Nearly all motile cilia contain a central apparatus (CA) composed of two connected singlet microtubules with attached projections that play crucial roles in regulating ciliary motility. Defects in CA assembly usually result in motility-impaired or paralyzed cilia, which in humans causes disease. Despite their importance, the protein composition and functions of the CA projections are largely unknown. Here, we integrated biochemical and genetic approaches with cryo-electron tomography to compare the CA of wild-type Chlamydomonas with CA mutants. We identified a large (>2 MD) complex, the C1a-e-c supercomplex, that requires the PF16 protein for assembly and contains the CA components FAP76, FAP81, FAP92, and FAP216. We localized these subunits within the supercomplex using nanogold labeling and show that loss of any one of them results in impaired ciliary motility. These data provide insight into the subunit organization and 3D structure of the CA, which is a prerequisite for understanding the molecular mechanisms by which the CA regulates ciliary beating.

中文翻译：

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睫状体中央装置内 C1a-ec 超级复合体的结构组织

几乎所有运动纤毛都含有一个中央装置（CA），该中央装置由两个相连的单线微管组成，其上附着有突起，在调节纤毛运动方面发挥着至关重要的作用。CA 组装缺陷通常会导致纤毛运动受损或瘫痪，从而导致人类疾病。尽管 CA 投影很重要，但其蛋白质组成和功能在很大程度上还是未知的。在这里，我们将生物化学和遗传学方法与冷冻电子断层扫描相结合，比较野生型衣藻的 CA 与 CA 突变体。我们鉴定了一个大的(>2MD)复合物，C1a-ec超级复合物，其需要PF16蛋白进行组装并且包含CA组分FAP76、FAP81、FAP92和FAP216。我们使用纳米金标记将这些亚基定位在超级复合物中，并表明其中任何一个亚基的丢失都会导致纤毛运动受损。这些数据可以深入了解 CA 的亚基组织和 3D 结构，这是了解 CA 调节纤毛跳动的分子机制的先决条件。