Structure-based design of substituted hexafluoroisopropanol-arylsulfonamides as modulators of RORc

The structure–activity relationships of T0901317 analogs were explored as RORc inverse agonists using the principles of property- and structure-based drug design. An X-ray co-crystal structure of T0901317 and RORc was obtained and provided molecular insight into why T0901317 functioned as an inverse agonist of RORc; whereas, the same ligand functioned as an agonist of FXR, LXR, and PXR. The structural data was also used to design inhibitors with improved RORc biochemical and cellular activities. The improved inhibitors possessed enhanced selectivity profiles (rationalized using the X-ray crystallographic data) against other nuclear receptors.     

Soil eutrophication shaped the composition of pollinator assemblages during the past century

Atmospheric nitrogen deposition and other sources of environmental eutrophication have increased substantially over the past century worldwide, notwithstanding the recent declining trends in Europe. Despite the recognized susceptibility of plants to eutrophication, few studies evaluated how impacts propagate to consumers, such as pollinators. Here we aim to test if soil eutrophication contributes to the temporal dynamics of pollinators and their larval resources. We used a temporally and spatially explicit historical dataset with information on species occurrences to test if soil eutrophication, and more specifically nitrogen deposition, contributes to the patterns of change of plant and pollinator richness in the Netherlands over an 80 yr period. We focus on bees and butterflies, two groups for which we have good knowledge of larval resources that allowed us to define groups of species with different nitrogen related diet preferences. For each group we estimated richness changes between different 20-yr periods at local, regional and national scale, using analytical methods developed for analyzing richness changes based on collection data. Our findings suggest that the impacts of soil eutrophication on plant communities propagate to higher trophic levels, but with a time-lag. Pollinators with nitrogen-related diet preferences were particularly affected, in turn potentially impairing the performance of pollinator-dependent plants. Pollinator declines continued even after their focal plants started to recover. In addition, our results suggest that current levels of nitrogen deposition still have a negative impact on most groups here analyzed, constraining richness recoveries and accentuating declines. Our results indicate that the global increase in nitrogen availability plays an important role in the ongoing pollinator decline. Consequently, species tolerances to soil nitrogen levels should be considered across all trophic levels in management plans that aim to halt biodiversity loss and enhance ecosystems services worldwide.     

A de novo synthesis citrate transporter, Vigna umbellata multidrug and toxic compound extrusion, implicates in Al-activated citrate efflux in rice bean (Vigna umbellata) root apex

Al-activated organic acid anion efflux from roots is an important Al resistance mechanism in plants. We have conducted homologous cloning and isolated Vigna umbellata multidrug and toxic compound extrusion (VuMATE), a gene encoding a de novo citrate transporter from rice bean. Al treatment up-regulated VuMATE expression in the root apex, but neither in the mature root region nor in the leaf. The degree of up-regulation of VuMATE was both partially Al concentration and time dependent, consistent with the delay in the onset of the Al-induced citrate efflux in rice bean roots. While La(3+) moderately induced VuMATE expression, Cd(2+) and Cu(2+) did not induce the expression. Electrophysiological analysis of Xenopus oocytes expressing VuMATE indicated this transporter can mediate significant anion efflux across the plasma membrane. [(14) C]citrate efflux experiments in oocytes demonstrated that VuMATE is a H(+) -dependent citrate transporter. In addition, expression of VuMATE in transgenic tomato resulted in increased Al resistance, which correlated with an enhanced citrate efflux. Taken together, these findings suggest that VuMATE is a functional homolog of the known citrate transporters in sorghum, barley, maize and Arabidopsis. The similarities and differences of all the known citrate transporters associated with Al stress in the MATE family are also discussed.     

MK-STYX, a catalytically inactive phosphatase regulating mitochondrially dependent apoptosis

Evasion of apoptosis is a significant problem affecting an array of cancers. In order to identify novel regulators of apoptosis, we performed an RNA interference (RNAi) screen against all kinases and phosphatases in the human genome. We identified MK-STYX (STYXL1), a catalytically inactive phosphatase with homology to the mitogen-activated protein kinase (MAPK) phosphatases. Despite this homology, MK-STYX knockdown does not significantly regulate MAPK signaling in response to growth factors or apoptotic stimuli. Rather, RNAi-mediated knockdown of MK-STYX inhibits cells from undergoing apoptosis induced by cellular stressors activating mitochondrion-dependent apoptosis. This MK-STYX phenotype mimics the loss of Bax and Bak, two potent guardians of mitochondrial apoptotic potential. Similar to loss of both Bax and Bak, cells without MK-STYX expression are unable to release cytochrome c. Proapoptotic members of the BCL-2 family (Bax, Bid, and Bim) are unable to trigger cytochrome c release in MK-STYX-depleted cells, placing the apoptotic deficiency at the level of mitochondrial outer membrane permeabilization (MOMP). MK-STYX was found to localize to the mitochondria but is neither released from the mitochondria upon apoptotic stress nor proximal to the machinery currently known to control MOMP, indicating that MK-STYX regulates MOMP using a distinct mechanism.     

Horizontal gene transfer amongst probiotic lactic acid bacteria and other intestinal microbiota: what are the possibilities? A review

Probiotics are live cultures, usually lactic acid bacteria, which are ingested to promote a healthy gastrointestinal tract. These organisms require certain traits to survive and compete in this niche, but these traits may be transferred to other microbiota in the gastrointestinal tract (GIT). Similarly, virulence factors from pathogens may be acquired by probiotic strains. Bacteria have developed a plethora of methods to transfer genetic material between strains, species and genera. In this review, the possible factors that may be exchanged and the methods of exchange are discussed.     

Mechanisms for maintaining cell shape in rod-shaped Gram-negative bacteria

For the rod-shaped Gram-negative bacterium Escherichia coli, changes in cell shape have critical consequences for motility, immune system evasion, proliferation and adhesion. For most bacteria, the peptidoglycan cell wall is both necessary and sufficient to determine cell shape. However, how the synthesis machinery assembles a peptidoglycan network with a robustly maintained micron-scale shape has remained elusive. To explore shape maintenance, we have quantified the robustness of cell shape in three Gram-negative bacteria in different genetic backgrounds and in the presence of an antibiotic that inhibits division. Building on previous modelling suggesting a prominent role for mechanical forces in shape regulation, we introduce a biophysical model for the growth dynamics of rod-shaped cells to investigate the roles of spatial regulation of peptidoglycan synthesis, glycan-strand biochemistry and mechanical stretching during insertion. Our studies reveal that rod-shape maintenance requires insertion to be insensitive to fluctuations in cell-wall density and stress, and even a simple helical pattern of insertion is sufficient for over sixfold elongation without significant loss in shape. In addition, we demonstrate that both the length and pre-stretching of newly inserted strands regulate cell width. In sum, we show that simple physical rules can allow bacteria to achieve robust, shape-preserving cell-wall growth.     

Lens intracellular hydrostatic pressure is generated by the circulation of sodium and modulated by gap junction coupling

We recently modeled fluid flow through gap junction channels coupling the pigmented and nonpigmented layers of the ciliary body. The model suggested the channels could transport the secretion of aqueous humor, but flow would be driven by hydrostatic pressure rather than osmosis. The pressure required to drive fluid through a single layer of gap junctions might be just a few mmHg and difficult to measure. In the lens, however, there is a circulation of Na(+) that may be coupled to intracellular fluid flow. Based on this hypothesis, the fluid would cross hundreds of layers of gap junctions, and this might require a large hydrostatic gradient. Therefore, we measured hydrostatic pressure as a function of distance from the center of the lens using an intracellular microelectrode-based pressure-sensing system. In wild-type mouse lenses, intracellular pressure varied from ～330 mmHg at the center to zero at the surface. We have several knockout/knock-in mouse models with differing levels of expression of gap junction channels coupling lens fiber cells. Intracellular hydrostatic pressure in lenses from these mouse models varied inversely with the number of channels. When the lens' circulation of Na(+) was either blocked or reduced, intracellular hydrostatic pressure in central fiber cells was either eliminated or reduced proportionally. These data are consistent with our hypotheses: fluid circulates through the lens; the intracellular leg of fluid circulation is through gap junction channels and is driven by hydrostatic pressure; and the fluid flow is generated by membrane transport of sodium.     

Novel N-terminal mutation of human apolipoprotein A-I reduces self-association and impairs LCAT activation

We have identified a novel mutation in apoA-I (serine 36 to alanine; S36A) in a human subject with severe hypoalphalipoproteinemia. The mutation is located in the N-terminal region of the protein, which has been implicated in several functions, including lipid binding and lecithin:cholesterol acyltransferase (LCAT) activity. In the present study, the S36A protein was produced recombinantly and characterized both structurally and functionally. While the helical content of the mutant protein was lower compared with wild-type (WT) apoA-I, it retained its helical character. The protein stability, measured as the resistance to guanidine-induced denaturation, decreased significantly. Interestingly, native gel electrophoresis, cross-linking, and sedimentation equilibrium analysis showed that the S36A mutant was primarily present as a monomer, notably different from the WT protein, which showed considerable oligomeric forms. Although the ability of S36A apoA-I to solubilize phosphatidylcholine vesicles and bind to lipoprotein surfaces was not altered, a significantly impaired LCAT activation compared with the WT protein was observed. These results implicate a region around S36 in apoA-I self-association, independent of the intact C terminus. Furthermore, the region around S36 in the N-terminus of human apoA-I is necessary for LCAT activation.