Hydroxyapatite binding domains in salivary proteins.

Abstract

One of the functions of proteins in human saliva is to maintain a balance between calcium phosphate remineralization and demineralization. Saliva is normally supersaturated with respect to calcium phosphate phases such as hydroxyapatite (HAP) and octacalcium phosphate (OCP), but it can also be undersaturated, locally, with respect to these phases (Gron, 1973). The proteins believed to be the strongest precipitation inhibitors are statherin and a group of acidic proline-rich phosphoproteins (PRPs), all of which adsorb strongly to HAP (Moreno et al., 1978, 1979). These molecules contain phosphoserine residues and have a significant number of negatively charged residues localized in their N-terminal regions, whereas the C-termini contain mainly uncharged residues (Schlesinger and Hay, 1977; Wong et al., 1979). The charged domains of both statherin and the PRPs have been shown to have high affinities for HAP surfaces and to be efficient inhibitors of HAP crystal growth in supersaturated solution (Schlesinger et al., 1987; Moreno et al., 1981). However, several other proteins containing charged domains may be moderate or weaker contributors to precipitation inhibition. HAP adsorption and crystallization modification in the presence of a protein depends on the manner in which it adsorbs at the surface. In this study, these data are compared for some salivary proteins.