Nucleotide-binding domain and leucine-rich repeat pyrin-domain containing protein 1 (NLRP1) is an inflammasome sensor that mediates the activation of caspase-1 to induce cytokine maturation and pyroptosis^1,2,3,4. Gain-of-function mutations of NLRP1 cause severe inflammatory diseases of the skin^4,5,6. NLRP1 contains a function-to-find domain that auto-proteolyses into noncovalently associated subdomains^7,8,9, and proteasomal degradation of the repressive N-terminal fragment of NLRP1 releases its inflammatory C-terminal fragment (NLRP1 CT)^10,11. Cytosolic dipeptidyl peptidases 8 and 9 (hereafter, DPP8/DPP9) both interact with NLRP1, and small-molecule inhibitors of DPP8/DPP9 activate NLRP1 by mechanisms that are currently unclear^10,12,13,14. Here we report cryo-electron microscopy structures of the human NLRP1–DPP9 complex alone and with Val-boroPro (VbP), an inhibitor of DPP8/DPP9. The structures reveal a ternary complex that comprises DPP9, full-length NLRP1 and the NLRPT CT. The binding of the NLRP1 CT to DPP9 requires full-length NLRP1, which suggests that NLRP1 activation is regulated by the ratio of NLRP1 CT to full-length NLRP1. Activation of the inflammasome by ectopic expression of the NLRP1 CT is consistently rescued by co-expression of autoproteolysis-deficient full-length NLRP1. The N terminus of the NLRP1 CT inserts into the DPP9 active site, and VbP disrupts this interaction. Thus, VbP weakens the NLRP1–DPP9 interaction and accelerates degradation of the N-terminal fragment¹⁰ to induce inflammasome activation. Overall, these data demonstrate that DPP9 quenches low levels of NLRP1 CT and thus serves as a checkpoint for activation of the NLRP1 inflammasome.

核苷酸结合结构域和富含亮氨酸的重复热蛋白结构域蛋白 1 (NLRP1) 是一种炎性体传感器，可介导 caspase-1 的激活以诱导细胞因子成熟和细胞焦亡^1,2,3,4。NLRP1的功能获得性突变会导致严重的皮肤炎症^4,5,6。NLRP1 包含一个功能查找域，该域自动蛋白水解成非共价关联​​的子域^7,8,9，并且 NLRP1 的抑制性 N 末端片段的蛋白酶体降解释放其炎症性 C 末端片段 (NLRP1 CT) ^10,11. 胞质二肽基肽酶 8 和 9（以下称为 DPP8/DPP9）均与 NLRP1 相互作用，DPP8/DPP9 的小分子抑制剂通过目前尚不清楚的机制激活 NLRP1 ^10,12,13,14. 在这里，我们报告了单独的人类 NLRP1-DPP9 复合物以及 DPP8/DPP9 抑制剂 Val-boroPro (VbP) 的冷冻电子显微镜结构。这些结构揭示了一个包含 DPP9、全长 NLRP1 和 NLRPT CT 的三元复合物。NLRP1 CT 与 DPP9 的结合需要全长 NLRP1，这表明 NLRP1 激活受 NLRP1 CT 与全长 NLRP1 的比率调节。通过 NLRP1 CT 的异位表达激活炎性体，通过共表达自身蛋白水解缺陷的全长 NLRP1 始终如一地挽救。NLRP1 CT 的 N 末端插入 DPP9 活性位点，VbP 破坏了这种相互作用。因此，VbP 削弱了 NLRP1–DPP9 相互作用并加速了 N 末端片段^10的降解以诱导炎性体激活。总的来说，这些数据表明 DPP9 淬灭低水平的 NLRP1 CT，因此充当激活 NLRP1 炎性体的检查点。