Functional role of C-terminal sequence elements in the transporter associated with antigen processing
Functional role of C-terminal sequence elements in the transporter associated with antigen processing
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DOI：
10.4049/jimmunol.174.1.328
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发表时间：
2005-01-01
影响因子：
4.4
通讯作者：
Knittler, MR
中科院分区：
文献类型：
--
作者：
Ehses, S;Leonhardt, RM;Knittler, MR
TAP将抗原肽递送到内质网（ER）中，这些抗原肽随后与MHC I类分子结合。TAP由两个亚基（TAP1和TAP2）组成，每个亚基都有一个跨膜（TMD）结构域和一个核苷酸结合（NBD）结构域。两个TAP - NBD具有不同的生化特性，并在肽转运过程中控制不同的步骤。我们之前注意到TAP1和TAP2的非同源C末端尾部决定了TAP - NBD1和 - NBD2的不同功能。为了确定导致NBD功能不对称的序列元件，我们构建了嵌合的大鼠TAP变体，在其中我们系统地交换了两个TAP - NBD之间不同长度的序列区域。我们的精细定位研究表明，包含α6/β10环以及下游转换区域的非同源区域直接导致了TAP - NBD的功能分离。α6/β10环决定了NBD1和NBD2的非同义核苷酸结合，而转换区域似乎在调节TAP结构域之间的功能性相互作用中起关键作用。基于我们的发现，我们推测这两个序列元件构成了一个最小的功能单元，它控制着两个TAP - NBD的不对称性。
TAP delivers antigenic peptides into the endoplasmic reticulum (ER) that are subsequently bound by MHC class I molecules. TAP consists of two subunits (TAP1 and TAP2), each with a transmembrane (TMD) and a nucleotide-binding (NBD) domain. The two TAP-NBDs have distinct biochemical properties and control different steps during the peptide translocation process. We noted previously that the nonhomologous C-terminal tails of tat TAN and TAP2 determine the distinct functions of TAP-NBD1 and -NBD2. To identify the sequence elements responsible for the asymmetrical NBD function, we constructed chimeric rat TAP variants in which we systematically exchanged sequence regions of different length between the two TAP-NBDs. Our fine-mapping studies demonstrate that a nonhomologous region containing the alpha6/beta10-loop in conjunction with the downstream switch region is directly responsible for the functional separation of the TAP-NBDs. The alpha6/beta10-loop determines the nonsynonymous nucleotide binding of NBD1 and NBD2, whereas the switch region seems to play a critical role in regulating the functional cross-talk between the structural domains of TAP. Based on our findings, we postulate that these two sequence elements build a minimal functional unit that controls the asymmetry of the two TAP-NBDs.