As organelles of the innate immune system, inflammasomes activate caspase-1 and other inflammatory caspases that cleave gasdermin D (GSDMD). Caspase-1 also cleaves inactive precursors of the interleukin (IL)-1 family to generate mature cytokines such as IL-1β and IL-18. Cleaved GSDMD forms transmembrane pores to enable the release of IL-1 and to drive cell lysis through pyroptosis^{1,2,3,4,5,6,7,8,9}. Here we report cryo-electron microscopy structures of the pore and the prepore of GSDMD. These structures reveal the different conformations of the two states, as well as extensive membrane-binding elements including a hydrophobic anchor and three positively charged patches. The GSDMD pore conduit is predominantly negatively charged. By contrast, IL-1 precursors have an acidic domain that is proteolytically removed by caspase-1¹⁰. When permeabilized by GSDMD pores, unlysed liposomes release positively charged and neutral cargoes faster than negatively charged cargoes of similar sizes, and the pores favour the passage of IL-1β and IL-18 over that of their precursors. Consistent with these findings, living—but not pyroptotic—macrophages preferentially release mature IL-1β upon perforation by GSDMD. Mutation of the acidic residues of GSDMD compromises this preference, hindering intracellular retention of the precursor and secretion of the mature cytokine. The GSDMD pore therefore mediates IL-1 release by electrostatic filtering, which suggests the importance of charge in addition to size in the transport of cargoes across this large channel.

作为先天免疫系统的细胞器，炎性体激活 caspase-1 和其他可切割 gasdermin D (GSDMD) 的炎性 caspase。Caspase-1 还切割白细胞介素 (IL)-1 家族的无活性前体以产生成熟的细胞因子，例如 IL-1β 和 IL-18。切割的 GSDMD 形成跨膜孔，以释放 IL-1 并通过细胞焦亡驱动细胞裂解^{1,2,3,4,5,6,7,8,9}. 在这里，我们报告了 GSDMD 的孔和前孔的低温电子显微镜结构。这些结构揭示了两种状态的不同构象，以及广泛的膜结合元件，包括疏水锚和三个带正电荷的补丁。GSDMD 孔导管主要带负电荷。相比之下，IL-1 前体具有被 caspase-1 蛋白水解去除的酸性结构域¹⁰. 当被 GSDMD 孔透化时，未裂解的脂质体比类似大小的带负电荷的货物更快地释放带正电荷和中性的货物，并且与它们的前体相比，这些孔有利于 IL-1β 和 IL-18 的通过。与这些发现一致，活的——但不是焦亡的——巨噬细胞在被 GSDMD 穿孔时优先释放成熟的 IL-1β。GSDMD 酸性残基的突变损害了这种偏好，阻碍了前体的细胞内保留和成熟细胞因子的分泌。因此，GSDMD 孔通过静电过滤介导 IL-1 释放，这表明除了尺寸之外，电荷在通过这个大通道运输货物时的重要性。