The architecture of outer dynein arms in situ.
ABSTRACT 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.
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ABSTRACT: Stenosed segments of arteries significantly alter the blood flow known from healthy vessels. In particular, the wall shear stress at critically stenosed arteries is at least an order of magnitude higher than in healthy situations. This alteration represents a change in physical force and might be used as a trigger signal for drug delivery. Mechanosensitive drug delivery systems, that preferentially release their payload under increased shear stress, are discussed. Therefore, besides biological or chemical markers, physical triggers are a further principle approach for targeted drug delivery. We hypothesize that such physical trigger is much more powerful to release drugs for vasodilation, plaque stabilization or clot lysis at stenosed arteries than any known biological or chemical ones.Cardiovascular research 05/2013; · 5.80 Impact Factor
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ABSTRACT: Understanding the molecular architecture of the flagellum is crucial to elucidate the bending mechanism produced by this complex organelle. The current known structure of the flagellum has not yet been fully correlated with the complex composition and localization of flagellar components. Using cryoelectron tomography and subtomogram averaging while distinguishing each one of the nine outer doublet microtubules, we systematically collected and reconstructed the three-dimensional structures in different regions of the Chlamydomonas flagellum. We visualized the radial and longitudinal differences in the flagellum. One doublet showed a distinct structure, whereas the other eight were similar but not identical to each other. In the proximal region, some dyneins were missing or replaced by minor dyneins, and outer-inner arm dynein links were variable among different microtubule doublets. These findings shed light on the intricate organization of Chlamydomonas flagella, provide clues to the mechanism that produces asymmetric flagellar beating, and pose a new challenge for the functional study of the flagella.The Journal of Cell Biology 09/2012; 198(5):913-25. · 10.82 Impact Factor
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ABSTRACT: Lanthanides are used since several decades to increase the magnetic alignability of bicelles. DMPE-DTPA (1,2-dimyristoyl-sn-glycero-3-phospho-ethanolamine-diethylenetri-aminepentaacetate) is commonly applied to anchor the lanthanides into the bicelles. However, since DMPE-DTPA has the tendency to accumulate at the highly curved edge region of the bicelles and if located there does not contribute to the magnetic orientation energy, we have tested cholesterol-DTPA complexed with thulium ions (Tm3+) as an alternative chelator to increase the magnetic alignability. Differential scanning calorimetric (DSC) measurements indicate the successful integration of cholesterol-DTPA into a DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) bilayer. Cryo transmission electron microscopy (TEM) and small angle neutron scattering (SANS) measurements show that the disk-like structure, i.e. bicelles is maintained if cholesterol-DTPA·Tm3+ is integrated into a mixture of DMPC, cholesterol and DMPE-DTPA·Tm3+. The size of the bicelles is increased compared to the size of the bicelles obtained from mixtures without cholesterol-DTPA·Tm3+. Magnetic field induced birefringence and SANS measurements in a magnetic field show that with addition of cholesterol-DTPA·Tm3+ the magnetic alignability of this bicelles is significantly increased compared to bicelles composed of DMPC, cholesterol and DMPE-DTPA·Tm3+ only.The Journal of Physical Chemistry B 11/2013; · 3.61 Impact Factor