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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:16/0  |  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.


  
Debates: Does Information Theory Provide a New Paradigm for Earth Science? Emerging Concepts and Pathways of Information Physics 期刊论文
WATER RESOURCES RESEARCH, 2020, 56 (2)
作者:  Perdigao, Rui A. P.;  Ehret, Uwe;  Knuth, Kevin H.;  Wang, Jingfeng
收藏  |  浏览/下载:7/0  |  提交时间:2020/07/02
information physics  information theory  thermodynamics  kinematic geometry  entropy  complex systems  
An orbital water-ice cycle on comet 67P from colour changes 期刊论文
NATURE, 2020, 578 (7793) : 49-+
作者:  Oh, Myoung Hwan;  Cho, Min Gee;  Chung, Dong Young;  Park, Inchul;  Kwon, Youngwook Paul;  Ophus, Colin;  Kim, Dokyoon;  Kim, Min Gyu;  Jeong, Beomgyun;  Gu, X. Wendy;  Jo, Jinwoung;  Yoo, Ji Mun;  Hong, Jaeyoung;  McMains, Sara;  Kang, Kisuk;  Sung, Yung-Eun;  Alivisatos, A. Paul;  Hyeon, Taeghwan
收藏  |  浏览/下载:52/0  |  提交时间:2020/07/03

Solar heating of a cometary surface provides the energy necessary to sustain gaseous activity, through which dust is removed(1,2). In this dynamical environment, both the coma(3,4) and the nucleus(5,6) evolve during the orbit, changing their physical and compositional properties. The environment around an active nucleus is populated by dust grains with complex and variegated shapes(7), lifted and diffused by gases freed from the sublimation of surface ices(8,9). The visible colour of dust particles is highly variable: carbonaceous organic material-rich grains(10) appear red while magnesium silicate-rich(11,12) and water-ice-rich(13,14) grains appear blue, with some dependence on grain size distribution, viewing geometry, activity level and comet family type. We know that local colour changes are associated with grain size variations, such as in the bluer jets made of submicrometre grains on comet Hale-Bopp(15) or in the fragmented grains in the coma(16) of C/1999 S4 (LINEAR). Apart from grain size, composition also influences the coma'  s colour response, because transparent volatiles can introduce a substantial blueing in scattered light, as observed in the dust particles ejected after the collision of the Deep Impact probe with comet 9P/Tempel 1(17). Here we report observations of two opposite seasonal colour cycles in the coma and on the surface of comet 67P/Churyumov-Gerasimenko through its perihelion passage(18). Spectral analysis indicates an enrichment of submicrometre grains made of organic material and amorphous carbon in the coma, causing reddening during the passage. At the same time, the progressive removal of dust from the nucleus causes the exposure of more pristine and bluish icy layers on the surface. Far from the Sun, we find that the abundance of water ice on the nucleus is reduced owing to redeposition of dust and dehydration of the surface layer while the coma becomes less red.


  
Fast and Slow Slip Events Emerge Due to Fault Geometrical Complexity 期刊论文
GEOPHYSICAL RESEARCH LETTERS, 2018, 45 (10) : 4809-4819
作者:  Romanet, Pierre;  Bhat, Harsha S.;  Jolivet, Romain;  Madariaga, Raul
收藏  |  浏览/下载:7/0  |  提交时间:2019/04/09
seismic cycle  rate and state  complex geometry  slow slip events