Multiple bacterial genera take advantage of the multifunctional autoprocessing repeats-in-toxin (MARTX) toxin to invade host cells. Secretion of the MARTX toxin by Vibrio vulnificus, a deadly opportunistic pathogen that causes primary septicemia, the precursor of sepsis, is a major driver of infection; however, the molecular mechanism via which the toxin contributes to septicemia remains unclear. Here, we report the crystal and cryo-electron microscopy (EM) structures of a toxin effector duet comprising the domain of unknown function in the first position (DUF1)/Rho inactivation domain (RID) complexed with human targets. These structures reveal how the duet is used by bacteria as a potent weapon. The data show that DUF1 acts as a RID-dependent transforming NADase domain (RDTND) that disrupts NAD⁺ homeostasis by hijacking calmodulin. The cryo-EM structure of the RDTND-RID duet complexed with calmodulin and Rac1, together with immunological analyses in vitro and in mice, provide mechanistic insight into how V. vulnificus uses the duet to suppress ROS generation by depleting NAD(P)⁺ and modifying Rac1 in a mutually-reinforcing manner that ultimately paralyzes first line immune responses, promotes dissemination of invaders, and induces sepsis. These data may allow development of tools or strategies to combat MARTX toxin-related human diseases.

多种细菌属利用多功能自动加工重复毒素（MARTX）毒素来侵入宿主细胞。创伤弧菌分泌的 MARTX 毒素是一种致命的机会性病原体，可导致原发性败血症（败血症的前兆），是感染的主要驱动因素；然而，该毒素导致败血症的分子机制仍不清楚。在这里，我们报告了毒素效应器二重体的晶体和冷冻电子显微镜（EM）结构，该毒素效应器二重体包含与人类靶标复合的第一位置的未知功能域（DUF1）/Rho失活域（RID）。这些结构揭示了细菌如何将二重奏用作有效的武器。数据显示，DUF1 作为 RID 依赖性转化 NAD 酶结构域 (RDTND)，通过劫持钙调蛋白来破坏 NAD ⁺稳态。与钙调蛋白和 Rac1 复合的 RDTND-RID 二重体的冷冻电镜结构，结合体外和小鼠体内的免疫学分析，为创伤弧菌如何利用二重体通过消耗 NAD(P) ⁺和以相互增强的方式修改 Rac1，最终瘫痪一线免疫反应，促进入侵者的传播，并诱发败血症。这些数据可能有助于开发对抗 MARTX 毒素相关人类疾病的工具或策略。