UDP-Glc:glycoprotein glucosyltransferase recognizes structured and solvent accessible hydrophobic patches in molten globule-like folding intermediates
UDP-Glc:glycoprotein glucosyltransferase recognizes structured and solvent accessible hydrophobic patches in molten globule-like folding intermediates
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DOI：
10.1073/pnas.262661199
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发表时间：
2003-01-07
影响因子：
11.1
通讯作者：
Parodi, AJ
中科院分区：
文献类型：
--
作者：
Caramelo, JJ;Castro, OA;Parodi, AJ
细胞中的蛋白质折叠涉及不同分子伴侣和折叠促进酶的作用。在内质网(ER)中，糖蛋白的折叠状态受到葡萄糖转移酶(GT)的严格控制，GT产生内质网凝集素(Calnexin/calreticrin，CNX/CRT)识别的单糖化结构。GT作为折叠传感器是因为它只对错误折叠或部分折叠的糖蛋白进行糖基化。然而，这种识别过程背后的分子机制在很大程度上仍不清楚。在本文中，我们使用一个单一结构域模型蛋白质来探索GT识别的结构决定因素。为此，我们使用了一系列来自胰凝乳酶抑制物-2的化学糖基化蛋白作为GT底物。对表现出较高葡萄糖受体能力的物种的结构特征表明，GT识别熔融的球状构象中模仿新生糖蛋白中间折叠阶段的溶剂可及的疏水斑块。进一步证实，Bip(结合蛋白，热休克蛋白70家族的伴侣蛋白)优先识别具有延长构象的新糖蛋白，从而为体内观察到的Bip-CNX/CRT与折叠糖蛋白的顺序相互作用提供了分子基础。
Protein folding in the cell involves the action of different molecular chaperones and folding-facilitating enzymes. In the endoplasmic reticulum (ER), the folding status of glycoproteins is stringently controlled by a glucosyltranferase enzyme (GT) that creates monoglucosylated structures recognized by ER resident lectins (calnexin/calreticulin, CNX/CRT). GT serves as a folding sensor because it only glucosylates misfolded or partly folded glycoproteins. Nevertheless, the molecular mechanism behind this recognition process remains largely unknown. In this paper we explore the structural determinants for GT recognition by using a single domain model protein. For this purpose we used a family of chemically glycosylated proteins derived from chymotrypsin inhibitor-2 as GT substrates. Structural characterization of species showing higher glucose acceptor capacity suggests that GT recognizes solvent accessible hydrophobic patches in molten globule-like conformers mimicking intermediate folding stages of nascent glycoproteins. It was further confirmed that BiP(binding protein, a chaperone of the heat shock protein 70 family) preferentially recognized neoglycoproteins displaying extended conformations, thus providing a molecular rationale for the sequential BiP-CNX/CRT interaction with folding glycoproteins observed in vivo.