Cysteines in CH1 underlie retention of unassembled ig heavy chains
Cysteines in CH1 underlie retention of unassembled ig heavy chains
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DOI：
10.1074/jbc.m500161200
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发表时间：
2005-04-15
影响因子：
4.8
通讯作者：
Bar-Nun, S
中科院分区：
文献类型：
--
作者：
Elkabetz, Y;Argon, Y;Bar-Nun, S
免疫球蛋白的构象、结构和寡聚状态不仅控制抗体的质量和功能特性，而且对免疫球蛋白的分泌也至关重要。未组装的免疫球蛋白重链通过C（H）1结构域的延迟折叠和BiP与该结构域的不可逆相互作用而保留在细胞内。在这里，我们表明，三个C（H）1半胱氨酸在免疫球蛋白折叠，组装和分泌中发挥着重要作用。值得注意的是，切除所有三个C（H）1半胱氨酸否定了保留，并使BiP循环和非规范折叠和组装成为可能。这种现象是由相互依赖的形成的结构域内和链间二硫化物，虽然这两个键是分泌。取代Cys-195不仅防止了结构域内二硫键的形成，而且防止了与轻链的链间二硫键的形成、BiP置换和分泌。突变轻链相互作用Cys-128阻碍了结构域内半胱氨酸的二硫键结合，允许它们与轻链机会结合，而不妨碍分泌。我们认为，C（H）1半胱氨酸在免疫球蛋白组装和分泌中的作用不仅仅是参与二硫键，而是指导正确的折叠并与保留机制相互作用。
Conformation, structure, and oligomeric state of immunoglobulins not only control quality and functional properties of antibodies but are also critical for immunoglobulins secretion. Unassembled immunoglobulin heavy chains are retained intracellularly by delayed folding of the C(H)1 domain and irreversible interaction of BiP with this domain. Here we show that the three C(H)1 cysteines play a central role in immunoglobulin folding, assembly, and secretion. Remarkably, ablating all three C(H)1 cysteines negates retention and enables BiP cycling and non-canonical folding and assembly. This phenomenon is explained by interdependent formation of intradomain and interchain disulfides, although both bonds are dispensable for secretion. Substituting Cys-195 prevents formation not only of the intradomain disulfide, but also of the interchain disulfide bond with light chain, BiP displacement, and secretion. Mutating the light chain-interacting Cys-128 hinders disulfide bonding of intradomain cysteines, allowing their opportunistic bonding with light chain, without hampering secretion. We propose that the role of C(H)1 cysteines in immunoglobulin assembly and secretion is not simply to engage in disulfide bridges, but to direct proper folding and interact with the retention machinery.