Serine racemases from barley, Hordeum vulgare L., and other plant species represent a distinct eukaryotic group: gene cloning and recombinant protein characterization

Several d-amino acids have been identified in plants. However, the biosynthetic pathway to them is unclear. In this study, we cloned and sequenced a cDNA encoding a serine racemase from barley which contained an open reading frame encoding 337 amino acid residues. The deduced amino acid sequence showed significant identity to plant and mammalian serine racemases and contained conserved pyridoxal 5-phosphate (PLP)-binding lysine and PLP-interacting amino acid residues. The purified gene product catalyzed not only racemization of serine but also dehydration of serine to pyruvate. The enzyme requires PLP and divalent cations such as Ca(2+), Mg(2+), or Mn(2+), but not ATP, whereas mammalian serine racemase activity is increased by ATP. In addition to the results regarding the effect of ATP on enzyme activity and the phylogenetic analysis of eukaryotic serine racemases, the antiserum against Arabidopsis serine racemase did not form a precipitate with barley and rice serine racemases. This suggests that plant serine racemases represent a distinct group in the eukaryotic serine racemase family and can be clustered into monocot and dicot types.     

Free fatty acids stimulate autophagy in pancreatic β-cells via JNK pathway

Recent studies have suggested that free fatty acids stimulate autophagy of pancreatic beta cells. The aim of this study was to verify the free fatty acids (FFA)-induced autophagy and investigate its molecular mechanism. As reported previously, palmitate strongly enhanced the conversion of light chain (LC)3-I to LC3-II, a marker of activation of autophagy in INS-1 beta cells. Palmitate-induced conversion of LC3-I to LC3-II was also observed in neuron-, muscle-, and liver-derived cells. In addition, palmitate induced the formation of typical autophagosomes and autolysosomes and enhanced the degradation rate of long-lived proteins. These results confirmed that palmitate activates autophagic flux in most of the cells. While FFAs reportedly activate several signal transduction pathways in beta cells, palmitate-induced autophagy was blocked by a JNK inhibitor. Although enhanced oxidative stress and endoplasmic reticulum (ER) stress are suspected to mediate FFA-induced activation of JNK1, the induction of autophagy was not associated with changes in molecular markers related to oxidative and endoplasmic reticulum stresses. On the other hand, phosphorylation of double stranded RNA-dependent protein kinase (PKR) paralleled JNK1 activation. Considered together, our study suggested that FFA stimulated functional autophagy possibly through the PKR-JNK1 pathway independent of ER or oxidative stress.     

Limnological features of glacier-fed rivers in the Southern Tibetan Plateau, China

We describe the limnological features of six glacier-fed rivers located at an altitude of over 4,000?m in Southern Tibetan Plateau, China, based on diurnal observations of the water environment and biota in the summer of 2010. The rivers showed significant diurnal changes in water level, temperature, and turbidity; clear and cool streams in the morning changed to cloudy rapid flow in the afternoon, and water temperature was elevated under strong light conditions where riparian forest did not cover the surface of the water. On the other hand, the pH and dissolved oxygen saturation did not show any diurnal fluctuations, which indicates low periphytic algal productivity. The aquatic insect communities were poor both in diversity and density, and the dominant life forms (from a functional feeding group perspective) were collectors, which depend on allochthonous organic matter; scrapers, which depend on autochthonous algal production, were scarce. We therefore suggest that diurnal or seasonal high waters transport products from marginal pools along dried riverbeds or from ponds on flood plains, and may serve as the source of organic matter in glacier-fed rivers.     

Theanine intake improves the shortened lifespan, cognitive dysfunction and behavioural depression that are induced by chronic psychosocial stress in mice

To evaluate the psychosocial effect on lifespan and cognitive function, this study investigated the effect of confrontational housing on mice because conflict among male mice is a psychosocial stress. In addition, it investigated the anti-stress effect of theanine (γ-glutamylethylamide), an amino acid in tea. Mice were housed under confrontation. That is, two male mice were separately housed in the same cage with a partition for establishing the territorial imperative in each mouse. Then, the partition was removed and mice were co-housed confrontationally (confront-housing) using a model mouse of accelerated-senescence (SAMP10) that exhibited cerebral atrophy and cognitive dysfunction with ageing. It was found that mice began to die earlier under confront-housing than group-housed control mice. Additionally, it was found that cerebral atrophy, learning impairment and behavioural depression were higher in mice under the stressed condition of confront-housing than age-matched mice under group-housing. Furthermore, the level of oxidative damage in cerebral DNA was higher in mice housed confrontationally than group-housed control mice. On the other hand, the consumption of purified theanine (20 μg/ml, 5-6 mg/kg) suppressed the shortened lifespan, cerebral atrophy, learning impairment, behavioural depression and oxidative damage in cerebral DNA. These results suggest that psychosocial stress accelerates age-related alterations such as oxidative damage, lifespan, cognitive dysfunction and behavioural depression. The intake of theanine might be a potential candidate for suppression of disadvantage under psychosocial stress.     

Methylobacterium Species Promoting Rice and Barley Growth and Interaction Specificity Revealed with Whole-Cell Matrix-Assisted Laser Desorption / Ionization-Time-of-Flight Mass Spectrometry (MALDI-TOF/MS) Analysis

Methylobacterium species frequently inhabit plant surfaces and are able to utilize the methanol emitted from plants as carbon and energy sources. As some of the Methylobacterium species are known to promote plant growth, significant attention has been paid to the mechanism of growth promotion and the specificity of plant–microbe interactions. By screening our Methylobacterium isolate collection for the high growth promotion effect in vitro, we selected some candidates for field and pot growth tests for rice and barley, respectively. We found that inoculation resulted in better ripening of rice seeds, and increased the size of barley grains but not the total yield. In addition, using whole-cell matrix-assister laser desorption/ionization- time-of-flight mass spectrometry (MALDI-TOF/MS) analysis, we identified and classified Methylobacterium isolates from Methylobacterium-inoculated rice plants. The inoculated species could not be recovered from the rice plants, and in some cases, the Methylobacterium community structure was affected by the inoculation, but not with predomination of the inoculated species. The isolates from non-inoculated barley of various cultivars grown in the same field fell into just two species. These results suggest that there is a strong selection pressure at the species level of Methylobacterium residing on a given plant species, and that selection of appropriate species that can persist on the plant is important to achieve growth promotion.     

Normal islet vascularization is dispensable for expansion of beta-cell mass in response to high-fat diet induced insulin resistance

The inability to increase of islet mass adequately to compensate for the demand of insulin due to insulin resistance is an important pathophysiological feature of type 2 diabetes. Previous studies suggested a relationship between pancreatic beta-cell mass and islet vascularization, although no evidence has confirmed this association in response to insulin resistance. Vascular endothelial growth factor-A (VEGF-A) in islets is essential for maintaining normal islet blood vessels. Here, insulin resistance was induced in mice carrying a beta-cell-specific VEGF-A gene mutation (RIP-Cre:Vegf^fl/fl) by 20-week feeding of high-fat diet as a model of impaired islet vascularization. These mice showed only a modest decrease in glucose tolerance, compared with control mice. In addition, although the endothelial cell area in the islets of high-fat-fed RIP-Cre:Vegf^fl/fl mice remained diminished, the pancreatic beta-cell area was modestly more than in high-fat-fed control mice. Thus, normal islet vascularization does not seem to be essential for expansion of beta cell mass in response to insulin resistance.     

Molecular and biochemical characterization of a serine racemase from Arabidopsis thaliana

A cDNA encoding a homolog of mammalian serine racemase, a unique enzyme in eukaryotes, was isolated from Arabidopsis thaliana and expressed in Escherichia coli cells. The gene product, of which the amino acid residues for binding pyridoxal 5'-phosphate (PLP) are conserved in this as well as mammalian serine racemases, catalyzes not only serine racemization but also dehydration of serine to pyruvate. The enzyme is a homodimer and requires PLP and divalent cations, Ca2+, Mg2+, Mn2+, Fe2+, or Ni2+, at alkaline pH for both activities. The racemization process is highly specific toward L-serine, whereas L-alanine, L-arginine, and L-glutamine were poor substrates. The Vmax/Km values for racemase activity of L- and D-serine are 2.0 and 1.4 nmol/mg/min/mM, respectively, and those values for L- and D-serine on dehydratase activity are 13 and 5.3 nmol/mg/min/mM, i.e. consistent with the theory of racemization reaction and the specificity of dehydration toward L-serine. Hybridization analysis showed that the serine racemase gene was expressed in various organs of A. thaliana.     

Prenylcoumarin with Rev-export inhibitory activity from Cnidii Monnieris Fructus

By use of the fission yeast expressing the model fusion protein comprised of GST, SV40 T antigen NLS, GFP, and Rev-NES in the bioassay, the prenylcoumarin osthol (1) was disclosed as the new Rev-export inhibitor from the MeOH extract of Cnidii Monnieris Fructus. Furthermore, 1 was also found to inhibit export the genuine Rev in HeLa cells by indirect fluorescent antibody technique. By the competitive experiment using the biotinylated probe 3, osthol (1) was revealed to inhibit nuclear export of Rev through a NES non-antagonistic mode. Structure–activity relationship analysis of several analogs of 1 clarified that both prenyl side chain and double bond adjacent to the lactone carbonyl residue play an important role in the Rev-export inhibitory potency of 1.