Accurately regulated ciliary beating in time and space is critical for diverse cellular activities, which impact the survival and development of nearly all eukaryotic species. An essential beating regulator is the conserved central apparatus (CA) of motile cilia, composed of a pair of microtubules (C1 and C2) associated with hundreds of protein subunits per repeating unit. It is largely unclear how the CA plays its regulatory roles in ciliary motility. Here, we present high-resolution structures of Chlamydomonas reinhardtii CA by cryo-electron microscopy (cryo-EM) and its dynamic conformational behavior at multiple scales. The structures show how functionally related projection proteins of CA are clustered onto a spring-shaped scaffold of armadillo-repeat proteins, facilitated by elongated rachis-like proteins. The two halves of the CA are brought together by elastic chain-like bridge proteins to achieve coordinated activities. We captured an array of kinesin-like protein (KLP1) in two different stepping states, which are actively correlated with beating wave propagation of cilia. These findings establish a structural framework for understanding the role of the CA in cilia.

在时间和空间上准确调节纤毛跳动对于多种细胞活动至关重要，这影响着几乎所有真核物种的生存和发育。重要的跳动调节器是运动纤毛的保守中央装置 (CA)，由一对微管（C1 和 C2）组成，每个重复单元与数百个蛋白质亚基相关。目前还不清楚 CA 如何在纤毛运动中发挥其调节作用。在这里，我们通过冷冻电子显微镜 (cryo-EM) 展示了莱茵衣藻CA 的高分辨率结构及其在多个尺度上的动态构象行为。这些结构显示了功能相关的 CA 投射蛋白如何在细长的轴状蛋白的促进下聚集到犰狳重复蛋白的弹簧状支架上。 CA的两半通过弹性链状桥蛋白连接在一起，以实现协调的活动。我们捕获了一系列处于两种不同步进状态的驱动蛋白样蛋白（KLP1），它们与纤毛的跳动波传播密切相关。这些发现为理解 CA 在纤毛中的作用建立了一个结构框架。