Department of Cell Biology, University of Texas, Southwestern Medical Center, Dallas, TX, USA.
Department of Pharmacology, University of Texas, Southwestern Medical Center, Dallas, TX, USA.
Nat Commun. 2023 Mar 30;14(1):1775. doi: 10.1038/s41467-023-37327-w.
The apical complex is a specialized collection of cytoskeletal and secretory machinery in apicomplexan parasites, which include the pathogens that cause malaria and toxoplasmosis. Its structure and mechanism of motion are poorly understood. We used cryo-FIB-milling and cryo-electron tomography to visualize the 3D-structure of the apical complex in its protruded and retracted states. Averages of conoid-fibers revealed their polarity and unusual nine-protofilament arrangement with associated proteins connecting and likely stabilizing the fibers. Neither the structure of the conoid-fibers nor the architecture of the spiral-shaped conoid complex change during protrusion or retraction. Thus, the conoid moves as a rigid body, and is not spring-like and compressible, as previously suggested. Instead, the apical-polar-rings (APR), previously considered rigid, dilate during conoid protrusion. We identified actin-like filaments connecting the conoid and APR during protrusion, suggesting a role during conoid movements. Furthermore, our data capture the parasites in the act of secretion during conoid protrusion.
顶复体复合物是顶复门寄生虫中一种特殊的细胞骨架和分泌机器的集合，包括引起疟疾和弓形体病的病原体。其结构和运动机制尚不清楚。我们使用冷冻 FIB 铣削和冷冻电子断层扫描来可视化顶复体复合物在突出和缩回状态下的三维结构。对圆锥纤维的平均值揭示了它们的极性和不寻常的九原丝排列，以及相关的蛋白质连接并可能稳定纤维。在突出或缩回过程中，圆锥纤维的结构和螺旋形圆锥复合体的结构都不会发生变化。因此，圆锥体作为一个刚体移动，而不是以前所认为的那样具有弹性和可压缩性。相反，之前被认为是刚性的顶极环（APR）在圆锥体突出时会扩张。我们在圆锥体突出过程中发现了连接圆锥体和 APR 的肌动蛋白样纤维，这表明它们在圆锥体运动中发挥作用。此外，我们的数据捕捉到了寄生虫在圆锥体突出过程中分泌的过程。
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