TERTIARY STRUCTURES OF SALIVARY PROTEINS

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Secretions from the parotid, submandibular and sublingual glands contain a significant amount of protein proteins and may be selectively adsorbed onto the hydroxyapatite-like surface of dental enamel. Once adsorbed onto the tooth surface, these proteins may be involved in the demineralization/remineralization of the tooth surface. In addition, these proteins may exhibit receptor-like domains which are important In the early colonization of specific oral microorganisms which may be involved in caries and/or periodontal disease. There is significant evidence that suggests that the receptor-like domain for certain salivary proteins is not accessible to bacteria unless the salivary protein is adsorbed onto a solid phase such as hydroxyapatite. The evidence has largely been derived from biochemical and microscopic techniques which suggest that the conformation around the bacterial binding site changes. These techniques, however, are limited by their low degrees of resolution. A new strategy, employed to study conformational changes in other protein complexes has been incorporated into this proposal in order to determine the location of conformational changes, with possible resolution to the specific amino acid residue. The specific aim of this proposal is: To perform covalent protein modification of amino acid side chains of statherin and/or histatin 5 and to determine changes in amino acid reactivity between protein labeled in solution and protein labeled following adsorption onto hydroxyapatite. In separate experiments, lysine-, tyrosine-, glutamine-, and histidine-specific reagents will be added to protein samples. Using combinations of amino acid analysis, amino acid sequencing, and liquid scintillation counting, the extent and locations of modified amino acids will be determined. Successful completion of this aim will provide the basis for a more extended study using acidic proline-rich proteins which, only when adsorbed onto hydroxyapatite, have been shown to bind Actinomyces viscosus, Bacteroides gingivalis, and Streptococcus mutans. The first phase of this project is important in developing the experimental method on small proteins, i.e., statherin and histatin 5, before its general application to the much larger acidic proline-rich proteins. Certain oral microorganisms also bind to statherin in an adsorption-dependent fashion so statherin will serve a useful role the method development. Histatin 5 will be used for the development of histidine modification since statherin does not contain any histidine residues. The ultimate goal of the project will be to determine which amino acids are involved in protein-bacteria interactions.