Tomazin R, Hill A B, Jugovic P, York I, van Endert P, Ploegh H L, Andrews D W, Johnson D C
Cancer Research Group, Molecular Biology and Biotechnology Program, McMaster University, Hamilton, Ontario, Canada.
EMBO J. 1996 Jul 1;15(13):3256-66.
The herpes simplex virus (HSV) ICP47 protein inhibits the MHC class I antigen presentation pathway by inhibiting the transporter associated with antigen presentation (TAP) which translocates peptides across the endoplasmic reticulum membrane. At present, ICP47 is the only inhibitor of TAP. Here, we show that ICP47 produced in bacteria can block human, but not mouse, TAP, and that heat denaturation of ICP47 has no effect on its ability to block TAP. ICP47 inhibited peptide binding to TAP without affecting ATP binding, consistent with previous observations that the peptide binding and ATP binding sites of TAP are distinct. ICP47 bound to TAP with a higher affinity (KD approximately 5 x 10(-8) M) than did peptides, and ICP47 did not dissociate from TAP. ICP47 was not transported by TAP and remained sensitive to proteases added from the cytosolic surface of the membrane. Peptides acted as competitive inhibitors of ICP47 binding to TAP, and this inhibition required a 100- to 1000-fold molar excess of peptide. These results demonstrate that ICP47 binds to a site which includes the peptide binding domain of TAP and remains bound to this site in a stable fashion.
单纯疱疹病毒（HSV）的ICP47蛋白通过抑制与抗原呈递相关的转运体（TAP）来抑制MHC I类抗原呈递途径，TAP可将肽转运穿过内质网膜。目前，ICP47是TAP的唯一抑制剂。在此，我们表明在细菌中产生的ICP47可阻断人类而非小鼠的TAP，并且ICP47的热变性对其阻断TAP的能力没有影响。ICP47抑制肽与TAP的结合而不影响ATP结合，这与之前关于TAP的肽结合位点和ATP结合位点不同的观察结果一致。ICP47与TAP结合的亲和力（KD约为5×10^(-8) M）高于肽，并且ICP47不会从TAP上解离。ICP47不会被TAP转运，并且对从膜的胞质表面添加的蛋白酶仍敏感。肽可作为ICP47与TAP结合的竞争性抑制剂，并且这种抑制需要肽的摩尔过量100至1000倍。这些结果表明，ICP47结合到一个包括TAP的肽结合结构域的位点，并以稳定的方式保持与该位点结合。
