Biophysics and Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, USA.
J Mol Biol. 2012 Feb 10;416(1):108-20. doi: 10.1016/j.jmb.2011.12.023. Epub 2011 Dec 17.
Calcitonin is a 32-residue peptide hormone known for its hypocalcemic effect and its inhibition of bone resorption. While calcitonin has been used in therapy for osteoporosis and Paget's disease for decades, human calcitonin (hCT) forms fibrils in aqueous solution that limit its therapeutic application. The molecular mechanism of fiber formation by calcitonin is not well understood. Here, high-resolution structures of hCT at concentrations of 0.3 mM and 1 mM have been investigated using NMR spectroscopy. Comparing the structures of hCT at different concentrations, we discovered that the peptide undergoes a conformational transition from an extended to a β-hairpin structure in the process of molecular association. This conformational transition locates the aromatic side chains of Tyr12 and Phe16 in a favorable way for intermolecular π-π stacking, which is proposed to be a crucial interaction for peptide association and fibrillation. One-dimensional (1)H NMR experiments confirm that oligomerization of hCT accompanies the conformational transition at 1 mM concentration. The effect of the polyphenol epigallocatechin 3-gallate (EGCG) on hCT fibrillation was also investigated by NMR and electron microscopy, which show that EGCG efficiently inhibits fibril formation of hCT by preventing the initial association of hCT before fiber formation. The NMR experiments also indicate that the interaction between aromatic rings of EGCG and the aromatic side chains of the peptide may play an important role in inhibiting fibril formation of hCT.
降钙素是一种 32 个氨基酸残基的肽类激素，以其降血钙作用和抑制骨吸收作用而闻名。虽然降钙素已在骨质疏松症和 Pagets 病的治疗中使用了几十年，但人降钙素（hCT）在水溶液中形成纤维，限制了其治疗应用。降钙素形成纤维的分子机制尚未得到很好的理解。在这里，使用 NMR 光谱研究了浓度为 0.3 mM 和 1 mM 的 hCT 的高分辨率结构。通过比较不同浓度下 hCT 的结构，我们发现该肽在分子缔合过程中经历了从伸展到β发夹结构的构象转变。这种构象转变将 Tyr12 和 Phe16 的芳基侧链定位在有利于分子间π-π堆积的方式，这被认为是肽缔合和纤维化的关键相互作用。一维（1）H NMR 实验证实，hCT 的寡聚化伴随着在 1 mM 浓度下的构象转变。还通过 NMR 和电子显微镜研究了多酚表没食子儿茶素没食子酸酯（EGCG）对 hCT 纤维化的影响，结果表明 EGCG 通过在纤维形成之前阻止 hCT 的初始缔合，有效地抑制 hCT 的纤维形成。NMR 实验还表明，EGCG 的芳环与肽的芳基侧链之间的相互作用可能在抑制 hCT 的纤维形成中起重要作用。
