Phenylalanine biosynthesis in Arabidopsis thaliana. Identification and characterization of arogenate dehydratases

There is much uncertainty as to whether plants use arogenate, phenylpyruvate, or both as obligatory intermediates in Phe biosynthesis, an essential dietary amino acid for humans. This is because both prephenate and arogenate have been reported to undergo decarboxylative dehydration in plants via the action of either arogenate (ADT) or prephenate (PDT) dehydratases; however, neither enzyme(s) nor encoding gene(s) have been isolated and/or functionally characterized. An in silico data mining approach was thus undertaken to attempt to identify the dehydratase(s) involved in Phe formation in Arabidopsis, based on sequence similarity of PDT-like and ACT-like domains in bacteria. This data mining approach suggested that there are six PDT-like homologues in Arabidopsis, whose phylogenetic analyses separated them into three distinct subgroups. All six genes were cloned and subsequently established to be expressed in all tissues examined. Each was then expressed as a Nus fusion recombinant protein in Escherichia coli, with their substrate specificities measured in vitro. Three of the resulting recombinant proteins, encoded by ADT1 (At1g11790), ADT2 (At3g07630), and ADT6 (At1g08250), more efficiently utilized arogenate than prephenate, whereas the remaining three, ADT3 (At2g27820), ADT4 (At3g44720), and ADT5 (At5g22630) essentially only employed arogenate. ADT1, ADT2, and ADT6 had k(cat)/Km values of 1050, 7650, and 1560 M(-1) S(-1) for arogenate versus 38, 240, and 16 M(-1) S(-1) for prephenate, respectively. By contrast, the remaining three, ADT3, ADT4, and ADT5, had k(cat)/Km values of 1140, 490, and 620 M(-1) S(-1), with prephenate not serving as a substrate unless excess recombinant protein (>150 microg/assay) was used. All six genes, and their corresponding proteins, are thus provisionally classified as arogenate dehydratases and designated ADT1-ADT6.     

基于GIS的西安市城市景观格局

以西安市三环以内QuickBird卫星影像为基础,在GIS技术的支持下,通过所选取的景观指数对粒度变化的响应,在确定出研究区的适宜研究粒度为20 m的基础上,对西安市的景观格局现状进行研究.结果表明:西安市居住工业用地集中,人工景观聚集,影响自然生态过程;绿地、水体景观破碎化程度高,分布分散;环城路内景观构成不合理,一、二环间各景观类型分布极为不均,二、三环间土地利用经济效益和生态效益有较大的发展空间.建议调整城市的空间布局与结构,从绿地景观的建设和河、湖水网的保护角度来维护景观生态过程与格局的连续性.     

Synthesis, biological evaluation and structural determination of beta-aminoacyl-containing cyclic hydrazine derivatives as dipeptidyl peptidase IV (DPP-IV) inhibitors

Inhibitors of dipeptidyl peptidase IV (DPP-IV) have been shown to be effective treatments for type 2 diabetes. A series of beta-aminoacyl-containing cyclic hydrazine derivatives were synthesized and evaluated as DPP-IV inhibitors. One member of this series, (R)-3-amino-1-(2-benzoyl-1,2-diazepan-1-yl)-4-(2,4,5-trifluorophenyl)butan-1-one (10f), showed potent in vitro activity, good selectivity and in vivo efficacy in mouse models. Also, the binding mode of compound 10f was determined by X-ray crystallography.     

Design, docking, and synthesis of novel indeno[1,2-c]isoquinolines for the development of antitumor agents as topoisomerase I inhibitors

An intramolecular radical cyclization reaction of 4-bromo-3-arylisoquinolines 11a-c allowed the efficient synthesis of 11-methylindenoisoquinolines 2a-c. 5-(2-Aminoethylamino)indeno[1,2-c]isoquinolin-11-one 4 was also prepared in the convenient manner. The synthesized compounds were tested in vitro for cytotoxicity and DNA-topoisomerase 1 (top 1) inhibitory activity. The dramatic enhancement of top 1 inhibitory activity of 4 was explained by a docking study using the FlexX program.     

Probing the local conformational change of alpha1-antitrypsin

The native form of serpins (serine protease inhibitors) is a metastable conformation, which converts into a more stable form upon complex formation with a target protease. It has been suggested that movement of helix-F (hF) and the following loop connecting to strand 3 of beta-sheet A (thFs3A) is critical for such conformational change. Despite many speculations inferred from analysis of the serpin structure itself, direct experimental evidence for the mobilization of hF/thFs3A during the inhibition process is lacking. To probe the mechanistic role of hF and thFs3A during protease inhibition, a disulfide bond was engineered in alpha(1)-antitrypsin, which would lock the displacement of thFs3A from beta-sheet A. We measured the inhibitory activity of each disulfide-locked mutant and its heat stability against loop-sheet polymerization. Presence of a disulfide between thFs3A and s5A but not between thFs3A and s3A caused loss of the inhibitory activity, suggesting that displacement of hF/thFs3A from strand 5A but not from strand 3A is required during the inhibition process. While showing little influence on the inhibitory activity, the disulfide between thFs3A and s3A retarded loop-sheet polymerization significantly. This successful protein engineering of alpha(1)-antitrypsin is expected to be of value in clinical applications. Based on our current studies, we propose that the reactive-site loop of a serpin glides through between s5A and thFs3A for the full insertion into beta-sheet A while a substantial portion of the interactions between hF and s3A is kept intact.     

Testing the role of genetic factors across multiple independent invasions of the shrub Scotch broom (Cytisus scoparius)

Knowledge of the introduction history of invasive plants informs on theories of invasiveness and assists in the invasives management. For the highly successful invasive shrub Scotch broom, Cytisus scoparius, we analysed a combination of nuclear and chloroplast microsatellites for eight native source regions and eight independent invasion events in four countries across three continents. We found that two exotic Australian populations came from different sources, one of which was derived from multiple native populations, as was an invasive sample from California. An invasive population from New Zealand appeared to be predominantly sourced from a single population, either from the native or exotic ranges. Four invasive populations from Chile were genetically differentiated from the native range samples analysed here and so their source of introduction could not be confirmed, but high levels of differentiation between the Chilean populations suggested a combination of different sources. This extensive global data set of replicated introductions also enabled tests of key theories of invasiveness in relation to genetic diversity. We conclude that invasive populations have similar levels of high genetic diversity to native ranges; levels of admixture may vary across invasive populations so admixture does not appear to have been an essential requirement for invasion; invasive and native populations exhibit similar level of genetic structure indicating similar gene flow dynamics for both types of populations. High levels of diversity and multiple source populations for invasive populations observed here discount founder effects or drift as likely explanations for previously observed seed size differences between ranges. The high levels of genetic diversity, differential and source admixture identified for most exotic populations are likely to limit the ability to source biocontrol agents from the native region of origin of invasive populations.     

Grassland ecosystems in China: review of current knowledge and research advancement

Grasslands are the dominant landscape in China, accounting for 40% of the national land area. Research concerning China's grassland ecosystems can be chronologically summarized into four periods: (i) pre-1950s, preliminary research and survey of grassland vegetation and plant species by Russians, Japanese and Western Europeans, (ii) 1950-1975, exploration and survey of vegetation, soils and topography as part of natural resource inventory programmes by regional and national institutions mainly led by the Chinese Academy of Sciences, (iii) 1976-1995, establishment of field stations for long-term ecological monitoring and studies of ecosystem processes, (iv) 1996-present, comprehensive studies of community dynamics and ecosystem function integrating multi-scale and multidisciplinary approaches and experimental manipulations.Major findings of scientific significance in China's grassland ecosystem research include: (i) improved knowledge on succession and biogeochemistry of the semi-arid and temperate grassland ecosystems, (ii) elucidation of life-history strategies and diapause characteristics of the native grasshopper species as one of the key grassland pests, and (iii) development of effective management strategies for controlling rodent pests in grassland ecosystems. Opportunities exist for using the natural grasslands in northern China as a model system to test ecosystem theories that so far have proven a challenge to ecologists worldwide.     

A rapid competitive binding nonseparation electrochemical enzyme immunoassay (NEEIA) test strip for microcystin-LR (MCLR) determination

A competitive binding nonseparation electrochemical enzyme immunoassay (NEEIA) is described for the determination of microcystin-LR (MCLR) using a double-sided microporous gold electrode in cartridge-type cells. A gold film sputtered on one side of porous nylon membrane constitutes a working electrode, while another gold film formed on the opposite side serves as a pseudo reference electrode. After immobilizing MCLR antibody on working electrode by physical adsorption, the double-sided electrode was placed simply in a diffusion U-type or within a dry strip-type cell with a conjugate pad pre-loaded with a glucose oxidase labeled MCLR (GOx-MCLR) on working electrode side. Assays were performed in two steps: an MCLR-containing sample mixed with a known amount of GOx-MCLR conjugate either in buffer solution or in pre-loaded dry pad was incubated for an appropriate period (about 10 min) to induce competitive reaction with an immobilized anti-MCLR antibody on working electrode, and a fixed concentration of glucose solution (substrate) was then added to the backside of the working electrode. Due to the competitive nature of the assay, enzymatically generated product, hydrogen peroxide (H2O2), was detected at the working gold electrode (at +800 mV versus Au) by oxidation, and the magnitude of amperometric current was inversely proportional to the concentration of MCLR in the sample. The response time after substrate addition was about 30s. Mean recovery of MCLR added to tap water was 93.5%, with a coefficient of variation (CV) of 6.6%. The proposed competitive NEEIA system is in general comparable to existing heterogeneous enzyme immunoassays with a similar detection limit (100 pg/mL MCLR), and suitable for developing a disposable type biosensor for on-site monitoring of environment.     

Parallel synthesis and SAR study of novel oxa-steroids as potent and selective progesterone receptor antagonists

Efficient parallel synthesis of novel 7-oxa-steroids 4 has been achieved from the key intermediate 3 via a one-pot four-step sequence. oxa-Steroids 4 with various ortho-, meta-, and para-monosubstituents on the phenyl ring, as well as disubstituted phenyl and heterocycles, were evaluated for progesterone receptor (PR) and glucocorticoid receptor (GR) antagonist activities. SAR study demonstrated that the para-fluorinated substituents on the phenyl ring not only increased the potency for PR in a T47D cell functional assay, but also improved the selectivity over GR in an A549 cell functional assay. The para-fluorophenyl oxa-steroid 4l and the para-trifluoromethylphenyl oxa-steroid 4p were found to be remarkably more potent and more selective PR antagonists than mifepristone, with subnanomolar potency and about 140-fold selectivity over GR. Molecular modeling of the oxa-steroid bound to PR provided meaningful insight for the SAR study. oxa-Steroids 4a and 4b were found to be more efficacious than mifepristone in vivo in a rat uterine complement C3 assay via the oral route, although they were less than or equally potent to mifepristone in the T47D assay.     

HYPERSENSITIVE TO RED AND BLUE 1 and its C-terminal regulatory function control FLOWERING LOCUS T expression

The red and far-red light-absorbing phytochromes and UV-A/blue light-absorbing cryptochromes regulate seedling de-etiolation and flowering responses. The signaling steps that mediate the photoreceptor regulation on key flowering genes remain largely unknown. We report that a previously identified photomorphogenic mutant, hypersensitive to red and blue 1 (hrb1), flowered late and showed attenuated expression of FLOWERING LOCUS T (FT) over both long days and short days. Transgenic plants that overexpress the full-length HRB1, or its C-terminal half, flowered early and accumulated more FT messages under short-day conditions. The transgenic plants also displayed hyposensitive de-etiolation phenotypes, and the expression of these phenotypes requires the action of PIF4. The double mutant of hrb1/cry2 showed a flowering phenotype and an FT expression pattern similar to hrb1 under long-day conditions, suggesting that HRB1 may function downstream of cry2 under long-day conditions. In contrast, hrb1/phyB-9 showed a flowering phenotype and an FT expression pattern similar to phyB-9 over both long days and short days, indicating a modulatory role of HRB1 in the flowering pathway mediated by phyB. Overexpression of HRB1 did not affect the expression of the central clock oscillators, TOC1 and CCA1. HRB1 therefore represents a signaling step that regulates FT expression downstream of red and blue light perception.