Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Ontario, Canada.
Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Ontario, Canada
J R Soc Interface. 2018 Oct 17;15(147):20180269. doi: 10.1098/rsif.2018.0269.
Formation of hydroxyapatite (HAP) within collagen fibrils, as found in bone, dentine and cementum, is thought to be mediated by proteins rich in aspartate (Asp) and glutamate such as osteopontin and bone sialoprotein, respectively. Indeed polyaspartate (pAsp), a homopolymer analogue of such proteins, has been shown to induce intrafibrillar mineralization of collagen from solutions of calcium and phosphate that are supersaturated with respect to HAP. To elucidate the role of pAsp in mineralization of collagen, we explored the effect of pAsp chain length on HAP deposition in demineralized mouse periodontal tissue sections. Through characterization of both tissue sections and mineralizing solution, we show that chain length contributes to the effectiveness of pAsp in mediating intrafibrillar mineralization. This function appears to be associated with inhibition of otherwise kinetically favoured crystallization in the bulk solution, which allows for intrafibrillar crystallization, though this does not preclude the possibility of a more active role for pAsp in addition. Inhibition of crystallization in solution by pAsp occurs by slowing the growth of amorphous calcium phosphate and stabilization of this phase, rather than by sequestration of Ca ions. These results suggest that the length of Asp-rich sequences of mineralizing proteins may be essential to their function, and could also be useful in optimization of mineralized tissue replacement synthesis.
在骨、牙本质和牙骨质中发现的胶原原纤维内羟基磷灰石（HAP）的形成被认为是由富含天冬氨酸（Asp）和谷氨酸的蛋白质介导的，分别为骨桥蛋白和骨涎蛋白。事实上，多聚天冬氨酸（pAsp）作为此类蛋白质的同聚物类似物，已被证明可诱导钙和磷酸盐溶液中胶原的纤维内矿化，这些溶液相对于 HAP 是过饱和的。为了阐明 pAsp 在胶原矿化中的作用，我们探索了 pAsp 链长对脱矿小鼠牙周组织切片中 HAP 沉积的影响。通过对组织切片和矿化溶液的特性进行研究，我们表明链长有助于 pAsp 在介导纤维内矿化中的有效性。该功能似乎与抑制否则在体相溶液中动力学有利的结晶有关，这允许纤维内结晶，尽管这不能排除 pAsp 除了具有更积极的作用之外的可能性。pAsp 通过减缓无定形磷酸钙的生长和稳定该相来抑制溶液中的结晶，而不是通过螯合 Ca 离子来抑制。这些结果表明，矿化蛋白中天冬氨酸丰富序列的长度可能对其功能至关重要，并且在优化矿化组织替代合成方面也可能有用。
