James T L, Liu H, Ulyanov N B, Farr-Jones S, Zhang H, Donne D G, Kaneko K, Groth D, Mehlhorn I, Prusiner S B, Cohen F E
Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94143, USA.
Proc Natl Acad Sci U S A. 1997 Sep 16;94(19):10086-91. doi: 10.1073/pnas.94.19.10086.
The scrapie prion protein (PrPSc) is the major, and possibly the only, component of the infectious prion; it is generated from the cellular isoform (PrPC) by a conformational change. N-terminal truncation of PrPSc by limited proteolysis produces a protein of approximately 142 residues designated PrP 27-30, which retains infectivity. A recombinant protein (rPrP) corresponding to Syrian hamster PrP 27-30 was expressed in Escherichia coli and purified. After refolding rPrP into an alpha-helical form resembling PrPC, the structure was solved by multidimensional heteronuclear NMR, revealing many structural features of rPrP that were not found in two shorter PrP fragments studied previously. Extensive side-chain interactions for residues 113-125 characterize a hydrophobic cluster, which packs against an irregular beta-sheet, whereas residues 90-112 exhibit little defined structure. Although identifiable secondary structure is largely lacking in the N terminus of rPrP, paradoxically this N terminus increases the amount of secondary structure in the remainder of rPrP. The surface of a long helix (residues 200-227) and a structured loop (residues 165-171) form a discontinuous epitope for binding of a protein that facilitates PrPSc formation. Polymorphic residues within this epitope seem to modulate susceptibility of sheep and humans to prion disease. Conformational heterogeneity of rPrP at the N terminus may be key to the transformation of PrPC into PrPSc, whereas the discontinuous epitope near the C terminus controls this transition.
瘙痒病朊病毒蛋白（PrPSc）是传染性朊病毒的主要成分，可能也是唯一成分；它由细胞异构体（PrPC）通过构象变化产生。通过有限蛋白酶解对PrPSc进行N端截短可产生一种约142个残基的蛋白质，称为PrP 27-30，其保留了传染性。在大肠杆菌中表达并纯化了与叙利亚仓鼠PrP 27-30对应的重组蛋白（rPrP）。将rPrP重折叠成类似PrPC的α-螺旋形式后，通过多维异核核磁共振解析了其结构，揭示了许多在先前研究的两个较短PrP片段中未发现的rPrP结构特征。113-125位残基广泛的侧链相互作用形成了一个疏水簇，该疏水簇与不规则的β-折叠堆积在一起，而90-112位残基几乎没有明确的结构。尽管rPrP的N端在很大程度上缺乏可识别的二级结构，但矛盾的是，这个N端增加了rPrP其余部分的二级结构量。一个长螺旋（200-227位残基）和一个结构化环（165-171位残基）的表面形成了一个不连续表位，用于结合一种促进PrPSc形成的蛋白质。该表位内的多态性残基似乎调节绵羊和人类对朊病毒病的易感性。rPrP在N端的构象异质性可能是PrPC转化为PrPSc的关键，而C端附近的不连续表位控制着这一转变。
