminal 20 amino acid residues of M-histatin 1.(ABSTRACT TRUNCATED AT 250 WORDS)

mRNAs for PRPs, statherin, and histatins in von Ebner's gland tissues

A search was made for expression of genes for proline-rich proteins (PRPs) and other salivary-type proteins, including statherin and histatins, in taste-bud tissues of mice and primates because of previous genetic findings in mice (Azen et al., 1986) that Prp and taste genes for certain bitter substances are either the same or closely linked. Taste-bud tissues and other tissues were tested for specific mRNAs with labeled DNA probes by Northern blotting and in situ hybridization. It was found that PRP mRNAs were present in von Ebner's glands of mice and macaques, and that there was a much greater degree of PRP mRNA induction in mouse parotid (16-fold) than in von Ebner's gland (two-fold) after in vivo isoproterenol stimulation. This difference may be due, in part, to differences in autonomic nerve innervation. Statherin and histatin mRNAs were found in macaque taste-bud tissues containing von Ebner's gland, and statherin protein was found in human von Ebner's gland by immunohistochemistry. The finding of PRP gene expression in von Ebner's gland, whose secretions have been suggested to play a role in taste stimulation, adds further support to a possible function of PRPs in bitter tasting. The possible functions of statherin and histatins in von Ebner's gland secretions may be related to statherin's regulation of salivary calcium and histatins' antibacterial and antifungal properties.

Phosphopeptides derived from human salivary acidic proline-rich proteins. Biological activities and concentration in saliva

Human saliva contains a large number of phosphopeptides derived by cleavage of acidic proline-rich proteins (APRPs). These peptides were purified by column chromatography and they constituted 0.5% of APRPs in parotid saliva, but 11% of APRPs in saliva expectorated from the mouth (whole saliva), indicating that there is considerable cleavage of APRPs after secretion from the gland. Similarly to APRP, the phosphopeptides bind Ca2+, but they accounted for only 4% of protein-bound Ca2+ in whole saliva. APRPs as well as the phosphopeptides inhibited formation of hydroxyapatite, but, whereas 19-20 micrograms of APRP was needed for 50% inhibition, only 0.7-3.3 micrograms of purified peptides was needed for the same degree of activity, and the phosphopeptides accounted for 18% of total inhibitory activity in whole saliva. All phosphopeptides adsorbed on hydroxyapatite in vitro, and adsorption of phosphopeptides on tooth surfaces in vivo could also be demonstrated, indicating that they would be able to inhibit unwanted mineral formation on the tooth surface in vivo. Degradation of APRPs after secretion therefore does not lead to a loss of their biological activities.

Structure and sequence determination of the gene encoding human salivary statherin

Human statherin (STT) is a low-Mr (43 amino acids) acidic phosphoprotein secreted mainly by salivary glands. It acts as an inhibitor of precipitation of Ca.phosphate salts in the oral cavity. DNA (12.2 kb) was isolated from human genomic phage lambda libraries as a series of overlapping clones, and the nucleotide sequence of the STT-encoding gene (STT) was determined. The transcribed region spans 6.5 kb and contains six exons and five introns. Upstream DNA (1.6 kb) was also sequenced and a number of possible regulatory elements were identified. The exon-intron boundaries of the STT gene roughly coincide with the protein-coding regions of the mRNA and with the functional domains of STT. This pattern of organization has been seen in a variety of eukaryotic genes and is consistent with the domain theory of gene evolution.