School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China.
State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, Shanghai 200031, China.
Int J Mol Sci. 2020 Apr 22;21(8):2946. doi: 10.3390/ijms21082946.
Tooth enamel is formed in an extracellular environment. Amelogenin, the major component in the protein matrix of tooth enamel during the developing stage, could assemble into high molecular weight structures, regulating enamel formation. However, the molecular structure of amelogenin protein assembly at the functional state is still elusive. In this work, we found that amelogenin is able to induce calcium phosphate minerals into hydroxyapatite (HAP) structure in vitro at pH 6.0. Assessed using X-ray diffraction (XRD) and P solid-state NMR (SSNMR) evidence, the formed HAP mimics natural enamel closely. The structure of amelogenin protein assembly coexisting with the HAP was also studied using atomic force microscopy (AFM), transmission electron microscopy (TEM) and XRD, indicating the β-amyloid structure of the protein. SSNMR was proven to be an important tool in detecting both the rigid and dynamic components of the protein assembly in the sample, and the core sequence EVLTPLKWYQSI was identified as the major segment contributing to the β-sheet secondary structure. Our research suggests an amyloid structure may be an important factor in controlling HAP formation at the right pH conditions with the help of other structural components in the protein assembly.
牙釉质是在细胞外环境中形成的。釉原蛋白是牙釉质发育阶段蛋白基质的主要成分，它可以组装成高分子量结构，调节釉质的形成。然而，釉原蛋白在功能状态下的分子结构仍然难以捉摸。在这项工作中，我们发现釉原蛋白在 pH 值为 6.0 的条件下能够在体外诱导磷酸钙矿化为羟基磷灰石（HAP）结构。使用 X 射线衍射（XRD）和 P 固态核磁共振（SSNMR）证据评估，形成的 HAP 与天然牙釉质非常相似。还使用原子力显微镜（AFM）、透射电子显微镜（TEM）和 XRD 研究了与 HAP 共存的釉原蛋白组装体的结构，表明该蛋白具有β-淀粉样结构。SSNMR 被证明是检测样品中蛋白组装体刚性和动态成分的重要工具，并且确定核心序列 EVLTPLKWYQSI 是形成β-折叠二级结构的主要片段。我们的研究表明，在适当 pH 值条件下，在蛋白组装体的其他结构成分的帮助下，淀粉样结构可能是控制 HAP 形成的一个重要因素。
