Atomic Force Microscopy Stiffness Tomography on Living Arabidopsis thaliana Cells Reveals the Mechanical Properties of Surface and Deep Cell-Wall Layers during Growth

Cell-wall mechanical properties play a key role in the growth and the protection of plants. However, little is known about genuine wall mechanical properties and their growth-related dynamics at subcellular resolution and in living cells. Here, we used atomic force microscopy (AFM) stiffness tomography to explore stiffness distribution in the cell wall of suspension-cultured Arabidopsis thaliana as a model of primary, growing cell wall. For the first time that we know of, this new imaging technique was performed on living single cells of a higher plant, permitting monitoring of the stiffness distribution in cell-wall layers as a function of the depth and its evolution during the different growth phases. The mechanical measurements were correlated with changes in the composition of the cell wall, which were revealed by Fourier-transform infrared (FTIR) spectroscopy. In the beginning and end of cell growth, the average stiffness of the cell wall was low and the wall was mechanically homogenous, whereas in the exponential growth phase, the average wall stiffness increased, with increasing heterogeneity. In this phase, the difference between the superficial and deep wall stiffness was highest. FTIR spectra revealed a relative increase in the polysaccharide/lignin content.     

Viral metagenomic analysis of bushpigs (Potamochoerus larvatus) in Uganda identifies novel variants of Porcine parvovirus 4 and Torque teno sus virus 1 and 2

ABSTRACT: BACKGROUND: As a result of rapidly growing human populations, intensification of livestock production and increasing exploitation of wildlife habitats for animal agriculture, the interface between wildlife, livestock and humans is expanding, with potential impacts on both domestic animal and human health. Wild animals serve as reservoirs for many viruses, which may occasionally result in novel infections of domestic animals and/or the human population. Given this background, we used metagenomics to investigate the presence of viral pathogens in sera collected from bushpigs (Potamochoerus larvatus), a nocturnal species of wild Suid known to move between national parks and farmland, in Uganda. RESULTS: Application of 454 pyrosequencing demonstrated the presence of Torque teno sus virus (TTSuV), porcine parvovirus 4 (PPV4), porcine endogenous retrovirus (PERV), a GB Hepatitis C--like virus, and a Sclerotinia hypovirulence-associated-like virus in sera from the bushpigs. PCR assays for each specific virus combined with Sanger sequencing revealed two TTSuV-1 variants, one TTSuV-2 variant as well as PPV4 in the serum samples and thereby confirming the findings from the 454 sequencing. CONCLUSIONS: Using a viral metagenomic approach we have made an initial analysis of viruses present in bushpig sera and demonstrated for the first time the presence of PPV4 in a wild African Suid. In addition we identified novel variants of TTSuV-1 and 2 in bushpigs.     

Screening for transglutaminase-catalyzed modifications by peptide mass finger printing using multipoint recalibration on recognized peaks for high mass accuracy.

Detection of posttranslational modifications is expected to be one of the major future experimental challenges for proteomics. We describe herein a mass spectrometric procedure to screen for protein modifications by peptide mass fingerprinting that is based on post-data acquisition improvement of the mass accuracy by exporting the peptide mass values into analytical software for multipoint recalibration on recognized peaks. Subsequently, the calibrated peak mass data set is used in searching for modified peptides, i.e., peptides possessing specific mass deviations. In order to identify the location of Lys- and Gln-residues available for transglutaminase-catalyzed isopeptide bond formation, mammalian small heat shock proteins (sHsps) were screened for labeling with the two hexapeptide probes GQDPVR and GNDPVK in presence of transglutaminase. Peptide modification due to cross-linking of the GQDPVR hexa-peptide probe was detected for C-terminal Lys residues. Novel transglutaminase-susceptible Gln sites were identified in two sHsps (Q31/Q27 in Hsp20 and HspB2, respectively), by cross-linking of the GNDPVK hexapeptide probe. Deamidation of specific Gln residues was also detected, as well an isopeptide derived from intramolecular Gln-Lys isopeptide bond formation. We conclude that peptide mass fingerprinting can be an efficient way of screening for various posttranslational modifications. Basically any instrumentation for MALDI mass spectrometry can be used, provided that post-data acquisition recalibration is applied.     

Synthesis of 5-(1-H or 1-alkyl-5-oxopyrrolidin-3-yl)-8-hydroxy-[1,6]-naphthyridine-7-carboxamide inhibitors of HIV-1 integrase

HIV-1 integrase catalyzes the insertion of viral DNA into the genome of the host cell. Integrase inhibitor N-(4-fluorobenzyl)-8-hydroxy-1,6-naphthyridine-7-carboxamide selectively inhibits the strand transfer process of integration. 4-Substituted pyrrolidinones possessing various groups on the pyrrolidinone nitrogen were introduced at the 5-position of the naphthyridine scaffold. These analogs exhibit excellent activity against viral replication in a cell-based assay. The preparation of these compounds was enabled by a three-step, two-pot reaction sequence from a common butenolide intermediate.     

Cannabinoids reduce markers of inflammation and fibrosis in pancreatic stellate cells

Background

While cannabinoids have been shown to ameliorate liver fibrosis, their effects in chronic pancreatitis and on pancreatic stellate cells (PSC) are unknown.

Methodology/Principal Findings

The activity of the endocannabinoid system was evaluated in human chronic pancreatitis (CP) tissues. In vitro, effects of blockade and activation of cannabinoid receptors on pancreatic stellate cells were characterized. In CP, cannabinoid receptors were detected predominantly in areas with inflammatory changes, stellate cells and nerves. Levels of endocannabinoids were decreased compared with normal pancreas. Cannabinoid-receptor-1 antagonism effectuated a small PSC phenotype and a trend toward increased invasiveness. Activation of cannabinoid receptors, however, induced de-activation of PSC and dose-dependently inhibited growth and decreased IL-6 and MCP-1 secretion as well as fibronectin, collagen1 and alphaSMA levels. De-activation of PSC was partially reversible using a combination of cannabinoid-receptor-1 and -2 antagonists. Concomitantly, cannabinoid receptor activation specifically decreased invasiveness of PSC, MMP-2 secretion and led to changes in PSC phenotype accompanied by a reduction of intracellular stress fibres.

Conclusions/Significance

Augmentation of the endocannabinoid system via exogenously administered cannabinoid receptor agonists specifically induces a functionally and metabolically quiescent pancreatic stellate cell phenotype and may thus constitute an option to treat inflammation and fibrosis in chronic pancreatitis.     

Neuropeptide γ-(l-9)-Peptide: A Major Product of the Posttranslational Processing of γ-Preprotachykinin in Rat Tissues

Abstract: γ-Preprotachykinin mRNA is the most abundant tachykinin mRNA in rat tissues, but the pathway of posttranslational processing of its translation product is unknown. An antiserum was raised against the synthetic peptide Asp-Ala-Gly-His-Gly-Gln-lle-Ser-His [neuropeptide γ-(1-9)-peptide, equivalent to γ-preprotachykinin-(72-80)-peptide], that showed <1% reactivity with intact neuropeptide γ and other tachykinins. Neuropeptide γ-(1-9)-peptide was detected by radioimmunoassay in relatively high concentrations in extracts of regions of rat brain and gastrointestinal tract. These concentrations correlated with (r = 0.99), but were significantly (p < 0.05) less than, the concentrations of neurokinin A-like immunoreactivity. The neuropeptide γ-(1-9)-like immunoreactivity in an extract of rat brain was eluted from a reverse-phase HPLC column in a single fraction with the same retention time as synthetic neuropeptide γ-(1 -9)-peptide. The synthetic peptide did not contract or relax isolated rat trachea, superior mesenteric artery, stomach fundus, or ileum, and the peptide did not affect the ability of neuropeptide 7 to contract the rat fundus. It is concluded that, in rat tissues, Lys⁷⁰-Arg⁷¹ in 7-preprotachykinin is a major site of posttranslational processing, but the resulting product, neuropeptide γ-(1-9)-peptide, is neither an agonist nor an antagonist at the neurokinin-2 (NK-2) receptor.     

Isolation and characterization of carnitine acetyltransferase from S. cerevisiae

Carnitine acetyltransferase was isolated from yeast Saccharomyces cerevisiae with an apparent molecular weight of 400,000. The enzyme contains identical subunits of 65,000 Da. The Km values of the isolated enzyme for acetyl-CoA and for carnitine were 17.7 microM and 180 microM, respectively. Carnitine acetyltransferase is an inducible enzyme, a 15-fold increase in the enzyme activity was found when the cells were grown on glycerol instead of glucose. Carnitine acetyltransferase, similarly to citrate synthase, has a double localization (approx. 80% of the enzyme is mitochondrial), while acetyl-CoA synthetase was found only in the cytosol. In the mitochondria carnitine acetyltransferase is located in the matrix space. The incorporation of 14C into CO2 and in lipids showed a similar ratio, 2.9 and 2.6, when the substrate was [1-14C]acetate and [1-14C]acetylcarnitine, respectively. Based on these results carnitine acetyltransferase can be considered as an enzyme necessary for acetate metabolism by transporting the activated acetyl group from the cytosol into the mitochondrial matrix.     

Loss of epithelial polarity: A novel hypothesis for reduced proximal tubule Na+ transport following ischemic injury

Summary Ischemia results in the marked reduction of renal proximal tubule function which is manifested by decreased Na⁺ and H₂O reabsorption. In the present studies the possibility that altered Na⁺ and H₂O reabsorption were due to ischemia-induced loss of surface membrane polarity was investigated. Following 15 min of renal ischemia and 2 hr of reperfusion, proximal tubule cellular ultrastructure was normal. However, abnormal redistribution of NaK-ATPase to the apical membrane domain was observed and large alterations in apical membrane lipid composition consistent with loss of surface membrane polarity were noted. These changes were associated with large decreases in Na⁺ (37.4vs. 23.0%,P<0.01) and H₂O (48.6vs. 36.9%,P<0.01) reabsorption at a time when cellular morphology, apical Na⁺ permeability, Na⁺-coupled cotransport, intracellular pH and single nephron filtration rates were normal. We propose that the abnormal redistribution of NaK-ATPase to the apical membrane domain is in part responsible for reduced Na⁺ and H₂O reabsorption following ischemic injury.     

Identification of crucial residues for the antibacterial activity of the proline-rich peptide, pyrrhocoricin.

Members of the proline-rich antibacterial peptide family, pyrrhocoricin, apidaecin and drosocin appear to kill responsive bacterial species by binding to the multihelical lid region of the bacterial DnaK protein. Pyrrhocoricin, the most potent among these peptides, is nontoxic to healthy mice, and can protect these animals from bacterial challenge. A structure-antibacterial activity study of pyrrhocoricin against Escherichia coli and Agrobacterium tumefaciens identified the N-terminal half, residues 2-10, the region responsible for inhibition of the ATPase activity, as the fragment that contains the active segment. While fluorescein-labeled versions of the native peptides entered E. coli cells, deletion of the C-terminal half of pyrrhocoricin significantly reduced the peptide's ability to enter bacterial or mammalian cells. These findings highlighted pyrrhocoricin's suitability for combating intracellular pathogens and raised the possibility that the proline-rich antibacterial peptides can deliver drug leads into mammalian cells. By observing strong relationships between the binding to a synthetic fragment of the target protein and antibacterial activities of pyrrhocoricin analogs modified at strategic positions, we further verified that DnaK was the bacterial target macromolecule. Inaddition, the antimicrobial activity spectrum of native pyrrhocoricin against 11 bacterial and fungal strains and the binding of labeled pyrrhocoricin to synthetic DnaK D-E helix fragments of the appropriate species could be correlated. Mutational analysis on a synthetic E. coli DnaK fragment identified a possible binding surface for pyrrhocoricin.