Assembly and secretion of heavy chains that do not associate posttranslationally with immunoglobulin heavy chain-binding protein.
Assembly and secretion of heavy chains that do not associate posttranslationally with immunoglobulin heavy chain-binding protein.
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DOI：
10.1083/jcb.104.3.761
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发表时间：
1987-03
影响因子：
7.8
通讯作者：
Kearney, J F
中科院分区：
文献类型：
--
作者：
Hendershot, L;Bole, D;Kohler, G;Kearney, J F
重链结合蛋白（BiP）与内质网（ER）中新生的IG重链在后发育期结合，并保持与这些重链的结合，直到它们与轻链组装。重链-BiP复合物可通过针对任一组分的抗体试剂沉淀。为了鉴定重链分子上与BiP相关的重要位点，我们检查了30个小鼠骨髓瘤和杂交瘤，它们合成了具有良好特征的缺失的IG重链。缺失CH 1结构域的突变型IG重链不能与BiP结合，而缺失CH 2或CH 3结构域的突变型IG重链仍然能够与BiP结合。在产生CH 1结构域缺失的重链的两个轻链阴性细胞系中，分泌游离重链。当在不与BiP相关的突变体中检查IG装配和分泌，并与正常亲本系进行比较时，发现突变体系中IG分泌速率增加，并且IG分子在装配的各个阶段分泌。在一个突变株系（CH 1-）中，约三分之一的分泌型IG分子未完全组装，而亲本株系分泌的IG分子完全组装。我们的数据表明，CH 1结构域是重要的协会与BiP，当这种协会不发生，不完全组装的重链可以分泌。这意味着BiP在阻止未组装的IG分子从ER转运中发挥作用。
Heavy chain-binding protein (BiP) associates posttranslationally with nascent Ig heavy chains in the endoplasmic reticulum (ER) and remains associated with these heavy chains until they assemble with light chains. The heavy chain-BiP complex can be precipitated by antibody reagents against either component. To identify sites on heavy chain molecules that are important for association with BiP, we have examined 30 mouse myelomas and hybridomas that synthesize Ig heavy chains with well characterized deletions. Mutant Ig heavy chains that lack the CH1 domain could not be demonstrated to associate with BiP, whereas mutant Ig heavy chains with deletions of the CH2 or CH3 domain were still able to associate with BiP. In two light chain negative cell lines that produced heavy chains with deletions of the CH1 domain, free heavy chains were secreted. When Ig assembly and secretion were examined in mutants that did not associate with BiP, and were compared with normal parental lines, it was found that the rate of Ig secretion was increased in the mutant lines and that the Ig molecules were secreted in various stages of assembly. In one mutant line (CH1-) approximately one-third of the secreted Ig molecules were incompletely assembled, whereas the Ig molecules secreted by the parental line were completely assembled. Our data show the CH1 domain to be important for association with BiP and that when this association does not occur, incompletely assembled heavy chains can be secreted. This implies a role for BiP in preventing the transport of unassembled Ig molecules from the ER.