Institute of Virology, Medical Center - University of Freiburg, Freiburg, Germany.
Faculty of Medicine, University of Freiburg, Hermann-Herder-Str 11, 79104, Freiburg, Germany.
Sci Rep. 2017 Jun 7;7(1):2933. doi: 10.1038/s41598-017-02994-5.
The transporter associated with antigen processing (TAP) translocates antigenic peptides into the endoplasmic reticulum (ER) lumen for loading onto MHC class I molecules. This is a key step in the control of viral infections through CD8+ T-cells. The herpes simplex virus type-1 encodes an 88 amino acid long species-specific TAP inhibitor, ICP47, that functions as a high affinity competitor for the peptide binding site on TAP. It has previously been suggested that the inhibitory function of ICP47 resides within the N-terminal region (residues 1-35). Here we show that mutation of the highly conserved PLL motif within the central region of ICP47 attenuates its inhibitory capacity. Taking advantage of the human cytomegalovirus-encoded TAP inhibitor US6 as a luminal sensor for conformational changes of TAP, we demonstrated that the PLL motif is essential for freezing of the TAP conformation. Moreover, hierarchical functional interaction sites on TAP dependent on PLL could be defined using a comprehensive set of human-rat TAP chimeras. This data broadens our understanding of the molecular mechanism underpinning TAP inhibition by ICP47, to include the PLL sequence as a stabilizer that tethers the TAP-ICP47 complex in an inward-facing conformation.
抗原加工相关转运体（TAP）将抗原肽转运到内质网（ER）腔中，以便与 MHC I 类分子结合。这是通过 CD8+T 细胞控制病毒感染的关键步骤。单纯疱疹病毒 1 编码一种 88 个氨基酸长的特异性 TAP 抑制剂 ICP47，它作为 TAP 肽结合位点的高亲和力竞争物起作用。先前曾有人提出，ICP47 的抑制功能位于其 N 端区域（残基 1-35）。在这里，我们发现 ICP47 中心区域高度保守的 PLL 基序的突变会削弱其抑制能力。利用人巨细胞病毒编码的 TAP 抑制剂 US6 作为 TAP 构象变化的腔内传感器，我们证明 PLL 基序对于 TAP 构象的冻结是必需的。此外，使用一组全面的人-大鼠 TAP 嵌合体，可以定义依赖于 PLL 的 TAP 上的分层功能相互作用位点。这些数据拓宽了我们对 ICP47 抑制 TAP 的分子机制的理解，将 PLL 序列包括在内作为一种稳定因子，将 TAP-ICP47 复合物固定在向内取向的构象中。
