Structural Aspects of Salivary Glycoproteins

Abstract

The protective functions of saliva are attributed, in part, to its serous and mucous glycoproteins. We have studied, as representative molecules, the proline-rich glycoprotein (PRG) from human parotid saliva and the high (MG1) and low (MG2) molecular weight mucins from submandibular-sublingual saliva. PRG (38.9 kDa) contains 40% carbohydrate consisting of 6 triantennary N-linked units and a single peptide chain of 231 amino acids, 75% of which = PRO + GLY + GLN. PRG's secondary structure is comprised of 70% random coil (naked regions) and 30% beta-turns (glycosylated domains). MG1 (greater than 10(3) kDa) contains 15% protein (several disulfide linked subunits), 78% carbohydrate (290 units of 4-16 residues), 7% sulfate, and small amounts of covalently linked fatty acids. MG2 (200-250 kDa) contains 30% protein (single peptide chain), 68% carbohydrate (170 units of 2-7 residues), and 2% sulfate. The major carbohydrate units of MG2 are: NeuAc alpha 2,3Gal beta 1,3GalNAc,Gal beta 1,3GalNAc, and Fuc alpha 1,2Gal beta 1,3GalNAc. MG1 contains hydrophobic domains, as evidenced by its ability to bind fluorescent hydrophobic probes; MG2 does not. Collectively, the biochemical and biophysical comparisons between MG1 and MG2 indicate that these two mucins are structurally different. Several functional properties of MG1, MG2, and PRG have been examined, including their presence in two-hour in vivo enamel pellicle, binding to synthetic hydroxyapatite, lubricating properties, and interactions with oral streptococci. The data presented suggest that these glycoproteins may have multiple functions which are predicated, in part on their carbohydrate units. The potential significance of the structure-function relationships of these glycoproteins to the oral ecology is discussed.

Saliva-Bacterium Interactions in Oral Microbial Ecology

“…Sialic acid and sialic acid containing oligosaccharides also inhibited the binding of S. sanguis to erythrocytes (Murray et al, 1982), the best inhibitor being the trisaccharide Neua2,3Gal,B1,3GalNAc, the major oligosaccharide of MG2 . These 0-linked oligosaccharides may allow MG2 to bind, agglutinate, and clear bacteria from the oral cavity (see below) Levine et al, 1987;Tabak et al, 1982). In this respect, a glycoprotein resembling MG2 has been isolated recently from submandibular sublingual saliva with agglutinating activity for Eikenella corrodens .…”

Salivary α-Amylase: Role in Dental Plaque and Caries Formation

“…Finally, the fact that a-amylase binds to teeth as a constituent of enamel pellicle (Al-Hashimi and and promotes the adhesion of amylase-binding bacteria to hydroxyapatite (HAP) in vitro (see the following) argues for a potential role in bacterial adhesion. These properties of a-amylase provide yet another example of multifunctionality that may prove to be the rule for most, if not all, salivary molecules (Bennick, 1982;Cohen and Levine, 1989;Gibbons and Hay, 1988;Levine et al, 1987;Tabak et al, 1982).…”

“…At least 50 macromolecular components have been reported to be secreted from salivary glands (for reviews, see Bennick, 1982;Cohen and Levine, 1989;Hay and Moreno, 1987;Levine et al, 1987;Mandel, 1987;Oppenheim, 1989;). a-Amylase, one of the most plentiful components in saliva (Aguirre et al, 1987), is a calcium-containing metalloenzyme that hydrolyzes the al,4 linkages of starch to glucose and maltose.…”

Mucoadhesive Polymers for Oral Transmucosal Drug Delivery: A Review

“…The most important salivary mucin is called MG1 [45] whose role are: to maintain hydration, to provide lubrication, to concentrate protective molecules such as secretory immunoglobulins, and to limit the attachment of microorganisms.…”