Human dental enamel forms over a period of 2–4 years by substituting the enamel matrix, a protein gel mostly composed of a single protein, amelogenin with fibrous apatite nanocrystals. Self-assembly of a dense amelogenin matrix is presumed to direct the growth of apatite fibers and their organization into bundles that eventually comprise the mature enamel, the hardest tissue in the mammalian body. This work aims to establish the physicochemical and biochemical conditions for the synthesis of fibrous apatite crystals under the control of a recombinant full-length human amelogenin matrix in combination with a programmable titration system. The growth of apatite substrates was initiated from supersaturated calcium phosphate solutions in the presence of dispersed amelogenin assemblies. It was shown earlier and confirmed in this study that binding of amelogenin onto apatite surfaces presents the first step that leads to substrate-specific crystal growth. In this work, we report enhanced nucleation and growth under conditions at which amelogenin and apatite carry opposite charges and adsorption of the protein onto the apatite seeds is even more favored. Experiments at pH below the isoelectric point of amelogenin showed increased protein binding to apatite and at low Ca/P molar ratios resulted in a change in crystal morphology from plate-like to fibrous and rod-shaped. Concentrations of calcium and phosphate ions in the supernatant did not show drastic decreases throughout the titration period, indicating controlled precipitation from the protein suspension metastable with respect to calcium phosphate. It is argued that ameloblasts in the developing enamel may vary the density of the protein matrix at the nano scale by varying local pH, and thus control the interaction between the mineral and protein phases. The biomimetic experimental setting applied in this study has thus proven as convenient for gaining insight into the fundamental nature of the process of amelogenesis.

中文翻译：

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从全长人釉蛋白溶胶中单轴生长的磷酸钙晶体的仿生沉淀。


人类牙釉质通过取代牙釉质基质而形成，牙釉质基质是一种主要由单一蛋白质、釉原蛋白和纤维状磷灰石纳米晶体组成的蛋白质凝胶。据推测，致密牙釉蛋白基质的自组装引导磷灰石纤维的生长及其组织成束，最终形成成熟的牙釉质，这是哺乳动物体内最坚硬的组织。这项工作旨在建立在重组全长人牙釉蛋白基质与可编程滴定系统相结合的控制下合成纤维状磷灰石晶体的物理化学和生化条件。磷灰石基质的生长是在分散的牙釉蛋白组装体存在下从过饱和磷酸钙溶液开始的。先前已表明并在本研究中证实，牙釉蛋白与磷灰石表面的结合是导致基材特异性晶体生长的第一步。在这项工作中，我们报告了在牙釉蛋白和磷灰石带有相反电荷的条件下成核和生长增强，并且更有利于蛋白质吸附到磷灰石种子上。 pH 值低于牙釉蛋白等电点的实验表明，蛋白质与磷灰石的结合增加，并且低 Ca/P 摩尔比导致晶体形态从板状变为纤维状和棒状。上清液中钙离子和磷酸根离子的浓度在整个滴定期间并未表现出急剧下降，这表明相对于磷酸钙亚稳定的蛋白质悬浮液中存在受控沉淀。 有人认为，发育中的牙釉质中的成釉细胞可能通过改变局部 pH 值在纳米尺度上改变蛋白质基质的密度，从而控制矿物质相和蛋白质相之间的相互作用。因此，本研究中应用的仿生实验设置已被证明可以方便地深入了解釉质形成过程的基本性质。