Programmed cell death-1 (PD-1) inhibits T cell responses. This function relies on interaction with SHP-2. PD-1 has one immunoreceptor tyrosine-based inhibitory motif (ITIM) at Y223 and one immunoreceptor tyrosine-based switch motif (ITSM) at Y248. Only ITSM-Y248 is indispensable for PD-1-mediated inhibitory function but how SHP-2 enzymatic activation is mechanistically regulated by one PD-1 phosphotyrosine remains a puzzle. We found that after PD-1 phosphorylation, SHP-2 can bridge phosphorylated ITSM-Y248 residues on two PD-1 molecules via its amino terminal (N)-SH2 and carboxyterminal (C)-SH2 domains forming a PD-1: PD-1 dimer in live cells. The biophysical ability of SHP-2 to interact with two ITSM-pY248 residues was documented by isothermal titration calorimetry. SHP-2 interaction with two ITSM-pY248 phosphopeptides induced robust enzymatic activation. Our results unravel a mechanism of PD-1: SHP-2 interaction that depends only on ITSM-Y248 and explain how a single docking site within the PD-1 cytoplasmic tail can activate SHP-2 and PD-1-mediated inhibitory function.

程序性细胞死亡1（PD-1）抑制T细胞反应。此功能依赖于与SHP-2的交互。PD-1在Y223具有一个基于免疫受体酪氨酸的抑制基序（ITIM），在Y248具有一个基于免疫受体酪氨酸的开关基序（ITSM）。对于PD-1介导的抑制功能，只有ITSM-Y248是必不可少的，但是如何通过一个PD-1磷酸酪氨酸机制调控SHP-2的酶促活化仍然是一个难题。我们发现，PD-1磷酸化后，SHP-2可以通过两个PD-1分子的氨基末端（N）-SH2和羧基末端（C）-SH2结构域桥接形成PD-1的磷酸化ITSM-Y248残基：PD-活细胞中有1个二聚体。SHP-2与两个ITSM-pY248残基相互作用的生物物理能力已通过等温滴定热法测定。SHP-2与两个ITSM-pY248磷酸肽的相互作用诱导了强大的酶促活化作用。我们的研究结果揭示了仅依赖于ITSM-Y248的PD-1：SHP-2相互作用的机理，并解释了PD-1细胞质尾部中的单个停靠位点如何激活SHP-2和PD-1介导的抑制功能。