Structural Biology Unit, National Institute of Immunology, New Delhi, India.
PLoS One. 2012;7(9):e43522. doi: 10.1371/journal.pone.0043522. Epub 2012 Sep 4.
Transthyretin (TTR) is a homotetrameric serum and cerebrospinal fluid protein that transports thyroxine (T4) and retinol by binding to retinol binding protein. Rate-limiting tetramer dissociation and rapid monomer misfolding and disassembly of TTR lead to amyloid fibril formation in different tissues causing various amyloid diseases. Based on the current understanding of the pathogenesis of TTR amyloidosis, it is considered that the inhibition of amyloid fibril formation by stabilization of TTR in native tetrameric form is a viable approach for the treatment of TTR amyloidosis.
We have examined interactions of the wtTTR with a series of compounds containing various substitutions at biphenyl ether skeleton and a novel compound, previously evaluated for binding and inhibiting tetramer dissociation, by x-ray crystallographic approach. High resolution crystal structures of five ligands in complex with wtTTR provided snapshots of negatively cooperative binding of ligands in two T4 binding sites besides characterizing their binding orientations, conformations, and interactions with binding site residues. In all complexes, the ligand has better fit and more potent interactions in first T4 site i.e. (AC site) than the second T4 site (BD site). Together, these results suggest that AC site is a preferred ligand binding site and retention of ordered water molecules between the dimer interfaces further stabilizes the tetramer by bridging a hydrogen bond interaction between Ser117 and its symmetric copy.
Novel biphenyl ether based compounds exhibit negative-cooperativity while binding to two T4 sites which suggests that binding of only single ligand molecule is sufficient to inhibit the TTR tetramer dissociation.
转甲状腺素蛋白（TTR）是一种四聚体血清和脑脊液蛋白，通过与视黄醇结合蛋白结合来转运甲状腺素（T4）和视黄醇。TTR 的四聚体解离限速以及单体错误折叠和快速解体导致在不同组织中形成淀粉样纤维，从而引起各种淀粉样变性疾病。基于对 TTR 淀粉样变性发病机制的现有认识，认为通过稳定 TTR 以保持天然四聚体形式来抑制淀粉样纤维形成是治疗 TTR 淀粉样变性的一种可行方法。
我们通过 X 射线晶体学方法研究了 wtTTR 与一系列含联苯醚骨架的化合物以及以前评估过结合和抑制四聚体解离的新型化合物的相互作用。五种配体与 wtTTR 复合物的高分辨率晶体结构提供了配体在两个 T4 结合位点中负协同结合的快照，除了表征其结合取向、构象和与结合位点残基的相互作用外。在所有复合物中，配体在第一个 T4 结合位点（即 AC 位点）中的拟合更好，相互作用更强，而在第二个 T4 结合位点（BD 位点）中的拟合和相互作用较弱。总之，这些结果表明 AC 位点是配体结合的首选位点，并且在二聚体界面之间保留有序水分子通过在 Ser117 和其对称拷贝之间形成氢键相互作用进一步稳定四聚体。
新型联苯醚基化合物在与两个 T4 结合位点结合时表现出负协同性，这表明仅结合单个配体分子就足以抑制 TTR 四聚体解离。
