Salivary proline-rich proteins

Proline-rich proteins and glycoproteins: expression of salivary gland multigene families

Our recent research interests have focused on a group of unusual proteins and glycoproteins high in proline content, or the so-called proline-rich proteins (PRPs). The PRPs are tissue-specific expressions of salivary gland multigene families. Normally PRPs are not detected or are present in very low amounts in rat, mouse and hamster salivary glands, but these unusual proteins are dramatically induced by treatment with the catecholamine isoproterenol. The structures and organizations of several PRP mRNAs and PRP genes have been determined. The amino acid sequences of all PRPs show 4 distinct regions, namely, a signal peptide, a transition region, a repeat region and a carboxyl-terminal region. Glycoproteins induced by isoproterenol treatment may be N-glycosylated or O-glycosylated. The N-glycosylated glycoprotein GP-158 from rat submandibular glands has a 12 amino acid glycopeptide which repeats possibly 49 times. Proline-rich proteins of the parotid glands of rats and mice are also greatly induced by dietary tannins. The apparent unique occurrence of PRPs in saliva suggests that one biological role is to neutralize the detrimental effects of dietary tannins and other polyphenols. The upstream regions of the mouse and hamster PRP genes contain cyclic AMP-regulated sequences as demonstrated by deletions and transient transfections. The PRP multigene family members of mouse are all located on chromosome 8.

Genetic polymorphisms of the Pmo1 and Pmo2 salivary proteins detected by the modified protein staining method

Two polymorphic proteins, Pmo1 and Pmo2, were found in human parotid saliva by modifying the protein staining method of Sung & Smithies (1969). The inheritance of each polymorphism was controlled by a dominant allele at an autosomal locus. This hypothesis was supported by studies in 50 families including 103 children. The gene frequencies were Pmo1+ = 0.308, Pmo1- = 0.692, Pmo2+ = 0.026, Pmo2- = 0.974. The Pmo1 and Pmo2 proteins reacted immunologically with antisera prepared to salivary proline-rich proteins (Pr and Gl). The isoelectric point was in excess of 8.58. These results showed that the Pmo1 and Pmo2 proteins belong to the basic proline-rich proteins in human parotid saliva.

Tannins, salivary proline-rich proteins and oesophageal cancer

No single dietary factor or ingested substance has been implicated in the aetiology of oesophageal carcinoma especially in high-risk areas of the world. Although not well defined, there is heavy consumption of tannin-rich foods, particularly sorghum, by populations at high risk for carcinoma. The carcinogenic properties of tannins and extracts of tannin-rich plants have been demonstrated experimentally. It is proposed herein that salivary proline-rich proteins (PRPs) by binding ingested tannins protect the oesophagus from the carcinogenic effects of the latter. It is also possible that genetic variants of PRPs may influence the incidence of oesophageal cancer in different populations.

The presence and origin of phosphopeptides in human saliva

The presence of phosphopeptides in whole saliva (saliva expectorated from the mouth) was demonstrated and their origin was evaluated. Whole saliva contained much larger numbers of small phosphopeptides than are found in the glandular secretions. Most of these originated from the acidic proline-rich proteins (PRPs) in the major salivary glands and were formed, after secretion into the oral cavity, as a result of rapid degradation by proteolytic enzymes from extraglandular sources contained in sediment from whole saliva. Some peptides may have been formed by cleavage of basic PRPs, but other phosphoproteins apparently contributed little to the observed phosphopeptides. Most of the enzymes that produced phosphopeptides are serine proteinases. The gel-electrophoretic band patterns of the phosphopeptides obtained from 26 individuals of various acidic-PRP phenotypes were remarkably similar, demonstrating that the enzymes responsible were generally present in the population surveyed and that similar cleavages occur regardless of the nature of the acidic PRPs. Many of these peptides were N-terminal proteolytic cleavage products of acidic PRPs. The N-terminal phosphorylated region of acidic PRPs contains various biological activities, such as inhibition of hydroxyapatite formation, calcium binding and binding to hydroxyapatite, the major mineral of teeth. The demonstration of these phosphopeptides in the saliva that is in contact with the oral surface may therefore be of biological importance.

Expression of human salivary protein genes

Human proline-rich proteins (PRPs) are polymorphic, homologous in sequence, and linked in a cluster called the human salivary protein complex (SPC). Recently this complex was localized to human chromosome band 12p13.2 (Mamula et al., Cytogenet. Cell Genet. 39:279, 1985). We have isolated a PRP cDNA, EO27, from a human parotid gland library, identified it by DNA sequencing, and used it to study the molecular and cellular biology of PRP production. Cell-free translation and mRNA characterization with EO27 indicate that the numerous PRPs seen in saliva are produced from relatively few, large precursors, probably by posttranslational cleavage. This supports an hypothesis originally proposed by Friedman and Karn in 1977 (Am. J. Hum. Genet. 29:44 A; Biochem. Genet. 15:549) and later supported by biochemical studies (Karn et al., Biochem Genet. 17:1061, 1979) and molecular studies (Mamula et al., Fed. Proc. 43:1522, 1984; Maeda et al., J. Biol. Chem. 260:1123, 1985). EO27 was also used in this study to localize PRP mRNA production to the acinar cells of the parotid gland by in situ hybridization.

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.

Identification of a long form of cystatin from human saliva by rapid microbore HPLC mapping

Microbore HPLC methodology permits rapid and sensitive mapping of human saliva proteins. Saliva is sampled and processed in less than one hour, greatly reducing the likelihood of artifactual protein degradation. As little as 50 microliters of saliva yields proteins in sufficient quantities and purity to obtain amino terminal sequences directly. By this route we have discovered a 14 kDa protein extremely homologous to Cystatin S, but amino-terminally extended by eight amino acids.

Similarities and differences among neuroendocrine, exocrine, and endocytic vesicles

Secretory and endocytic vesicles have analogous functions as cyclic carriers between specific cellular compartments. The centrifugally functioning secretory system operates from the Golgi complex, whereas the centripetally functioning endocytic system operates from the cell surface. Further, within polarized epithelial cells the export traffic can be directed to a distinct plasmalemmal domain which distinguishes exocrine from endocrine secretion and import traffic can be directed transcellularly. These shuttle operations involve a special class of lipid-rich, protein-poor membranes that appear to use an inwardly directed H+-translocase activity to varying extents for pH-dependent sorting and for accumulation and concentration of transported molecules. Comparative analyses of purified membrane preparations from exocrine and endocrine sources identify compositional overlap between different types of shuttle membrane. However, the structural elements that specify a particular origin or destination for a given carrier or determine function in storage and stimulus-dependent shuttling remain unknown.

Structural and genetic aspects of proline-rich proteins

Considerable advances have been made in the genetics of salivary proline-rich proteins (PRP). The genes for acidic, basic, and glycosylated PRP have been cloned. They code for precursor proteins that all have an acidic N-terminal followed by proline-rich repeat sequences. Structural studies on secreted proteins have demonstrated that not only acidic but also some basic PRPs have this general structure. It is possible that mRNA for different PRP may have originated from a single gene by differential mRNA splicing, but post-translational cleavages of the primary translation product apparently also occur. In vitro translation of salivary gland mRNA results in a single precursor protein for acidic PRP. Such in vitro translated protein can be cleaved by salivary kallikrein, giving rise to two commonly secreted acidic PRPs, and kallikrein or kallikrein-like enzymes may be responsible for other post-translational cleavages of PRPs. Acidic as well as some basic PRPs are phosphorylated. A protein kinase has been demonstrated in salivary glands which phosphorylates the PRPs and other secreted salivary proteins in a cAMP and Ca2+-calmodulin-independent manner. Knowledge of the conformation of PRPs is limited. There is no conclusive evidence of polyproline-like structure in the proline-rich part of PRPs. Ca2+ binding studies on acidic PRPs indicate that there is interaction between the Ca2+ binding N-terminal end and the proline-rich C-terminal part. This interaction is relieved by modification of arginine side-chains. 1H, 32P, and 43Ca NMR studies have further elucidated the conformation of acidic PRPs in solution.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of salivary proteins

Previous studies have shown that several factors--such as alloxan-induced diabetes, adrenalectomy, or removal of the thyroid-parathyroid gland complex--can influence the flow rate, protein concentration, and protein composition of rat parotid saliva. The present study was undertaken to explore further the influence of glucocorticoids and thyroxine on rat parotid saliva in hormonally intact animals. As compared with untreated animals, adult male rats treated with 10 micrograms dexamethasone per 100 g body weight for eight days demonstrated a 75% reduction in volume of parotid saliva secreted in response to a uniform stimulus. The protein concentration of the saliva was increased three-fold. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed relative decreases in acidic and basic proline-rich proteins and in a protein identified as Fraction V, while amylase was increased. The electron microscopic appearance of the granules was markedly different from that of the control, in that the granules exhibited an electron-dense periphery and core, with the remainder of the granule having an electronlucent appearance. In contrast, rats treated for eight days with 20 micrograms thyroxine per 100 g body weight exhibited a 50% increase in volume of saliva collected in response to a secretory stimulus. Although the concentration of protein was not different from that of the control, gel electrophoresis showed relative increases in acidic and basic proline-rich proteins and a decrease in Fraction V. Amylase was unchanged. The secretory granules of thyroxine-treated rats were electronlucent and amorphous. The granules appeared to coalesce within the cell.(ABSTRACT TRUNCATED AT 250 WORDS)

Proteolytic activities in the supragingival plaque of monkeys (Macaca fascicularis)

Thirteen peptidase substrates were hydrolysed by this plaque. After fasting the monkeys for 24 h, the rates of hydrolysis of N-leucyl-, N-alanyl-, N-isoleucyl- and N-tyrosyl-2-naphthylamines, glycyl-L-proline 4-nitroanilide, N alpha-benzoyl-DL-arginine-2-naphthylamine and L-leucyglycine were significantly increased. Changes in these peptidase activities may serve to enhance the mobilization of amino acids and peptides, and they may explain why the growth rates of dental-plaque bacteria in vivo are generally unaffected by the availability of the host's diet.

Neural and dietary modulation of proline-rich protein and 4 beta-galactosyltransferase biosynthesis in rat parotid glands

Maintenance of rats on a bulk diet (50 per cent inert cellulose and 50 per cent laboratory chow) before or after the removal of the submandibular-sublingual glands resulted in hypertrophy of the parotid gland, and the induction of basic proline-rich proteins in that gland with apparent molecular weights similar to those found after chronic administration of isoproterenol. Surgical removal of either the sympathetic or parasympathetic nerve, or of both, impeded both gland hypertrophy and the gene expression for proline-rich protein in the denervated gland. Rats fed normal chow did not have induction of these proteins in the innervated control parotid nor in the denervated contralateral gland. The experimental regimen also showed in-vitro translation of mRNA with electrophoretic protein patterns similar to those with isoproterenol treatment. There was also increased synthesis of the enzyme 4 beta-galactosyltransferase (EC 2.4.1.38).

Comparison of five techniques for the determination of protein content in mixed human saliva

This study was conducted to assess the relative accuracy of five different assay techniques for the determination of protein concentration in human mixed saliva. The protein concentration of paraffin-stimulated saliva from 20 individuals was determined using the biuret reaction, the Lowry assay, a modified Lowry technique using bicinchoninic acid, and two dye-binding assays. Using bovine serum albumin as the standard, mean values ranged from 0.67 to 2.37 mg/ml. The use of bovine serum albumin, trypsinogen, lysozyme, bovine pancreatic ribonuclease, and poly-L-lysine as standards with the five different assay techniques to measure protein concentration of pooled mixed saliva from the above subjects produced results ranging from 0.74 to 65.5 mg/ml. The protein concentration obtained for this saliva sample by amino acid analysis was consistent with the value obtained for the biuret reaction using any of the five different standard proteins. Thus, the protein concentration obtained for human saliva depends upon both the technique used and the protein standard.

Basic proline-rich proteins from human parotid saliva: complete covalent structures of proteins IB-1 and IB-6

The complete amino acid sequences of two basic proline-rich proteins, IB-1 and IB-6, from human parotid saliva have been determined. Fragments for sequence analysis were obtained by enzymatic digestions. The proteins have molecular weights of 9571 (IB-1) and 11,530 (IB-6) and contain 34 and 39 mol % proline, respectively. IB-1 and IB-6 contain an identical sequence of 54 residues except for an alanine in position 52 of IB-6, where IB-1 has proline. An unusually high number of repeated sequences occurs in both molecules. IB-1 has a blocked amino-terminal residue, pyroglutamic acid, and also contains one phosphoserine residue in position 8. The relationship of these proteins to the basic proline-rich protein IB-9 [Kauffman, D., Wong, R., Bennick, A., & Keller, P. (1982) Biochemistry 21, 6558-6562] and to other salivary proline-rich proteins is discussed.

Complete covalent structure of a proline-rich phosphoprotein, PRP-2, an inhibitor of calcium phosphate crystal growth from human parotid saliva

Human salivary secretions contain many proteins in which proline forms an unusually large fraction of the amino-acid residues present, typically from 20% to over 40%. These proteins are also unusually rich in glycine and glutamine, generally account for over half the total protein in saliva, and include acidic, basic and glycosylated molecules. The functions of most of these are not clearly defined. One group, however, the acidic proline-rich phosphoproteins (PRP), have been shown to be potent inhibitors of secondary precipitation (crystal growth) of calcium phosphate salts. Acting together with a salivary protein inhibitor of primary precipitation of calcium phosphates, statherin, the PRP stabilize saliva which is supersaturated with respect to the calcium phosphate salts which form dental enamel. These inhibitory activities act to provide a protective, reparative, but stable environment for dental enamel, which is important for maintaining the health of the teeth. The PRP are a complex group of phosphoproteins which include four major and at least eight minor members. The primary structures of three of the major proteins have been determined. These are PRP-1, also designated Protein-C, PRP-3, also designated Protein-A (17), and PRP-4. The designations PRP-1,-2,-3 and -4 will be used here. The purpose of this paper is to report the complete primary structure of PRP-2 as a further step towards establishing the structural basis of the biological activity of the PRP, and clarifying the genetic and biosynthetic relationships of these closely related proteins.

Phosphorylation of salivary proteins by salivary gland protein kinase

Human saliva contains a number of phosphorylated acidic proline-rich proteins (APRP). Monkey parotid saliva contains a similar protein with the same phosphorylated sequences as the human proteins. A crude protein kinase was prepared from Macaca fascicularis parotid glands which phosphorylated human APRP. The enzyme was activated by Mg2+, it had a pH optimum between pH 7.0 and 7.5, the Km for ATP was 78 mumol/L, and for APRP it was 85 mumol/L. Phosphorylation of APRP was independent of cAMP and calmodulin. Phosphate was incorporated as phosphoserine, and the kinase phosphorylated the same residues in dephosphorylated APRP which are phosphorylated in the secreted protein. In addition, the enzyme preparation also phosphorylated dephosphorylated and native APRP in a region which is not phosphorylated in the secreted protein. There was no difference in the rate of phosphorylation of APRPs and their tryptic peptides. The kinase also phosphorylated other dephosphorylated salivary phosphoproteins. An enzyme was demonstrated in the human salivary gland which gave the same pattern of phosphorylation of APRP as did the simian kinase. More than one kinase may be necessary for the observed phosphorylation.

Circular dichroism and fluorescence spectroscopic analyses of a proline-rich glycoprotein from human parotid saliva

A proline-rich glycoprotein (PRG) was isolated from human parotid saliva and examined by circular dichroism and fluorescence spectroscopy. Addition of guanidine hydrochloride to PRG labeled with an extrinsic dansyl probe had no effect on the fluorescence spectra's 511 nm lambda-max location. Thermodynamic calculations supported the contention that PRG has no significant tertiary structure. Circular dichroism results for PRG were simulated by computer and a secondary structure composed of 70% random coil and 30% beta-form conformation was predicted. Circular dichroism of PRG failed to detect either poly-L-proline type I or II structures. Deglycosylation of PRG had no measurable effect on the circular dichroism spectrum, indicating that the carbohydrate side chains had little influence on PRG secondary structure. Based upon mathematical calculations, beta-turns were predicted around three glycosylated Asn residues of PRG. These collective data suggest that PRG is composed of a disordered polypeptide chain with at least three of the N-linked Asn residues participating in some type of beta-turn.

Immunocytochemistry of acinic cell carcinomas and mixed tumors of salivary glands

Antisera of several secretory products of the salivary gland were used to investigate the histogenesis of acinic cell tumors and mixed salivary gland tumors for comparison. Amylase, lactoferrin, secretory piece, and proline-rich protein (PRP) immunoreactivity was detected in the majority of acinic cell tumors; staining was focal, except for PRP, which was diffuse. Lysozyme immunoreactivity was rare. There was discordance for immunoreactivity with several antisera in identifiable tumor lobules of half of the neoplasms. An antikeratin serum outlined microcystic and follicular areas but rarely solid foci. These findings support the contention that acinic cell tumors derive from a tubular type stem cell. Lactoferrin and secretory piece immunoreactivity was not common in mixed tumors and was confined to scattered ductal cells and luminal contents. Rare small foci of amylase and PRP immunoreactivity were found in two mixed tumors only.

Isolation and characterization of histamine-releasing peptides from human parotid saliva

Peptides responsible for releasing histamine were purified from human parotid saliva. The amino acid composition of the peptides showed a high proportion of histidine, lysine and arginine. Molecular weights of these peptides were between 3000 and 5000 as determined by SDS-acrylamide gel electrophoresis. These peptides induced histamine release from rat-isolated mast cells accompanied with degranulation in a dose-dependent manner over the concentration range 5-50 micrograms/ml.

Inheritance of the human salivary proline-rich proteins: a reinterpretation in terms of six loci forming two subfamilies

DNA studies suggest that six loci control the synthesis of human salivary proline-rich proteins (PRPs). Genes at two of these loci (proposed names, PRH1 and PRH2) contain regions that strongly hybridize to a probe made from a cDNA in which sites for the restriction enzyme HaeIII occur repeatedly; they code for the acidic PRPs. Genes at the remaining four loci (PRB1, PRB2, PRB3, and PRB4) contain regions that strongly hybridize to a probe with repeated BstN1 sites; they probably code for the basic and glycosylated PRPs. In contrast to these data suggesting six loci forming two gene subfamilies, studies of protein polymorphisms and families have led to the postulation of 13 loci with 11 common null alleles. The discrepancy in the number of loci is partly resolved by the hypothesis that the three acidic PRPs, Db, Pa, and PIF, are coded for by alleles at one of the HaeIII-type loci rather than by three discrete loci.

Isolation and characterization of new proteins produced by the infusion of colchicine in goat mammary gland

Three new proteins have now been isolated from goat milk obtained after colchicine is infused into the mammary gland. Two of the proteins are proline-rich, and a third is a very acidic phosphoprotein. One of the proline-rich proteins is related compositionally to a sheep colostrum proline-rich protein, which has been shown to have a regulatory effect on the immune response (Janusz, M., Stavoscik, K., Zimecki, M., Wieczorek, Z., and Lisowski, J. (1981) Biochem. J. 199, 9-15). Other aspects of colchicine-treated milks are described.

Genetic polymorphisms of Pe and Po salivary proteins with probable linkage of their genes to the salivary protein gene complex (SPC)

Two new genetic polymorphisms (Pe and Po) are found in human parotid saliva. Each polymorphism is determined by the autosomal inheritance of one expressed (dominant) and one unexpressed (recessive) allele. Autosomal inheritance is supported by studies of 63 families including 264 children for Pe and 57 families including 242 children for Po. For randomly collected salivas, gene frequencies in 317 whites are Pe+ = 0.76 and Pe- = 0.24; in 408 whites, Po+ = 0.75 and Po- = 0.25; in 51 blacks, Pe+ = 0.76 and Pe- = 0.24; and in 59 blacks, Po+ = 0.77 and Po- = 0.23. Both Pe and Po proteins react immunologically with polyclonal antisera prepared to proline-rich proteins PRPs. The Pe protein has an isoelectric point of approximately pH 6.1-6.3, and the Po protein has an isoelectric point greater than pH 8.0. In randomly collected salivas, the Pe and Po proteins are associated with other known salivary PRPs. The Pe protein is most strongly associated with the CON 1 and Ps proteins, is less strongly associated with the Pr and Pa proteins, and is not significantly associated with the PmF, PmS, PIF, Db, Con 2, or Gl proteins. If it is assumed that the strength of these associations (presumed linkage disequilibrium) may be related in part to map distance, then these data roughly fit the linear order of PRP genes as previously determined from recombination data derived from family linkage studies. The Po protein is associated with the PmS protein. There is evidence for probable linkage of Pe and Po to the SPC (salivary protein gene complex): Pe to Pa (nine families, lod score at theta = 0 is 2.67) and Po to CON 2 (three families, lod score at theta = 0 is 2.35).

Potassium-39 and sodium-23 NMR studies of cation binding to phosvitin

The binding of Na+ and K+ to hen egg-yolk phosvitin has been studied by 23Na and 39K NMR. A transition in the binding behaviour of these cations is shown to accompany deprotonation of the phosphate groups on this highly charged protein. At lower pH the data are well described by a purely mass-action binding model, whereas at higher pH significant polyelectrolyte effects are apparent. From single ion as well as competition experiments K+ is shown to bind more strongly to phosvitin than does Na+. The temperature and magnetic field strength dependences of the 23Na and 39K relaxation rates provide a picture of phosvitin as a highly flexible macromolecule. This work demonstrates the potential of 39K NMR as a useful tool in the study of protein-cation interactions.

Isolation of milligram quantities of a group of histidine-rich polypeptides from human parotid saliva

Freshly collected parotid saliva collected from human donors were shown by polyacrylamide gel electrophoresis to continuously secrete a group of low-molecular-weight cationic polypeptides. Up to 14 bands could be identified by Coomassie blue staining, and all bands migrated more rapidly than purified human leukemic lysozyme in cationic polyacrylamide gel electrophoresis. These peptides could be isolated as a group relatively free of other salivary components and recovered in high yields from concentrated parotid saliva by Sephadex G-25 chromatography. In sodium dodecyl sulfate gel electrophoresis, the histidine-rich polypeptide bands appeared as just two bands migrating at the tracking dye and ahead of insulin chain B. Amino acid analysis of the mixture revealed an average content of at least 48% cationic residues, of which half were histidine. When stained bands were eluted from electrophoretic gels, hydrolyzed, and subjected to amino acid analyses, they were found to be enriched in histidine. There was also a correlation of the electrophoretic mobility with the content of basic amino acids. Sephadex G-25 chromatography is a convenient, simple method for preparing milligram quantities of the histidine-rich polypeptides for chemical and biochemical studies.

Restriction of C1 hemolytic function by human proline-rich salivary proteins

Acidic proline-rich salivary proteins, PRPI, PRPII, PRPIII, PRPIV, upper Db and Statherin, were isolated from parotid saliva and tested for interaction with complement. It was determined that each of the isolated proline-rich proteins blocked C1 hemolytic activity in assay systems where C1 was rate-limiting. Further studies comparing the specific activity of the proline-rich proteins to unfractionated parotid saliva indicated that other salivary substances (sensitive to urea treatment of parotid saliva) were also interacting with the first complement component but in a time-dependent manner. Based on a series of experiments examining the effect of the sequence of addition of the proline-rich proteins in the complement assay systems, it is postulated that these salivary proteins are able to block the proper interaction of C1 with EAC4 cells (sheep erythrocytes coated with antibody and C4gp). The proline-rich salivary proteins had no effect on C1 once C1 was bound to the immune complexes on the EAC4 cells. The C1 macromolecular complex undergoes conformational changes upon interaction with immune complexes resulting in a more avid binding of the C1q-Clr-Cls subunits with one another. Thus it is speculated that the EAC4-bound C1 becomes resistant to disruption by the proline-rich salivary proteins. Although the urea-sensitive factors had the highest specific C1-fixing activity, the activity of the acidic proline-rich proteins on C1 is important because of their relatively high concern in salivary secretions. Since complement-containing serous exudates and transudates are present on inflamed mucosal tissues, salivary substances which interact with C1 may play a role in regulating the initiation of the classical complement pathway, particularly at those mucosal sites where there is a high ratio of salivary secretion to serous exudate.

Genetic polymorphism of CON 1 and CON 2 salivary proteins detected by immunologic and concanavalin A reactions on nitrocellulose with linkage of CON 1 and CON 2 genes to the SPC (salivary protein gene complex)

Two new genetic protein polymorphisms (CON 1 and CON 2) were identified in parotid saliva. Genetic polymorphisms of salivary CON 1 (concanavalin A) and CON 2 proteins are determined by autosomal inheritance of one expressed (dominant) and one unexpressed (recessive) allele for each gene. Autosomal inheritance is supported by studies in 26 families including 105 children for CON 1 and 23 families including 95 children for CON 2. Gene frequencies determined for randomly collected salivas from 134 whites, 79 Chinese, and 74 blacks are as follows: for whites, CON 1+ = 0.396 and CON 1- = 0.604, CON 2+ = 0.034 and CON 2- = 0.966; for Chinese, CON 1+ = 0.580 and CON 1- = 0.420, CON 2+ = 0 and CON 2- = 1; for blacks, CON 1+ = 0.581 and CON 1- = 0.419, CON 2+ = 0.007 and CON 2- = 0.993. Both CON 1 and CON 2 proteins, transferred from SDS gels to nitrocellulose, react with concanavalin A. The CON 1 and CON 2 proteins react with antisera prepared to proline-rich proteins (PRP), and the CON 1 and CON 2 proteins have isoelectric points greater than pH 8.5. In randomly collected salivas, the CON 1 protein shows a strong association with Ps proteins, and the CON 2 protein shows a strong association with the PmF protein. On the basis of association data, PmS and CON 2 genes may be outside markers in a linear arrangement of the three genes, PmS, PmF, and CON 2. There is strong evidence for linkage of CON 1 and CON 2 to the SPC (salivary protein gene complex), CON 1 to Ps (15 families, lod score at theta = 0 is 6.77), CON 2 to PmF (7 families, lod score at theta = 0 is 5.93), and CON 2 to G1 (5 families, lod score at theta = 0 is 3.91). In addition to immunologic reactions with the CON 1 and CON 2 proteins, antisera to PRP show extensive immunologic reactions with many other salivary proteins when tested by immunoblotting on nitrocellulose. Some of these proteins were previously identified PRP (proline-rich proteins) that are determined by different PRP loci.

Changes in rat parotid salivary proteins associated with liquid diet-induced gland atrophy and isoproterenol-induced gland enlargement

The composition of secretory proteins in the parotid saliva of untreated rats, fed a stock pelleted diet (CON), was compared to that of rats maintained on a liquefied diet (LIQ), so as to reduce gland secretory activity, and to rats treated chronically with isoproterenol (ISO), so as to enhance activity. Each experimental treatment resulted in marked changes in protein composition. In CON rats, the basic and acidic proline-rich proteins accounted for 25 per cent of all secretory protein. In LIQ rats, the proportion was 13 per cent. Several basic proline-rich proteins were absent and the major acidic proline-rich protein was markedly reduced. Amylase was reduced whereas DNase and a leucine-rich protein (fraction I) were increased. The proportion of cystine-rich protein (fraction V) was not different from CON rats. The changes observed in the saliva of ISO rats were in marked contrast to these findings. Basic and acidic proline-rich proteins were increased and accounted for 90 per cent of all secretory protein, amylase was responsible for the remaining 10 per cent. Thus the composition of secretory proteins in the parotid saliva of rats can be altered by experimental conditions which affect gland secretory activity. The mechanisms by which these changes occur is not known.

External incubation alters the composition of squamate eggshells

Eggshells of the skink, Eumeces fasciatus, and of the rough green snake, Opheodrys vernalis, contain 28-40% of total shell mass as calcium at oviposition. After incubation, both calcium concentration and content were reduced 17-41%. Protein accounted for 33-65% of shell mass in Eumeces and Opheodrys eggshells at oviposition. Reductions in protein concentration and content from 22-86% following incubation were observed. Comparing amino acid compositions of eggshells collected following oviposition with those collected from the same clutch after hatching reveals similarities among all eggshells except those of Eumeces from Michigan which lack desmosine and isodesmosine. Concentrations of desmosines in eggshells from Missouri and Michigan Eumeces appeared to decrease following incubation by 49.7% and 12.2%, respectively. Although neither the mechanisms involved in apparent losses of calcium and protein, nor the fate of the mobilized materials are known, possible pathways for mobilization of eggshell constituents are outlined and their pertinence to the physiology of squamate eggs and the evolution of viviparity in reptiles is suggested.

Modulation of proline-rich protein biosynthesis in rat parotid glands by sorghums with high tannin levels

Feeding of sorghum with a high level of tannin (high-tannin sorghum) to rats caused changes in gene expression in parotid glands similar to isoproterenol treatment. Within 3 days the parotid glands were enlarged about 3-fold and a series of proline-rich proteins were increased about 12-fold. Unlike isoproterenol treatment, no changes were observed in the submandibular glands, and a Mr 220,000 glycoprotein in parotid glands was not induced. Amino acid analyses, electrophoretic patterns, and cell-free translations of mRNAs all confirmed that the proline-rich proteins induced by feeding high-tannin sorghum were identical to those induced by isoproterenol treatment. Binding curves for proline-rich proteins to tannins showed affinities 10-fold greater than bovine serum albumin and tannins.

Possible amino acid repetitive sequences in the proline-rich glycoprotein of human parotid saliva

The amino acid sequence of the proline-rich glycoprotein from human parotid saliva was studied using different preparations: native glycoprotein, tryptic glycopeptides, and their chemically deglycosylated homologous derivatives. The results indicate very similar structural features of the proline-rich glycoprotein and the tryptic glycopeptides and suggest that the peptide backbone of the glycoprotein comprises several repetitive domains containing one carbohydrate-peptide linkage and a proline-rich sequence. These data are in fair agreement with a preceding circular dichroism study (Aubert, J.P., Porchet, N., Boersma, A., Loucheux-Lefevbre, M.H. and Degand, P. (1982) Biochim. Biophys. Acta 704, 361-365).

Differences in basic proline-rich proteins in rat parotid saliva following chronic isoproterenol treatment or maintenance on a liquid diet

The basic proline-rich proteins (BPRP) in the stimulated parotid saliva of rats treated for 8 days with isoproterenol and rats fed a liquid diet for 2 weeks were compared to those in the stimulated parotid saliva of untreated rats fed a stock pelleted-diet (control). In the control, the BPRP were separated into 5 groups designated Peak A (the basic proline-rich glycoprotein), SP-1, SP-2, SP-3 and SP-4. The percentage of BPRP in each group was as follows: Peak A, 6.5 per cent; SP-1, 37 per cent; SP-2, 6.5 per cent; SP-3, 32.4 per cent; SP-4, 17.6 per cent. In the parotid saliva of rats fed the liquid diet, proteins corresponding to Peak A and SP-2 were not present, the proportion of BPRP in SP-4 was increased to almost 90 per cent while the proportions of material in SP-1 and SP-3 were reduced to 3 and 8 per cent, respectively. In the saliva of rats subjected to chronic isoproterenol treatment, a protein corresponding to SP-4 was not present; proteins corresponding to Peak A, SP-1 and SP-3 were present and in amounts similar to their proportion in untreated rats although material in SP-2 increased to 36 per cent.