The membrane protein NINJ1 mediates plasma membrane rupture in pyroptosis and other lytic cell death pathways. Here, we report the cryo-EM structure of a NINJ1 oligomer segmented from NINJ1 rings. Each NINJ1 subunit comprises amphipathic (⍺1, ⍺2) and transmembrane (TM) helices (⍺3, ⍺4) and forms a chain of subunits, mainly by the TM helices and ⍺1. ⍺3 and ⍺4 are kinked, and the Gly residues are important for function. The NINJ1 oligomer possesses a concave hydrophobic side that should face the membrane and a convex hydrophilic side formed by ⍺1 and ⍺2, presumably upon activation. This structural observation suggests that NINJ1 can form membrane disks, consistent with membrane fragmentation by recombinant NINJ1. Live-cell and super-resolution imaging uncover ring-like structures on the plasma membrane that are released into the culture supernatant. Released NINJ1 encircles a membrane inside, as shown by lipid staining. Therefore, NINJ1-mediated membrane disk formation is different from gasdermin-mediated pore formation, resulting in membrane loss and plasma membrane rupture.

中文翻译：

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NINJ1通过切割和释放膜盘介导质膜破裂

膜蛋白 NINJ1 在焦亡和其他裂解细胞死亡途径中介导质膜破裂。在这里，我们报告了从 NINJ1 环分段的 NINJ1 寡聚物的冷冻电镜结构。每个 NINJ1 亚基均包含两亲性 (⍺1、⍺2) 和跨膜 (TM) 螺旋 (⍺3、⍺4)，并形成亚基链，主要由 TM 螺旋和⍺1 组成。 ⍺3 和⍺4 是扭结的，甘氨酸残基对于功能很重要。 NINJ1 寡聚物具有应面向膜的凹疏水侧和由 ⍺1 和 ⍺2 形成的凸亲水侧（可能是在激活后）。这一结构观察表明 NINJ1 可以形成膜盘，与重组 NINJ1 的膜断裂一致。活细胞和超分辨率成像揭示了质膜上的环状结构，这些结构被释放到培养物上清液中。脂质染色显示，释放的 NINJ1 包围内部膜。因此，NINJ1介导的膜盘形成不同于gasdermin介导的孔形成，导致膜损失和质膜破裂。