The purpose of this project is to determine the structure-function relationship of enamel matrix proteins as potential regulators of enamel mineral formation. Our working hypothesis is that soluble hydrophilic enamel proteins (e.g. enamelin) in association with insoluble matrix components (e.g. amelogenin aggregates) provide the appropriate surface characteristics to induce the nucleation of calcium phosphates. In the presence of appropriate concentrations of mineral ions, this results in the formation of very thin ribbons of enamel mineral. The growth of these enamel ribbons in thickness and width is immediately inhibited by hydrophobic proteins (e.g. amelogenins in solution) which absorb onto specific faces of the forming crystals. It is further hypothesized that the onset of growth of these mineral ribbons during tissue maturation is controlled by the degradation of these absorbed protein inhibitors by enamel proteinases. To gain a better understanding how matrix proteins can control mineralization in a tissue like enamel, we gain a better understanding how matrix proteins can control mineralization in a tissue like enamel, we proposed to determine the adsorption isotherms for the major enamel matrix proteins onto hydroxyapatite (HA) and octacalcium phosphate (OCP) crystals, using recombinant amelogenin and enamelin. HA and OCP were chosen for study as prototypes for forming enamel mineral. We further propose to determine the inhibitory effect of adsorbed recombinant amelogenin and enamelin on HA seeded crystal growth and relate these findings to the extent of protein adsorption. We will further assess the ability of recombinant enamel proteinases (e.g. enameylsin and EMPSl) to degrade enamel proteins which are absorbed onto HA and OCP surfaces, since this may be an important mechanism by which enamel proteinases can control mineralization. We further propose to assess the ability of recombinant amelogenin and enamelin to promote calcium phosphate nucleation in vitro, using agarose gels and proteins covalently linked to sepharose beads, and to influence crystal morphology. Long term, these studies may be important to the development of new biomimetic approaches which could be used to treat damaged or diseased teeth.
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