Prominence of beta 2-microglobulin, class I heavy chain conformation, and tapasin in the interactions of class I heavy chain with calreticulin and the transporter associated with antigen processing.
Prominence of beta 2-microglobulin, class I heavy chain conformation, and tapasin in the interactions of class I heavy chain with calreticulin and the transporter associated with antigen processing.
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DOI：
10.4049/jimmunol.158.5.2236
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发表时间：
1997-03
影响因子：
4.4
通讯作者：
J. Solheim;M. Harris;C. Kindle;Ted H. Hansen
中科院分区：
文献类型：
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作者：
J. Solheim;M. Harris;C. Kindle;Ted H. Hansen
新合成的I类重（H）链/β 2 m异二聚体在内质网中等待肽与Ag加工相关的转运蛋白（TAP）相关。我们在这里提出的证据表明，钙网蛋白，但不是钙连接蛋白，显示稳态协会与I类/TAP复合物。为了将β 2 m与TAP和钙网蛋白结合的能力与H链的能力分开，我们研究了缺乏β 2 m或H链表达的人细胞系。在β 2 m-细胞系Daudi中几乎没有检测到与TAP和钙网蛋白相关的H链。相比之下，在H链缺陷细胞系LCL 721.221中发现TAP和钙网蛋白具有高水平的β 2 m，即使在预先清除该细胞系表达的痕量IB类蛋白之后。因此，β 2 m似乎在没有H链的情况下结合TAP，提供了一种优雅的机制将β 2 m保留在内质网中的肽加载位点。为了研究其他分子是否参与β 2 m和H链与TAP和钙网蛋白的结合，我们分析了缺失tapasin的缺失突变细胞系LCL 721.220。在721.220中，TAP和钙网蛋白彼此不相关。此外，在这些细胞中，H链/β 2 m与TAP无关，但H链和低水平的β 2 m与钙网蛋白相关。这些结果表明，Tapasin是钙网蛋白/H链/β 2 m与TAP组装的强制性介质。
Newly synthesized class I heavy (H) chain/beta 2m heterodimers awaiting peptides in the endoplasmic reticulum are associated with the transporter associated with Ag processing (TAP). We present evidence here that calreticulin, but not calnexin, displays steady state association with class I/TAP complexes. To separate the ability of beta 2m to bind with TAP and calreticulin from that of H chain, we studied human cell lines that lack expression of beta 2m or H chain. Little if any H chain was detected in association with TAP and calreticulin in the beta 2m- cell line Daudi. By contrast, high levels of beta 2m are found with TAP and calreticulin in the H chain-deficient cell line LCL 721.221, even after preclearance of the trace amount of class IB protein expressed by this cell line. Thus, beta 2m appears to bind TAP in the absence of H chain, providing an elegant mechanism to retain beta 2m in the endoplasmic reticulum at the site of peptide loading. To investigate whether other molecules participate in the binding of beta 2m and H chain to TAP and calreticulin, we analyzed the deletion mutant cell line LCL 721.220, which lacks tapasin. In 721.220, TAP and calreticulin are not associated with each other. Also, in these cells, H chain/beta 2m are not associated with TAP, but H chain and a low level of beta 2m are associated with calreticulin. These results suggest that tapasin is an obligatory mediator of the assemblage of calreticulin/H chain/beta 2m with TAP.