Department of Biomedical Sciences, National Chung Cheng University, 168 University Road, Min-Hsiung Chia-Yi 62102, Taiwan.
Int J Mol Sci. 2021 Feb 11;22(4):1800. doi: 10.3390/ijms22041800.
Misfolding of prion protein (PrP) into amyloid aggregates is the central feature of prion diseases. PrP has an amyloidogenic C-terminal domain with three α-helices and a flexible tail in the N-terminal domain in which multiple octapeptide repeats are present in most mammals. The role of the octapeptides in prion diseases has previously been underestimated because the octapeptides are not located in the amyloidogenic domain. Correlation between the number of octapeptide repeats and age of onset suggests the critical role of octapeptide repeats in prion diseases. In this study, we have investigated four PrP variants without any octapeptides and with 1, 5 and 8 octapeptide repeats. From the comparison of the protein structure and the thermal stability of these proteins, as well as the characterization of amyloids converted from these PrP variants, we found that octapeptide repeats affect both folding and misfolding of PrP creating amyloid fibrils with distinct structures. Deletion of octapeptides forms fewer twisted fibrils and weakens the cytotoxicity. Insertion of octapeptides enhances the formation of typical silk-like fibrils but it does not increase the cytotoxicity. There might be some threshold effect and increasing the number of peptides beyond a certain limit has no further effect on the cell viability, though the reasons are unclear at this stage. Overall, the results of this study elucidate the molecular mechanism of octapeptides at the onset of prion diseases.
朊病毒蛋白（PrP）错误折叠成淀粉样蛋白聚集体是朊病毒病的核心特征。PrP 具有一个具有三个α螺旋和一个在 N 端结构域中灵活的尾部的淀粉样蛋白源性 C 末端结构域，其中大多数哺乳动物中存在多个八肽重复。以前，由于八肽不位于淀粉样蛋白源性结构域中，因此低估了八肽在朊病毒病中的作用。八肽重复的数量与发病年龄之间的相关性表明，八肽重复在朊病毒病中起着关键作用。在这项研究中，我们研究了四个没有任何八肽且具有 1、5 和 8 个八肽重复的 PrP 变体。通过比较这些蛋白质的结构和热稳定性，以及这些 PrP 变体转化为的淀粉样蛋白的特征，我们发现八肽重复影响 PrP 的折叠和错误折叠，从而形成具有不同结构的淀粉样纤维。八肽的缺失形成较少扭曲的纤维并减弱细胞毒性。插入八肽增强了典型丝素样纤维的形成，但不会增加细胞毒性。可能存在某种阈值效应，即在超过一定限制后增加肽的数量对细胞活力没有进一步的影响，尽管在现阶段原因尚不清楚。总的来说，这项研究阐明了朊病毒病发病机制中八肽的分子机制。
