ERp57 is involved in the oxidative folding of the low-density lipoprotein receptor in the endoplasmic reticulum
ERp57 is involved in the oxidative folding of the low-density lipoprotein receptor in the endoplasmic reticulum
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ERp57 参与内质网低密度脂蛋白受体的氧化折叠
DOI：
10.1093/biohorizons/hzp003
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发表时间：
2009
影响因子：
--
通讯作者：
Berry J
中科院分区：
文献类型：
--
作者：
Berry J
这项工作探索了硫醇氧化还原酶ERp57在低密度脂蛋白受体(LDL-R)翻译后氧化折叠中的作用，低密度脂蛋白受体是一种细胞表面糖蛋白，负责从血浆中摄取胆固醇。低密度脂蛋白受体为分析内质网中多结构域蛋白质的氧化折叠提供了一个通用模型；然而，它的折叠途径也是特别感兴趣的，因为在家族性高胆固醇血症中，蛋白质富含二硫键的结构域有很高比例的突变是显而易见的。以往的研究表明，低密度脂蛋白受体在折叠过程中会形成一系列不同的非天然二硫化物中间体，这些中间体在天然构象分泌之前被广泛异构化。此外，ERp57被认为在体内主要被还原，并与低密度脂蛋白-R形成混合的二硫化物。在这项研究中，在防止二硫化物形成的条件下，在野生型细胞和缺乏硫醇氧化还原酶ERp57的细胞中都表达了低密度脂蛋白-R。然后让蛋白质在氧化条件下折叠，并在不同的时间点采集样本。比较了基因敲除细胞和野生型细胞折叠中间产物的电泳率。结果表明，两种细胞类型之间形成不同的二硫化物中间体，特别是在折叠的早期阶段。ERp57的一个突变形式，能够形成但不能分解混合的二硫化物，也被发现与低密度脂蛋白-R形成混合的二硫化物。这些结果表明ERp57在低密度脂蛋白-R的氧化折叠过程中是必需的，也表明非天然的二硫化物中间体可能是多结构域蛋白质折叠过程的中心。
This work explores the role of the thiol-oxidoreductase ERp57 in the post-translational oxidative folding of the low-density lipoprotein receptor (LDL-R), a cell-surface glycoprotein responsible for the uptake of cholesterol from plasma. The LDL-R provides a general model to analyse oxidative folding of multi-domain proteins in the endoplasmic reticulum; yet its folding pathway is also of specific interest as a high proportion of mutations in disulphide-rich domains of the protein are evident in familial hypercholesterolemia. Previous studies have suggested that the LDL-R forms a set of distinct non-native disulphide intermediates during folding, which are extensively isomerized prior to secretion of the native conformer. In addition, ERp57 has been suggested to be predominantly reducedin vivoand to form a mixed disulphide with the LDL-R. In this study, the LDL-R was expressed in both wild-type cells and those lacking the thiol-oxidoreductase ERp57 under conditions that prevent disulphide formation. The protein was then allowed to fold under oxidizing conditions, and samples taken at various timepoints. The electrophoretic mobility of folding intermediates from knock-out cells was compared with that of wild-type cells. The results show that dissimilar disulphide intermediates form between the two cell types, particularly during early stages of folding. A mutant form of ERp57, able to form but unable to resolve mixed disulphides, was also found to form mixed disulphides with the LDL-R. The results signify the requirement for ERp57 in oxidative folding of the LDL-R and also suggest that non-native disulphide intermediates may be central to the process of multi-domain protein folding.
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