Castro-Rodrigues Artur F, Gales Luís, Saraiva Maria J, Damas Ana M
IBMC - Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal.
Acta Crystallogr D Biol Crystallogr. 2011 Dec;67(Pt 12):1035-44. doi: 10.1107/S090744491104491X. Epub 2011 Nov 5.
Human transthyretin (TTR) is a homotetrameric protein that is responsible for the formation of amyloid in patients with familiar amyloidotic polyneuropathy (FAP), familiar amyloidotic cardiomyopathy (FAC) and senile systemic amyloidosis (SSA). Amyloid fibrils are characterized by a cross-β structure. However, details of how TTR monomers are organized to form such an assembly remain unknown. The effect of Zn(2+) in increasing TTR L55P amyloidogenecity has been reported. Crystals of the TTR L55P-Zn(2+) complex were grown under conditions similar to those leading to higher amyloidogenic potential of the variant protein and the three-dimensional structure of the complex was determined by X-ray crystallography. Two different tetrahedral Zn(2+)-binding sites were identified: one cross-links two tetramers, while the other lies at the interface between two monomers in a dimer. The association of monomers involving the two Zn(2+)-binding sites leads to a bidimensional array with a cross-β structure. The formation of this structure and subsequent organization into amyloid fibrils was monitored by fluorescence spectroscopy and electron microscopy. The TTR L55P-Zn(2+) structure offers the first molecular insights into the role of Zn(2+) as a mediator of cross-β-type structure in TTR amyloidosis and the relevance of a Zn(2+)-dependent pathway leading to the production of early amyloidogenic intermediates is discussed.
人转甲状腺素蛋白（TTR）是一种同四聚体蛋白，在家族性淀粉样多发性神经病（FAP）、家族性淀粉样心肌病（FAC）和老年系统性淀粉样变（SSA）患者中，它负责淀粉样蛋白的形成。淀粉样纤维的特征是具有交叉β结构。然而，TTR单体如何组装形成这样的聚集体的细节仍不清楚。已有报道锌离子（Zn(2+)）可增加TTR L55P的淀粉样蛋白生成能力。在与导致变体蛋白具有更高淀粉样蛋白生成潜力的条件相似的情况下，培养了TTR L55P-Zn(2+)复合物的晶体，并通过X射线晶体学确定了该复合物的三维结构。鉴定出两个不同的四面体Zn(2+)结合位点：一个交联两个四聚体，另一个位于二聚体中两个单体之间的界面处。涉及两个Zn(2+)结合位点的单体缔合导致形成具有交叉β结构的二维阵列。通过荧光光谱和电子显微镜监测了这种结构的形成以及随后组装成淀粉样纤维的过程。TTR L55P-Zn(2+)结构首次从分子层面揭示了Zn(2+)作为TTR淀粉样变中交叉β型结构介质的作用，并讨论了Zn(2+)依赖性途径与早期淀粉样蛋白生成中间体产生的相关性。
