Outer dynein arms, the force generators for axonemal motion, form arrays on microtubule doublets in situ, although they are bouquet-like complexes with separated heads of multiple heavy chains when isolated in vitro. To understand how the three heavy chains are folded in the array, we reconstructed the detailed 3D structure of outer dynein arms of Chlamydomonas flagella in situ by electron cryo-tomography and single-particle averaging. The outer dynein arm binds to the A-microtubule through three interfaces on two adjacent protofilaments, two of which probably represent the docking complex. The three AAA rings of heavy chains, seen as stacked plates, are connected in a striking manner on microtubule doublets. The tail of the alpha-heavy chain, identified by analyzing the oda11 mutant, which lacks alpha-heavy chain, extends from the AAA ring tilted toward the tip of the axoneme and towards the inside of the axoneme at 50 degrees , suggesting a three-dimensional power stroke. The neighboring outer dynein arms are connected through two filamentous structures: one at the exterior of the axoneme and the other through the alpha-tail. Although the beta-tail seems to merge with the alpha-tail at the internal side of the axoneme, the gamma-tail is likely to extend at the exterior of the axoneme and join the AAA ring. This suggests that the fold and function of gamma-heavy chain are different from those of alpha and beta-chains.
"This is true especially for analyses performed at room temperature, either after chemical fixation (see, e.g., Mayorovits et al., 2008; Acehan et al., 2009; Liu et al., 2006) or freeze substitution (see, e.g., Noske et al., 2008; Marsh et al., 2007; Marsh, 2005; Richter et al., 2008), as well as for the small number of high-tech laboratories able to perform tomography of frozen hydrated samples (see, e.g., Beck et al., 2007; Morris and Jensen, 2008; He et al., 2009; Izard et al., 2008). Together with the use of standard ET, i.e., the collection of the tilt series and the 3D reconstruction of the tomogram , is also progressively increasing the number of ultra-structural studies in which a post-processing of the tomograms is performed, consisting of 3D alignment and averaging of equivalent structures contained in the map (see, e.g., Nicastro et al., 2006; Ishikawa et al., 2007; Liu et al., 2008; Bui et al., 2008). "
"The coiled-coil domain present between the fourth and fifth AAA motif forms a small stalk with a globular domain that acts as the ATP-sensitive microtubule-binding site (MTBD).39) Recent advances in cryoEM and tomographic observation have shown that multiple AAA ring heads are stacked atop each other and the plane of each ring runs through the axis of the adjacent B-tubule (Fig. 2b and 2c).40,41) Attempts have been made to detect the conformational changes of dynein during the mechano-chemical cycle by using biochemical methods. "
[Show abstract][Hide abstract] ABSTRACT: Eukaryotic flagella and cilia have attracted the attention of many researchers over the last century, since they are highly arranged organelles and show sophisticated bending movements. Two important cytoskeletal and motor proteins, tubulin and dynein, were first found and described in flagella and cilia. Half a century has passed since the discovery of these two proteins, and much information has been accumulated on their molecular structures and their roles in the mechanism of microtubule sliding, as well as on the architecture, the mechanism of bending movement and the regulation and signal transduction in flagella and cilia. Historical background and the recent advance in this field are described.(Communicated by Nobutaka HIROKAWA, M.J.A.).
Proceedings of the Japan Academy Ser B Physical and Biological Sciences 10/2012; 88(8):397-415. DOI:10.2183/pjab.88.397 · 2.65 Impact Factor
"Surface rendering was done by Chimera (Pettersen et al., 2004). Segmentation of components (ODA, IDA and RS) was carried out based on our analysis of mutants which lack these components (Ishikawa et al., 2007; Bui et al., 2008; Pigino et al., 2011). DRC was located based on Heuser et al., 2009, except one part which we proved to belong to dynein, not DRC (in Section 3). "
[Show abstract][Hide abstract] ABSTRACT: Although eukaryotic flagella and cilia all share the basic 9+2 microtubule-organization of their internal axonemes, and are capable of generating bending-motion, the waveforms, amplitudes, and velocities of the bending-motions are quite diverse. To explore the structural basis of this functional diversity of flagella and cilia, we here compare the axonemal structure of three different organisms with widely divergent bending-motions by electron cryo-tomography. We reconstruct the 3D structure of the axoneme of Tetrahymena cilia, and compare it with the axoneme of the flagellum of sea urchin sperm, as well as with the axoneme of Chlamydomonas flagella, which we analyzed previously. This comparative structural analysis defines the diversity of molecular architectures in these organisms, and forms the basis for future correlation with their different bending-motions.
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