排序方式: 共有72条查询结果,搜索用时 15 毫秒
31.
The hydroxide ion plays an important role in many chemical and biochemical processes in aqueous solution. But our molecular-level understanding of its unusual and fast transport in water, and of the solvation patterns that allow fast transport, is far from complete. One proposal seeks to explain the properties and behaviour of the hydroxide ion by essentially regarding it as a water molecule that is missing a proton, and by inferring transport mechanisms and hydration structures from those of the excess proton. A competing proposal invokes instead unique and interchanging hydroxide hydration complexes, particularly the hypercoordinated OH(-)(H(2)O)(4) species and tri-coordinated OH(-)(H(2)O)(3) that can form a transient hydrogen bond between the H atom of the OH(-) and a neighbouring water molecule. Here we report measurements of core-level photoelectron emission and intermolecular Coulombic decay for an aqueous hydroxide solution, which show that the hydrated hydroxide ion is capable of transiently donating a hydrogen bond to surrounding water molecules. In agreement with recent experimental studies of hydroxide solutions, our finding thus supports the notion that the hydration structure of the hydroxide ion cannot be inferred from that of the hydrated excess proton. 相似文献
32.
Manfred Breit Manfred Vogel Fritz Hubi Fabian Mrki Micheal Raps iDs University of Applied Sciences Northwestern Switzerland Steinackerstrasse CH- Windisch Switzerland 《清华大学学报》2008,13(Z1):179-184
The objective of this ongoing joint research program is to determine how 3D/4D modeling, simulation and visualization of Products (buildings), Organizations and Processes (POP) can support lean construction. Initial findings suggest that Process Design Pattern may have the potential to intuitively support ICT based lean construction. We initiated a "Process Archeology" in order to reveal the requirements for tools that can support the planning, simulation and control of lean construction methods. First findings show that existing tools provide only limited support and therefore, we started to develop new methodologies and technologies to overcome these shortcomings. Through the introduction of Process Design Patterns, we intent to establish process thinking in the interdisciplinary POP design. Optimized construction processes may be synthesized with semi-automatic methods by applying Process Design Patterns on building structures. By providing process templates that integrate problem solution and expert knowledge, Process Design Patterns may have the potential to ensure high quality process models. 相似文献
33.
Mikkelsen TS Wakefield MJ Aken B Amemiya CT Chang JL Duke S Garber M Gentles AJ Goodstadt L Heger A Jurka J Kamal M Mauceli E Searle SM Sharpe T Baker ML Batzer MA Benos PV Belov K Clamp M Cook A Cuff J Das R Davidow L Deakin JE Fazzari MJ Glass JL Grabherr M Greally JM Gu W Hore TA Huttley GA Kleber M Jirtle RL Koina E Lee JT Mahony S Marra MA Miller RD Nicholls RD Oda M Papenfuss AT Parra ZE Pollock DD Ray DA Schein JE Speed TP Thompson K VandeBerg JL Wade CM Walker JA Waters PD Webber C 《Nature》2007,447(7141):167-177
We report a high-quality draft of the genome sequence of the grey, short-tailed opossum (Monodelphis domestica). As the first metatherian ('marsupial') species to be sequenced, the opossum provides a unique perspective on the organization and evolution of mammalian genomes. Distinctive features of the opossum chromosomes provide support for recent theories about genome evolution and function, including a strong influence of biased gene conversion on nucleotide sequence composition, and a relationship between chromosomal characteristics and X chromosome inactivation. Comparison of opossum and eutherian genomes also reveals a sharp difference in evolutionary innovation between protein-coding and non-coding functional elements. True innovation in protein-coding genes seems to be relatively rare, with lineage-specific differences being largely due to diversification and rapid turnover in gene families involved in environmental interactions. In contrast, about 20% of eutherian conserved non-coding elements (CNEs) are recent inventions that postdate the divergence of Eutheria and Metatheria. A substantial proportion of these eutherian-specific CNEs arose from sequence inserted by transposable elements, pointing to transposons as a major creative force in the evolution of mammalian gene regulation. 相似文献
34.
Kwok T Zabler D Urman S Rohde M Hartig R Wessler S Misselwitz R Berger J Sewald N König W Backert S 《Nature》2007,449(7164):862-866
Integrins are important mammalian receptors involved in normal cellular functions as well as pathogenesis of chronic inflammation and cancer. We propose that integrins are exploited by the gastric pathogen and type-1 carcinogen Helicobacter pylori for injection of the bacterial oncoprotein cytotoxin-associated gene A (CagA) into gastric epithelial cells. Virulent H. pylori express a type-IV secretion pilus that injects CagA into the host cell; CagA then becomes tyrosine-phosphorylated by Src family kinases. However, the identity of the host cell receptor involved in this process has remained unknown. Here we show that the H. pylori CagL protein is a specialized adhesin that is targeted to the pilus surface, where it binds to and activates integrin alpha5beta1 receptor on gastric epithelial cells through an arginine-glycine-aspartate motif. This interaction triggers CagA delivery into target cells as well as activation of focal adhesion kinase and Src. Our findings provide insights into the role of integrins in H.-pylori-induced pathogenesis. CagL may be exploited as a new molecular tool for our further understanding of integrin signalling. 相似文献
35.
Jones FC Grabherr MG Chan YF Russell P Mauceli E Johnson J Swofford R Pirun M Zody MC White S Birney E Searle S Schmutz J Grimwood J Dickson MC Myers RM Miller CT Summers BR Knecht AK Brady SD Zhang H Pollen AA Howes T Amemiya C;Broad Institute Genome Sequencing Platform & Whole Genome Assembly Team Baldwin J Bloom T Jaffe DB Nicol R Wilkinson J Lander ES Di Palma F Lindblad-Toh K Kingsley DM 《Nature》2012,484(7392):55-61
Marine stickleback fish have colonized and adapted to thousands of streams and lakes formed since the last ice age, providing an exceptional opportunity to characterize genomic mechanisms underlying repeated ecological adaptation in nature. Here we develop a high-quality reference genome assembly for threespine sticklebacks. By sequencing the genomes of twenty additional individuals from a global set of marine and freshwater populations, we identify a genome-wide set of loci that are consistently associated with marine-freshwater divergence. Our results indicate that reuse of globally shared standing genetic variation, including chromosomal inversions, has an important role in repeated evolution of distinct marine and freshwater sticklebacks, and in the maintenance of divergent ecotypes during early stages of reproductive isolation. Both coding and regulatory changes occur in the set of loci underlying marine-freshwater evolution, but regulatory changes appear to predominate in this well known example of repeated adaptive evolution in nature. 相似文献
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37.
Since 1992, the study of biological functions of HIV-1 gp41 has made great progress. Experimental evidence from several research groups demonstrated that gp41 has a putative cellular receptor. A recombinant soluble gp41 (aa539–684) and gp41 immunosuppressive peptide (aa583–599) could bind to human B lymphocytes and monocytes, but weakly bind to T lymphocytes. It was found that gp41 contains two cellular binding sites (aa583–599 and 641–675). GP41 could selectively inhibit cell proliferation of human T, B lymphocytes and monocytes, enhance human MHC class I, II and ICAM-1 molecule expression on cell surface. Gp41 binding proteins and a monoclonal antibody against the first binding site could inhibit this modulation effect. Amino acid sequence homology exists between gp41 and human type I interferons, and the homologous region is located in the first binding site on gp41 and in the receptor binding site on type I interferons. Studies in other groups indicate that both binding sites in gp41 may be associated with HIV infection of cells. Peptides containing two binding sites could respectively inhibit HIV infection of cells. A monoclonal antibody recognizing the second binding site could neutralize lab-strains and recently separated strains of HIV-1. Besides, antibodies against two regions (homologous with gp41 binding sites) of SIV transmembrane protein gp32 could protect macaques from SIV infection. These results suggest that the study of gp41 binding sites and cellular receptor could contribute to understanding the mechanism of HIV infection and to developing HIV vaccine and anti-HIV drugs. 相似文献
38.
Accessibility of host cell lineages to medaka stem cells depends on genetic background and irradiation of recipient embryos 总被引:1,自引:0,他引:1
Ni Hong Mingyou Li Zhiqiang Zeng Meisheng Yi Jiaorong Deng Jianfang Gui Christoph Winkler Manfred Schartl Yunhan Hong 《Cellular and molecular life sciences : CMLS》2010,67(7):1189-1202
Chimera formation is a powerful tool for analyzing pluripotency in vivo. It has been widely accepted that host cell lineages
are generally accessible to embryonic stem (ES) cells with the actual contribution depending solely on the intrinsic pluripotency
of transplanted donor cells. Here, we show in the fish medaka (Oryzias latipes) that the host accessibility to ES cell contribution exhibits dramatic differences. Specifically, of three albino host strains
tested (i
1
, i
3 and af), only strain i
1 generated pigmented chimeras. Strikingly, this accessibility is completely lost in i
1 but acquired in i
3 after host γ-irradiation. Host irradiation also differentially affected ES cell contribution to somatic organs and gonad.
Therefore, the accessibility of various host cell lineages can vary considerably depending on host strains and cell lineages
as well as on irradiation. Our findings underscore the importance of host genotypes for interpreting donor cell pluripotency
and for improving ES-derived chimera production. 相似文献
39.
40.
Opitz CA Litzenburger UM Sahm F Ott M Tritschler I Trump S Schumacher T Jestaedt L Schrenk D Weller M Jugold M Guillemin GJ Miller CL Lutz C Radlwimmer B Lehmann I von Deimling A Wick W Platten M 《Nature》2011,478(7368):197-203
Activation of the aryl hydrocarbon receptor (AHR) by environmental xenobiotic toxic chemicals, for instance 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin), has been implicated in a variety of cellular processes such as embryogenesis, transformation, tumorigenesis and inflammation. But the identity of an endogenous ligand activating the AHR under physiological conditions in the absence of environmental toxic chemicals is still unknown. Here we identify the tryptophan (Trp) catabolite kynurenine (Kyn) as an endogenous ligand of the human AHR that is constitutively generated by human tumour cells via tryptophan-2,3-dioxygenase (TDO), a liver- and neuron-derived Trp-degrading enzyme not yet implicated in cancer biology. TDO-derived Kyn suppresses antitumour immune responses and promotes tumour-cell survival and motility through the AHR in an autocrine/paracrine fashion. The TDO-AHR pathway is active in human brain tumours and is associated with malignant progression and poor survival. Because Kyn is produced during cancer progression and inflammation in the local microenvironment in amounts sufficient for activating the human AHR, these results provide evidence for a previously unidentified pathophysiological function of the AHR with profound implications for cancer and immune biology. 相似文献