So Masatomo, Hata Yasuko, Naiki Hironobu, Goto Yuji
Institute for Protein Research, Osaka University, Osaka, 565-0871, Japan.
Faculty of Medical Sciences, University of Fukui, Fukui, 910-1193, Japan.
Protein Sci. 2017 May;26(5):1024-1036. doi: 10.1002/pro.3149. Epub 2017 Mar 12.
Amyloid fibrils are fibrillar deposits of denatured proteins associated with amyloidosis and are formed by a nucleation and growth mechanism. We revisited an alternative and classical view of amyloid fibrillation: amyloid fibrils are crystal-like precipitates of denatured proteins formed above solubility upon breaking supersaturation. Various additives accelerate and then inhibit amyloid fibrillation in a concentration-dependent manner, suggesting that the combined effects of stabilizing and destabilizing forces affect fibrillation. Heparin, a glycosaminoglycan and anticoagulant, is an accelerator of fibrillation for various amyloidogenic proteins. By using β -microglobulin, a protein responsible for dialysis-related amyloidosis, we herein examined the effects of various concentrations of heparin on fibrillation at pH 2. In contrast to previous studies that focused on accelerating effects, higher concentrations of heparin inhibited fibrillation, and this was accompanied by amorphous aggregation. The two-step effects of acceleration and inhibition were similar to those observed for various salts. The results indicate that the anion effects caused by sulfate groups are one of the dominant factors influencing heparin-dependent fibrillation, although the exact structures of fibrils and amorphous aggregates might differ between those formed by simple salts and matrix-forming heparin. We propose that a conformational phase diagram, accommodating crystal-like amyloid fibrils and glass-like amorphous aggregates, is important for understanding the effects of various additives.
淀粉样纤维是与淀粉样变性相关的变性蛋白质的纤维状沉积物，由成核和生长机制形成。我们重新审视了淀粉样纤维形成的一种传统观点：淀粉样纤维是变性蛋白质在过饱和状态被打破后，在溶解度以上形成的类晶体沉淀。各种添加剂以浓度依赖的方式加速然后抑制淀粉样纤维形成，这表明稳定和不稳定力量的综合作用影响纤维形成。肝素是一种糖胺聚糖和抗凝剂，是多种淀粉样蛋白纤维形成的促进剂。通过使用与透析相关的淀粉样变性有关的蛋白质β-微球蛋白，我们在此研究了不同浓度的肝素在pH 2时对纤维形成的影响。与之前专注于促进作用的研究不同，较高浓度的肝素抑制了纤维形成，并伴有无定形聚集。促进和抑制的两步效应与各种盐所观察到的相似。结果表明，硫酸根引起的阴离子效应是影响肝素依赖性纤维形成的主要因素之一，尽管由简单盐类形成的纤维和形成基质的肝素所形成的无定形聚集体的确切结构可能有所不同。我们提出，一个容纳类晶体淀粉样纤维和玻璃状无定形聚集体的构象相图，对于理解各种添加剂的作用很重要。
