Biogenesis of functional antigenic peptide transporter TAP requires assembly of pre-existing TAP1 with newly synthesized TAP2
Biogenesis of functional antigenic peptide transporter TAP requires assembly of pre-existing TAP1 with newly synthesized TAP2
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DOI：
10.1074/jbc.m602360200
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发表时间：
2006-06-30
影响因子：
4.8
通讯作者：
Knittler, Michael R.
中科院分区：
文献类型：
--
作者：
Keusekotten, Kirstin;Leonhardt, Ralf M.;Knittler, Michael R.
与抗原处理相关的转运蛋白(TAP)是将抗原肽从胞浆运送到内质网(ER)的关键，在内质网中，抗原肽被装载到主要组织相容性复合体I类分子上。TAP是一种异源二聚体跨膜蛋白，由同源亚基TAP1和TAP2组成。对于在内质网中合成的许多其他寡聚蛋白质复合体来说，亚基组装过程对于TAP获得天然功能状态是必不可少的。在这里，我们分析了TAP1和TAP2形成功能TAP复合体的个体需求。与TAP1不同，TAP2在分离表达时非常不稳定。我们表明，TAP亚基的异二聚化是维持TAP2稳定水平所必需的。通过体外表达系统，我们证明了功能TAP的生物发生依赖于现有的TAP1和新合成的TAP2的组装，而不是相反。体外表达的TAP2的孔形成核心跨膜结构域(Core TMD)是与预先存在的TAP1形成功能复合体的必要条件和充分条件。我们认为，观察到的TAP的组装机制保护了新合成的TAP2免受快速降解，并控制了运输活性转运蛋白分子的数量。我们的发现为研究TAP的功能和结构特性开辟了新的可能性，并提供了一个强大的模型系统来解决内质网中寡聚跨膜蛋白的生物合成组装问题。
The transporter associated with antigen processing (TAP) is essential for the delivery of antigenic peptides from the cytosol into the endoplasmic reticulum (ER), where they are loaded onto major histocompatibility complex class I molecules. TAP is a heterodimeric transmembrane protein that comprises the homologous subunits TAP1 and TAP2. As for many other oligomeric protein complexes, which are synthesized in the ER, the process of subunit assembly is essential for TAP to attain a native functional state. Here, we have analyzed the individual requirements of TAP1 and TAP2 for the formation of a functional TAP complex. Unlike TAP1, TAP2 is very unstable when expressed in isolation. We show that heterodimerization of TAP subunits is required for maintaining a stable level of TAP2. By using an in vitro expression system we demonstrate that the biogenesis of functional TAP depends on the assembly of preexisting TAP1 with newly synthesized TAP2, but not vice versa. The pore forming core transmembrane domain ( core TMD) of in vitro expressed TAP2 is necessary and sufficient to allow functional complex formation with pre-existing TAP1. We propose that the observed assembly mechanism of TAP protects newly synthesized TAP2 from rapid degradation and controls the number of transport active transporter molecules. Our findings open up new possibilities to investigate functional and structural properties of TAP and provide a powerful model system to address the biosynthetic assembly of oligomeric transmembrane proteins in the ER.