Mucins are the principal organic constituents of mucus, the slimy visco‐elastic material that coats all mucosal surfaces. Compelling evidence suggests that they play an integral role in non‐immune protection of the oral cavity. Specific protective functions include: 1) protection against desiccation and environmental insult, 2) lubrication, and 3) antimicrobial effects against potential pathogens. Biosynthesis of mucin is regulated by both intrinsic (“cooperative sequential specificity”) and extrinsic (“structural modulation”) controls. These controls form the basis by which mucin's structure can be modified to meet a dynamically changing biological need.

Salivary a-amylase, a major component of human saliva, plays a role in the initial digestion of starch and may be involved in the colonization of bacteria involved in early dental plaque formation. The three-dimensional atomic structure of salivary amylase has been determined to understand the structure-function relationships of this enzyme. This structure was refined to an R value of 18.4% with 496 amino-acid residues, one calcium ion, one chloride ion and 170 water molecules. Salivary amylase folds into a multidomain structure consisting of three domains, A, B and C. Domain A has a (/3/a)8-barrel structure, domain B has no definite topology and domain C has a Greek-key barrel structure. The Ca 2+ ion is bound to Asnl00, Arg158, Asp167, His201 and three water molecules. The C1-ion is bound to Arg195, Asn298 and Arg337 and one water molecule. The highly mobile glycine-rich loop 304-310 may act as a gateway for substrate binding and be involved in a 'trap-release' mechanism in the hydrolysis of substrates. Strategic placement of calcium and chloride ions, as well as histidine and tryptophan residues may play a role in differentiating between the glycone and aglycone ends of the polysaccharide substrates. Salivary amylase also possesses a suitable site for binding to enamel surfaces and provides potential sites for the binding of bacterial adhesins.

Salivary a-amylase, one of the most plentiful components in human saliva, has at least three distinct biological functions. The enzymatic activity of a-amylase undoubtedly plays a role in carbohydrate digestion. Amylase in solution binds with high affinity to a selected group of oral streptococci, a function that may contribute to bacterial clearance and nutrition. The fact that a-amylase is also found in acquired enamel pellicle suggests a role in the adhesion of a-amylase-binding bacteria. All of these biological activities seem to depend on an intact enzyme conformation. Binding of a-amylase to bacteria and teeth may have important implications for dental plaque and caries formation. a-Amylase bound to bacteria in plaque may facilitate dietary starch hydrolysis to provide additional glucose for metabolism by plaque microorganisms in close proximity to the tooth surface. The resulting lactic acid produced may be added to the pool of acid in plaque to contribute to tooth demineralization.

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