1,689 research outputs found
Topoisomer Differentiation of Molecular Knots by FTICR MS: Lessons from Class II Lasso Peptides
Lasso peptides constitute a class of bioactive peptides sharing a knotted
structure where the C-terminal tail of the peptide is threaded through and
trapped within an N-terminalmacrolactamring. The structural characterization of
lasso structures and differentiation from their unthreaded topoisomers is not
trivial and generally requires the use of complementary biochemical and
spectroscopic methods. Here we investigated two antimicrobial peptides
belonging to the class II lasso peptide family and their corresponding
unthreaded topoisomers: microcin J25 (MccJ25), which is known to yield
two-peptide product ions specific of the lasso structure under collisioninduced
dissociation (CID), and capistruin, for which CID does not permit to
unambiguously assign the lasso structure. The two pairs of topoisomers were
analyzed by electrospray ionization Fourier transform ion cyclotron resonance
mass spectrometry (ESI-FTICR MS) upon CID, infrared multiple photon
dissociation (IRMPD), and electron capture dissociation (ECD). CID and
ECDspectra clearly permitted to differentiate MccJ25 from its non-lasso
topoisomer MccJ25-Icm, while for capistruin, only ECD was informative and
showed different extent of hydrogen migration (formation of c\bullet/z from
c/z\bullet) for the threaded and unthreaded topoisomers. The ECD spectra of the
triply-charged MccJ25 and MccJ25-lcm showed a series of radical b-type product
ions {\eth}b0In{\TH}. We proposed that these ions are specific of
cyclic-branched peptides and result from a dual c/z\bullet and y/b
dissociation, in the ring and in the tail, respectively. This work shows the
potentiality of ECD for structural characterization of peptide topoisomers, as
well as the effect of conformation on hydrogen migration subsequent to electron
capture
Feasibility of using Grindr⢠to distribute HIV self-test kits to men who have sex with men in Los Angeles, California
Background: Our study aimed to determine if Grindr⢠is an effective means of reaching high-risk men who have sex with men (MSM) for HIV testing. In Los Angeles (LA), Black and Latino MSM have the highest rate of HIV infection, and Black MSM in LA are four-fold more likely than white MSM to not know they are infected with HIV. Those MSM are also major users of social networking apps. Grindr⢠was used to provide access to free HIV self-testing. Methods: Free HIV self-test kits were advertised on Grindr⢠from 13 October to 11 November 2014, consisting of 300 000 banner ads and three broadcast messages targeting a high-risk HIV population in LA. Eligible participants, Black or Latino, MSM and who were aged âĽ18 years of age, were invited to take a survey 2 weeks after test delivery. Results: The website received 4389 unique visitors and 333 test requests, of which 247 (74%) were requests for mailed tests, 58 (17%) were for vouchers and 28 (8%) were for vending machines. Of the 125 participants, 74% reported at least one episode of condomless anal intercourse in the past 3 months, 29% last tested for HIV over 1 year ago and 9% had never been tested. Conclusions: It was feasible to use Grindr⢠to distribute HIV self-test kits. Users are willing to provide personal information in exchange for a free self-test and found self-tests acceptable and easy to use. HIV self-testing promotion through apps has a high potential to reach untested high-risk populations
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The JAK inhibitor tofacitinib suppresses synovial JAK1-STAT signalling in rheumatoid arthritis.
ObjectiveTofacitinib is an oral Janus kinase (JAK) inhibitor for the treatment of rheumatoid arthritis (RA). The pathways affected by tofacitinib and the effects on gene expression in situ are unknown. Therefore, tofacitinib effects on synovial pathobiology were investigated.MethodsA randomised, double-blind, phase II serial synovial biopsy study (A3921073; NCT00976599) in patients with RA with an inadequate methotrexate response. Patients on background methotrexate received tofacitinib 10â
mg twice daily or placebo for 28â
days. Synovial biopsies were performed on Days -7 and 28 and analysed by immunoassay or quantitative PCR. Clinical response was determined by disease activity score and European League Against Rheumatism (EULAR) response on Day 28 in A3921073, and at Month 3 in a long-term extension study (A3921024; NCT00413699).ResultsTofacitinib exposure led to EULAR moderate to good responses (11/14 patients), while placebo was ineffective (1/14 patients) on Day 28. Tofacitinib treatment significantly reduced synovial mRNA expression of matrix metalloproteinase (MMP)-1 and MMP-3 (p<0.05) and chemokines CCL2, CXCL10 and CXCL13 (p<0.05). No overall changes were observed in synovial inflammation score or the presence of T cells, B cells or macrophages. Changes in synovial phosphorylation of signal transducer and activator of transcription 1 (STAT1) and STAT3 strongly correlated with 4-month clinical responses (p<0.002). Tofacitinib significantly decreased plasma CXCL10 (p<0.005) at Day 28 compared with placebo.ConclusionsTofacitinib reduces metalloproteinase and interferon-regulated gene expression in rheumatoid synovium, and clinical improvement correlates with reductions in STAT1 and STAT3 phosphorylation. JAK1-mediated interferon and interleukin-6 signalling likely play a key role in the synovial response.Trial registration numberNCT00976599
When the Genome Plays Dice: Circumvention of the Spindle Assembly Checkpoint and Near-Random Chromosome Segregation in Multipolar Cancer Cell Mitoses
Background: Normal cell division is coordinated by a bipolar mitotic spindle, ensuring symmetrical segregation of chromosomes. Cancer cells, however, occasionally divide into three or more directions. Such multipolar mitoses have been proposed to generate genetic diversity and thereby contribute to clonal evolution. However, this notion has been little validated experimentally.Principal Findings: Chromosome segregation and DNA content in daughter cells from multipolar mitoses were assessed by multiphoton cross sectioning and fluorescence in situ hybridization in cancer cells and non-neoplastic transformed cells. The DNA distribution resulting from multipolar cell division was found to be highly variable, with frequent nullisomies in the daughter cells. Time-lapse imaging of H2B/GFP-labelled multipolar mitoses revealed that the time from the initiation of metaphase to the beginning of anaphase was prolonged and that the metaphase plates often switched polarity several times before metaphase-anaphase transition. The multipolar metaphase-anaphase transition was accompanied by a normal reduction of cellular cyclin B levels, but typically occurred before completion of the normal separase activity cycle. Centromeric AURKB and MAD2 foci were observed frequently to remain on the centromeres of multipolar ana-telophase chromosomes, indicating that multipolar mitoses were able to circumvent the spindle assembly checkpoint with some sister chromatids remaining unseparated after anaphase. Accordingly, scoring the distribution of individual chromosomes in multipolar daughter nuclei revealed a high frequency of nondisjunction events, resulting in a near-binomial allotment of sister chromatids to the daughter cells.Conclusion: The capability of multipolar mitoses to circumvent the spindle assembly checkpoint system typically results in a near-random distribution of chromosomes to daughter cells. Spindle multipolarity could thus be a highly efficient generator of genetically diverse minority clones in transformed cell populations
Quantum Ising model in a transverse random field: A density-matrix renormalization group analysis
The spin-1/2 quantum Ising chain in a transverse random magnetic field is
studied by means of the density-matrix renormalization group. The system
evolves from an ordered to a paramagnetic state as the amplitude of the random
field is increased. The dependence of the magnetization on a uniform magnetic
field in the z direction and the spontaneous magnetization as a function of the
amplitude of the transverse random magnetic field are determined. The behavior
of the spin-spin correlation function both above and at criticality is studied.
The scaling laws for magnetization and correlation functions are tested against
previous numerical and renormalization-group results.Comment: 5 pages with 7 figures inside them, proper format of authors' names
use
Yang-Baxter R operators and parameter permutations
We present an uniform construction of the solution to the Yang- Baxter
equation with the symmetry algebra and its deformations: the
q-deformation and the elliptic deformation or Sklyanin algebra. The R-operator
acting in the tensor product of two representations of the symmetry algebra
with arbitrary spins and is built in terms of products of
three basic operators which are
constructed explicitly. They have the simple meaning of representing elementary
permutations of the symmetric group , the permutation group of
the four parameters entering the RLL-relation.Comment: 22 pages LaTex, comments added, version to be published in Nucl.
Phys.
Ordered phase and scaling in models and the three-state antiferromagnetic Potts model in three dimensions
Based on a Renormalization-Group picture of symmetric models in three
dimensions, we derive a scaling law for the order parameter in the
ordered phase. An existing Monte Carlo calculation on the three-state
antiferromagnetic Potts model, which has the effective symmetry, is shown
to be consistent with the proposed scaling law. It strongly supports the
Renormalization-Group picture that there is a single massive ordered phase,
although an apparently rotationally symmetric region in the intermediate
temperature was observed numerically.Comment: 5 pages in REVTEX, 2 PostScript figure
Global Bethe lattice consideration of the spin-1 Ising model
The spin-1 Ising model with bilinear and biquadratic exchange interactions
and single-ion crystal field is solved on the Bethe lattice using exact
recursion equations. The general procedure of critical properties investigation
is discussed and full set of phase diagrams are constructed for both positive
and negative biquadratic couplings. In latter case we observe all remarkable
features of the model, uncluding doubly-reentrant behavior and ferrimagnetic
phase. A comparison with the results of other approximation schemes is done.Comment: Latex, 11 pages, 13 ps figures available upon reques
Ground state of the random-bond spin-1 Heisenberg chain
Stochastic series expansion quantum Monte Carlo is used to study the ground
state of the antiferromagnetic spin-1 Heisenberg chain with bond disorder.
Typical spin- and string-correlations functions behave in accordance with
real-space renormalization group predictions for the random-singlet phase. The
average string-correlation function decays algebraically with an exponent of
-0.378(6), in very good agreement with the prediction of , while the average spin-correlation function is found to decay with an
exponent of about -1, quite different from the expected value of -2. By
implementing the concept of directed loops for the spin-1 chain we show that
autocorrelation times can be reduced by up to two orders of magnitude.Comment: 9 pages, 10 figure
Impurity-Induced Virtual Bound States in d-Wave Superconductors
It is shown that a single, strongly scattering impurity produces a bound or a
virtual bound quasiparticle state inside the gap in a -wave superconductor.
The explicit form of the bound state wave function is found to decay
exponentially with angle-dependent range. These states provide a natural
explanation of the second Cu NMR rate arising from the sites close to Zn
impurities in the cuprates. Finally, for finite concentration of impurities in
a -wave superconductor, we reexamine the growth of these states into an
impurity band, and discuss the Mott criterion for this band.Comment: 12 pages and 2 figures, RevTex, LA-UR-94-194
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