Poly-(L-alanine) expansions form core β-sheets that nucleate amyloid assembly
Poly-(L-alanine) expansions form core β-sheets that nucleate amyloid assembly
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DOI：
10.1002/prot.20536
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发表时间：
2005-11-15
影响因子：
2.9
通讯作者：
Kirschner, DA
中科院分区：
文献类型：
--
作者：
Shinchuk, LM;Sharma, D;Kirschner, DA
在成人发病的显性遗传性眼咽肌营养不良症（OPMD）中，多聚腺嘌呤结合蛋白核-1（PABPN 1）中的正常数目10个连续丙氨酸残基扩展到总共11-17个连续丙氨酸残基，导致骨骼肌和下丘脑神经元中核内纤维状包涵体的形成。为了理解均聚长度在导致内含物的蛋白质错误折叠中可能发挥的作用，我们分析了具有3-20个残基的合成聚（（L）-丙氨酸）肽的自组装。我们发现，溶液中的聚丙氨酸（polyAla）组件的构象转变和结构不仅是长度依赖性的，而且还取决于浓度，温度和孵育时间。对于那些特征为n < 8的肽，没有检测到P-折叠复合物，其中n是丙氨酸残基的数目。第二组7 < n < 15的肽显示不同水平的复合物形成，而对于那些n > 15的肽，在任何测试的实验条件下，从单体到β-折叠复合物的相互转化过程都是完全的。与淀粉样蛋白原纤维的典型着色性质不同，聚丙氨酸原纤维不显示硫磺素T的荧光或刚果红的苹果绿双折射;然而，与淀粉样蛋白一样，X射线衍射显示这些原纤维中的肽链垂直于原纤维轴取向（即，在交叉beta协议中）。相邻的β-片层在氢键方向上四分之一交错，使得丙氨酸侧链紧密堆积在片层间空间中。在这种排列中，侧链之间强的货车德瓦尔斯接触可能是大分子纤维状复合物在溶液中在宽的温度（5-85 ℃）和pH（2-10.5）范围内的高稳定性，以及其对变性剂（< 8 M尿素）和蛋白酶（蛋白酶K，胰蛋白酶）的抗性的原因。我们假设，一个类似的稳定的扩展的聚丙氨酸拉伸可以形成一个核心β-片层结构，介导的分子间关联的突变蛋白质成纤维状夹杂物在人类病理。Proteins 2005;61：579-589. (c)2005 Wiley-Liss，Inc.
Expansion to a total of 11-17 sequential alanine residues from the normal number of 10 in the polyadenine-binding protein nuclear-1 (PABPN1) results in formation of intranuclear, fibrillar inclusions in skeletal muscle and hypothalamic neurons in adult-onset, dominantly inherited oculopharyngeal muscular dystrophy (OPMD). To understand the role that homopolymeric length may play in the protein misfolding that leads to the inclusions, we analyzed the self-assembly of synthetic poly-((L)-alanine) peptides having 3-20 residues. We found that the conformational transition and structure of polyalanine (polyAla) assemblies in solution are not only length-dependent but also are determined by concentration, temperature, and incubation time. No P-sheet complex was detected for those peptides characterized by n < 8, where n is number of alanine residues. A second group of peptides with 7 < n < 15 showed varying levels of complex formation, while for those peptides having n > 15, the interconversion process from the monomeric to the beta-sheet complex was complete under any of the tested experimental conditions. Unlike the typical tinctorial properties of amyloid fibrils, polyalanine fibrils did not show fluorescence with thioflavin T or apple-green birefringence with Congo red; however, like amyloid, X-ray diffraction showed that the peptide chains in these fibrils were oriented normal to the fibril axis (i.e., in the cross-beta arrangement). Neighboring beta-sheets are quarter-staggered in the hydrogen-bonding direction such that the alanine side-chains were closely packed in the intersheet space. Strong van der Waals contacts between side-chains in this arrangement likely account for the high stability of the macromolecular fibrillar complex in solution over a wide range of temperature (5-85 degrees C), and pH (2-10.5), and its resistance to denaturant (< 8 M urea) and to proteases (protease K, trypsin). We postulate that a similar stabilization of an expanded polyalanine stretch could form a core beta-sheet structure that mediates the intermolecular association of mutant proteins into fibrillar inclusions in human pathologies. Proteins 2005;61:579-589. (c) 2005 Wiley-Liss, Inc.