共查询到20条相似文献，搜索用时 239 毫秒
1.
Brohawn SG Leksa NC Spear ED Rajashankar KR Schwartz TU 《Science (New York, N.Y.)》2008,322(5906):1369-1373
Nuclear pore complexes (NPCs) facilitate nucleocytoplasmic transport. These massive assemblies comprise an eightfold symmetric scaffold of architectural proteins and central-channel phenylalanine-glycine-repeat proteins forming the transport barrier. We determined the nucleoporin 85 (Nup85)*Seh1 structure, a module in the heptameric Nup84 complex, at 3.5 angstroms resolution. Structural, biochemical, and genetic analyses position the Nup84 complex in two peripheral NPC rings. We establish a conserved tripartite element, the ancestral coatomer element ACE1, that reoccurs in several nucleoporins and vesicle coat proteins, providing structural evidence of coevolution from a common ancestor. We identified interactions that define the organization of the Nup84 complex on the basis of comparison with vesicle coats and confirmed the sites by mutagenesis. We propose that the NPC scaffold, like vesicle coats, is composed of polygons with vertices and edges forming a membrane-proximal lattice that provides docking sites for additional nucleoporins. 相似文献
2.
Beck M Förster F Ecke M Plitzko JM Melchior F Gerisch G Baumeister W Medalia O 《Science (New York, N.Y.)》2004,306(5700):1387-1390
Nuclear pore complexes (NPCs) are gateways for nucleocytoplasmic exchange. To analyze their structure in a close-to-life state, we studied transport-active, intact nuclei from Dictyostelium discoideum by means of cryoelectron tomography. Subvolumes of the tomograms containing individual NPCs were extracted in silico and subjected to three-dimensional classification and averaging, whereby distinct structural states were observed. The central plug/transporter (CP/T) was variable in volume and could occupy different positions along the nucleocytoplasmic axis, which supports the notion that it essentially represents cargo in transit. Changes in the position of the CP/T were accompanied by structural rearrangements in the NPC scaffold. 相似文献
3.
Manganas LN Zhang X Li Y Hazel RD Smith SD Wagshul ME Henn F Benveniste H Djuric PM Enikolopov G Maletic-Savatic M 《Science (New York, N.Y.)》2007,318(5852):980-985
The identification of neural stem and progenitor cells (NPCs) by in vivo brain imaging could have important implications for diagnostic, prognostic, and therapeutic purposes. We describe a metabolic biomarker for the detection and quantification of NPCs in the human brain in vivo. We used proton nuclear magnetic resonance spectroscopy to identify and characterize a biomarker in which NPCs are enriched and demonstrated its use as a reference for monitoring neurogenesis. To detect low concentrations of NPCs in vivo, we developed a signal processing method that enabled the use of magnetic resonance spectroscopy for the analysis of the NPC biomarker in both the rodent brain and the hippocampus of live humans. Our findings thus open the possibility of investigating the role of NPCs and neurogenesis in a wide variety of human brain disorders. 相似文献
4.
该文较详细地归纳了迄今为止有关绝干和湿润状态木材细胞壁的空隙构造，木材细胞壁中物质的输运过程、物质在细胞壁中的平衡态分布、影响物质输运过程的主要因素等.为进一步深入开展这方面的研究，作者提出了值得商榷的几点问题及今后开展这方面研究的一些设想. 相似文献
5.
木材细胞壁的空隙构造及物质的输运过程 总被引：2，自引：1，他引：2
该文较详细地归纳了迄今为止有关绝干和湿润状态木材细胞壁的空隙构造 ,木材细胞壁中物质的输运过程、物质在细胞壁中的平衡态分布、影响物质输运过程的主要因素等 .为进一步深入开展这方面的研究 ,作者提出了值得商榷的几点问题及今后开展这方面研究的一些设想 相似文献
6.
Long unfolded linkers facilitate membrane protein import through the nuclear pore complex 总被引：1，自引：0，他引：1
Meinema AC Laba JK Hapsari RA Otten R Mulder FA Kralt A van den Bogaart G Lusk CP Poolman B Veenhoff LM 《Science (New York, N.Y.)》2011,333(6038):90-93
Active nuclear import of soluble cargo involves transport factors that shuttle cargo through the nuclear pore complex (NPC) by binding to phenylalanine-glycine (FG) domains. How nuclear membrane proteins cross through the NPC to reach the inner membrane is presently unclear. We found that at least a 120-residue-long intrinsically disordered linker was required for the import of membrane proteins carrying a nuclear localization signal for the transport factor karyopherin-α. We propose an import mechanism for membrane proteins in which an unfolded linker slices through the NPC scaffold to enable binding between the transport factor and the FG domains in the center of the NPC. 相似文献
7.
目的：探讨基质金属蛋白酶2、9(MMP-2、MMP-9)在鼻咽癌及其淋巴结转移灶组织中的表达、意义及与EB病毒潜伏膜蛋白1(LMPl)的相关关系。方法：应用免疫组化(SP法)检测LMPl和MMP-2、MMP-9在人鼻咽粘膜慢性炎(30例)、鼻咽癌(30例)和鼻咽癌颈部淋巴结转移灶(24例)组织中的表达。结果：鼻咽癌和鼻咽癌颈部淋巴结转移灶组织中LMPl和MMP-2、MMP-9的阳性率明显高于鼻咽粘膜慢性炎。在鼻咽癌及鼻咽癌颈部淋巴结转移灶标本中还发现癌巢周边的成纤维细胞、癌周浸润的单核细胞、淋巴细胞以及血管内皮细胞中也有MMP-2和MMP-9的表达。Spearman相关分析显示，在鼻咽癌组织中LMPl与MMP-2、MMP-9的表达无相关性；而在鼻咽癌颈部淋巴结转移灶组织中，LMPl的表达与MMP-2、MMP-9的表达呈中度正相关。结论：MMP-2、MMP-9在鼻咽癌细胞突破基底膜向外扩散及转移中起到重要作用；在鼻咽癌淋巴结转移灶中LMPl与MMP-2、MMP-9的表达呈正相关；LMPl可能参与鼻咽部疾病的恶性转化和癌细胞的浸润转移。 相似文献
8.
Schermelleh L Carlton PM Haase S Shao L Winoto L Kner P Burke B Cardoso MC Agard DA Gustafsson MG Leonhardt H Sedat JW 《Science (New York, N.Y.)》2008,320(5881):1332-1336
Fluorescence light microscopy allows multicolor visualization of cellular components with high specificity, but its utility has until recently been constrained by the intrinsic limit of spatial resolution. We applied three-dimensional structured illumination microscopy (3D-SIM) to circumvent this limit and to study the mammalian nucleus. By simultaneously imaging chromatin, nuclear lamina, and the nuclear pore complex (NPC), we observed several features that escape detection by conventional microscopy. We could resolve single NPCs that colocalized with channels in the lamin network and peripheral heterochromatin. We could differentially localize distinct NPC components and detect double-layered invaginations of the nuclear envelope in prophase as previously seen only by electron microscopy. Multicolor 3D-SIM opens new and facile possibilities to analyze subcellular structures beyond the diffraction limit of the emitted light. 相似文献
9.
RanGTPase的活性蛋白RanGAP1位于细胞质中,是RanGTP/GDP循环的一个关键调节器,对细胞的核质运输和有丝分裂都有重要作用。RanGAP1是第一个为人们所证实的可被SUMO-1的蛋白质,SUMO化的RanGAP1位于核孔,与核孔蛋白RanBP2/Nup358及其相关因子相结合,对细胞周期起到调控作用。 相似文献
10.
采用室内柱迁移实验,研究了在不同离子强度下多孔介质粒径和孔隙水流速对大肠杆菌在饱和石英砂柱中沉积与释放行为的影响。结果表明,介质粒径和孔隙水流速均能影响大肠杆菌在石英砂中的迁移过程。介质粒径的减小可增强大肠杆菌在多孔介质中的筛滤效应,增加其沉积率和滞留率,减小水化学扰动引起的释放效应,流速的降低有利于提高大肠杆菌的沉积率和滞留率。离子强度的高低可改变粒径和流速对大肠杆菌迁移影响的大小,在较高离子强度条件下,减小介质粒径和孔隙水流速对提高大肠杆菌的沉积率和滞留率的作用增强。由于自然环境的复杂性,今后的研究应注重真实地下水环境中多因素对大肠杆菌迁移行为的复合影响,以便更加准确地掌握大肠杆菌在多孔介质中迁移的规律。 相似文献
11.
通过对港西油田产油气储层的岩石学、孔隙类型和孔隙结构特征等的研究,结合X-射线衍射和扫描电镜等的测试结果,分析了储层损害的潜在地质因素。结果表明,研究区储层砂岩主要为中细粒岩屑长石砂岩和长石岩屑砂岩,储集空间主要为粒间孔,孔喉类型为中孔中喉-中孔细喉型组合类型。填隙物中的石英、黄铁矿、碳酸盐矿物和粘土矿物是造成储层损害的主要敏感性矿物,潜在的损害主要为酸化过程中的新生沉淀物与脱落微粒、固体微体迁移和与地层水不配伍的流体造成的地层损害。 相似文献
12.
致密砂岩油藏是塔里木盆地石油增储上产的重要资源基础之一。台盆区志留系柯下段是近几年新发现的一套海相碎屑岩含油气储盖组合,储层为典型致密砂岩。依合2A井是新钻探的一口重要的区域探井,该井在志留系柯下段获良好油气显示,通过该井系统取心、取样分析,使深入研究这套致密储层特征成为可能。通过对岩心样品进行岩石薄片、物性、铸体薄片、扫描电镜、高压压汞和黏土矿物等系统测试分析,详细研究了柯下段致密含油砂岩储层特征及其主控因素。研究表明,柯下段致密砂岩储层主要为细粒、细—中粒岩屑砂岩,岩屑含量高,成分成熟度低,结构成熟度中等;为特低—超低孔、特低—超低渗储层;孔隙类型主要为晶间孔、粒内孔等微孔隙,次为粒间孔;孔喉结构为细孔 —微孔微细喉型,根据毛细管压力曲线的特点可分为4类。造成储层致密的主要控制因素是强烈的压实作用和胶结作用以及较弱的溶解作用,使得孔隙不发育,同时黏土矿物含量较高,孔隙空间和结构进一步变差,储层渗透性进一步降低,并具较强敏感性。 相似文献
13.
再生水中典型PAHs垂向迁移特征研究 总被引：1，自引：0，他引：1
[目的]探究在模拟灌溉条件下,再生水中典型多环芳烃的迁移特征和影响因素。[方法]通过土柱模拟试验,以再生水中多环芳烃萘、菲、芘为对象,北京市东南郊再生水灌区典型土壤为试验介质,对再生水连续灌溉时多环芳烃的迁移情况以及土柱出水中DOM的性质进行分析。[结果]实际土壤介质对多环芳烃的吸附能力不能单纯用土壤有机碳含量很好地描述,组成复杂的介质对多环芳烃的吸附能力增强,萘的实际阻滞因子超过理论值约7倍;多环芳烃在非均质介质中的迁移存在界面效应,土壤有机碳含量差距越大,界面效应越明显;孔隙水流速以及孔隙尺寸增大,会造成固相上多环芳烃的解吸,发生二次迁移。微生物活动能促进多环芳烃的迁移。[结论]该研究可为建立基于地下水质量安全的再生水灌溉模式的提出奠定基础。 相似文献
14.
不同生物质来源生物炭品质的因子分析与综合评价 总被引：2，自引：1，他引：1
【目的】建立一套适合生物炭品质评价的方法,探求影响生物炭品质的主要影响因子。【方法】选用8种不同生物质材料,在3种温度下制备并获得24种生物炭材料(Y1～Y24),测定16项相关品质指标,采用隶属函数法对各项指标数据进行转化,采用软件SPSS19.0进行因子分析,采用四次方最大旋转法获得因子载荷矩阵,计算样品每个公因子分值与相应权重之积的累加和,得到综合评价分值。对16项指标进行相关性分析和因子分析,建立基于因子分析的生物炭品质的综合评价体系,并根据综合评价得分对生物炭进行优良度排序。【结果】24种生物炭16个品质指标经因子分析,提取了5个特征根1的公因子,累计方差贡献率达到77.910%,第1公因子以C含量、阳离子交换量(CEC)和pH贡献率较大,达到31.090%,第2公因子以比表面积和孔容贡献率较大,达到19.878%,第3公因子以H原子含量贡献率较大,达到12.819%,第4公因子以磷、钾含量贡献率较大,达到7.479%,第5公因子以NH4+-N吸附量贡献率较大,达到6.643%。【结论】因子分析方法可以作为评价生物炭品质的方法,根据因子分析评价方法,确定影响生物炭品质最关键的因子是化学性质因子(C含量、C/N比、C/H比、pH、CEC)、物理性质因子(比表面积和孔容)、活化能量因子(H原子含量)、营养因子(P和K含量)和氨态氮吸附能力因子。 相似文献
15.
Hinds BJ Chopra N Rantell T Andrews R Gavalas V Bachas LG 《Science (New York, N.Y.)》2004,303(5654):62-65
An array of aligned carbon nanotubes (CNTs) was incorporated across a polymer film to form a well-ordered nanoporous membrane structure. This membrane structure was confirmed by electron microscopy, anisotropic electrical conductivity, gas flow, and ionic transport studies. The measured nitrogen permeance was consistent with the flux calculated by Knudsen diffusion through nanometer-scale tubes of the observed microstructure. Data on Ru(NH3)6(3+) transport across the membrane in aqueous solution also indicated transport through aligned CNT cores of the observed microstructure. The lengths of the nanotubes within the polymer film were reduced by selective electrochemical oxidation, allowing for tunable pore lengths. Oxidative trimming processes resulted in carboxylate end groups that were readily functionalized at the entrance to each CNT inner core. Membranes with CNT tips that were functionalized with biotin showed a reduction in Ru(NH3)6(3+) flux by a factor of 15 when bound with streptavidin, thereby demonstrating the ability to gate molecular transport through CNT cores for potential applications in chemical separations and sensing. 相似文献
16.
【目的】探讨秸秆覆盖对广西甘蔗地土壤孔隙结构、孔隙数量、连通性等性质的影响,分析土壤孔隙结构特点及水分运移通道特征,为广西地区甘蔗生产中的科学合理种植提供理论依据。【方法】设秸秆覆盖（SM）与无秸秆覆盖对照（CK）2种处理,利用CT扫描成像技术和ImageJ软件获取土壤孔隙结构数据并测定土壤有机质,结合原位监测获得的5、20、40 cm深度的土壤含水量数据,对比分析不同处理的孔隙结构特点及土壤水分运移通道特征。【结果】SM处理0~10 cm土层的有机质含量显著高于CK （P<0.05,下同）;相同深度下SM处理的土壤含水量均高于CK。0~40 cm土层中,SM处理的土壤孔隙面密度显著大于CK,而CK的土壤孔隙复杂度显著高于SM处理。SM处理的孔隙数量（19190个）、直径≥1 mm孔隙数量（952个）、孔隙度（0.07%）及比表面积（1.64 mm-1）均显著大于CK对应值（9415个,690个,0.06%,1.43 mm-1）。土壤孔隙三维结构显示,CK的总孔隙数量少且多分散在0~20 cm土层,空间分布呈明显的分层现象;而SM处理的总土壤孔隙数量多且均匀分布在整个空间,无明显孔隙分布分层现象,且其连通性孔隙发育较完善。【结论】秸秆覆盖处理可有效提高广西甘蔗地的土壤含水量,增加土壤孔隙数量,从而整体提高土壤孔隙连通性,对土壤孔隙结构改善有一定积极影响,有利于促进甘蔗根系的生长发育。 相似文献
17.
Lim RY Fahrenkrog B Köser J Schwarz-Herion K Deng J Aebi U 《Science (New York, N.Y.)》2007,318(5850):640-643
The nuclear pore complex regulates cargo transport between the cytoplasm and the nucleus. We set out to correlate the governing biochemical interactions to the nanoscopic responses of the phenylalanineglycine (FG)-rich nucleoporin domains, which are involved in attenuating or promoting cargo translocation. We found that binding interactions with the transport receptor karyopherin-beta1 caused the FG domains of the human nucleoporin Nup153 to collapse into compact molecular conformations. This effect was reversed by the action of Ran guanosine triphosphate, which returned the FG domains into a polymer brush-like, entropic barrier conformation. Similar effects were observed in Xenopus oocyte nuclei in situ. Thus, the reversible collapse of the FG domains may play an important role in regulating nucleocytoplasmic transport. 相似文献
18.
The nucleoporins Nup58 and Nup45 are part of the central transport channel of the nuclear pore complex, which is thought to have a flexible diameter. In the crystal structure of an alpha-helical region of mammalian Nup58/45, we identified distinct tetramers, each consisting of two antiparallel hairpin dimers. The intradimeric interface is hydrophobic, whereas dimer-dimer association occurs through large hydrophilic residues. These residues are laterally displaced in various tetramer conformations, which suggests an intermolecular sliding by 11 angstroms. We propose that circumferential sliding plays a role in adjusting the diameter of the central transport channel. 相似文献
19.
20.
FG-rich repeats of nuclear pore proteins form a three-dimensional meshwork with hydrogel-like properties 总被引：1，自引：0，他引：1
Nuclear pore complexes permit rapid passage of cargoes bound to nuclear transport receptors, but otherwise suppress nucleocytoplasmic fluxes of inert macromolecules >/=30 kilodaltons. To explain this selectivity, a sieve structure of the permeability barrier has been proposed that is created through reversible cross-linking between Phe and Gly (FG)-rich nucleoporin repeats. According to this model, nuclear transport receptors overcome the size limit of the sieve and catalyze their own nuclear pore-passage by a competitive disruption of adjacent inter-repeat contacts, which transiently opens adjoining meshes. Here, we found that phenylalanine-mediated inter-repeat interactions indeed cross-link FG-repeat domains into elastic and reversible hydrogels. Furthermore, we obtained evidence that such hydrogel formation is required for viability in yeast. 相似文献