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

The visco-elastic properties of salivary secretions are due to high molecular-weight glycoproteins, known as mucins. Mucins are composed of numerous oligosaccharide side-chains O-glycosidically linked through 2-acetamido-2-deoxy-alpha-D-galactose to the hydroxyl groups of seryl and threonyl residues of the protein core; on the average, every fourth amino acid residue is involved in such a bond. This work conveys their isolation and purification, compiles the compositional analysis of several mammalian submaxillary and sublingual mucins; defines the conditions of the alkaline beta-elimination reaction, its mechanism, and importance in structural studies of glycoprotens, and briefly discusses the influence of stimuli on mucous secretions, as well as biosynthesis, structural diversity, and physiological role of salivary mucous glycoproteins.

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