Kaneko K, Zulianello L, Scott M, Cooper C M, Wallace A C, James T L, Cohen F E, Prusiner S B
Department of Neurology, University of California, San Francisco, CA 94143, USA.
Proc Natl Acad Sci U S A. 1997 Sep 16;94(19):10069-74. doi: 10.1073/pnas.94.19.10069.
Studies on the transmission of human (Hu) prions to transgenic (Tg) mice suggested that another molecule provisionally designated protein X participates in the formation of nascent scrapie isoform of prion protein (PrPSc). We report the identification of the site at which protein X binds to the cellular isoform of PrP (PrPC) using scrapie-infected mouse (Mo) neuroblastoma cells transfected with chimeric Hu/MoPrP genes even though protein X has not yet been isolated. Substitution of a Hu residue at position 214 or 218 prevented PrPSc formation. The side chains of these residues protrude from the same surface of the C-terminal alpha-helix and form a discontinuous epitope with residues 167 and 171 in an adjacent loop. Substitution of a basic residue at positions 167, 171, or 218 also prevented PrPSc formation: at a mechanistic level, these mutant PrPs appear to act as "dominant negatives" by binding protein X and rendering it unavailable for prion propagation. Our findings seem to explain the protective effects of basic polymorphic residues in PrP of humans and sheep and suggest therapeutic and prophylactic approaches to prion diseases.
关于人类（Hu）朊病毒向转基因（Tg）小鼠传播的研究表明，另一种暂称为蛋白X的分子参与了朊病毒蛋白（PrPSc）新生瘙痒病异构体的形成。我们报告了利用转染了嵌合Hu/MoPrP基因的瘙痒病感染小鼠（Mo）神经母细胞瘤细胞，鉴定蛋白X与PrP细胞异构体（PrPC）结合位点的情况，尽管蛋白X尚未分离出来。在第214或218位替换一个Hu残基可阻止PrPSc的形成。这些残基的侧链从C端α螺旋的同一表面突出，并与相邻环中的第167和171位残基形成一个不连续表位。在第167、171或218位替换一个碱性残基也可阻止PrPSc的形成：在机制层面，这些突变型PrP似乎通过结合蛋白X并使其无法用于朊病毒传播而起到“显性负性”作用。我们的发现似乎解释了人类和绵羊PrP中碱性多态性残基的保护作用，并提示了针对朊病毒疾病的治疗和预防方法。
