Building a prion? In a model of prion formation, misshapen PrP proteins (red) stack up into amyloid fibrils.
1997年，美国加利福尼亚大学的神经病学和病毒学教授S.Prusiner由于发现了羊瘙痒病的致病因子是朊病毒（prion），以及提出了疯牛病、Creutz-feldt-Jakob氏病、Kuru病等脑退化性疾病是由朊病毒引起的理论，而获得了诺贝尔医学奖。然而朊病毒究竟是一种传染性因子，还是由正常基因突变形成的结构异常的蛋白质，至今仍处于争论之中。
其中“朊蛋白假说”提出，折叠有误的蛋白（朊蛋白）是导致比如人类克雅氏病和疯牛病等疾病的传染介质。假说的要点是朊蛋白独立行动破坏脑组织，和其他感染介质一样传播自身。研究人员试图将合成的朊蛋白注入小鼠来证明这一假说，合成朊蛋白消除了其已经带有其他病原体的可能性，但这些试验一直不成功。
在7月30日出版的《科学》杂志上，加利福尼亚大学的Giuseppe Legname和来自美国和德国的同事在大肠杆菌（Escherichia coli ）中合成了朊蛋白，他们将蛋白纯化，将其错误地折叠成淀粉体(amyloid)，然后注入转基因小鼠。他们发现，初期，没有任何症状，但是，在注入朊蛋白380到660天后，小鼠出现大脑疾病的症状。研究人员取出生病小鼠的脑物质再注入给其他小鼠，这些小鼠在90到150天后也出现朊蛋白疾病症状。这些合成的朊蛋白看起来不同于其他已知的朊蛋白，排除了其注入只是激活了其他潜伏期朊蛋白的可能性。
这一发现填补了“朊蛋白假说”的空白，但是，因此说，有关prion的争论将因此而终结，还为时过早。
Synthetic Mammalian Prions
Recombinant mouse prion protein (recMoPrP) produced in Escherichia coli was polymerized into amyloid fibrils that represent a subset of ß sheet–rich structures. Fibrils consisting of recMoPrP(89–230) were inoculated intracerebrally into transgenic (Tg) mice expressing MoPrP(89–231). The mice developed neurologic dysfunction between 380 and 660 days after inoculation. Brain extracts showed protease-resistant PrP by Western blotting; these extracts transmitted disease to wild-type FVB mice and Tg mice overexpressing PrP, with incubation times of 150 and 90 days, respectively. Neuropathological findings suggest that a novel prion strain was created. Our results provide compelling evidence that prions are infectious proteins.
Fig. 2. The distinguishing neuropathological features of unseeded recPrP amyloid (A and B), seeded recPrP amyloid (C and D), and RML prions (E and F) in the pons of Tg9949 mice. Left column: hematoxylin and eosin (H&E) stain (scale bar, 50 µm); right column: immunohistochemistry of PrPSc by the hydrated autoclaving method using the PrP-specific HuM-R2 monoclonal antibody fragment (43) (scale bar, 25 µm).
Fig. 4. Comparison of neuropathological changes in the pons associated with inoculation of seeded recPrP preparations into Tg9949 mice (A to C) and of MoSP1 (prions derived from clinically ill Tg9949 mice inoculated with seeded recPrP amyloid) inoculated into FVB mice (D to F). Both passages show the neurohistological characteristics of a prion disease: vacuoles (spongiform degeneration) shown by H&E staining (left); reactive astrocytic gliosis shown by glial fibrillary acidic protein immunohistochemistry (center); and accumulation of PrPSc visualized by hydrated autoclaving immunohistochemistry with HuM-R2 monoclonal antibody (right). Scale bars, 50 µm [(A), (B), (D), (E)], 25 µm [(C) and (F)].
