2,410 research outputs found
Superimposition of Viral Protein Structures: A Means to Decipher the Phylogenies of Viruses
Superimposition of protein structures is key in unravelling structural homology across proteins whose sequence similarity is lost. Structural comparison provides insights into protein function and evolution. Here, we review some of the original findings and thoughts that have led to the current established structure-based phylogeny of viruses: starting from the original observation that the major capsid proteins of plant and animal viruses possess similar folds, to the idea that each virus has an innate “self”. This latter idea fueled the conceptualization of the PRD1-adenovirus lineage whose members possess a major capsid protein (innate “self”) with a double jelly roll fold. Based on this approach, long-range viral evolutionary relationships can be detected allowing the virosphere to be classified in four structure-based lineages. However, this process is not without its challenges or limitations. As an example of these hurdles, we finally touch on the difficulty of establishing structural “self” traits for enveloped viruses showcasing the coronaviruses but also the power of structure-based analysis in the understanding of emerging viruse
Gell-Mann and Low formula for degenerate unperturbed states
The Gell-Mann and Low switching allows to transform eigenstates of an
unperturbed Hamiltonian into eigenstates of the modified Hamiltonian . This switching can be performed when the initial eigenstate is not
degenerate, under some gap conditions with the remainder of the spectrum. We
show here how to extend this approach to the case when the ground state of the
unperturbed Hamiltonian is degenerate. More precisely, we prove that the
switching procedure can still be performed when the initial states are
eigenstates of the finite rank self-adjoint operator \cP_0 V \cP_0, where
\cP_0 is the projection onto a degenerate eigenspace of
Hamiltonian Thermodynamics of Charged Black Holes
We consider the most general diffeomorphism invariant action in 1+1 spacetime
dimensions that contains a metric, dilaton and Abelian gauge field, and has at
most second derivatives of the fields. Our action contains a topological term
(linear in the Abelian field strength) that has not been considered in previous
work. We impose boundary conditions appropriate for a charged black hole
confined to a region bounded by a surface of fixed dilaton field and
temperature. By making some simplifying assumptions about the quantum theory,
the Hamiltonian partition function is obtained. This partition function is
analyzed in some detail for the Reissner-Nordstrom black hole and for the
rotating BTZ black hole.Comment: 30 pages, Latex, 1 figur
Effect of mesoscopic inhomogeneities on the critical current of bulk melt-textured YBCO
The downsizing 211-inclusions and an increase of their density leads to rise
in mean critical current value in Y-based melt textured material. Very often
211-inclusion are spread in the material volume non-homogeneous, with typical
scale 50 - 100 micrometer. Therefore it is difficult to find the real
correlation between local critical current and the inclusions distribution. We
performed a study of a local critical current using modified magneto-optic
technique on a melt-textured YBaCuO ceramic, found the areas with constant
current and studied the real structure of the material in the areas, inclusions
distribution and their sizes, by scanning electron microscopy and X-ray
microanalysis. The estimation of a pinning in these places, by taking into
account the amount of inclusions and the length of their boundaries, and
comparison with the value of local critical current reveals a strait
correlation between the density of inclusions and the current but shows
remarkable quantitative disagreement.Comment: PDF (8 pages, 4 figures
Gut microbiota composition in himalayan and andean populations and its relationship with diet, lifestyle and adaptation to the high-altitude environment
Human populations living at high altitude evolved a number of biological adjustments to cope with a challenging environment characterised especially by reduced oxygen availability and limited nutritional resources. This condition may also affect their gut microbiota composition. Here, we explored the impact of exposure to such selective pressures on human gut microbiota by considering different ethnic groups living at variable degrees of altitude: the high-altitude Sherpa and low-altitude Tamang populations from Nepal, the high-altitude Aymara population from Bolivia, as well as a low-altitude cohort of European ancestry, used as control. We thus observed microbial profiles common to the Sherpa and Aymara, but absent in the low-altitude cohorts, which may contribute to the achievement of adaptation to high-altitude lifestyle and nutritional conditions. The collected evidences suggest that microbial signatures associated to these rural populations may enhance metabolic functions able to supply essential compounds useful for the host to cope with high altitude-related physiological changes and energy demand. Therefore, these results add another valuable piece of the puzzle to the understanding of the beneficial effects of symbiosis between microbes and their human host even from an evolutionary perspective
LKB1 and AMPK differentially regulate pancreatic β-cell identity.
Fully differentiated pancreatic β cells are essential for normal glucose homeostasis in mammals. Dedifferentiation of these cells has been suggested to occur in type 2 diabetes, impairing insulin production. Since chronic fuel excess ("glucotoxicity") is implicated in this process, we sought here to identify the potential roles in β-cell identity of the tumor suppressor liver kinase B1 (LKB1/STK11) and the downstream fuel-sensitive kinase, AMP-activated protein kinase (AMPK). Highly β-cell-restricted deletion of each kinase in mice, using an Ins1-controlled Cre, was therefore followed by physiological, morphometric, and massive parallel sequencing analysis. Loss of LKB1 strikingly (2.0-12-fold, E<0.01) increased the expression of subsets of hepatic (Alb, Iyd, Elovl2) and neuronal (Nptx2, Dlgap2, Cartpt, Pdyn) genes, enhancing glutamate signaling. These changes were partially recapitulated by the loss of AMPK, which also up-regulated β-cell "disallowed" genes (Slc16a1, Ldha, Mgst1, Pdgfra) 1.8- to 3.4-fold (E<0.01). Correspondingly, targeted promoters were enriched for neuronal (Zfp206; P=1.3×10(-33)) and hypoxia-regulated (HIF1; P=2.5×10(-16)) transcription factors. In summary, LKB1 and AMPK, through only partly overlapping mechanisms, maintain β-cell identity by suppressing alternate pathways leading to neuronal, hepatic, and other characteristics. Selective targeting of these enzymes may provide a new approach to maintaining β-cell function in some forms of diabetes.-Kone, M., Pullen, T. J., Sun, G., Ibberson, M., Martinez-Sanchez, A., Sayers, S., Nguyen-Tu, M.-S., Kantor, C., Swisa, A., Dor, Y., Gorman, T., Ferrer, J., Thorens, B., Reimann, F., Gribble, F., McGinty, J. A., Chen, L., French, P. M., Birzele, F., Hildebrandt, T., Uphues, I., Rutter, G. A. LKB1 and AMPK differentially regulate pancreatic β-cell identity
A measurement of the tau mass and the first CPT test with tau leptons
We measure the mass of the tau lepton to be 1775.1+-1.6(stat)+-1.0(syst.) MeV
using tau pairs from Z0 decays. To test CPT invariance we compare the masses of
the positively and negatively charged tau leptons. The relative mass difference
is found to be smaller than 3.0 10^-3 at the 90% confidence level.Comment: 10 pages, 4 figures, Submitted to Phys. Letts.
Search for the glueball candidates f0(1500) and fJ(1710) in gamma gamma collisions
Data taken with the ALEPH detector at LEP1 have been used to search for gamma
gamma production of the glueball candidates f0(1500) and fJ(1710) via their
decay to pi+pi-. No signal is observed and upper limits to the product of gamma
gamma width and pi+pi- branching ratio of the f0(1500) and the fJ(1710) have
been measured to be Gamma_(gamma gamma -> f0(1500)). BR(f0(1500)->pi+pi-) <
0.31 keV and Gamma_(gamma gamma -> fJ(1710)). BR(fJ(1710)->pi+pi-) < 0.55 keV
at 95% confidence level.Comment: 10 pages, 3 figure
Measurement of the B0 Lifetime and Oscillation Frequency using B0->D*+l-v decays
The lifetime and oscillation frequency of the B0 meson has been measured
using B0->D*+l-v decays recorded on the Z0 peak with the OPAL detector at LEP.
The D*+ -> D0pi+ decays were reconstructed using an inclusive technique and the
production flavour of the B0 mesons was determined using a combination of tags
from the rest of the event. The results t_B0 = 1.541 +- 0.028 +- 0.023 ps, Dm_d
= 0.497 +- 0.024 +- 0.025 ps-1 were obtained, where in each case the first
error is statistical and the second systematic.Comment: 17 pages, 4 figures, submitted to Phys. Lett.
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