Genotoxicity of heated cooking oil vapors.

Epidemiological studies of lung cancer in Chinese women indicated that factors other than cigarette smoking are related to lung cancer risk. A case-control study suggested that indoor air pollution, particularly from cooking oil emissions, may be involved. Condensates of volatile emissions from rapeseed and soybean cooking oils were prepared and found to be genotoxic in short-term tests including the Salmonella mutation assay, SV50 forward-mutation assay, and sister-chromatid exchange assay, as well as the micronucleus assay in mouse bone marrow. In contrast, condensates from rapeseed oil with butylated hydroxyanisole or hydrogenated rapeseed oil were not mutagenic, implicating oxidation products as the cause for mutagenicity. Peanut oil and lard condensates were not mutagenic in any assay. The association of exposure to Chinese rapeseed cooking-oil emissions and lung-cancer risk may be related to the mutagenic component of these condensates.     

A cytoplasmic chaperonin that catalyzes beta-actin folding.

We have isolated a cytoplasmic chaperonin based on its ability to catalyze the folding of denatured beta-actin. The cytoplasmic chaperonin is organized as a multisubunit toroid and requires Mg2+ and ATP for activity. The folding reaction proceeds via the rapid ATP-independent formation of a binary complex, followed by a slower ATP-dependent release of the native product. Electron microscopic observations reveal a striking structural change that occurs upon addition of Mg2+ and ATP. The eukaryotic cytoplasm thus contains a chaperonin that is functionally analagous to its prokaryotic, mitochondrial, and chloroplastic counterparts.     

Mechanism of action of the peptide antibiotic nisin in liposomes and cytochrome c oxidase-containing proteoliposomes.

The interaction of the peptide antibiotic nisin with liposomes has been studied. The effect of this interaction was analyzed on the membrane potential (inside negative) and the pH gradient (inside alkaline) in liposomes made from Escherichia coli phosphatidylethanolamine and egg phosphatidylcholine (9:1, wt/wt). The membrane potential and pH gradient were generated by artificial ion gradients or by the oxidation of ascorbate, N,N,N',N'-tetramethyl-p-phenylenediamine, and cytochrome c by the beef heart cytochrome c oxidase incorporated in the liposomal membranes. Nisin dissipated the membrane potential and the pH gradient in both types of liposomes and inhibited oxygen consumption by cytochrome c oxidase in proteoliposomes. The dissipation of the proton motive force in proteoliposomes was only to a minor extent due to a decrease of the oxidase activity by nisin. The results in these model systems show that a membrane potential and/or a pH gradient across the membrane enhances the activity of nisin. Nisin incorporates into the membrane and makes the membrane permeable for ions. As a result, both the membrane potential and pH gradient are dissipated. The activity of nisin was found to be influenced by the phospholipid composition of the liposomal membrane.     

Molecular structure of antitumor drug steffimycin and modelling of its binding to DNA.

The molecular and crystal structure of steffimycin have been determined by single crystal X-ray diffraction to 0.9 angstrom resolution. The triclinic crystals are in the space group P1, with the unit cell dimensions of a = 8.606(3) angstrom, b = 22.168(7) angstrom, c = 8.448(2) angstrom, alpha = 97.56(3) degrees, beta = 95.97(2) degrees, gamma = 87.94(3) degrees, Z = 2. The structure was solved by direct methods and refined by the full-matrix least-squares method to a final R value of 0.065 with 3405 (Inet greater than 2.0 sigma (Inet] observed reflections using the NRCVAX software package. The crystal lattice includes 2 independent steffimycin, 3 water and one 2-methyl-2,4-pentanediol molecules. The conformation of steffimycin is grossly similar to other anthracycline antibiotics including daunorubicin. The crystal packing interactions of steffimycin suggest a preferred stacking of the aglycone chromophore of the antibiotic which resembles the intercalative interactions seen in the daunorubicin-d(CGTACG) (Wang et al., Biochemistry 26, 1152 (1987] and nogalamycin-d(CGT(pS)ACG) (Liaw et al., Biochemistry 28, 9913 (1989] complexes. The atomic coordinates data from these complexes were used to model the intercalative binding of steffimycin to DNA. The models were then stereochemically idealized by the constraint refinement program NUCLSQ. Subsequently XPLOR software package was used for energy minimization of these models in vacuo. The model building studies suggest that steffimycin has a higher CpG base sequence specificity over the TpA step, similar to that of daunorubicin and nogalamycin.     

Binding of the antitumor drug nogalamycin and its derivatives to DNA: structural comparison

The three-dimensional molecular structures of the complexes between a novel antitumor drug nogalamycin and its derivative U-58872 with a modified DNA hexamer d[m5CGT(pS)Am5CG] have been determined at 1.7- and 1.8-A resolution, respectively, by X-ray diffraction analyses. Both structures (in space group P6(1)) have been refined with constrained refinement procedure to final R factors of 0.208 (3386 reflections) and 0.196 (2143 reflections). In both complexes, two nogalamycins bind to the DNA hexamer double helix in a 2:1 ratio with the elongated aglycon chromophore intercalated between the CpG steps at both ends of the helix. The aglycon chromophore spans across the GC Watson-Crick base pairs with its nogalose lying in the minor groove and the aminoglucose lying in the major groove of the distorted B-DNA double helix. Most of the sugars remain in the C2'-endo pucker family, except three deoxycytidine residues (terminal C1, C7, and internal C5). All nucleotides are in the anti conformation. Specific hydrogen bonds are found in the complex between the drug and guanine-cytosine bases in both grooves of the helix. One hydroxyl group of the aminoglucose donates a hydrogen bond to the N7 of guanine, while the other receives a hydrogen bond from the N4 amino group of cytosine. The orientation of these two hydrogen bonds suggests that nogalamycin prefers a GC base pair with its aglycon chromophore intercalating at the 5'-side of a guanine (between NpG), or at the 3'-side of a cytosine (between CpN) with the sugars pointing toward the GC base pair. The binding of nogalamycin to DNA requires that the base pairs in DNA open up transiently to allow the bulky sugars to go through, suggesting that nogalamycin prefers GC sequences embedded in a stretch of AT sequences.     

益生菌调控肠道屏障功能预防家禽球虫病的研究进展

球虫病给养禽业带来巨大经济损失,人们对绿色健康食品的迫切需求使球虫病的防控面临新的挑战.伴随世界"禁抗"进程的不断推进,家禽养殖业亟需一种安全有效的新型抗球虫方法.益生菌可竞争性排斥病原菌定殖以防止球虫病继发感染,可刺激宿主抗菌肽、黏蛋白和紧密连接蛋白的分泌以抵御球虫入侵,还可激活免疫反应以增强机体抗球虫感染的能力.本...     

Optogenetic manipulation of cyclic guanosine monophosphate to probe phosphodiesterase activities in megakaryocytes

Cyclic guanosine monophosphate (cGMP) signalling plays a fundamental role in many cell types, including platelets. cGMP has been implicated in platelet formation, but mechanistic detail about its spatio-temporal regulation in megakaryocytes (MKs) is lacking. Optogenetics is a technique which allows spatio-temporal manipulation of molecular events in living cells or organisms. We took advantage of this method and expressed a photo-activated guanylyl cyclase, Blastocladiella emersonii Cyclase opsin (BeCyclop), after viral-mediated gene transfer in bone marrow (BM)-derived MKs to precisely light-modulate cGMP levels. BeCyclop-MKs showed a significantly increased cGMP concentration after illumination, which was strongly dependent on phosphodiesterase (PDE) 5 activity. This finding was corroborated by real-time imaging of cGMP signals which revealed that pharmacological PDE5 inhibition also potentiated nitric oxide-triggered cGMP generation in BM MKs. In summary, we established for the first-time optogenetics in primary MKs and show that PDE5 is the predominant PDE regulating cGMP levels in MKs. These findings also demonstrate that optogenetics allows for the precise manipulation of MK biology.     

锰矿区大叶胡枝子灌丛土壤的丛枝菌根真菌多样性

大叶胡枝子(Lespedeza davidii)为一种豆科灌木,具有较强耐受重金属胁迫及固氮能力,也是矿区一种重要修复植物。丛枝菌根真菌(Arbuscular mycorrhizal fungi,AMF)是一类植物共生真菌,它在矿区与植物共生可促进植物生长、提高植物的抗逆性;但其种类、分布及其影响机制尚不够清楚。以大叶胡枝子灌丛土壤AMF群落为研究对象,采集矿区与非矿区大叶胡枝子冠下及其相邻空旷地土壤进行内部转录间隔区(ITS)测序,分析土壤理化性质,揭示不同样地土壤AMF群落的多样性及其影响因素。研究结果表明:(1)土壤样本共得到2961个可操作分类单元(OTU),其中属于AMF的OTU为66个;Silva数据库比对发现AMF有7目10科16属24种。AMF总体物种丰度为矿区相邻空旷地土壤>矿区冠下土壤>非矿区冠下土壤>非矿区相邻空旷地土壤,Shannon指数和Simpson指数与该趋势保持一致。(2)矿区土壤AMF群落以内养囊霉属(Entrophospora)等为优势属,非矿区冠下以斗管囊霉属(Funneliformis)等为优势属。稀有内养囊霉(Entrophospora infrequens)是4个样地共有的优势种,该种为广谱生态型种;Archaeospora sp.和Paraglomerales sp.为矿区冠下的优势种,它们对锰胁迫有较强的耐受性;Funneliformis sp.为非矿区冠下的优势种。(3)冗余分析(RDA)表明,AMF的种类和数量受到锰含量、土壤pH值以及全磷含量的显著影响。本研究结果说明AMF种类及多样性受到土壤理化性质的影响;矿区一些耐性AMF的存在提高了AMF多样性,它们有利于逆境条件下植物的生长。