Synthetic (p)ppGpp analogue is an inhibitor of stringent response in mycobacteria

Bacteria elicit an adaptive response against hostile conditions such as starvation and other kinds of stresses. Their ability to survive such conditions depends, in part, on stringent response pathways. (p)ppGpp, considered to be the master regulator of the stringent response, is a novel target for inhibiting the survival of bacteria. In mycobacteria, the (p)ppGpp synthetase activity of bifunctional Rel is critical for stress response and persistence inside a host. Our aim was to design an inhibitor of (p)ppGpp synthesis, monitor its efficiency using enzyme kinetics, and assess its phenotypic effects in mycobacteria. As such, new sets of inhibitors targeting (p)ppGpp synthesis were synthesized and characterized by mass spectrometry and nuclear magnetic resonance spectroscopy. We observed significant inhibition of (p)ppGpp synthesis by Rel(Msm) in the presence of designed inhibitors in a dose-dependent manner, which we further confirmed by monitoring the enzyme kinetics. The Rel enzyme inhibitor binding kinetics were investigated by isothermal titration calorimetry. Subsequently, the effects of the compounds on long-term persistence, biofilm formation, and biofilm disruption were assayed in Mycobacterium smegmatis, where inhibition in each case was observed. In vivo, (p)ppGpp levels were found to be downregulated in M. smegmatis treated with the synthetic inhibitors. The compounds reported here also inhibited biofilm formation by the pathogen Mycobacterium tuberculosis. The compounds were tested for toxicity by using an MTT assay with H460 cells and a hemolysis assay with human red blood cells, for which they were found to be nontoxic. The permeability of compounds across the cell membrane of human lung epithelial cells was also confirmed by mass spectrometry

Not Available

Not AvailableNot AvailableNot Availabl

Not Available

Not AvailableNot AvailableNot Availabl

A generalized cohesive element technique for arbitrary crack motion

A computational method for arbitrary crack motion through a finite element mesh, termed as the generalized cohesive element technique, is presented. In this method, an element with an internal discontinuity is replaced by two superimposed elements with a combination of original and imaginary nodes. Conventional cohesive zone modeling, limited to crack propagation along the edges of the elements, is extended to incorporate the intra-element mixed-mode crack propagation. Proposed numerical technique has been shown to be quite accurate, robust and mesh insensitive provided the cohesive zone ahead of the crack tip is resolved adequately. A series of numerical examples is presented to demonstrate the validity and applicability of the proposed method. © 2009 Elsevier B.V. All rights reserved

Nanostructured multiferroics

Multiferroic materials exhibit both ferromagnetic and ferroelectric order. Single phase multiferroics are rare innature. Also the magnetodielectric coupling parameters exhibited by them are not large enough for practicalapplications. There has been active research in the last few years to synthesize nanoscale composites of ferroelectricand ferromagnetic systems. In this article we have reviewed the recent developments in this area. The compositesdescribed have a range of nanostructural configurations, viz. core-shell nanostructure, particulate composites,glass-crystal nanocomposites, nanocomposte films and nanocomposites made by using Na-4 mica nanochannels.Nanocomposite films have shown high magnetodielectric effect. Some unusual systems like nanostructured Co3O4 and GaN have exhibited multiferroic behaviour with the latter showing a giant magnetodielectric effect. It is expectedthat by a suitable choice of combination of the matrix phase and the nanophase one could tune the magnetodielectricbehaviour to suit a particular application

Synthesis of nanocrystalline YFeO₃ and its magnetic properties

Single phase nanocrystalline YFeO3 has been synthesized by a simple solution method. The average particle diameter is 42.2 nm. The particles exhibit ferromagnetic behaviour in the temperature range 10–300 K with a coercivity of 23 kOe. The magnetization versus temperature over the temperature range 2–300 K obeys Bloch equation with a Bloch constant value 9.98×10−6 K−3/2. Ferromagnetic hysteresis loops have been observed up to a temperature of 300 K. At 10 K a field-cooled sample shows an exchange bias field

Role of CD80, CD86, and CTLA4 on mouse CD4+TCD4^+ T lymphocytes in enhancing cell-cycle progression and survival after activation with PMA and ionomycin

Cell surface interactions between the T cell costimulatory receptors, CD28 and cytotoxic T-lymphocyte antigen-(CTLA4), with their cognate ligands, CD80 and CD86, on antigen-presenting cells play an important role in T cell activation. Although CD80 and CD86 are induced on T cells after activation, not much is known about their role in modulating T cell function. We show that CD80, CD86, and CTLA4 are induced on purified CD4 T cells after in vitro activation with phorbol 12-myristate 13-acetate (PMA) and ionomycin,and they play an essential role for proliferation and survival. Blockade of CTLA4-CD80/CD86 interactions greatly reduces PMA and ionomycin-mediated mouse CD4 T cell activation. The three key features of this inhibition of activation are: First,late events in T cell activation (after 18 h) are affected; second, these cells do not undergo anergy; and third, CD4CD25 regulatory T cells are not responsible. Activation of T cells with PMA and ionomycin together with CTLA4-CD80/CD86 blockade results in decreased induction of CD25 and Bcl-XL, reduced interleukin (IL)-2, and enhanced transforming growth factor- (TGF-) production.Furthermore, extended CTLA4-CD80/CD86 blockade results in decreased cell-cycle progression and enhanced apoptosis in a large proportion of cells. This inhibition of T cell proliferation can be rescued completely with anti-CD28 or IL-2 and partially with TGF- antagonists. This study reveals a functional role for CD80, CD86,and CTLA4 on CD4 T lymphocytes and sheds light on the mechanisms by which these molecules enhance activation and survival with PMA and ionomycin. J. Leukoc. Biol. 72: 921-931; 2002