Department of Structural Biology, Genentech, South San Francisco, CA 94080, USA.
Department of Biochemical Pharmacology, Genentech, South San Francisco, CA 94080, USA.
Structure. 2019 Jan 2;27(1):125-133.e4. doi: 10.1016/j.str.2018.10.025. Epub 2018 Nov 29.
Enhancement of antigen-specific T cell immunity has shown significant therapeutic benefit in infectious diseases and cancer. Hematopoietic progenitor kinase-1 (HPK1) is a negative-feedback regulator of T cell receptor signaling, which dampens T cell proliferation and effector function. A recent report showed that a catalytic dead mutant of HPK1 phenocopies augmented T cell responses observed in HPK1-knockout mice, indicating that kinase activity is critical for function. We evaluated active and inactive mutants and determined crystal structures of HPK1 kinase domain (HPK1-KD) in apo and ligand bound forms. In all structures HPK1-KD displays a rare domain-swapped dimer, in which the activation segment comprises a well-conserved dimer interface. Biophysical measurements show formation of dimer in solution. The activation segment adopts an α-helical structure which exhibits distinct orientations in active and inactive states. This face-to-face configuration suggests that the domain-swapped dimer may possess alternative selectivity for certain substrates of HPK1 under relevant cellular context.
增强抗原特异性 T 细胞免疫在传染病和癌症中显示出显著的治疗益处。造血祖细胞激酶-1（HPK1）是 T 细胞受体信号的负反馈调节剂，可抑制 T 细胞增殖和效应功能。最近的一份报告显示，HPK1 的催化失活突变体模拟了 HPK1 敲除小鼠中观察到的增强的 T 细胞反应，表明激酶活性对于功能至关重要。我们评估了活性和非活性突变体，并确定了 HPK1 激酶结构域（HPK1-KD）在无配体和配体结合形式下的晶体结构。在所有结构中，HPK1-KD 均显示出罕见的结构域交换二聚体，其中激活片段包含一个高度保守的二聚体界面。生物物理测量显示溶液中二聚体的形成。激活片段采用 α-螺旋结构，在活性和非活性状态下呈现出不同的取向。这种面对面的构象表明，在相关的细胞环境下，结构域交换二聚体可能对 HPK1 的某些底物具有替代选择性。
