The activity and stability of wheat nitrate reductase in vitro

The activity and decay characteristics of nitrate reductase from wheat (Triticum aestivum) were studied in crude, partially-purified and highly-purified preparations. The decay of nitrate reductase activity in crude extracts was due to spontaneous dissociation of the enzyme and to the effects of two decay factors, one present in the 0–30% and the other in the 50–70% saturated (NH₄)₂SO₄ fraction of a crude extract. Low rates of factor-mediated NR decay in vitro were associated with high levels of NR activity in vivo.     

24β-Ethyl-31-norlanosta-8,25(27)-dien-3β-ol and 24β-ethyl-25(27)-dehydrolophenol in seeds of three cucurbitaceae species

The structures of two 4α-methylsterols is isolated from Cucumis sativus(Cucurbitaceae) seeds were determined based mainly on their ¹³CNMR spectra as 24β-ethyl-31-norlanosta-8,25(27)-dien-3β-ol and 24β-ethyl-25(27)- dehydrolophenol, respectively, of which the former is a new sterol from natural sources. These two 4α-methylsterols were identified in the seeds of two other Cucurbitaceae species, Lagenaria leucantha var. Gourda and Citrullus battich. The probable biogenetic significance of the two 4α-methylsterols is discussed. Other 4α-methylsterols identified in the seeds of the three Cucurbitaceae species were obtusifoliol, cycloeucalenol and gramisterol.     

Adaptive foraging by predators as a cause of predator-prey cycles

Summary When foraging has costs, it is generally adaptive for foragers to adjust their foraging effort in response to changes in the population density of their food. If effort decreases in response to increased food density, this can result in a type-2 functional response; intake rate increases in a negatively accelerated manner as prey density increases. Unlike other mechanisms for type-2 responses, adaptive foraging usually involves a timelag, because foraging behaviours do not often change instantaneously with changes in food density or risks. This paper investigates predator-prey models in which there are explicit dynamics for the rate of adaptive change. Models appropriate to both behavioural and evolutionary change are considered. Both types of change can produce cycles under similar circumstances, but under some evolutionary models there is not sufficient genetic variability for evolutionary change to produce cycles. If there is sufficient variability, the remaining conditions required for cycles are surprisingly insensitive to the nature of the adaptive process. A predator population that approaches the optimum foraging strategy very slowly usually produces cycles under similar conditions as does a very rapidly adapting population.     

Recurrent alpha beta loop structures in TIM barrel motifs show a distinct pattern of conserved structural features.

A systematic survey of seven parallel alpha/beta barrel protein domains, based on exhaustive structural comparisons, reveals that a sizable proportion of the alpha beta loops in these proteins--20 out of a total of 49--belong to either one of two loop types previously described by Thornton and co-workers. Six loops are of the alpha beta 1 type, with one residue between the alpha-helix and beta-strand, and 13 are of the alpha beta 3 type, with three residues between the helix and the strand. Protein fragments embedding the identified loops, and termed alpha beta connections since they contain parts of the flanking helix and strand, have been analyzed in detail revealing that each type of connection has a distinct set of conserved structural features. The orientation of the beta-strand relative to the helix and loop portions is different owing to a very localized difference in backbone conformation. In alpha beta 1 connections, the chain enters the beta-strand via a residue adopting an extended conformation, while in alpha beta 3 it does so via a residue in a near alpha-helical conformation. Other conserved structural features include distinct patterns of side chain orientation relative to the beta-sheet surface and of main chain H-bonds in the loop and the beta-strand moieties. Significant differences also occur in packing interactions of conserved hydrophobic residues situated in the last turn of the helix. Yet the alpha-helix surface of both types of connections adopts similar orientations relative to the barrel sheet surface. Our results suggest furthermore that conserved hydrophobic residues along the sequence of the connections, may be correlated more with specific patterns of interactions made with neighboring helices and sheet strands than with helix/strand packing within the connection itself. A number of intriguing observations are also made on the distribution of the identified alpha beta 1 and alpha beta 3 loops within the alpha/beta-barrel motifs. They often occur adjacent to each other; alpha beta 3 loops invariably involve even numbered beta-strands, while alpha beta 1 loops involve preferentially odd beta-strands; all the analyzed proteins contain at least one alpha beta 3 loop in the first half of the eightfold alpha/beta barrel. Possible origins of all these observations, and their relevance to the stability and folding of parallel alpha/beta barrel motifs are discussed.     

Inhibition of ADP-ribosylation of histone by diadenosine 5', 5"' -p (1), p(4)-tetraphosphate

Diadenosine 5′, 5?-p¹, p⁴-tetraphosphate (Ap4A) strongly inhibited ADP-ribosylation reaction of histone by purified bovine thymus poly(ADP-ribose) polymerase. This compound showed a relatively weak inhibitory effect on Mg²⁺-dependent, enzyme-bound poly(ADP-ribose) synthesis. Among various adenine nucleotides tested, including several diadenosine nucleotides with varying phosphate chain length, Ap4A was the most effective inhibitor of the histone-modification reaction. Ap5A and Ap6A showed slightly lower inhibitory effect than Ap4A. Kinetic analysis of the inhibitor (Ap4A) with varying concentration of substrate (NAD⁺) revealed that this compound is a “mixed type inhibitor”, with a Ki value of 5.1 μM.     

Brucella suis vaccine strain S2-infected immortalized caprine endometrial epithelial cell lines induce non-apoptotic ER-stress

Brucella, which is regarded as an intracellular pathogen responsible for a zoonotic disease called brucellosis, survives and proliferates within several types of phagocytic and non-phagocytic cells. Brucella infects not only their preferred hosts but also other domestic and wild animal species, inducing abortion and infertility. Therefore, the interaction between uterine cells and Brucella is important for understanding the pathogenesis of this disease. In this study, we describe the Brucella suis vaccine strain S2 (B.suis.S2) infection and replication in the immortalized caprine endometrial epithelial cell line hTERT-EECs and the induced cellular and molecular response modulation in vitro. We found that B.suis S2 was able to infect and replicate to high titers and inhibit the proliferation of EECs and induce non-apoptotic pathways, as determined by B.suis.S2 detection using MTT and acridine orange/ethidium bromide (AO/EB) staining and flow cytometry. We explored the evidence of non-apoptotic pathways using real-time quantitative RT-PCR and by western blot analysis. Finally, we discovered the over-expression of GRP78, ATF4, ATF6, PERK, eIF2α, CHOP, and cytochrome c (Cyt-c) but not IRE1, xbp-1, and caspase-3 in B.suis.S2 (HK)-attacked and B.suis.S2-infected cells, suggesting that the molecular mechanism of ER stress sensor activation by B.suis.S2 is basically concomitant with that by B.suis.S2 (HK) and that ER stress, especially the PERK pathway, plays an important role in the process of B.suis.S2 infecting EEC, which may, in part, explain the role of the uterus in the pathogenesis of B.suis.S2.

Electronic supplementary material

The online version of this article (doi:10.1007/s12192-014-0564-x) contains supplementary material, which is available to authorized users.     

Regulation of neuronal excitability by release of proteins from glial cells

Effects of glial cells on electrical isolation and shaping of synaptic transmission between neurons have been extensively studied. Here we present evidence that the release of proteins from astrocytes as well as microglia may regulate voltage-activated Na⁺ currents in neurons, thereby increasing excitability and speed of transmission in neurons kept at distance from each other by specialized glial cells. As a first example, we show that basic fibroblast growth factor and neurotrophin-3, which are released from astrocytes by exposure to thyroid hormone, influence each other to enhance Na⁺ current density in cultured hippocampal neurons. As a second example, we show that the presence of microglia in hippocampal cultures can upregulate Na⁺ current density. The effect can be boosted by lipopolysaccharides, bacterial membrane-derived stimulators of microglial activation. Comparable effects are induced by the exposure of neuron-enriched hippocampal cultures to tumour necrosis factor-α, which is released from stimulated microglia. Taken together, our findings suggest that release of proteins from various types of glial cells can alter neuronal excitability over a time course of several days. This explains changes in neuronal excitability occurring in states of thyroid hormone imbalance and possibly also in seizures triggered by infectious diseases.     

Twist2的生物学功能及其分子机制

碱性螺旋-环-螺旋(Basic helix-loop-helix protein,bHLH)家族成员Twist2对间质细胞系的发生和发育起转录调节作用,经直接或间接机制发挥分子开关功能,从而激活或抑制靶基因。Twist2能直接结合DNA上 E-box保守序列,招募共激活物或抑制剂;能与E蛋白调节因子发生蛋白-蛋白相互作用,干扰激活或抑制功能。Twist2无义突变导致Setleis综合征。对Twist2的早期研究多集中在骨骼发育,随后在多种肿瘤中发现其有表达差异,研究表明Twist2在肿瘤的上皮-间质转化(Epithelial-mesenchymal transition,EMT)中发挥着重要作用。Twist2参与了多条通路的调控,其调控作用的发挥受到时空表达、磷酸化、二聚化和细胞定位的调节,在机体的正常发育、体内平衡和疾病发生机制中研究Twist2的作用显得尤为重要。文章对Twist2在成骨分化、肿瘤形成和EMT中的作用及其分子机制进行综述,以便帮助了解Twist2的生物学功能,为进一步在疾病的诊断、发展、以及治疗等方面的转化应用研究提供依据。