Adsorption of Amelogenin Nanopheres onto Charged Surfaces, A Model for Tooth Enamel Matrix Re-construction
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Adsorption of Amelogenin Nanopheres onto Charged Surfaces, A Model for Tooth Enamel Matrix Re-construction 1Moradian-Oldak 1
J., 2Gergely C., 3Bouropoulos N., and 2Cuisinier F.J.G.
Center for Craniofacial Molecular Biology, University of Southern California, LA, CA , USA. INSERM U 595, Faculté de Chirurgie Dentaire, Université Louis Pasteur, Strasbourg, France. 3 Department of Material Science, University of Patras, GR-26500 Patras, Greece.
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ABSTRACT Amelogenins are hydrophobic proteins that constitute more than 90% of the secretory stage enamel matrix. The assembly of amelogenin into nanospheres has been postulated to be a key factor in controlling the structural organization of the enamel extracellular matrix framework, which provides the scaffolding for the elongated and oriented growth of enamel apatite crystals. To get insight into the structure and function of amelogenin in controlling the process of crystal growth we have utilized two different approaches to investigate adsorption of amelogenin nanospheres onto charged surfaces: A) analysis of adsorption of amelogenin onto hydroxyapatite crystals by means of Langmuir Model for protein adsorption. B) analysis of amelogenin mono or multi-layer formation by sequential adsorption process onto auto-assembled polyelctrolytes films. Our data indicate that amelogenin nanospheres adsorb onto the surface of apatite crystals as binding units with defined adsorption sites. We found that amelogenin nanospheres are negatively charged and a monolayer of these nanospheres adsorbed in an irreversible way on positively ending polyelectrolyte multilayers most likely through electrostatic interactions. INTRODUCTION Dental enamel biomineralization involves a variety of extra and intracellular events resulting in the formation of unusually elongated carbonated hydroxyapatite crystals which are oriented to construct a highly ordered microarchitecture [1-3] . In enamel, like many other biomineralizing systems the processes of crystal nucleation and growth are actively controlled at the molecular level by the protein components of the extracellular matrix . Amelogenins, the major protein component of the developing enamel extracellular matrix self assemble to form nanosphere structures [4-5]. Current evidence indicates that during the early stage of enamel mineralization amelogenin nanospheres are found along the side faces of enamel apatite crystals and provide the organized microstructure for the initiation and oriented growth of the crystals [6]. Recent atomic force microscope images of developing enamel from pig mandibular molar showed rows of amelogenin nanospheres among the crystallite structures and in the intercrystalline areas implying that the binding of proteins may play an integral role in the final morphology of mature enamel [7]. Recent experimental data using different in vitro chemical models have demonstrated that amelogenin affects the habit of octacalcium phosphate and apatite to result crystals that are more elongated and with a higher thickness to wi
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