Gabizon R, McKinley M P, Groth D, Westaway D, DeArmond S J, Carlson G A, Prusiner S B
Department of Neurology, University of California, San Francisco 94143.
Prog Clin Biol Res. 1989;317:583-600.
The scrapie agent causes a degenerative neurologic disease and can be transmitted to laboratory rodents. The unusual properties of the scrapie agent prompted introduction of the term prion in order to distinguish this class of novel pathogens from viruses and viroids. The scrapie prion protein (PrPSc) is the only component of the infectious scrapie prion identified, to date. Although many biochemical and genetic lines of evidence argue that PrPSc is a major component of the infectious particle, the most convincing data is derived from immunoaffinity purification studies. Limited proteinase K digestion of hamster brain PrPSc produced PrP 27-30. After dispersion of brain microsomes isolated from scrapie-infected hamsters into detergent-lipid-protein complexes (DLPC), copurification of PrPSc and scrapie infectivity was obtained with PrP 27-30 monoclonal antibody affinity columns. PrPSc was enriched approximately 5700-fold with respect to total brain protein while scrapie prion infectivity was enriched approximately -4000-fold. The ratio of prion titer to PrPSc remained constant throughout purification. Heterologous monoclonal antibody columns failed to bind either PrpSc or scrapie infectivity. Polyclonal rabbit PrP antiserum raised against sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE)-purified PrP 27-30 reduced scrapie infectivity dispersed into DLPC by a factor of 100. Our findings represent the first direct immunologic and chromatographic demonstrations of a relationship between PrPSc and prion infectivity as well as providing additional support for the contention that PrPSc is a major component of the infectious scrapie particle. While these results and those of other studies establish that PrPSc is a component of the infectious prion, the possibility of a second component such as a small nucleic acid which might be required for infection must still be considered. PrPSc is encoded by a single copy cellular gene and not by a hypothetical-nucleic acid within purified prion preparations. Normal, uninfected cells express the cellular prion protein (PrPC). Both PrPSc and PrPC appear to be translated from the same 2.1-kb mRNA. The N-terminal amino acid sequences of hamster PrPC and PrPSc are identical; both correspond to that predicted by the translated prion protein (PrP) gene sequence. While the chemical difference between PrPC and PrPSc remains unknown, the organization of the PrP gene argues that it results from a posttranslational event. The mouse PrP gene is on chromosome 2 and is linked to a gene controlling the scrapie incubation time (Prn-i).(ABSTRACT TRUNCATED AT 400 WORDS)
羊瘙痒病病原体可引发一种退行性神经疾病，并能传播给实验啮齿动物。羊瘙痒病病原体的异常特性促使了“朊病毒”这一术语的引入，以便将这类新型病原体与病毒和类病毒区分开来。羊瘙痒病朊病毒蛋白（PrPSc）是迄今为止所鉴定出的感染性羊瘙痒病朊病毒的唯一成分。尽管许多生化和遗传学证据表明PrPSc是感染性颗粒的主要成分，但最有说服力的数据来自免疫亲和纯化研究。用蛋白酶K对仓鼠脑PrPSc进行有限消化产生了PrP 27-30。将从感染羊瘙痒病的仓鼠中分离出的脑微粒体分散到去污剂-脂质-蛋白质复合物（DLPC）中后，利用PrP 27-30单克隆抗体亲和柱实现了PrPSc与羊瘙痒病感染性的共纯化。相对于全脑蛋白，PrPSc富集了约5700倍，而羊瘙痒病朊病毒感染性富集了约4000倍。在整个纯化过程中，朊病毒滴度与PrPSc的比值保持恒定。异源单克隆抗体柱未能结合PrpSc或羊瘙痒病感染性。针对十二烷基硫酸钠-聚丙烯酰胺凝胶电泳（SDS-PAGE）纯化的PrP 27-30制备的兔PrP多克隆抗血清使分散到DLPC中的羊瘙痒病感染性降低了100倍。我们的研究结果首次直接从免疫学和色谱学角度证明了PrPSc与朊病毒感染性之间的关系，同时也为PrPSc是感染性羊瘙痒病颗粒的主要成分这一论点提供了更多支持。虽然这些结果以及其他研究结果证实PrPSc是感染性朊病毒的一个成分，但仍必须考虑是否存在第二种成分（如可能是感染所必需的小核酸）的可能性。PrPSc由单拷贝细胞基因编码，而非由纯化的朊病毒制剂中的假设核酸编码。正常未感染细胞表达细胞朊病毒蛋白（PrPC）。PrPSc和PrPC似乎都由相同的2.1-kb mRNA翻译而来。仓鼠PrPC和PrPSc的N端氨基酸序列相同；两者都与翻译后的朊病毒蛋白（PrP）基因序列所预测的一致。虽然PrPC和PrPSc之间的化学差异尚不清楚，但PrP基因的结构表明这是一个翻译后事件导致的。小鼠PrP基因位于2号染色体上，并与一个控制羊瘙痒病潜伏期的基因（Prn-i）连锁。（摘要截选至400词）
