Amelogenin Nanoribbons In Enamel Development And Engineering

牙釉质是唯一矿化的上皮组织。它在一种细胞外基质中发育，由 高度特化的上皮细胞，成釉细胞，它合成了一系列特殊的基质蛋白，几乎没有 与任何其他已知蛋白质同源。釉原蛋白是发育中的牙釉质中最大的成分。 基质(DEM)约占所有分泌蛋白质的90%。釉原蛋白的一级结构编码了一系列关键的 DEM的功能，最终允许控制磷灰石纳米纤维的单轴生长及其 三维组织成为坚硬、坚硬和抗骨折的组织，优化用于咀嚼和 与底层牙本质结合。在此之前，我们已经证明了该基因的生物学意义 釉原蛋白具有类淀粉样蛋白的特性，它允许蛋白质采用？片状结构并自组装 形成纳米带(AMEL-NR)，用于指导矿物带的生长。在此基础上，提出了一种新的釉质模型 生物矿化建立在酶促裂解矿化过程的基础上 基质金属蛋白酶-20(MMP20)的釉原蛋白已被提出，并将在本研究中得到进一步的评价 申请。到目前为止，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-NRS相互作用从而引发无定形磷酸钙(ACP)的沉积 一层。随后，ACP转变为晶态磷灰石，呈带状矿物形式，约为15-20 nm。 这与AMEL-NRS的形态相似。观察到的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，并加强了新兴的 生物矿化不仅适用于牙釉质，也适用于其他硬组织。这些概念包括：a)生物矿化是 受蛋白质降解调节；b)存在作为过程引导剂的载体蛋白质，并提供 矿物质离子到自组装的蛋白质骨架；c)载体与蛋白质的相互作用产生无定形矿物 沉积在蛋白质骨架上；d)有机相的超分子结构指导相 通过定向结晶转变成规定的结晶习性。 在以往研究的基础上，我们建议确定数字高程模型中对 晶体磷灰石纳米纤维与蛋白质纳米带结合的模板生长。通过确定 在近原子分辨率下AMEL-NRS的三维结构，进一步的功能域将是 确定并与牙釉质形成中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 通过微米和纳米尺度的分层设计。

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.