Proteins, proline-rich

As noted earher (Sect. 12.1.3), the reduced enamel epithelium is replaced with adherent salivary proteins, mostly amylase and acidic proline-rich proteins. The acidic PRPs are at about a three times greater concentration than in secreted saliva. The acidic domain of these proteins especially has a high affinity for hydroxyapatite. Once bound to pelhcle, the N-terminus of acidic-PRPs forms an attachment site for the major classes of commensal bacteria (viridans streptococci and Actinomyces spp.) that occupy the mucosal surfaces and saliva of a healthy oral cavity. Some streptococci grow by themselves in dental biofilms, but many others grow better if certain Actinomyces spp. are also present. 

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L23. Lyons, K. M., Stein, J. H., and Smithies, O., Length polymorphisms in human proline-rich protein genes generated by intragenic unequal crossing over. Genetics 120, 267-278 (1988). 

Hamsters, unlike mice and rats, are not able to adjust to high levels of tannins in their diet by producing more proline-rich proteins in their saliva. A diet high in tannin has no effect on the salivary glands, and proline-rich proteins are not... 

Browsers such as mule deer, 0. hcmionus, have proUne-rich salivary proteins that bind tannins this enables them to feed on tanniniferous plants (Robbins etal, 1991). By contrast, grazers such as sheep and cattle do not possess tanninbinding proteins (Austin etal, 1989 Robbins etal, 1991), and neither do mixed feeders such as goats (Distel and Provenza, 1991). Rat and mouse saliva also contain proline-rich proteins that bind tannins. In human saliva, about 70% of total protein is rich in proline (Fig. 11.9) (Mehansho etal, 1987). 

McArthur, C., Sanson, G. D., and Beal, A. M. (1995). Salivaiy proline-rich proteins in mammals roles in oral homeostasis and counteracting dietary tannin. Journal of ChemicalEcology 11,663-691. 

Mehansho, H., Hagerman, A., Clements, S., etal. (1983). Modulation of proline-rich protein biosynthesis in rat parotid glands by sorghums with high tannin levels. Proceedings ofthe National Academy of Sciences USA 80, 3948-3952. 

Mehansho, H., Butler, L. G., and Carlson, D. M. (1987). Dietary tannins and salivary proline-rich proteins interactions, induction, and defense mechanism. Ann Review of Nutrition 7,423-440. 

Warner, T. F. and Azen, E. A. (1988). Tannins, salivary proline-rich proteins and oesophageal cancer. Medical Hypotheses 26,99-102. 

NT265 Tesfaigzi, ]., J. Th ng, J. A. Hotchkiss, J. R. Harkema, and P. S. Wright. A small proline-rich protein, SPRRl, is upregulated early during tobacco smoke-induced squamous metaplasia in rat nasal epithelia. Am J Respir Cell Mol Biol 1996 14(5) 478-486. 

Baxter, N.J. et ak. Multiple interactions between polyphenols and a salivary proline-rich protein repeat result in complexation and precipitation. Biochemistry 36, 5566, 1997. 

Luck, G. et ak. Polyphenols, astringency and prolin-rich proteins. Phytochemistry 37, 357, 1994. 

Charlton, A.J., Haslam, E., and Williamson, M.P., Multiple conformations of the proline-rich-protein/epigallocatechin gallate complex determined by time-averaged nuclear Overhauser effects. J. Am. Chem. Soc. 124, 9899, 2002. 

Edelmann, A. et al., Dynamic light scattering study of the complexation between proline rich proteins and flavan-3-ols influence of molecular structure, polyphenol/protein ratio and ionic strength. In Oenologie 2003 (eds A. Lonvaud-Funel, G. De Revel, and P. Darriet), Tec et Doc, Arcachon, 2003, p. 408. 

Data for the metabolites in plasma are generally for the unbound forms, but there is ample evidence that PPT bind noncovalently to proteins. Most studies on PPT-protein interaction have focused on protein utilization or astringency but a few studies have addressed binding to plasma proteins and lipoproteins. " " Strongest binding has been associated with 1,2-dihydroxyphenols and proline-rich proteins such as those character-istic of human saliva and structure-activity relationships have been reported. 

Bacon, J.R. and Rhodes, M.J., Binding affinity of hydrolyzable tannins to parotid saliva and to proline-rich proteins derived from it, J. Agric. Food Chem., 48, 838, 2000. 

Despite their very short sequence (7 to 38 amino acid residues for the 12 histatins identified so far), the histidine-rich salivary protein histatins have also been reported to precipitate tannins, eventually more efficiently than proline-rich proteins, especially at neutral pH and high tannin concentration. A detailed NMR analysis of the binding between EGCG and histatin 5, a 24-mer that is very rich in basic His, Lys, and Arg residues ( 60%) and devoid of secondary structure, has revealed noncooperative binding of six to seven flavanol molecules with a dissociation constant of 1 mM (pH 3.0, 25°C). ... 

Murray, N.J. et al.. Study of the interaction between salivary proline-rich proteins and a polyphenol by IH-NMR spectroscopy, Eur. J. Biochem., 219, 923, 1994. 

Charlton, A.J. et al.. Tannin interactions with a full-length human salivary proline-rich protein display a stronger affinity than with single proline-rich repeats, FEBS Lett, 382, 289, 1996. 

Fragments of hydroxy-L-proline-rich protein obtained from the primary cell-walls of dicots invariably contain arabinosyl and galactosyl residues and a series of hydroxy-L-proline arabinosides mono-, di-, tri-, and tetra-arabinosides, glycosidically linked to the hydroxyl group of hydroxy-L-proline have been isolated from wall preparations obtained from suspension-cultured sycamore- and tomato-cells,228,230 and separated chromatographically on Chromobeads B.231 The hydroxy-L-proline tetraarabinoside is the preponderant molecular species obtained from the dicot primary cell-wall protein. Little or no nonglycosylated hydroxy-L-proline appears to be present.41,42,231 This wall protein is, therefore, clearly a glycoprotein. 

The covalent attachment of arabinose and galactose to the hydroxy-L-proline-rich protein of primary cell-walls is now generally accepted,228230 but the evidence available suggests that the glycoprotein is not covalently attached to any of the other cell-wall polymers, This, of course, does not preclude the possibility of the existence of strong, non-covalent forces binding protein to wall polysaccharides.228,230... 

In contrast to dicots, 65-75% of the hydroxy-L-prolyl residues in the hydroxy-L-proline-rich proteins from the primary wall of four monocot species, including Zea mays (pericarp), Avena sativa (coleoptile), Iris kaempferi (pericarp), and Allium porum (pericarp), are reported to have no arabinoside residues attached.231 Of the glycosylated hydroxy-L-prolyl residues, the majority are bonded to triarabinosides, although smaller proportions of tetra-, di-, and mono-arabinosides have also been detected.231... 

The hydroxy-L-proline-rich protein present in the culture medium of suspension-cultured sycamore-cells was shown to be covalently linked to an arabinogalactan,57 and this led to speculation regarding the existence of a similar interconnection within the cell wall. However, it has now been established that the hydroxy-L-proline-rich protein of the primary wall is structurally different from that present in the extracellular fluid234 (see Section VII, 1), and thus the latter cannot be used as a model for the cell-wall glycoprotein. 

On the basis of this limited evidence, the most feasible conclusion is that hydroxy-L-proline-rich protein, synthesized on ribosomes, is glycosylated in the Golgi bodies, transported to the cell surface in Golgi vesi-... 

Human saliva is supersaturated with basic calcium phosphate, to allow recalcification and protection of the dental enamel. Precipitation in the saliva is prevented by certain calcium binding proteins, which include statherin268 (a 5380 molecular weight tyrosine-rich protein that also contains many proline and glutamic acid residues), and a group of proline-rich proteins.269... 

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