Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
Institute of Structural Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
Nat Commun. 2023 Aug 9;14(1):4800. doi: 10.1038/s41467-023-40520-6.
The phylum Apicomplexa comprises important eukaryotic parasites that invade host tissues and cells using a unique mechanism of gliding motility. Gliding is powered by actomyosin motors that translocate host-attached surface adhesins along the parasite cell body. Actin filaments (F-actin) generated by Formin1 play a central role in this critical parasitic activity. However, their subcellular origin, path and ultrastructural arrangement are poorly understood. Here we used cryo-electron tomography to image motile Cryptosporidium parvum sporozoites and reveal the cellular architecture of F-actin at nanometer-scale resolution. We demonstrate that F-actin nucleates at the apically positioned preconoidal rings and is channeled into the pellicular space between the parasite plasma membrane and the inner membrane complex in a conoid extrusion-dependent manner. Within the pellicular space, filaments on the inner membrane complex surface appear to guide the apico-basal flux of F-actin. F-actin concordantly accumulates at the basal end of the parasite. Finally, analyzing a Formin1-depleted Toxoplasma gondii mutant pinpoints the upper preconoidal ring as the conserved nucleation hub for F-actin in Cryptosporidium and Toxoplasma. Together, we provide an ultrastructural model for the life cycle of F-actin for apicomplexan gliding motility.
肉足鞭毛门包含重要的真核寄生虫，它们利用独特的滑行运动机制入侵宿主组织和细胞。滑行运动由肌动球蛋白马达驱动，该马达沿着寄生虫细胞本体将附着在宿主上的表面黏附素向前输送。Formin1 产生的肌动蛋白丝 (F-actin) 在这一关键的寄生活动中发挥着核心作用。然而，它们的亚细胞起源、路径和超微结构排列仍知之甚少。在这里，我们使用冷冻电子断层扫描来对运动中的微小隐孢子虫孢子虫进行成像，并以纳米级分辨率揭示 F-actin 的细胞结构。我们证明 F-actin 在顶端定位的 preconoidal 环上起始，并以依赖于锥体挤出的方式被引导到寄生虫质膜和内膜复合物之间的膜下空间中。在膜下空间中，内膜复合物表面上的细丝似乎引导 F-actin 的顶-基极流。F-actin 一致地在寄生虫的基底末端积累。最后，分析 Formin1 缺失的刚地弓形虫突变体指出，上预锥环是隐孢子虫和刚地弓形虫中 F-actin 的保守起始枢纽。总的来说，我们为肉足鞭毛门的滑行运动提供了 F-actin 生命周期的超微结构模型。
