Functions of ERp57 in the Folding and Assembly of Major Histocompatibility Complex Class I Molecules*
Functions of ERp57 in the Folding and Assembly of Major Histocompatibility Complex Class I Molecules*
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DOI：
10.1074/jbc.m512073200
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发表时间：
2006-05
影响因子：
4.8
通讯作者：
Yinan Zhang;E. Baig;David B. Williams
中科院分区：
文献类型：
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作者：
Yinan Zhang;E. Baig;David B. Williams
ERp 57是内质网的硫醇氧化还原酶，其似乎通过其与分子伴侣钙连接蛋白和钙网蛋白的缔合而被间接募集至底物。然而，其在活细胞中的功能一直难以证明。在I类组织相容性分子的生物发生过程中，已经检测到ERp 57与游离I类重链相关，并且在稍后阶段，与称为肽加载复合物的大复合物相关。这表明ERp 57参与重链二硫键形成、异构化或还原，以及将肽装载到I类分子上。在这项研究中，我们发现ERp 57确实参与了重链的氧化折叠。通过RNA干扰消除ERp 57延迟了重链二硫键的形成，减缓了重链α3结构域的折叠，并导致I类分子从内质网向高尔基体转运的轻微延迟。相反，重链-β2-微球蛋白结合动力学正常，表明重链和β2 -微球蛋白之间的相互作用不依赖于氧化的α3结构域。同样，肽加载复合物正确组装，并且在ERp 57耗尽后肽加载表现正常。这些研究表明，ERp 57参与体内二硫键形成，但不支持ERp 57在I类分子的肽负载中的作用。有趣的是，另一种硫醇氧化还原酶ERp 72的耗竭对I类生物发生没有可检测的影响，这与ERp 57在该过程中的专门作用一致。
ERp57 is a thiol oxidoreductase of the endoplasmic reticulum that appears to be recruited to substrates indirectly through its association with the molecular chaperones calnexin and calreticulin. However, its functions in living cells have been difficult to demonstrate. During the biogenesis of class I histocompatibility molecules, ERp57 has been detected in association with free class I heavy chains and, at a later stage, with a large complex termed the peptide loading complex. This implicates ERp57 in heavy chain disulfide formation, isomerization, or reduction as well as in the loading of peptides onto class I molecules. In this study, we show that ERp57 does indeed participate in oxidative folding of the heavy chain. Depletion of ERp57 by RNA interference delayed heavy chain disulfide bond formation, slowed folding of the heavy chain α3 domain, and caused slight delays in the transport of class I molecules from the endoplasmic reticulum to the Golgi apparatus. In contrast, heavy chain-β2-microglobulin association kinetics were normal, suggesting that the interaction between heavy chain and β2 -microglobulin does not depend on an oxidized α3 domain. Likewise, the peptide loading complex assembled properly, and peptide loading appeared normal upon depletion of ERp57. These studies demonstrate that ERp57 is involved in disulfide formation in vivo but do not support a role for ERp57 in peptide loading of class I molecules. Interestingly, depletion of another thiol oxidoreductase, ERp72, had no detectable effect on class I biogenesis, consistent with a specialized role for ERp57 in this process.