Amelogenin Nanoribbons In Enamel Development And Engineering

牙釉质是唯一的上皮来源的组织，矿化。它在细胞外基质中发育， 高度特化的上皮细胞，即成釉细胞，合成大量特异性基质蛋白， 与其他已知蛋白质的同源性。釉原蛋白是发育中的釉质中最大的成分 基质（DEM）包含约90%的所有分泌蛋白。釉原蛋白的一级结构编码一系列关键的 最终允许控制磷灰石纳米纤维的单轴生长的DEM的功能及其 三维组织成一个僵硬，坚硬和耐磨损的组织优化咀嚼， 与下面的牙本质结合。在此之前，我们已经证明了 釉原蛋白的淀粉样特征，允许蛋白质采用折叠结构并自组装 纳米带（Amel-NR）引导矿物带的生长。根据这些数据，一种新的搪瓷模型 生物矿化作用是通过酶促裂解激活矿化过程， 已提出通过基质金属蛋白酶-20（MMP 20）诱导釉原蛋白，并将在本研究中进一步评估。 应用程序.迄今为止，我们已经表明，去除亲水性C-末端结构域允许酸性 聚合物与Amel-NR相互作用，从而引发无定形磷酸钙（ACP）的沉积， 层.随后，ACP转变为约15-20 nm的带状矿物形式的结晶磷灰石 宽，遵循Amel-NR的形态。生物矿化的顺序过程， 我们的体外模型与组织矿化的生物学事件相关， 生物矿化不仅对牙釉质有效，而且对其他硬组织也有效。这些概念包括：a）生物矿化是 由蛋白水解调节; B）存在载体蛋白，其充当过程导向剂并递送 c）载体-蛋白质相互作用产生无定形矿物离子 沉积到蛋白质框架上; d）有机相的超分子结构引导相 通过定向结晶转变成确定的晶体习性。 在继续以前的研究，我们建议确定DEM的组成部分，是至关重要的 与蛋白质纳米带结合的结晶磷灰石纳米纤维的模板化生长。通过确定 在近原子分辨率的Amel-NR的三维结构中，将进一步研究 与釉质形成的关键分子和结构机制有关。最终我们 计划利用Amel-NRs的独特能力来指导磷灰石的纤维生长和合成纳米材料 通过在微米和纳米长度尺度上的分级设计。

Enamel is the only epithelial derived tissue that mineralizes. It develops in an extracellular matrix secreted by highly specialized epithelial cells, the ameloblasts, which synthesizes a host of specific matrix proteins with little homology to any other known proteins. Amelogenin is by far the largest constituent of the developing enamel matrix (DEM) comprising ~90% of all secreted protein. Amelogenin’s primary structure encodes a series of critical functions of the DEM that ultimately allow for control over the uniaxial growth of apatite nanofibers and their three-dimensional organization into a stiff, hard and fracture-resistant tissue optimized for mastication and integration with the underlying dentin. Previously, we have demonstrated the biological significance of the amyloid-like character of amelogenin which allows the protein to adopt ß-sheet structure and to self-assemble into nanoribbons (Amel-NR) that guide the growth of mineral ribbons. Based on this data, a new model of enamel biomineralization founded on the activation of the mineralization process by the enzymatic cleavage of amelogenin by matrix metalloprotease-20 (MMP20) has been proposed and will be further evaluated in this application. We have hitherto shown, that removal of the hydrophilic C-terminal domain allowed an acidic polymer to interact with Amel-NRs thereby initiating the deposition of an amorphous calcium phosphate (ACP) layer. Subsequently, ACP transformed into crystalline apatite in the form of ribbon-like mineral about 15-20 nm wide that followed the morphology of the Amel-NRs. The sequential process of biomineralization observed in our in vitro model correlates with biological events of tissue mineralization and reinforces emerging concepts of biomineralization not only valid to enamel but other hard tissues. Such concepts include: a) biomineralization is regulated by proteolysis; b) presence of a carrier-protein that acts as a process-directing agent and delivers mineral ions to a self-assembled protein framework; c) carrier-protein interactions produce amorphous mineral deposits onto the protein framework; d) the supramolecular structure of the organic phase directs the phase transformation into defined crystal habits by oriented crystallization. In continuation of previous studies, we propose to identify constituents of the DEM that are critical for the templated growth of crystalline apatite nanofibers in association with the protein nanoribbons. By determining the three-dimensional structure of Amel-NRs at near-atomic resolution, further functional domains will be identified and associated with critical molecular and structural mechanisms in enamel formation. Ultimately, we plan to use the unique ability of Amel-NRs to direct the fibrous growth of apatite and synthesize nanomaterials through hierarchical design at the micro- and nanometer length scale.