Many key insights into actin regulation have been derived through examining how microbial pathogens intercept the actin cytoskeleton during infection. Mycobacterium marinum, a close relative of the human pathogen Mycobacterium tuberculosis, polymerizes host actin at the bacterial surface to drive intracellular movement and cell-to-cell spread during infection. However, the mycobacterial factor that commandeers actin polymerization has remained elusive. Here, we report the identification and characterization of the M. marinum actin-based motility factor designated mycobacterial intracellular rockets A (MirA), which is a member of the glycine-rich PE_PGRS protein family. MirA contains an amphipathic helix to anchor into the mycobacterial outer membrane and, surprisingly, also the surface of host lipid droplet organelles. MirA directly binds to and activates the host protein N-WASP to stimulate actin polymerization through the Arp2/3 complex, directing both bacterial and lipid droplet actin-based motility. MirA is dissimilar to known N-WASP activating ligands and may represent a new class of microbial and host actin regulator. Additionally, the MirA-N-WASP interaction represents a model to understand how the enigmatic PE_PGRS proteins contribute to mycobacterial pathogenesis.

通过检查微生物病原体在感染过程中如何拦截肌动蛋白细胞骨架，获得了许多关于肌动蛋白调控的关键见解。海分枝杆菌是人类病原体结核分枝杆菌的近亲，它在细菌表面聚合宿主肌动蛋白，在感染期间驱动细胞内运动和细胞间传播。然而，支配肌动蛋白聚合的分枝杆菌因素仍然难以捉摸。在这里，我们报告了M. marinum的鉴定和表征基于肌动蛋白的运动因子称为分枝杆菌胞内火箭 A (MirA)，它是富含甘氨酸的 PE_PGRS 蛋白家族的成员。MirA 含有一个两亲螺旋，可锚定在分枝杆菌外膜中，而且令人惊讶的是，它还锚定在宿主脂滴细胞器的表面。MirA 直接结合并激活宿主蛋白 N-WASP，通过 Arp2/3 复合物刺激肌动蛋白聚合，指导细菌和脂滴基于肌动蛋白的运动。MirA 与已知的 N-WASP 激活配体不同，可能代表一类新的微生物和宿主肌动蛋白调节剂。此外，MirA-N-WASP 相互作用代表了一个模型，可以了解神秘的 PE_PGRS 蛋白如何促成分枝杆菌发病机制。