DeMarco Mari L, Daggett Valerie
Department of Medicinal Chemistry, Biomolecular Structure and Design Program, University of Washington, Seattle, Washington 98195-7610, USA.
Biochemistry. 2007 Mar 20;46(11):3045-54. doi: 10.1021/bi0619066. Epub 2007 Feb 22.
Conformational changes in the prion protein cause transmissible spongiform encephalopathies, also referred to as prion diseases. In its native state, the prion protein is innocuous (PrPC), but it can misfold into a neurotoxic and infectious isoform (PrPSc). The full-length cellular form of the prion protein consists of residues 23-230, with over half of the sequence belonging to the unstructured N-terminal domain and the remaining residues forming a small globular domain. During misfolding and aggregation, portions of both the structured and unstructured domains are incorporated into the aggregates. After limited proteolysis by proteinase K, the most abundant fragment from brain-derived prion fibrils is a 141-residue fragment composed of residues 90-230. Here we describe simulations of this fragment of the human prion protein at low pH, which triggers misfolding, and at neutral pH as a control. The simulations, in agreement with experiment, show that this biologically and pathologically relevant prion construct is stable and native-like at neutral pH. In contrast, at low pH the prion protein is destabilized via disruption of critical long-range salt bridges. In one of the low pH simulations this destabilization resulted in a conformational transition to a PrPSc-like isoform consistent with our previous simulations of a smaller construct.
朊病毒蛋白的构象变化会导致传染性海绵状脑病，也被称为朊病毒疾病。在其天然状态下，朊病毒蛋白是无害的（PrPC），但它可以错误折叠成一种神经毒性和传染性的异构体（PrPSc）。朊病毒蛋白的全长细胞形式由23 - 230位氨基酸残基组成，其中超过一半的序列属于无结构的N端结构域，其余残基形成一个小的球状结构域。在错误折叠和聚集过程中，结构化和非结构化结构域的部分都会被纳入聚集体中。经蛋白酶K有限水解后，脑源性朊病毒纤维中最丰富的片段是一个由90 - 230位氨基酸残基组成的141个残基的片段。在这里，我们描述了在低pH值（会引发错误折叠）和中性pH值（作为对照）条件下对人朊病毒蛋白这一片段的模拟。与实验结果一致，模拟结果表明，这种在生物学和病理学上相关的朊病毒构建体在中性pH值下是稳定的且类似天然状态。相比之下，在低pH值下，朊病毒蛋白会因关键的长程盐桥被破坏而变得不稳定。在一次低pH值模拟中，这种不稳定导致了构象转变为一种类似PrPSc的异构体，这与我们之前对一个较小构建体的模拟结果一致。
