Cilia are thin microtubule-based protrusions of eukaryotic cells. The swimming of ciliated protists and sperm cells is propelled by the beating of cilia. Cilia propagate the flow of mucus in the trachea and protect the human body from viral infections. The main force generators of ciliary beating are the outer dynein arms (ODAs) which attach to the doublet microtubules. The bending of cilia is driven by the ODAs' conformational changes caused by ATP hydrolysis. Here, we report the native ODA complex structure attaching to the doublet microtubule by cryo-electron microscopy and mass spectrometry. The structure reveals how the ODA complex is attached to the doublet microtubule via the docking complex in its native state. Combined with coarse-grained molecular dynamics simulations, we present a model of how the attachment of the ODA to the doublet microtubule induces remodeling and activation of the ODA complex.

Cilia were purified from Tetrahymena thermophila wild types and mutants. The dataset contains both ATP-induced splitted doublet microtubule or salt-treated doublet microtubules.