Stahl N, Baldwin M A, Teplow D B, Hood L, Gibson B W, Burlingame A L, Prusiner S B
Department of Neurology, University of California, San Francisco 94143.
Biochemistry. 1993 Mar 2;32(8):1991-2002. doi: 10.1021/bi00059a016.
The only component of the infectious scrapie prion identified to date is a protein designated PrPSc. A posttranslational process converts the cellular PrP isoform (PrPC) into PrPSc. Denatured PrPSc was digested with endoproteases, and the resulting fragments were isolated by HPLC. By both mass spectrometry and Edman sequencing, the primary structure of PrPSc was found to be the same as that deduced from the PrP gene sequence, arguing that neither RNA editing nor protein splicing feature in the synthesis of PrPSc. Mass spectrometry also was used to search for posttranslational chemical modifications other than the glycosylinositol phospholipid anchor attached to the C-terminus and two Asn-linked oligosaccharides already known to occur on both PrPSc and PrPC. These results contend that PrPSc molecules do not differ from PrPC at the level of an amino acid substitution or a posttranslational chemical modification; however, we cannot eliminate the possibility that a small fraction of PrPSc is modified by an as yet unidentified posttranslational process or that PrPC carries a modification that is removed in the formation of PrPSc. It seems likely that PrPSc differs from PrPC in its secondary and tertiary structure, but the possibility of a tightly bound, disease-specific molecule which purifies with PrPSc must also be considered.
迄今为止，已鉴定出的传染性羊瘙痒病朊病毒的唯一成分是一种名为PrPSc的蛋白质。一种翻译后过程将细胞型PrP异构体（PrPC）转化为PrPSc。用内切蛋白酶消化变性的PrPSc，所得片段通过高效液相色谱法分离。通过质谱分析和埃德曼测序，发现PrPSc的一级结构与从PrP基因序列推导的结构相同，这表明在PrPSc的合成过程中既没有RNA编辑也没有蛋白质剪接特征。质谱分析还用于寻找除了附着在C末端的糖基化肌醇磷脂锚以及已知在PrPSc和PrPC上都存在的两个天冬酰胺连接的寡糖之外的翻译后化学修饰。这些结果表明，PrPSc分子在氨基酸取代或翻译后化学修饰水平上与PrPC没有差异；然而，我们不能排除一小部分PrPSc通过尚未鉴定的翻译后过程进行修饰的可能性，或者PrPC携带在PrPSc形成过程中被去除的修饰的可能性。PrPSc似乎在二级和三级结构上与PrPC不同，但也必须考虑与PrPSc一起纯化的紧密结合的、疾病特异性分子的可能性。
