INTERACTION OF AMELOGENIN WITH HYDROXYAPATITE CRYSTALS - AN ADHERENCEEFFECT THROUGH AMELOGENIN MOLECULAR SELF-ASSOCIATION

At the secretory stage of tooth enamel formation the majority of the o rganic matrix is composed of amelogenin proteins that are believed to provide the scaffolding for the initial carbonated hydroxyapatite crys tals to grow. The primary objective of this this study was to investig ate the interaction between amelogenins and growing apatite crystals. Two in vitro strategies were used: first, we examined the influence of amelogenins as compared to two other macromolecules, on the kinetics of seeded growth of apatite crystals; second, using transmission elect ron micrographs of the crystal powders, based on a particle size distr ibution study, we evaluated the effect of the macromolecules on the ag gregation of growing apatite crystals. Two recombinant amelogenins (rM 179, rM166), the synthetic leucine-rich amelogenin polypeptide (LRAP), poly (L-proline), and phosvitin were used. it was shown that the rM17 9 amelogenin had some inhibitory effect on the kinetics of calcium hyd roxyapatite seeded growth. The inhibitory effect, however, was not as destructive as that of other macromolecules tested. The degree of inhi bition of the macromolecules was in the order of phosvitin > LRAP > po ly(L-proline) > rM179 > rM166. Analysis of particle size distribution of apatite crystal aggregates indicated that the full-length amelogeni n protein (rM179) caused aggregation of the growing apatite crystals m ore effectively than other macromolecules. We propose that during the formation of hydroxyapatite crystal clusters, the growing apatite crys tals adhere to each other through the molecular self-association of in teracting amelogenin molecules. The biological implications of this ad herence effect with respect To enamel biomineralization are discussed. (C) 1998 John Wiley & Sons, Inc.