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Insights into the assembly and activation of the microtubule nucleator gamma-TuRC 期刊论文
NATURE, 2020, 578 (7795) : 467-+
作者:  Cyranoski, David
收藏  |  浏览/下载:41/0  |  提交时间:2020/07/03

Microtubules are dynamic polymers of alpha- and beta-tubulin and have crucial roles in cell signalling, cell migration, intracellular transport and chromosome segregation(1). They assemble de novo from alpha beta-tubulin dimers in an essential process termed microtubule nucleation. Complexes that contain the protein gamma-tubulin serve as structural templates for the microtubule nucleation reaction(2). In vertebrates, microtubules are nucleated by the 2.2-megadalton gamma-tubulin ring complex (gamma-TuRC), which comprises gamma-tubulin, five related gamma-tubulin complex proteins (GCP2-GCP6) and additional factors(3). GCP6 is unique among the GCP proteins because it carries an extended insertion domain of unknown function. Our understanding of microtubule formation in cells and tissues is limited by a lack of high-resolution structural information on the gamma-TuRC. Here we present the cryo-electron microscopy structure of gamma-TuRC from Xenopus laevis at 4.8 angstrom global resolution, and identify a 14-spoked arrangement of GCP proteins and gamma-tubulins in a partially flexible open left-handed spiral with a uniform sequence of GCP variants. By forming specific interactions with other GCP proteins, the GCP6-specific insertion domain acts as a scaffold for the assembly of the gamma-TuRC. Unexpectedly, we identify actin as a bona fide structural component of the gamma-TuRC with functional relevance in microtubule nucleation. The spiral geometry of gamma-TuRC is suboptimal for microtubule nucleation and a controlled conformational rearrangement of the gamma-TuRC is required for its activation. Collectively, our cryo-electron microscopy reconstructions provide detailed insights into the molecular organization, assembly and activation mechanism of vertebrate gamma-TuRC, and will serve as a framework for the mechanistic understanding of fundamental biological processes associated with microtubule nucleation, such as meiotic and mitotic spindle formation and centriole biogenesis(4).


The cryo-EM structure of the gamma-tubulin ring complex (gamma-TuRC) from Xenopus laevis provides insights into the molecular organization of the complex, and shows that actin is a structural component that is functionally relevant to microtubule nucleation.


  
Layered nanocomposites by shear-flow-induced alignment of nanosheets 期刊论文
NATURE, 2020, 580 (7802) : 210-+
作者:  Rollie, Clare;  Chevallereau, Anne;  Watson, Bridget N. J.;  Chyou, Te-yuan;  Fradet, Olivier;  McLeod, Isobel;  Fineran, Peter C.;  Brown, Chris M.;  Gandon, Sylvain;  Westra, Edze R.
收藏  |  浏览/下载:65/0  |  提交时间:2020/07/03

Layered nanocomposites fabricated using a continuous and scalable process achieve properties exceeding those of natural nacre, the result of stiffened matrix polymer chains confined between highly aligned nanosheets.


Biological materials, such as bones, teeth and mollusc shells, are well known for their excellent strength, modulus and toughness(1-3). Such properties are attributed to the elaborate layered microstructure of inorganic reinforcing nanofillers, especially two-dimensional nanosheets or nanoplatelets, within a ductile organic matrix(4-6). Inspired by these biological structures, several assembly strategies-including layer-by-layer(4,7,8), casting(9,10), vacuum filtration(11-13) and use of magnetic fields(14,15)-have been used to develop layered nanocomposites. However, how to produce ultrastrong layered nanocomposites in a universal, viable and scalable manner remains an open issue. Here we present a strategy to produce nanocomposites with highly ordered layered structures using shear-flow-induced alignment of two-dimensional nanosheets at an immiscible hydrogel/oil interface. For example, nanocomposites based on nanosheets of graphene oxide and clay exhibit a tensile strength of up to 1,215 +/- 80 megapascals and a Young'  s modulus of 198.8 +/- 6.5 gigapascals, which are 9.0 and 2.8 times higher, respectively, than those of natural nacre (mother of pearl). When nanosheets of clay are used, the toughness of the resulting nanocomposite can reach 36.7 +/- 3.0 megajoules per cubic metre, which is 20.4 times higher than that of natural nacre  meanwhile, the tensile strength is 1,195 +/- 60 megapascals. Quantitative analysis indicates that the well aligned nanosheets form a critical interphase, and this results in the observed mechanical properties. We consider that our strategy, which could be readily extended to align a variety of two-dimensional nanofillers, could be applied to a wide range of structural composites and lead to the development of high-performance composites.


  
How to make more out of community data? A conceptual framework and its implementation as models and software 期刊论文
ECOLOGY LETTERS, 2017, 20 (5)
作者:  Ovaskainen, Otso;  Tikhonov, Gleb;  Norberg, Anna;  Blanchet, F. Guillaume;  Duan, Leo;  Dunson, David;  Roslin, Tomas;  Abrego, Nerea
收藏  |  浏览/下载:24/0  |  提交时间:2019/04/09
Assembly process  biotic filtering  community distribution  community modelling  community similarity  environmental filtering  functional trait  joint species distribution model  metacommunity  phylogenetic signal