GSTDTAP

浏览/检索结果: 共9条,第1-9条 帮助

已选(0)清除 条数/页:   排序方式:
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:38/0  |  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.


  
FERONIA controls pectin- and nitric oxide-mediated male-female interaction 期刊论文
NATURE, 2020, 579 (7800) : 561-+
作者:  Venkadesan, Madhusudhan;  Yawar, Ali;  Eng, Carolyn M.;  Dias, Marcelo A.;  Singh, Dhiraj K.;  Tommasini, Steven M.;  Haims, Andrew H.;  Bandi, Mahesh M.;  Mandre, Shreyas
收藏  |  浏览/下载:43/0  |  提交时间:2020/07/03

Species that propagate by sexual reproduction actively guard against the fertilization of an egg by multiple sperm (polyspermy). Flowering plants rely on pollen tubes to transport their immotile sperm to fertilize the female gametophytes inside ovules. In Arabidopsis, pollen tubes are guided by cysteine-rich chemoattractants to target the female gametophyte(1,2). The FERONIA receptor kinase has a dual role in ensuring sperm delivery and blocking polyspermy(3). It has previously been reported that FERONIA generates a female gametophyte environment that is required for sperm release(4). Here we show that FERONIA controls several functionally linked conditions to prevent the penetration of female gametophytes by multiple pollen tubes in Arabidopsis. We demonstrate that FERONIA is crucial for maintaining de-esterified pectin at the filiform apparatus, a region of the cell wall at the entrance to the female gametophyte. Pollen tube arrival at the ovule triggers the accumulation of nitric oxide at the filiform apparatus in a process that is dependent on FERONIA and mediated by de-esterified pectin. Nitric oxide nitrosates both precursor and mature forms of the chemoattractant LURE1(1), respectively blocking its secretion and interaction with its receptor, to suppress pollen tube attraction. Our results elucidate a mechanism controlled by FERONIA in which the arrival of the first pollen tube alters ovular conditions to disengage pollen tube attraction and prevent the approach and penetration of the female gametophyte by late-arriving pollen tubes, thus averting polyspermy.


FERONIA prevents polyspermy in Arabidopsis by enabling pectin-stimulated nitric oxide accumulation at the filiform apparatus after the first pollen tube arrives, which disengages LURE1 chemoattraction to prevent late-arriving pollen tubes from entering the ovule.


  
Limits on gas impermeability of graphene 期刊论文
NATURE, 2020, 579 (7798) : 229-+
作者:  Pagano, Justin K.;  Xie, Jing;  Erickson, Karla A.;  Cope, Stephen K.;  Scott, Brian L.;  Wu, Ruilian;  Waterman, Rory;  Morris, David E.;  Yang, Ping;  Gagliardi, Laura;  Kiplinger, Jaqueline L.
收藏  |  浏览/下载:37/0  |  提交时间:2020/07/03

Despite being only one-atom thick, defect-free graphene is considered to be completely impermeable to all gases and liquids(1-10). This conclusion is based on theory(3-8) and supported by experiments(1,9,10) that could not detect gas permeation through micrometre-size membranes within a detection limit of 10(5) to 10(6) atoms per second. Here, using small monocrystalline containers tightly sealed with graphene, we show that defect-free graphene is impermeable with an accuracy of eight to nine orders of magnitude higher than in the previous experiments. We are capable of discerning (but did not observe) permeation of just a few helium atoms per hour, and this detection limit is also valid for all other gases tested (neon, nitrogen, oxygen, argon, krypton and xenon), except for hydrogen. Hydrogen shows noticeable permeation, even though its molecule is larger than helium and should experience a higher energy barrier. This puzzling observation is attributed to a two-stage process that involves dissociation of molecular hydrogen at catalytically active graphene ripples, followed by adsorbed atoms flipping to the other side of the graphene sheet with a relatively low activation energy of about 1.0 electronvolt, a value close to that previously reported for proton transport(11,12). Our work provides a key reference for the impermeability of two-dimensional materials and is important from a fundamental perspective and for their potential applications.


  
Hidden diversity of vacancy networks in Prussian blue analogues 期刊论文
NATURE, 2020, 578 (7794) : 256-+
作者:  Hendrickx, N. W.;  Franke, D. P.;  Sammak, A.;  Scappucci, G.;  Veldhorst, M.
收藏  |  浏览/下载:28/0  |  提交时间:2020/07/03

Prussian blue analogues (PBAs) are a diverse family of microporous inorganic solids, known for their gas storage ability(1), metal-ion immobilization(2), proton conduction(3), and stimuli-dependent magnetic(4,5), electronic(6) and optical(7) properties. This family of materials includes the double-metal cyanide catalysts(8,9) and the hexacyanoferrate/ hexacyanomanganate battery materials(10,11). Central to the various physical properties of PBAs is their ability to reversibly transport mass, a process enabled by structural vacancies. Conventionally presumed to be random(12,13), vacancy arrangements are crucial because they control micropore-network characteristics, and hence the diffusivity and adsorption profiles(14,15). The long-standing obstacle to characterizing the vacancy networks of PBAs is the inaccessibility of single crystals(16). Here we report the growth of single crystals of various PBAs and the measurement and interpretation of their X-ray diffuse scattering patterns. We identify a diversity of non-random vacancy arrangements that is hidden from conventional crystallographic powder analysis. Moreover, we explain this unexpected phase complexity in terms of a simple microscopic model that is based on local rules of electroneutrality and centrosymmetry. The hidden phase boundaries that emerge demarcate vacancynetwork polymorphs with very different micropore characteristics. Our results establish a foundation for correlated defect engineering in PBAs as a means of controlling storage capacity, anisotropy and transport efficiency.


  
Attribution of the Hemispheric Asymmetries in Trends of Stratospheric Trace Gases Inferred From Microwave Limb Sounder (MLS) Measurements 期刊论文
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 2019, 124 (12) : 6283-6293
作者:  Han, Yuanyuan;  Tian, Wenshou;  Chipperfield, Martyn P.;  Zhang, Jiankai;  Wang, Feiyang;  Sang, Wenjun;  Luo, Jiali;  Feng, Wuhu;  Chrysanthou, Andreas;  Tian, Hongying
收藏  |  浏览/下载:25/0  |  提交时间:2019/11/26
stratospheric trace gas trend  hemispheric asymmetry  dynamical transport process  residual circulation  eddy mixing  
Determining and Modeling Dominant Processes of Interrill Soil Erosion 期刊论文
WATER RESOURCES RESEARCH, 2019, 55 (1) : 4-20
作者:  Zhang, X. C.
收藏  |  浏览/下载:12/0  |  提交时间:2019/04/09
interrill erosion process  interrill erosion modeling  raindrop detachment  raindrop-impacted flow transport  
Modeling the Origin of Anthropogenic Black Carbon and Its Climatic Effect Over the Tibetan Plateau and Surrounding Regions 期刊论文
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 2018, 123 (2) : 671-692
作者:  Yang, Junhua;  Kang, Shichang;  Ji, Zhenming;  Chen, Deliang
收藏  |  浏览/下载:15/0  |  提交时间:2019/04/09
black carbon  emission origin  Tibetan Plateau  South Asia  transport process  
Stochastic dynamics of intermittent pore-scale particle motion in three-dimensional porous media: Experiments and theory 期刊论文
GEOPHYSICAL RESEARCH LETTERS, 2017, 44 (18)
作者:  Morales, V. L.;  Dentz, M.;  Willmann, M.;  Holzner, M.
收藏  |  浏览/下载:15/0  |  提交时间:2019/04/09
anomalous transport  non-Fickian  velocity process  continuous time random walk  particle tracking  intermittent particle velocity  
Understanding watershed hydrogeochemistry: 1. Development of RT-Flux-PIHM 期刊论文
WATER RESOURCES RESEARCH, 2017, 53 (3)
作者:  Bao, Chen;  Li, Li;  Shi, Yuning;  Duffy, Christopher
收藏  |  浏览/下载:13/0  |  提交时间:2019/04/09
watershed hydrogeochemistry  reactive transport  process-based model  complex model  concentration-discharge relationship