The barley MATE gene,HvAACT1, increases citrate efflux and Al3+ tolerance when expressed in wheat and barley

Background and Aims

Aluminium is toxic in acid soils because the soluble Al³⁺ inhibits root growth. A mechanism of Al³⁺ tolerance discovered in many plant species involves the release of organic anions from root apices. The Al³⁺-activated release of citrate from the root apices of Al³⁺-tolerant genotypes of barley is controlled by a MATE gene named HvAACT1 that encodes a citrate transport protein located on the plasma membrane. The aim of this study was to investigate whether expressing HvAACT1 with a constitutive promoter in barley and wheat can increase citrate efflux and Al³⁺ tolerance of these important cereal species.

Methods HvAACT1

was over-expressed in wheat (Triticum aestivum) and barley (Hordeum vulgare) using the maize ubiquitin promoter. Root apices of transgenic and control lines were analysed for HvAACT1 expression and organic acid efflux. The Al³⁺ tolerance of transgenic and control lines was assessed in both hydroponic solution and acid soil.

Key Results and Conclusions

Increased HvAACT1 expression in both cereal species was associated with increased citrate efflux from root apices and enhanced Al³⁺ tolerance, thus demonstrating that biotechnology can complement traditional breeding practices to increase the Al³⁺ tolerance of important crop plants.     

Heterochromatin Protein 1a (HP1a) Partner Specificity Is Determined by Critical Amino Acids in the Chromo Shadow Domain and C-terminal Extension

Drosophila melanogaster Heterochromatin Protein 1a (HP1a) is an essential protein critical for heterochromatin assembly and regulation. Its chromo shadow domain (CSD) homodimerizes, a requirement for binding protein partners that contain a PXVXL motif. How does HP1a select among its many different PXVXL-containing partners? HP1a binds tightly to Heterochromatin Protein 2 (HP2), but weakly to PIWI. We investigated differences in homodimerization and the impact of the C-terminal extension (CTE) by contrasting HP1a to its paralogue, HP1b. HP1a and HP1b differ in the dimerization interface, with HP1a having an Arg at position 188 rather than Glu. We find that while this substitution reduces the dimerization constant, it does not impact the binding surface as demonstrated by unchanged partner binding affinities. However, the CTE (only 4 residues in HP1a as compared with 87 residues in HP1b) is critical; the charged residues in HP1a are necessary for tight peptide binding. Examining a panel of amino acid substitutions in the HP1a CSD, we find that Leu-165 in HP1a interacts with HP2 but not PIWI, supporting the conclusion that different sites in the binding surface provide discrimination for partner selection. Partner sequence is also critical for affinity, as the remaining difference in binding between HP2 and PIWI polypeptides is eliminated by swapping the PXVXL motifs between the two. Taken together, these studies indicate that the binding surface of the HP1a CSD plus its short CTE provide the needed discrimination among HP1a''s partners, and that the CTE is important for differentiating the interactions of the Drosophila HP1 paralogs.     

Solid-state NMR Study Reveals Collagen I Structural Modifications of Amino Acid Side Chains upon Fibrillogenesis

In vivo, collagen I, the major structural protein in human body, is found assembled into fibrils. In the present work, we study a high concentrated collagen sample in its soluble, fibrillar, and denatured states using one and two dimensional {¹H}-¹³C solid-state NMR spectroscopy. We interpret ¹³C chemical shift variations in terms of dihedral angle conformation changes. Our data show that fibrillogenesis increases the side chain and backbone structural complexity. Nevertheless, only three to five rotameric equilibria are found for each amino acid residue, indicating a relatively low structural heterogeneity of collagen upon fibrillogenesis. Using side chain statistical data, we calculate equilibrium constants for a great number of amino acid residues. Moreover, based on a ¹³C quantitative spectrum, we estimate the percentage of residues implicated in each equilibrium. Our data indicate that fibril formation greatly affects hydroxyproline and proline prolyl pucker ring conformation. Finally, we discuss the implication of these structural data and propose a model in which the attractive force of fibrillogenesis comes from a structural reorganization of 10 to 15% of the amino acids. These results allow us to further understand the self-assembling process and fibrillar structure of collagen.     

Ablation of Promyelocytic Leukemia Protein (PML) Re-patterns Energy Balance and Protects Mice from Obesity Induced by a Western Diet

The promyelocytic leukemia protein is a well known tumor suppressor, but its role in metabolism is largely unknown. Mice with a deletion in the gene for PML (KO mice) exhibit altered gene expression in liver, adipose tissue, and skeletal muscle, an accelerated rate of fatty acid metabolism, abnormal glucose metabolism, constitutive AMP-activating kinase (AMPK) activation, and insulin resistance in skeletal muscle. Last, an increased rate of energy expenditure protects PML KO mice from the effects of obesity induced by a Western diet. Collectively, our study uncovers a previously unappreciated role of PML in the regulation of metabolism and energy balance in mice.     

The Bile Acid Receptor TGR5 Does Not Interact with β-Arrestins or Traffic to Endosomes but Transmits Sustained Signals from Plasma Membrane Rafts

TGR5 is a G protein-coupled receptor that mediates bile acid (BA) effects on energy balance, inflammation, digestion, and sensation. The mechanisms and spatiotemporal control of TGR5 signaling are poorly understood. We investigated TGR5 signaling and trafficking in transfected HEK293 cells and colonocytes (NCM460) that endogenously express TGR5. BAs (deoxycholic acid (DCA), taurolithocholic acid) and the selective agonists oleanolic acid and 3-(2-chlorophenyl)-N-(4-chlorophenyl)-N, 5-dimethylisoxazole-4-carboxamide stimulated cAMP formation but did not induce TGR5 endocytosis or recruitment of β-arrestins, as assessed by confocal microscopy. DCA, taurolithocholic acid, and oleanolic acid did not stimulate TGR5 association with β-arrestin 1/2 or G protein-coupled receptor kinase (GRK) 2/5/6, as determined by bioluminescence resonance energy transfer. 3-(2-chlorophenyl)-N-(4-chlorophenyl)-N, 5-dimethylisoxazole-4-carboxamide stimulated a low level of TGR5 interaction with β-arrestin 2 and GRK2. DCA induced cAMP formation at the plasma membrane and cytosol, as determined using exchange factor directly regulated by cAMP (Epac2)-based reporters, but cAMP signals did not desensitize. AG1478, an inhibitor of epidermal growth factor receptor tyrosine kinase, the metalloprotease inhibitor batimastat, and methyl-β-cyclodextrin and filipin, which block lipid raft formation, prevented DCA stimulation of ERK1/2. Bioluminescence resonance energy transfer analysis revealed TGR5 and EGFR interactions that were blocked by disruption of lipid rafts. DCA stimulated TGR5 redistribution to plasma membrane microdomains, as localized by immunogold electron microscopy. Thus, TGR5 does not interact with β-arrestins, desensitize, or traffic to endosomes. TGR5 signals from plasma membrane rafts that facilitate EGFR interaction and transactivation. An understanding of the spatiotemporal control of TGR5 signaling provides insights into the actions of BAs and therapeutic TGR5 agonists/antagonists.     

Sialylneolacto-N-tetraose c (LSTc)-bearing Liposomal Decoys Capture Influenza A Virus

Influenza is a severe disease in humans and animals with few effective therapies available. All strains of influenza virus are prone to developing drug resistance due to the high mutation rate in the viral genome. A therapeutic agent that targets a highly conserved region of the virus could bypass resistance and also be effective against multiple strains of influenza. Influenza uses many individually weak ligand binding interactions for a high avidity multivalent attachment to sialic acid-bearing cells. Polymerized sialic acid analogs can form multivalent interactions with influenza but are not ideal therapeutics due to solubility and toxicity issues. We used liposomes as a novel means for delivery of the glycan sialylneolacto-N-tetraose c (LSTc). LSTc-bearing decoy liposomes form multivalent, polymer-like interactions with influenza virus. Decoy liposomes competitively bind influenza virus in hemagglutination inhibition assays and inhibit infection of target cells in a dose-dependent manner. Inhibition is specific for influenza virus, as inhibition of Sendai virus and respiratory syncytial virus is not observed. In contrast, monovalent LSTc does not bind influenza virus or inhibit infectivity. LSTc decoy liposomes prevent the spread of influenza virus during multiple rounds of replication in vitro and extend survival of mice challenged with a lethal dose of virus. LSTc decoy liposomes co-localize with fluorescently tagged influenza virus, whereas control liposomes do not. Considering the conservation of the hemagglutinin binding pocket and the ability of decoy liposomes to form high avidity interactions with influenza hemagglutinin, our decoy liposomes have potential as a new therapeutic agent against emerging influenza strains.     

Yolk hydrolases in the eggs of Anticarsia gemmatalis hubner (Lepidoptera: Noctuidae): A role for inorganic polyphosphate towards yolk mobilization

Despite being the main insect pest on soybean crops in the Americas, very few studies have approached the general biology of the lepidopteran Anticarsia gemmatalis and there is a paucity of studies with embryo formation and yolk mobilization in this species. In the present work, we identified an acid phosphatase activity in the eggs of A. gemmatalis (agAP) that we further characterized by means of biochemistry and cell biology experiments. By testing several candidate substrates, this enzyme proved chiefly active with phosphotyrosine; in vitro assays suggested a link between agAP activity and dephosphorylation of egg yolk phosphotyrosine. We also detected strong activity with endogenous and exogenous short chain polyphosphates (PolyP), which are polymers of phosphate residues involved in a number of physiological processes. Both agAP activity and PolyP were shown to initially concentrate in small vesicles clearly distinct from typically larger yolk granules, suggesting subcellular compartmentalization. As PolyP has been implicated in inhibition of yolk proteases, we performed in vitro enzymatic assays with a cysteine protease to test whether it would be inhibited by PolyP. This cysteine protease is prominent in Anticarsia egg homogenates. Accordingly, short chain PolyP was a potent inhibitor of cysteine protease. We thereby suggest that PolyP hydrolysis by agAP is a triggering mechanism of yolk mobilization in A. gemmatalis.     

Comparing Sleep‐Loss Sleepiness and Sleep Inertia: Lapses Make the Difference

To compare the behavioral effects of sleep‐loss sleepiness (performance impairment due to sleep loss) and sleep inertia (period of impaired performance that follows awakening), mean response latencies and number of lapses from a visual simple reaction‐time task were analyzed. Three experimental conditions were designed to manipulate sleepiness and sleep‐inertia levels: uninterrupted sleep, partial sleep reduction, and total sleep deprivation. Each condition included two consecutive nights (the first always a night of uninterrupted sleep, and the second either a night of uninterrupted sleep, a night when sleep was reduced to 3 h, or a night of total sleep deprivation), as well as two days in which performance was assessed at 10 different time points (08:00, 08:30, 09:00, 09:30, 10:00, 11:00, 14:00, 17:00, 20:00, and 23:00 h). From 08:00 to 09:00 h, reaction times in the partial sleep‐reduction and total sleep‐deprivation conditions were at a similar level and were slower than those observed in the uninterrupted sleep condition. In the same time period, the frequency of lapses in the total sleep‐deprivation condition was higher than in the partial sleep‐reduction condition, while this latter condition never differed from the uninterrupted sleep condition. The results indicate that both sleep inertia and sleep‐loss sleepiness lead to an increase in response latencies, but only extreme sleepiness leads to an increase in lapse frequency. We conclude that while reaction times slow as a result of both sleep inertia and sleep‐loss sleepiness, lapses appear to be a specific feature of sleep‐loss sleepiness.     

Estimation of Free Energy Systematic Errors in Molecular Simulations of Globular Proteins Surrounded by Finite Water Clusters. One Center Multipole Expansion of Reaction Field Differences

Free energy calculated in simulations on the atomic level (Monte Carlo or Molecular Dynamics) has a systematic error, if the water shell surrounding a globular protein is finite. The error (“cluster error”) is equal to a difference of free energies obtained in simulations with an infinite and finite water shell. In this work a continuum dielectric model was used to estimate the “cluster error”. A multipole expansion of the estimate was performed for a water shell with a spherical outer boundary. The expansion has very simple form. Each term is a product of two functions, one of them depending only on the charge's conformation, and the other one only on dielectric properties of the system. There are two practical uses of the expansion. First, it may be used to estimate the “cluster error” in a simulation already made; second, it may be used to plan a simulation in such a way that the “cluster error” is minimal. Numerical values of the largest terms in the multipole expansion corresponding to a typical system in simulations of globular proteins are given.