Calcium is required for folding of newly made subunits of the asialoglycoprotein receptor within the endoplasmic reticulum.
Calcium is required for folding of newly made subunits of the asialoglycoprotein receptor within the endoplasmic reticulum.
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DOI：
10.1016/s0021-9258(18)42340-x
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发表时间：
1992-06
期刊：
影响因子：
--
通讯作者：
H. Lodish;N. Kong;L. Wikström
中科院分区：
文献类型：
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作者：
H. Lodish;N. Kong;L. Wikström
通过解决非还原性十二烷基硫酸钠凝胶上的免疫沉淀，我们已经检测到几个二硫键合中间体在折叠内的内质网的新制作的H1亚基的去唾液酸糖蛋白受体。内质网（ER）中的H1可以通过用二硫苏糖醇处理细胞而部分解折叠，但高尔基体或高尔基体后细胞器中的H1对这种解折叠具有抗性。这定义了H1折叠的后期步骤，其发生在从ER退出之前。无论是用A23187还是毒胡萝卜素处理，消耗内质网中的钙，对新产生的白蛋白的折叠或分泌没有影响，但完全阻断了ER中H1的成熟。在用A23187或毒胡萝卜素处理的细胞中没有形成H1折叠中的ER中间体，表明H1折叠中的至少早期步骤需要ER腔中的高Ca2+浓度。通过交联实验判断，H1二聚体和三聚体的形成发生在肽链生物合成后，单体折叠之前，并且通常发生在ER Ca2+减少且单体从未正确折叠的细胞中。钙是必不可少的去唾液酸糖蛋白受体结合半乳糖，我们的研究结果表明，Ca2+也是必不可少的受体多肽折叠在ER。
By resolving immunoprecipitates on nonreducing sodium dodecyl sulfate gels, we have detected several disulfide-bonded intermediates in folding within the endoplasmic reticulum of newly made H1 subunits of the asialoglycoprotein receptor. H1 in the endoplasmic reticulum (ER) can be partially unfolded by treatment of cells with dithiothreitol, but H1 in Golgi or post-Golgi organelles is resistant to such unfolding. This defines a late step in H1 folding that occurs just prior to exit from the ER. Depletion of calcium from the endoplasmic reticulum, either by treatment with A23187 or thapsigargin, has no effect on folding or secretion of newly made albumin, but totally blocks H1 maturation from the ER. No ER intermediates in H1 folding are formed in cells treated with A23187 or thapsigargin, indicating that at least an early step in H1 folding requires a high Ca2+ concentration in the ER lumen. As judged by cross-linking experiments, formation of H1 dimers and trimers occurs immediately after biosynthesis of the peptide chain, before monomer folding, and occurs normally in cells in which ER Ca2+ is reduced and where the monomer never folds properly. Calcium is essential for the asialoglycoprotein receptor to bind galactose, and our results suggest that Ca2+ is also essential for the receptor polypeptides to fold in the ER.