Adsorption of Human Salivary Proteins to Hydroxyapatite: A Comparison Between Whole Saliva and Glandular Salivary Secretions

Abstract

The protein compositions of in vitro pellicles formed from whole saliva and parotid and submandibular secretions were determined by use of synthetic hydroxyapatite as a model for dental enamel. The adsorbed and unadsorbed protein fractions were analyzed by amino acid analysis and both anionic and cationic discontinuous polyacrylamide gel electrophoresis. For further characterization of the in vitro pellicle, the adsorbed fractions were subjected to gel filtration on Sephadex G-100 and reversed-phase chromatography on C18 columns. Amylase, acidic and glycosylated proline-rich proteins, statherins, and histatins were identified in the parotid-derived pellicle. Detailed analysis of the statherin-containing fractions resulted in the observation of several statherin-like proteins. The use of cationic gel electrophoresis allowed for the identification of histatin 3 and histatin 5, which have not been previously detected in pellicle formed in vitro. The protein composition of submandibular-derived pellicle was similar to that of parotid-derived pellicle except for the presence of cystatins and the absence of glycosylated proline-rich proteins. In contrast, in vitro pellicle derived from whole saliva exhibited a vastly different composition, consisting primarily of amylase, acidic proline-rich proteins, cystatins, and proteolytically-derived peptides. The results indicate that acidic phosphoproteins as well as neutral and basic histatins from pure secretions selectively adsorb to hydroxyapatite, whereas in whole saliva some of these proteins are proteolytically degraded, dramatically changing its adsorption pattern.