The radial spoke (RS) heads of motile cilia and flagella contact projections of the central pair (CP) apparatus to coordinate motility, but the morphology is distinct for protozoa and metazoa. Here we show the murine RS head is compositionally distinct from that of Chlamydomonas. Our reconstituted murine RS head core complex consists of Rsph1, Rsph3b, Rsph4a, and Rsph9, lacking Rsph6a and Rsph10b, whose orthologs exist in the protozoan RS head. We resolve its cryo-electron microscopy (cryo-EM) structure at 3.2-Å resolution. Our atomic model further reveals a twofold symmetric brake pad-shaped structure, in which Rsph4a and Rsph9 form a compact body extended laterally with two long arms of twisted Rsph1 β-sheets and potentially connected dorsally via Rsph3b to the RS stalk. Furthermore, our modeling suggests that the core complex contacts the periodic CP projections either rigidly through its tooth-shaped Rsph4a regions or elastically through both arms for optimized RS–CP interactions and mechanosignal transduction.

运动纤毛的径向辐条 (RS) 头和中央对 (CP) 装置的鞭毛接触投影以协调运动，但原生动物和后生动物的形态不同。在这里，我们展示了鼠 RS 头部在成分上与衣藻不同. 我们重建的鼠 RS 头部核心复合体由 Rsph1、Rsph3b、Rsph4a 和 Rsph9 组成，缺少 Rsph6a 和 Rsph10b，它们的直系同源物存在于原生动物 RS 头部。我们以 3.2 Å 的分辨率解析其冷冻电子显微镜 (cryo-EM) 结构。我们的原子模型进一步揭示了一个双重对称的刹车片状结构，其中 Rsph4a 和 Rsph9 形成一个紧凑的主体，横向延伸，带有两个扭曲的 Rsph1 β-折叠长臂，并可能通过 Rsph3b 背侧连接到 RS 茎。此外，我们的模型表明，核心复合物通过其齿形 Rsph4a 区域刚性接触周期性 CP 投影，或通过双臂弹性接触周期性 CP 投影，以优化 RS-CP 相互作用和机械信号转导。