Le Norcy Elvire, Kwak Seo-Young, Allaire Marc, Fratzl Peter, Yamakoshi Yasuo, Simmer James P, Margolis Henry C
Department of Biomineralization, The Forsyth Institute, Cambridge, MA 02142, USA.
Eur J Oral Sci. 2011 Dec;119 Suppl 1(Suppl 1):97-102. doi: 10.1111/j.1600-0722.2011.00900.x.
Amelogenin undergoes self-assembly and plays an essential role in guiding enamel mineral formation. The leucine-rich amelogenin peptide (LRAP) is an alternative splice product of the amelogenin gene and is composed of the N terminus (containing the only phosphate group) and the C terminus of full-length amelogenin. This study was conducted to investigate further the role of phosphorylation in LRAP self-assembly in the presence and absence of calcium using small angle X-ray scattering (SAXS). Consistent with our previous dynamic light-scattering findings for phosphorylated (+P) and non-phosphorylated (-P) LRAP, SAXS analyses revealed radii of gyration (R(g)) for LRAP(-P) (46.3-48.0 Å) that were larger than those for LRAP(+P) (25.0-27.4 Å) at pH 7.4. However, added calcium (up to 2.5 mM) induced significant increases in the R(g) of LRAP(+P) (up to 46.4 Å), while it had relatively little effect on LRAP(-P) particle size. Furthermore, SAXS analyses suggested compact folded structures for LRAP(-P) in the presence and absence of calcium, whereas the conformation of LRAP(+P) changed from an unfolded structure to a more compact structure upon the addition of calcium. We conclude that the single phosphate group in LRAP(+P) induces functionally important conformational changes, suggesting that phosphorylation may also influence amelogenin conformation and protein-mineral interactions during the early stages of amelogenesis.
釉原蛋白会进行自我组装，并在引导牙釉质矿物质形成过程中发挥重要作用。富含亮氨酸的釉原蛋白肽（LRAP）是釉原蛋白基因的一种可变剪接产物，由全长釉原蛋白的N端（含有唯一的磷酸基团）和C端组成。本研究旨在利用小角X射线散射（SAXS）进一步探究在有钙和无钙情况下磷酸化对LRAP自我组装的作用。与我们之前对磷酸化（+P）和非磷酸化（-P）LRAP的动态光散射研究结果一致，SAXS分析显示，在pH 7.4时，LRAP（-P）的回转半径（R(g)）（46.3 - 48.0 Å）大于LRAP（+P）的回转半径（25.0 - 27.4 Å）。然而，添加钙（高达2.5 mM）会导致LRAP（+P）的R(g)显著增加（高达46.4 Å），而对LRAP（-P）的粒径影响相对较小。此外，SAXS分析表明，无论有无钙存在，LRAP（-P）都具有紧密折叠结构，而添加钙后，LRAP（+P）的构象从展开结构变为更紧密的结构。我们得出结论，LRAP（+P）中的单个磷酸基团会诱导功能上重要的构象变化，这表明磷酸化可能也会在釉质形成早期影响釉原蛋白的构象以及蛋白质 - 矿物质相互作用。
