Structural insights into the evolutionary paths of oxylipin biosynthetic enzymes

The oxylipin pathway generates not only prostaglandin-like jasmonates but also green leaf volatiles (GLVs), which confer characteristic aromas to fruits and vegetables. Although allene oxide synthase (AOS) and hydroperoxide lyase are atypical cytochrome P450 family members involved in the synthesis of jasmonates and GLVs, respectively, it is unknown how these enzymes rearrange their hydroperoxide substrates into different products. Here we present the crystal structures of Arabidopsis thaliana AOS, free and in complex with substrate or intermediate analogues. The structures reveal an unusual active site poised to control the reactivity of an epoxyallylic radical and its cation by means of interactions with an aromatic pi-system. Replacing the amino acid involved in these steps by a non-polar residue markedly reduces AOS activity and, unexpectedly, is both necessary and sufficient for converting AOS into a GLV biosynthetic enzyme. Furthermore, by combining our structural data with bioinformatic and biochemical analyses, we have discovered previously unknown hydroperoxide lyase in plant growth-promoting rhizobacteria, AOS in coral, and epoxyalcohol synthase in amphioxus. These results indicate that oxylipin biosynthetic genes were present in the last common ancestor of plants and animals, but were subsequently lost in all metazoan lineages except Placozoa, Cnidaria and Cephalochordata.     

Magnetic support of the optical emission line filaments in NGC 1275

The giant elliptical galaxy NGC 1275, at the centre of the Perseus cluster, is surrounded by a well-known giant nebulosity of emission-line filaments, which are plausibly in excess of 10(8) years old. The filaments are dragged out from the centre of the galaxy by radio-emitting 'bubbles' rising buoyantly in the hot intracluster gas, before later falling back. They act as markers of the feedback process by which energy is transferred from the central massive black hole to the surrounding gas. The mechanism by which the filaments are stabilized against tidal shear and dissipation into the surrounding extremely hot (4 x 10(7) K) gas has been unclear. Here we report observations that resolve thread-like structures in the filaments. Some threads extend over 6 kpc, yet are only 70 pc wide. We conclude that magnetic fields in the threads, in pressure balance with the surrounding gas, stabilize the filaments, so allowing a large mass of cold gas to accumulate and delay star formation.     

TGFB2 mutations cause familial thoracic aortic aneurysms and dissections associated with mild systemic features of Marfan syndrome

A predisposition for thoracic aortic aneurysms leading to acute aortic dissections can be inherited in families in an autosomal dominant manner. Genome-wide linkage analysis of two large unrelated families with thoracic aortic disease followed by whole-exome sequencing of affected relatives identified causative mutations in TGFB2. These mutations-a frameshift mutation in exon 6 and a nonsense mutation in exon 4-segregated with disease with a combined logarithm of odds (LOD) score of 7.7. Sanger sequencing of 276 probands from families with inherited thoracic aortic disease identified 2 additional TGFB2 mutations. TGFB2 encodes transforming growth factor (TGF)-β2, and the mutations are predicted to cause haploinsufficiency for TGFB2; however, aortic tissue from cases paradoxically shows increased TGF-β2 expression and immunostaining. Thus, haploinsufficiency for TGFB2 predisposes to thoracic aortic disease, suggesting that the initial pathway driving disease is decreased cellular TGF-β2 levels leading to a secondary increase in TGF-β2 production in the diseased aorta.     

年青煤在石油重油中加氢液化的研究

在小型高压釜中试验了不同石油重油和催化剂对煤加氢液化的影响。结果表明,煤的转化率随石油重油中芳烃含量增加而提高,在试验条件下以红旗煤在羊三木减二线油中加氢的转化率为最高,达到60%,向石油重油添加四氢蔡或甲基萘油馏份对煤液化有利。不同的氧化铁型催化剂对煤在石油重油中加氢液化生成油都有一定的催化作用,其中以山东赤泥为最好,在试验条件下可使煤转化率增加7.4%,油与气产率增加22.4%,沥青烯产率下降15%,此外还考察了九种煤在石油重油中加氢液化的性能。     

蒽和咔唑在若干有机溶剂中的液固相平衡研究

利用液固相平衡实验装置,测定了蒽和咔唑在二甲基甲酰胺、Ｎ－甲基吡咯烷酮、环己酮、二甲苯、二氯乙烷和四氯乙烯中的溶解度,并作出溶解度曲线,为粗蒽的分离和粗制提供了有用数据。实验发现ＤＭＦ对粗蒽制取精蒽效果较好,四氯乙烯对粗咔唑的精制效果明显优于传统工艺。     

The large-scale structure of the Universe

Research over the past 25 years has led to the view that the rich tapestry of present-day cosmic structure arose during the first instants of creation, where weak ripples were imposed on the otherwise uniform and rapidly expanding primordial soup. Over 14 billion years of evolution, these ripples have been amplified to enormous proportions by gravitational forces, producing ever-growing concentrations of dark matter in which ordinary gases cool, condense and fragment to make galaxies. This process can be faithfully mimicked in large computer simulations, and tested by observations that probe the history of the Universe starting from just 400,000 years after the Big Bang.     

Alzheimer’s disease: the impact of age-related changes in reproductive hormones

Differences in the prevalence and age of onset of Alzheimer disease (AD) in men and women, and observations that hormone replacement therapy (HRT) may prevent the development of AD, caused many to hypothesize that estrogen deficiency contributes to AD. However, recent trials using estrogen failed to show any benefit in preventing or alleviating the disease. To address this and other inconsistencies in the estrogen hypothesis, we suspect that another hormone of the hypothalamic-pituitary-gonadal axis, luteinizing hormone (LH), as a major factor in AD pathogenesis. Individuals with AD have elevated levels of LH when compared with controls, and both LH and its receptor are present in increased quantities in brain regions susceptible to degeneration in AD. LH is also known to be mitogenic, and could therefore initiate the cell cycle abnormalities known to be present in AD-affected neurons. In cell culture, LH increases amyloidogenic processing of amyloid- protein precursor, and in animal models of AD, pharmacologic suppression of LH and FSH reduces plaque formation. Given the evidence supporting a pathogenic role for LH in AD, a trial of leuprolide acetate, which suppresses LH release, has been initiated in patients.