Structures of outer-arm dynein array on microtubule doublet reveal a motor coordination mechanism

Abstract

Thousands of outer-arm dyneins (OADs) are arrayed in the axoneme to drive a rhythmic ciliary beat. Coordination among multiple OADs is essential for generating mechanical forces to bend microtubule doublets (MTDs). Using electron microscopy, we determined high-resolution structures of Tetrahymena thermophila OAD arrays bound to MTDs in two different states. OAD preferentially binds to MTD protofilaments with a pattern resembling the native tracks for its distinct microtubule-binding domains. Upon MTD binding, free OADs are induced to adopt a stable parallel conformation, primed for array formation. Extensive tail-to-head (TTH) interactions between OADs are observed, which need to be broken for ATP turnover by the dynein motor. We propose that OADs in an array sequentially hydrolyze ATP to slide the MTDs. ATP hydrolysis in turn relaxes the TTH interfaces to effect free nucleotide cycles of downstream OADs. These findings lead to a model explaining how conformational changes in the axoneme produce coordinated action of dyneins.

Structure of dynein-dynactin on microtubules shows tandem recruitment of cargo adaptors

“…The sparse microtubule decoration meant that typical microtubule reconstruction techniques [Zhang and Nogales, 2015;Cook et al, 2020] could not be used to solve the structure. Furthermore, applying conventional single particle analysis techniques was unsuccessful due to the dominating signal of the microtubule, as was observed previously by cryo-ET [Grotjahn et al, 2018] and in cryo-EM of axonemal dyneins bound to microtubule doublets [Ma et al, 2019;Walton et al, 2021;Kubo et al, 2021;Rao et al, 2021]. To overcome this, we developed a pipeline (described below) to subtract the microtubule signal from the micrographs (Figure 1A), which ultimately allowed us to successfully align the complexes (Figure 1B).…”

Cryo-EM structure of an active central apparatus

“…45 unique non-tubulin proteins of CA were identified by combining previously published mass spectrometry data (46, 47), structure prediction by Phyre2, and sequence pattern search using own scripts (86). First, each of the subunits that show clear backbones was manually built as a poly-Ala model in the local regions with the best resolutions in Coot (87, 88).…”

Consensus nomenclature for dyneins and associated assembly factors

“…Whether it forms a homodimer or heterodimer with another light chain remains to be confirmed, although there is evidence to suggest that, unlike the other light chains, the DYNLT2B subunit may be monomeric ( DiBella et al, 2001 ). Recent structural studies of Tetrahymena ODAs have revealed a Tctex-family heterodimer ( Rao et al, 2021 ).…”