3,096 research outputs found
Optical fluid and biomolecule transport with thermal fields
A long standing goal is the direct optical control of biomolecules and water for applications ranging from microfluidics over biomolecule detection to non-equilibrium biophysics. Thermal forces originating from optically applied, dynamic microscale temperature gradients have shown to possess great potential to reach this goal. It was demonstrated that laser heating by a few Kelvin can generate and guide water flow on the micrometre scale in bulk fluid, gel matrices or ice without requiring any lithographic structuring. Biomolecules on the other hand can be transported by thermal gradients, a mechanism termed thermophoresis, thermal diffusion or Soret effect. This molecule transport is the subject of current research, however it can be used to both characterize biomolecules and to record binding curves of important biological binding reactions, even in their native matrix of blood serum. Interestingly, thermophoresis can be easily combined with the optothermal fluid control. As a result, molecule traps can be created in a variety of geometries, enabling the trapping of small biomolecules, like for example very short DNA molecules. The combination with DNA replication from thermal convection allows us to approach molecular evolution with concurrent replication and selection processes inside a single chamber: replication is driven by thermal convection and selection by the concurrent accumulation of the DNA molecules. From the short but intense history of applying thermal fields to control fluid flow and biological molecules, we infer that many unexpected and highly synergistic effects and applications are likely to be explored in the future
Understanding the emergence of bacterial pathogens in novel hosts
This is the author accepted manuscript.Data accessibility statement:
The computer code to generate the stochastic simulation model can be downloaded fromOur understanding of the ecological and evolutionary context of novel infections is largely
based on viral diseases, even though bacterial pathogens may display key differences in the
processes underlying their emergence. For instance, host-shift speciation, in which the jump
of a pathogen into a novel host species is followed by the specialisation on that host and the
loss of infectivity of previous host(s), is commonly observed in viruses, but less often in
bacteria. Here, we suggest that adaptation to dealing with different environments, rates of
molecular evolution and recombination may influence the extent to which pathogens evolve
host generalism or specialism following a jump into a novel host. We then test these
hypotheses using a formal model and show that the high levels of phenotypic plasticity, low
rates of evolution and the ability to recombine typical of bacterial pathogens should reduce
their propensity to specialise on novel host. Novel bacterial infections may therefore be more
likely to result in transient spillovers or increased host ranges than in host shifts. Finally,
consistent with our predictions, we show that, in two unusual cases of contemporary bacterial
host shifts, the bacterial pathogens both have small genomes and rapid rates of substitution.
Further tests are required across a greater number of emerging pathogens to assess the
validity of our predictions.Natural Environment Research Council (NERC)Wellcome TrustRoyal SocietyLeverhulme Trus
Gating NO Release from Nitric Oxide Synthase
We have investigated the kinetics of NO escape from Geobacillus stearothermophilus nitric oxide synthase (gsNOS). Previous work indicated that NO release was gated at position 223 in mammalian enzymes; our kinetics experiments include mutants at that position along with measurements on the wild type enzyme. Employing stopped-flow UV–vis methods, reactions were triggered by mixing a reduced enzyme/N-hydroxy-l-arginine complex with an aerated buffer solution. NO release kinetics were obtained for wt NOS and three mutants (H134S, I223V, H134S/I223V). We have confirmed that wt gsNOS has the lowest NO release rate of known NOS enzymes, whether bacterial or mammalian. We also have found that steric clashes at positions 223 and 134 hinder NO escape, as judged by enhanced rates in the single mutants. The empirical rate of NO release from the gsNOS double mutant (H134/I223V) is nearly as rapid as that of the fastest mammalian enzymes, demonstrating that both positions 223 and 134 function as gates for escape of the product diatomic molecule
Studies in t)le Sphingolipids Series. XII. Structure of the Cerebrin Anhydro Base of Yeast (C20 - Phytosphingosine Anhydro Base)
It was confirmed that the cerebrin anhydro base from yeast (Ila) isolated according to the procedure established by Reindel et ai.2 ,a h as a C20 -structure rather than C1 s-structure as one might conclude erroneously by simple comparison of physical constants \u27C/f both bases. The tetrahydrofuran structure was a lso d emonstrated by means of the IR spectroscopy. For this purpose following new compounds derived from C20 -anhydro b ase were prepared: N,0-diacetyl (lib), N,0-ditosyl (Ile), 0-acetyl-N-benzoyl (!Id) and Nphthaloyl derivative (III);· in addition, 2-hexadecyl-3 ,4-dihydroxytetrahydrofuran(IV) - a deamination product of the base was described
Strain and structure driven complex magnetic ordering of a CoO overlayer on Ir(100)
We have investigated the magnetic ordering in the ultrathin c(102)
CoO(111) film supported on Ir(100) on the basis of ab-initio calculations. We
find a close relationship between the local structural properties of the oxide
film and the induced magnetic order, leading to alternating ferromagnetically
and anti-ferromagnetically ordered segments. While the local magnetic order is
directly related to the geometric position of the Co atoms, the mismatch
between the CoO film and the Ir substrate leads to a complex long-range order
of the oxide.Comment: 5 pages, 4 figure
Social Networking Site Use Resumption: A Model of Return Migration
This research explains why individuals resume using social networking sites (SNSs) after terminating their use. Drawing on return migration theory, we developed a theory-driven model of SNS resumption that includes two novel antecedents of SNS resumption behavior: nonuse-related dissatisfaction and use-related satisfaction. We also hypothesize that dispositional resistance to change moderates the impact of nonuse-related dissatisfaction and use-related satisfaction on resumption. We used a mixed methods approach to refine and evaluate the research model. Study 1 used the critical incident method to identify SNS-specific antecedents of nonuse-related satisfaction and use-related satisfaction, allowing us to refine the research model. Study 2 used structural equation modeling to evaluate our research model using two three-wave surveys: one with recent ex-users who recently decided to stop using and delete their profiles on Facebook and one with long-standing ex-users who stopped using and deleted their profiles on Facebook a long time ago. We found support for most relationships in our model: nonuse-related dissatisfaction and use-related satisfaction drive resumption intentions, and dispositional resistance moderates these relationships. Furthermore, we found that the time elapsed since users discontinued Facebook moderated these relationships such that the effect of nonuse-related dissatisfaction on resumption intention is stronger for recent ex-users and the effect of use-related satisfaction is stronger for long-standing ex-users. Our findings advance the understanding of resumption, an understudied behavior of the IT lifecycle and IT use and acceptance research
Mol. Cell. Proteomics
Post-translational modification of proteins by ubiquitin is a fundamentally important regulatory mechanism. However, proteome-wide analysis of endogenous ubiquitylation remains a challenging task, and almost always has relied on cells expressing affinity tagged ubiquitin. Here we combine single-step immunoenrichment of ubiquitylated peptides with peptide fractionation and high-resolution mass spectrometry to investigate endogenous ubiquitylation sites. We precisely map 11,054 endogenous putative ubiquitylation sites (diglycine-modified lysines) on 4,273 human proteins. The presented data set covers 67% of the known ubiquitylation sites and contains 10,254 novel sites on proteins with diverse cellular functions including cell signaling, receptor endocytosis, DNA replication, DNA damage repair, and cell cycle progression. Our method enables site-specific quantification of ubiquitylation in response to cellular perturbations and is applicable to any cell type or tissue. Global quantification of ubiquitylation in cells treated with the proteasome inhibitor MG-132 discovers sites that are involved in proteasomal degradation, and suggests a nonproteasomal function for almost half of all sites. Surprisingly, ubiquitylation of about 15% of sites decreased more than twofold within four hours of MG-132 treatment, showing that inhibition of proteasomal function can dramatically reduce ubiquitylation on many sites with non-proteasomal functions. Comparison of ubiquitylation sites with acetylation sites reveals an extensive overlap between the lysine residues targeted by these two modifications. However, the crosstalk between these two post-translational modifications is significantly less frequent on sites that show increased ubiquitylation upon proteasome inhibition. Taken together, we report the largest site-specific ubiquitylation dataset in human cells, and for the first time demonstrate proteome-wide, site-specific quantification of endogenous putative ubiquitylation sites
Versuche zur Waermeabfuhr von einem SNR-Brennelement in einer mit Natrium gefuellten Transportbuechse
Exhaustive generation of -critical -free graphs
We describe an algorithm for generating all -critical -free
graphs, based on a method of Ho\`{a}ng et al. Using this algorithm, we prove
that there are only finitely many -critical -free graphs, for
both and . We also show that there are only finitely many
-critical graphs -free graphs. For each case of these cases we
also give the complete lists of critical graphs and vertex-critical graphs.
These results generalize previous work by Hell and Huang, and yield certifying
algorithms for the -colorability problem in the respective classes.
Moreover, we prove that for every , the class of 4-critical planar
-free graphs is finite. We also determine all 27 4-critical planar
-free graphs.
We also prove that every -free graph of girth at least five is
3-colorable, and determine the smallest 4-chromatic -free graph of
girth five. Moreover, we show that every -free graph of girth at least
six and every -free graph of girth at least seven is 3-colorable. This
strengthens results of Golovach et al.Comment: 17 pages, improved girth results. arXiv admin note: text overlap with
arXiv:1504.0697
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