Crystal structure of the low-dimensional uranium pentatelluride: UTe5

The crystal structure of UTe₅ (a = 17.915(5), b = 10.407(3), c = 4.220(2) Å, Pnma, Pn2₁a, Z =4) was refined from 822 intensities with I>3σ(I) to a conventional R factor of 0.060. The uranium coordination polyhedron is a three capped tellurium trigonal prism, and all the Te atoms are involved in TeTe bonds. The structure is built up with infinite chains of prisms stacked in the $\text{c}$ direction. The chains are linked into (b, c) layers by a single Te atom which exhibits some positional disorder.     

Unrevealed structural requirements for auxin-like molecules by theoretical and experimental evidences

An computational-biostatistical approach, supported by ab initio optimizations of auxin-like molecules, was used to find biologically meaningful relationships between quantum chemical variables and fresh bioassay's data. It is proven that the auxin-like recognition requires different molecular assembling states. We suggest that the carboxyl group is not the determining factor in explaining the biological auxin-like conduct. The biological effects depends essentially on the chemical condition of the ring system. The aim to find active molecules (quantum objects) via statistical grouping-analysis of molecular quantum similarity measures was verified by bioactivity assays. Next, this approach led to the discovery of a non-carboxylated active auxin-like molecule (2,6-dibromo-phenol). This is the first publication on structure activity relationship of auxin-like molecules, which relies on highly standardized bioassays of different auxins screened in parallel as well as analysed by multi-dimensional scaling.     

African trypanosomiasis: naturally occurring regulatory T cells favor trypanotolerance by limiting pathology associated with sustained type 1 inflammation

Tolerance to African trypanosomes requires the production of IFN-gamma in the early stage of infection that triggers the development of classically activated macrophages controlling parasite growth. However, once the first peak of parasitemia has been controlled, down-regulation of the type 1 immune response has been described. In this study, we have evaluated whether regulatory T cells (Tregs) contribute to the limitation of the immune response occurring during Trypanosoma congolense infection and hereby influence the outcome of the disease in trypanotolerant C57BL/6 host. Our data show that Foxp3+ Tregs originating from the naturally occurring Treg pool expanded in the spleen and the liver of infected mice. These cells produced IL-10 and limited the production of IFN-gamma by CD4+ and CD8+ effector T cells. Tregs also down-regulated classical activation of macrophages resulting in reduced TNF-alpha production. The Treg-mediated suppression of the type 1 inflammatory immune response did not hamper parasite clearance, but was beneficial for the host survival by limiting the tissue damages, including liver injury. Collectively, these data suggest a cardinal role for naturally occurring Tregs in the development of a trypanotolerant phenotype during African trypanosomiasis.     

Using reaction mechanism to measure enzyme similarity

The concept of reaction similarity has been well studied in terms of the overall transformation associated with a reaction, but not in terms of mechanism. We present the first method to give a quantitative measure of the similarity of reactions based upon their explicit mechanisms. Two approaches are presented to measure the similarity between individual steps of mechanisms: a fingerprint-based approach that incorporates relevant information on each mechanistic step; and an approach based only on bond formation, cleavage and changes in order. The overall similarity for two reaction mechanisms is then calculated using the Needleman-Wunsch alignment algorithm. An analysis of MACiE, a database of enzyme mechanisms, using our measure of similarity identifies some examples of convergent evolution of chemical mechanisms. In many cases, mechanism similarity is not reflected by similarity according to the EC system of enzyme classification. In particular, little mechanistic information is conveyed by the class level of the EC system.     

Phosphatidylinositol ether lipid analogues that inhibit AKT also independently activate the stress kinase, p38alpha, through MKK3/6-independent and -dependent mechanisms

Previously, we identified five active phosphatidylinositol ether lipid analogues (PIAs) that target the pleckstrin homology domain of Akt and selectively induce apoptosis in cancer cells with high levels of Akt activity. To examine specificity, PIAs were screened against a panel of 29 purified kinases. No kinase was inhibited, but one isoform of p38, p38alpha, was uniformly activated 2-fold. Molecular modeling of p38alpha revealed the presence of two regions that could interact with PIAs, one in the activation loop and a heretofore unappreciated region in the upper lobe that resembles a pleckstrin homology domain. In cells, two phases of activation were observed, an early phase that was independent of the upstream kinase MKK3/6 and inhibited by the p38 inhibitor SB203580 and a latter phase that was coincident with MKK3/6 activation. In short term xenograft experiments that employed immunohistochemistry and immunoblotting, PIA administration increased phosphorylation of p38 but not MKK3/6 in tumors in a statistically significant manner. Although PIAs rapidly activated p38 with similar time and dose dependence as Akt inhibition, p38 activation and Akt inhibition were independent events induced by PIAs. Using SB203580 or p38alpha(-/-) cells, we showed that p38alpha is not required for PIA-induced apoptosis but is required for H(2)O(2)- and anisomycin-induced apoptosis. Nonetheless, activation of p38a contributes to PIA-induced apoptosis, because reconstitution of p38a into p38alpha(-/-) cells increased apoptosis. These studies indicate that p38alpha is activated by PIAs through a novel mechanism and show that p38alpha activation contributes to PIA-induced cell death. Independent modulation of Akt and p38alpha could account for the profound cytotoxicity of PIAs.     

Rational design of 6-(2,4-diaminopyrimidinyl)-1,4-benzoxazin-3-ones as small molecule renin inhibitors

We report the design and synthesis of a series of 6-(2,4-diaminopyrimidinyl)-1,4-benzoxazin-3-ones as orally bioavailable small molecule inhibitors of renin. Compounds with a 2-methyl-2-aryl substitution pattern exhibit potent renin inhibition and good permeability, solubility, and metabolic stability. Oral bioavailability was found to be dependent on metabolic clearance and cellular permeability, and was optimized through modulation of the sidechain that binds in the S3(sp) subsite.     

Molecular dissection and expression of the LdK39 kinesin in the human pathogen, Leishmania donovani

In this study we show for the first time the intracellular distribution of a K39 kinesin homologue in Leishmania donovani, a medically important parasite of humans. Further, we demonstrated that this motor protein is expressed in both the insect and mammalian developmental forms (i.e. promastigote and amastigotes) of this organism. Moreover, in both of these parasite developmental stages, immunofluorescence indicated that the LdK39 kinesin accumulated at anterior and posterior cell poles and that it displayed a peripheral localization consistent with the cortical cytoskeleton. Using a molecular approach, we identified, cloned and characterized the first complete open reading frame for the gene (LdK39) encoding this large (> 358 kDa) motor protein in L. donovani. Based on these observations, we subsequently used a homologous episomal expression system to dissect and express the functional domains that constitute the native molecule. Cell fractionation experiments demonstrated that LdK39 was soluble and that it bound to detergent-extracted cytoskeletons of these parasites in an ATP-dependent manner. The cumulative results of these experiments are consistent with LdK39 functioning as an ATP-dependent kinesin which binds to and travels along the cortical cytoskeleton of this important human pathogen.     

Epithelial expression of TLR4 is modulated in COPD and by steroids,salmeterol and cigarette smoke

The toll-like receptors (TLRs) are a key component of host defense in the respiratory epithelium. Cigarette smoking is associated with increased susceptibility to infection, while COPD is characterised by bacterial colonisation and infective exacerbations. We found reduced TLR4 gene expression in the nasal epithelium of smokers compared with non-smoking controls, while TLR2 expression was unchanged. Severe COPD was associated with reduced TLR4 expression compared to less severe disease, with good correlation between nasal and tracheal expression. We went on to examine the effect of potential modulators of TLR4 expression in respiratory epithelium pertinent to airways disease. Using an airway epithelial cell line, we found a dose-dependent downregulation in TLR4 mRNA and protein expression by stimulation with cigarette smoke extracts. Treatment with the corticosteroids fluticasone and dexamethasone resulted in a dose-dependent reduction in TLR4 mRNA and protein. The functional significance of this effect was demonstrated by impaired IL-8 and HBD2 induction in response to LPS. Stimulation with salmeterol (10^-6 M) caused upregulation of TLR4 membrane protein presentation with no upregulation of mRNA, suggesting a post-translational effect. The effect of dexamethasone and salmeterol in combination was additive, with downregulation of TLR4 gene expression, and no change in membrane receptor expression. Modulation of TLR4 in respiratory epithelium may have important implications for airway inflammation and infection in response to inhaled pathogens.     

BRCA1 Is Required for Maintenance of Phospho-Chk1 and G2/M Arrest during DNA Cross-Link Repair in DT40 Cells

The Fanconi anemia DNA repair pathway is pivotal for the efficient repair of DNA interstrand cross-links. Here, we show that FA-defective (Fancc⁻) DT40 cells arrest in G₂ phase following cross-link damage and trigger apoptosis. Strikingly, cell death was reduced in Fancc⁻ cells by additional deletion of the BRCA1 tumor suppressor, resulting in elevated clonogenic survival. Increased resistance to cross-link damage was not due to loss of toxic BRCA1-mediated homologous recombination but rather through the loss of a G₂ checkpoint. This proapoptotic role also required the BRCA1-A complex member ABRAXAS (FAM175A). Finally, we show that BRCA1 promotes G₂ arrest and cell death by prolonging phosphorylation of Chk1 on serine 345 after DNA damage to sustain arrest. Our data imply that DNA-induced cross-link death in cells defective in the FA pathway is dependent on the ability of BRCA1 to prolong cell cycle arrest in G₂ phase.