Moradian-Oldak Janet, Goldberg Michel
Center for Craniofacial Molecular Biology, University of Southern California School of Dentistry, Los Angeles, Calif. 90033, USA.
Cells Tissues Organs. 2005;181(3-4):202-18. doi: 10.1159/000091382.
Tooth enamel is formed in the extracellular space within an organic matrix enriched in amelogenin proteins. Amelogenin nanosphere assembly is a key factor in controlling the oriented and organized growth of enamel apatite crystals. Recently, we have reported the formation of higher ordered structures resulting from organized association and self-orientation of amelogenin nanospheres in vitro. This remarkable hierarchical organization includes self-assembly of amelogenin molecules into subunits of 4-6 nm in diameter followed by their assembly to form nanospheres of 15-25 nm in radii. Chains of >100 nm length are then formed as the result of nanosphere association. These linear arrays of nanospheres assemble to form the microribbons that are hundreds of microns in length, tens of microns in width, and a few microns in thickness. Here, we review the step by step process of amelogenin self-assembly during the formation of microribbon structures in vitro. Assembly properties of selected amelogenins lacking the hydrophilic C terminus will then be reviewed. We will consider amelogenin as a template for the organized growth of crystals in vitro. Finally, we will compare the structures formed in vitro with globular and periodic structures observed earlier, in vivo, by different sample preparation conditions. We propose that the alignment of amelogenin nanospheres into long chains is evident in vivo, and is an important indication for the function of this protein in controlling the oriented and elongated growth of apatite crystals during enamel biomineralization.
牙釉质在富含釉原蛋白的有机基质的细胞外空间中形成。釉原蛋白纳米球组装是控制釉质磷灰石晶体定向和有序生长的关键因素。最近，我们报道了在体外由釉原蛋白纳米球的有组织缔合和自组装形成的更高有序结构。这种显著的层次结构包括釉原蛋白分子自组装成直径为4 - 6纳米的亚基，随后组装形成半径为15 - 25纳米的纳米球。然后，由于纳米球缔合形成长度大于100纳米的链。这些纳米球的线性阵列组装形成长度为数百微米、宽度为数十微米、厚度为几微米的微带。在这里，我们回顾了体外微带结构形成过程中釉原蛋白自组装的逐步过程。然后将综述缺乏亲水性C末端的选定釉原蛋白的组装特性。我们将把釉原蛋白视为体外晶体有序生长的模板。最后，我们将把体外形成的结构与早期在体内通过不同样品制备条件观察到的球状和周期性结构进行比较。我们提出，釉原蛋白纳米球排列成长链在体内是明显的，并且是该蛋白在牙釉质生物矿化过程中控制磷灰石晶体定向和伸长生长功能的重要指示。
