21-April-2022

Noëmi Zimmermann (Ishikawa group, PSI)

16.00 on Zoom: https://ethz.zoom.us/j/67396710587

3D structure of the axonemal dyneins determined with subtomogram averaging.

Abstract:
Axonemal dyneins, gigantic (~4500a.a.) ATPase motor proteins, in the outer arm dynein (ODA) generate force for ciliary beating. To investigate the different states present during the power stroke cycle, we analyzed 3D structures of the ODA using in situ cryo-electron tomography (cryo-ET), subtomogram averaging and classification. We improved spatial resolution by switching from our previous classification analysis algorithm based on template matching (Bui and Ishikawa, 2013) to maximum-likelihood-based 3D classification by RELION3D. With this, structures presenting various states of force generation could be separated, depicting pre-power and post-power stoke conformations, as well as an intermediate state. We further compared these structures to the published in vitro atomic structure of the apo ODA resolved by single particle cryo-EM (Kubo et al., 2020; Rao et al., 2020; Walton et al., 2021). The cryo-EM atomic model of the tail complex matches well with that of our cryo-ET structures. However the orientation and position of the dynein head and linker part of the ODA differs between cryo-ET and single particle cryo-EM, indicating interaction to the adjacent B-tubule reorients dynein motor domains. We build a pseudo-atomic model from these single particle cryo-EM structures to generate a best fitting atomic model. The pre-power stroke state is characterized by, in addition to the rotation and displacement of the head domains and reorientation of the linker as reported previously, conformational change of the tail anchored on the A-tubule. This suggests that power stroke of ODA in the axoneme takes place globally as complex interactions of proteins. With the apo ODA atomic model of Kubo et al. together with the Shulin-ODA complex (Mali et al., 2021) we build a pseudo-atomic model for the pre-power stroke conformation.