Raman-assisted crystallography reveals end-on peroxide intermediates in a nonheme iron enzyme

Iron-peroxide intermediates are central in the reaction cycle of many iron-containing biomolecules. We trapped iron(III)-(hydro)peroxo species in crystals of superoxide reductase (SOR), a nonheme mononuclear iron enzyme that scavenges superoxide radicals. X-ray diffraction data at 1.95 angstrom resolution and Raman spectra recorded in crystallo revealed iron-(hydro)peroxo intermediates with the (hydro)peroxo group bound end-on. The dynamic SOR active site promotes the formation of transient hydrogen bond networks, which presumably assist the cleavage of the iron-oxygen bond in order to release the reaction product, hydrogen peroxide.     

A microRNA in a multiple-turnover RNAi enzyme complex

In animals, the double-stranded RNA-specific endonuclease Dicer produces two classes of functionally distinct, tiny RNAs: microRNAs (miRNAs) and small interfering RNAs (siRNAs). miRNAs regulate mRNA translation, whereas siRNAs direct RNA destruction via the RNA interference (RNAi) pathway. Here we show that, in human cell extracts, the miRNA let-7 naturally enters the RNAi pathway, which suggests that only the degree of complementarity between a miRNA and its RNA target determines its function. Human let-7 is a component of a previously identified, miRNA-containing ribonucleoprotein particle, which we show is an RNAi enzyme complex. Each let-7-containing complex directs multiple rounds of RNA cleavage, which explains the remarkable efficiency of the RNAi pathway in human cells.     

Visualization of dioxygen bound to copper during enzyme catalysis

X-ray crystal structures of three species related to the oxidative half of the reaction of the copper-containing quinoprotein amine oxidase from Escherichia coli have been determined. Crystals were freeze-trapped either anaerobically or aerobically after exposure to substrate, and structures were determined to resolutions between 2.1 and 2.4 angstroms. The oxidation state of the quinone cofactor was investigated by single-crystal spectrophotometry. The structures reveal the site of bound dioxygen and the proton transfer pathways involved in oxygen reduction. The quinone cofactor is regenerated from the iminoquinone intermediate by hydrolysis involving Asp383, the catalytic base in the reductive half-reaction. Product aldehyde inhibits the hydrolysis, making release of product the rate-determining step of the reaction in the crystal.     

The Fos protein complex is associated with DNA in isolated nuclei and binds to DNA cellulose

The properties of the viral and cellular fos proteins (Fos) were investigated as a first step toward understanding the function of the fos gene. Treatment of nuclei with salt and nonionic detergents solubilized a complex that contained Fos together with several other cellular proteins. The majority of the Fos protein complex was released from isolated nuclei incubated in the presence of deoxyribonuclease I or micrococcal nuclease but not with ribonuclease A, suggesting that Fos is associated with chromatin. This hypothesis is supported by the finding that Fos protein from native or denatured nuclear extracts exhibited DNA-binding activity in vitro. These results suggest that Fos is involved in the regulation of gene expression.     

离体法在饲料复合酶配方筛选中的应用

通过模拟动物消化生理规律,采用胃蛋白酶盐酸溶液（ＰＰＳ）和猪小肠液（ＰＩＦ）两步处理为特点的离体法分别测定９种鸡复合酶饲料和９种猪复合酶饲料的能量消化率,从而筛选出最佳复合酶组织。结果表明,最佳鸡伺料复合酶组合为纤维素酶１号＋植酸酶２号＋蛋白酶３号＋淀粉酶２号,最佳猪伺料复合酶组合为纤维素酶３号＋植酸酶３＋蛋白酶３号。肉鸡伺养试验结果表明,最佳复合酶试验组较对照组平均日增重提高９．６０％,料肉比降低２６．１０％;仔猪伺养试验结果表明,最佳复合酶试验组较对照组平均日增重提高９．６０％,料肉比降低２６．１％;仔猪伺养试验结果表明,最佳复合酶试验组较对照组平均日增重增高１２．４７％,料肉比降低３．２１％。结果验证了离体法在筛选伺料复合酶组合中的可行性。     

A chemically synthesized Antennapedia homeo domain binds to a specific DNA sequence

A peptide 60 residues in length that corresponds to the homeo domain of Antennapedia (Antp), a protein governing development in Drosophila, was synthesized by segment condensation with protected peptide segments prepared on an oxime resin. A footprinting assay showed that the homeo domain binds specifically to a TAA repeat DNA sequence in the Antp gene. Thus the Antp homeo domain has a sequence-specific DNA binding property. The circular dichroism spectra of the homeo domain peptide showed the presence of a significant amount of alpha-helical structure in aqueous solution and in 50 percent trifluoroethanol. The alpha helicity measured in water appears to depend on the peptide concentration, which suggests that the peptide aggregates. These results support the hypothesis that the homeo domain binds to DNA through a helix-turn-helix motif.     

Cu对植物毒害研究进展

随着含Cu杀菌剂的大量使用以及工业污染的加重,植物遭受Cu毒害也越来越严重.本文综述了国内外有关植物Cu毒害的研究:(1)Cu对植物生长的影响以及Cu在植物中的分配;(2)植物对Cu毒害的生理生化反应;(3)植物对Cu毒害的抗性及Cu毒害的治理.     

Xeroderma pigmentosum group E cells lack a nuclear factor that binds to damaged DNA

The disease xeroderma pigmentosum is characterized by deficient repair of damaged DNA. Fusions of cells from different patients have defined nine genetic complementation groups (A through I), implying that DNA repair in humans involves multiple gene products. In this report, an extension of the gel electrophoresis binding assay was used to identify at least one nuclear factor that (i) bound to DNA damaged by ultraviolet radiation or the antitumor drug cisplatin, but (ii) was notably absent in cells from complementation group E. Therefore, the factor appears to participate in a versatile DNA repair pathway at the stage of binding and recognition.     

Schizophrenia: diverse approaches to a complex disease

Schizophrenia is a debilitating mental illness that affects 1% of the population. Despite intensive study, its molecular etiology remains enigmatic. Like many common diseases, schizophrenia is multifactorial in origin, with both genetic and environmental contributions likely playing an important role in the manifestation of symptoms. Recent advances based on pharmacological studies, brain imaging analyses, and genetic research are now converging on tantalizing leads that point to a central role for several neurotransmitters, including dopamine, glutamate, and serotonin, that may interface with neurodevelopmental defects reflecting disease-related genetic aberrations. Here, we provide a brief overview of the parallel approaches being used to identify the molecular causes of schizophrenia and discuss possible directions for future research.     

Freezing as a path to build complex composites

Materials that are strong, ultralightweight, and tough are in demand for a range of applications, requiring architectures and components carefully designed from the micrometer down to the nanometer scale. Nacre, a structure found in many molluscan shells, and bone are frequently used as examples for how nature achieves this through hybrid organic-inorganic composites. Unfortunately, it has proven extremely difficult to transcribe nacre-like clever designs into synthetic materials, partly because their intricate structures need to be replicated at several length scales. We demonstrate how the physics of ice formation can be used to develop sophisticated porous and layered-hybrid materials, including artificial bone, ceramic-metal composites, and porous scaffolds for osseous tissue regeneration with strengths up to four times higher than those of materials currently used for implantation.     

日粮中添加复合酶制剂对临高猪生产性能和肉品质的影响

为研究日粮中添加不同剂量酶制剂对临高猪生产性能和肉品质的影响,选取健康、体重接近的断奶临高猪96头,随机分为4个处理组,每个处理组设3个重复,每重复8头猪,其中1个对照组,不添加酶制剂,3个试验组,分别为试验Ⅰ组、试验Ⅱ组和试验Ⅲ组,分别在基础日粮中添加0.1％、0.3％、0.5％的复合酶制剂.试验期为45 d.结果表明:(1)试验组临高猪的日增重、采食量和料重比显著高于对照组.(2)试验Ⅱ组的日增重和料重比显著高于试验Ⅰ组,高于试验Ⅲ组.(3)日粮中添加复合酶制剂显著影响临高乳猪肉的pH值,而对临高乳猪的屠宰率、滴水损失和熟肉率的影响差异不显著.综合认为,复合酶制剂的添加能够对临高猪的生产性能和肉品质产生影响,生产中建议断奶临高猪日粮中复合酶制剂的添加量为0.3％.     

Selective pancreatic enzyme secretion due to a new peptide called chymodenin

Chymodenin, a peptide newly isolated from porcine duodenum, elicited a rapid threefold increase in secretion of chymotrypsinogen while increasing secrelion of total protein by only, about 40 percent; lipase secretion was unaffected. The pancreas appears able, under chymodenin stimulation, to rapidly alter the transport of an individual enzyme as opposed to producing en masse secretion of enzyme.     

生物炭对铜胁迫下红壤地油菜苗期叶绿素和保护性酶活性的影响

通过盆栽试验,研究了不同生物炭添加量(质量分数为0、2%、5%)对铜胁迫(300 mg·kg~(-1))下红壤地油菜(Brassica campestris L.)苗期叶绿素含量、抗氧化酶活性[超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和过氧化物酶(POD)]、可溶性蛋白含量及丙二醛含量(MDA)的影响。结果表明:铜胁迫下油菜叶片的叶绿素a、b和总叶绿素含量均有所降低,SOD、CAT、POD、MDA及可溶性蛋白含量均增加;随着生物炭添加量的增加,油菜叶片的叶绿素a、b及总叶绿素含量呈上升趋势,油菜叶片的SOD、CAT、POD、MDA及可溶性蛋白含量则均呈一定的下降趋势。综合来看,施加生物炭有利于提高红壤地铜污染(300 mg·kg~(-1))中油菜苗期的叶绿素含量,减缓铜胁迫的毒害作用,从而有利于维持油菜正常生长。