Extended Data Fig. 4. The parallel conformation of arrayed OAD in apo state.

(a) Detailed index models of the subdomains in the β-Linker region, motor domains AAA extensions (only the extensions used in this study are shown here), and CT-cap region. The subdomain of Linker and CT-cap of α-, γ-HC are the same as that of β-HC. The Linker helix H12 is the hinge helix⁴³ for the Linker and AAA + ring swing. LS, Linker subdomain. (b-c) Detailed index models of the subdomains of the tail region of β-HC (b) and γ-HC (c). The subdomain of α-tail is the same as that of β-tail. (d) Top view of the cryo-EM structure of OAD-PF unit shows that the three motor domains are organized in a nearly parallel architecture (the three pink lines). The relative positions of the α- and β-motor domains are aligned with the tubulin lattice. The center of the γ-motor domain is slightly ahead of the lattice line defined by connecting the centers of the other two (cyan polyline) in both MTBS-1 and MTBS-2. The OAD appears as a triangle shape from top view, with the β- and γ-tail twisting toward the α-tail with respect to the motor domains. (e) Rigid body fitting of our OAD array into cryo-ET maps of axonemes from T. thermophila (EMD-7805)⁹. The four OAD units were fitted into the cryo-ET density en bloc rather than individually which verified the TTH interaction. The N-terminal regions of the tails are also close to the docking complex and they are bridged by clear density connections. (f) Local densities of the nucleotides in AAA1-AAA4 of β-motor domain. Nucleotide density does not appear in β-AAA1. ATP in β-AAA2 and ADP in β-AAA3/AAA4 were unambiguously identified from the density. Other motor domains have the same nucleotide binding states.