Short-Term In Vitro Culture and Molecular Analysis of the Microsporidian, Enterocytozoon bieneusi

ABSTRACT. The microsporidium, Enterocytozoon bieneusi , causes a severe, debilitating, chronic diarrhea in patients with the acquired immunodeficiency syndrome. Specific diagnosis of intestinal microsporidiosis, especially due to Enterocytozoon , is difficult and there is no known therapy that can completely eradicate this parasite. Preliminary studies indicate that a short term (about 6 months) in vitro culture of this parasite yielding low numbers of spores, may be established by inoculating human lung fibroblasts and/or monkey kidney cell cultures with duodenal aspirates and or biopsy from infected patients. The cultures may subsequently be used for the isolation and molecular analysis of parasite DNA.     

Three-dimensional solution structure of the HIV-1 protease complexed with DMP323, a novel cyclic urea-type inhibitor, determined by nuclear magnetic resonance spectroscopy.

The three-dimensional solution structure of the HIV-1 protease homodimer, MW 22.2 kDa, complexed to a potent, cyclic urea-based inhibitor, DMP323, is reported. This is the first solution structure of an HIV protease/inhibitor complex that has been elucidated. Multidimensional heteronuclear NMR spectra were used to assemble more than 4,200 distance and angle constraints. Using the constraints, together with a hybrid distance geometry/simulated annealing protocol, an ensemble of 28 NMR structures was calculated having no distance or angle violations greater than 0.3 A or 5 degrees, respectively. Neglecting residues in disordered loops, the RMS deviation (RMSD) for backbone atoms in the family of structures was 0.60 A relative to the average structure. The individual NMR structures had excellent covalent geometry and stereochemistry, as did the restrained minimized average structure. The latter structure is similar to the 1.8-A X-ray structure of the protease/DMP323 complex (Chang CH et al., 1995, Protein Science, submitted); the pairwise backbone RMSD calculated for the two structures is 1.22 A. As expected, the mismatch between the structures is greatest in the loops that are disordered and/or flexible. The flexibility of residues 37-42 and 50-51 may be important in facilitating substrate binding and product release, because these residues make up the respective hinges and tips of the protease flaps. Flexibility of residues 4-8 may play a role in protease regulation by facilitating autolysis.     

The effects of Anabaena spiroides (Cyanophyceae) exopolysaccharide on copper toxicity to Simocephalus serrulatus (Cladocera, Daphnidae)

1. This work investigated the consumption of a microalgal (Anabaena spiroides) exopolysaccharide by the cladoceran Simocephalus serrulatus (Cladocera, Daphnidae) and its effect on copper toxicity. 2. Total organic carbon concentration was used to quantify the microalgal exopolysaccharide. Both copper‐complexed exopolysaccharides and copper‐free exopolysaccharides were taken up by S. serrulatus. 3. A reduction of free copper ions was obtained in the presence of A. spiroides exopolysaccharide. Copper toxicity (EC₅₀) and zooplankton concentrations were inversely correlated to exopolysaccharide concentration in experimental media. 4. An increase of free copper ions in experimental media was obtained after exopolysaccharide consumption, suggesting that S. serrulatus excreted copper to the surrounding environment.     

锁阳和肉苁蓉寄生方式的区别

锁阳和肉苁蓉都是中医药里重要的补益类药材,但由于过度采挖和采挖方式不当,目前它们的野生资源已濒临枯竭。肉苁蓉和锁阳分别是我国濒危和易危珍稀植物,研究二者寄生方式的特点与区别不仅可以促进锁阳和肉苁蓉的人工栽培,从而使野生药材得到一定的保护,而且对了解寄生植物在荒漠地区等极端严酷环境中的适应机制具有重要的生态学意义。该研究采用形态学观察结合常规石蜡切片法,对锁阳和肉苁蓉分别在各自寄主植物上的寄生方式进行了研究。结果表明：(1)锁阳的营养繁殖体在寄主植物根部呈串状分布,与寄主植物的连接方式属于非末端寄生;锁阳的吸器侵入寄主根系韧皮部和木质部的一部分区域,但是韧皮部和木质部大部分区域未被锁阳吸器占据,即有部分营养物质被锁阳“截取”。(2)肉苁蓉在其肉质茎基部长出新的芽体,与寄主植物的连接方式属于末端寄生;肉苁蓉的吸器侵入寄主根韧皮部和木质部全部区域。因此,锁阳寄生后,被寄生的寄主根依然能够向前生长,具有正常的功能;肉苁蓉寄生后,寄生点的寄主根失去根系的正常功能,成为一个为肉苁蓉生长发育提供营养物质的“输送通道( Transport channel)”。     

Partitioning of Carbohydrates in Annual and Perennial Cotton (Gossypium hirsutum L.)

An analysis of the partitioning of carbohydrates in annual andperennial cotton was made to ascertain the distribution of assimilatesand constitution of reserves. Root/shoot dry matter ratio ishigh in perennial cotton and this plant shows a preferentialaccumulation of dry matter in roots corresponding to its adaptationto drought. Starch content is also higher in perennial cottonroots than in annual. It can be said that the earlier maturingthe cultivar, the lower the root/shoot ratio and the lower thestarch content. Nevertheless, at the whole plant level in annualcotton the starch content is highest in leaves where it is accumulatedbefore migration, and stem wood, and lowest in root and bark.While starch content in roots of annuals declines after 3 months,it is still increasing in perennials. Accumulation of carbohydratesas reserve material can be modified by selection and such selectionis accompanied by an increase in the activities of ß-amylasein exporting organs: leaves, woody tissue of the stem, and barkbut not in roots. Invertase activities were highest in leavesbut did not respond to selection. Non-irrigated cotton had ahigher activity of ß-amylase in leaves and stem woodcorresponding to the mobilization of reserve assimilates. Smallerincreases were observed in the activity of invertase. High yieldingannual cottons show a higher activity of ß-amylaseand invertase in leaves corresponding to a higher capacity ofassimilate transfer. Also a comparison was made from emergenceto 4 months of the partitioning of carbohydrates between leaf,stem and roots in annual and perennial cotton. In conclusionperennial cotton apparently owes its drought resistance to apartitioning of assimilates that favours the growth of the rootsystem and the accumulation of starch reserves in roots. Key words: Gossypium hirsutum L, carbohydrates, partitioning     

Evidence for stereospecific collision complexes of cyclo(tri-L-prolyl) with benzene

NMR spectra of cyclo(tri-L -prolyl), c-(P)₃, show large shifts of the H_α resonance on adding C₆D₆ to a solution of c-(P)₃ in CD₂Cl₂. CPK models and observed coupling constants indicate a rigid c-(P)₃ conformation, independent of solvent composition, suggesting that these shifts result from formation of stereospecific C₆D₆–c-(P)₃ collision complexes in which the c-(P)₃ H_α lie near the face of the aromatic ring. The temperature dependence of the H_α shifts and the solvent dependent shifts observed on adding toluene-d₈ or nitrobenzene-d₅ to the c-(P)₃ solution suggest that preferred C₆D₆–c-(P)₃ orientations result from attractive interactions between the electron-rich aromatic ring and the electropositive H_α's and/or δ⁺ nitrogen atoms in the peptide backbone. Reports of such interactions in increasingly diverse peptide model systems suggest that they may play a role in stabilizing protein structures.     

Germ Layer Interactions in Pattern Formation of Amphibian Mesoderm during Primary Embryonic Induction

Mesodermal differentiation of dorsal marginal zone (DMZ) before and after invagination was analyzed by a series of combination experiments with different kinds of ectoderm.
Lower DMZ of early gastrula didn't show any axial-mesoderm (notochord and somitic mesoderm) but lateral mesoderm (mesenchyme, mesothelium, or blood cells) in combinant with non-competent ventral ectoderm, while combinant with competent ectoderm was found to have well-differentiated axial-mesoderm with deutero-spinocaudal neurals. The axial-mesoderms have origin in the ectoderm. Uninvaginated DMZ of middle gastrula also showed difference in mesodermal differentiation between competent and non-competent ectoderms; axial-mesoderm differentiation was much better in competent than in non-competent. The axial-mesoderm originated from the uninvaginated DMZ. Archenteron roof of late gastrula showed regional difference in mesodermal differentiation in both combinants with competent and non-competent. The present study further demonstrated that there was regionality in promoting effect of induced neurectoderm on axial-mesoderm differentiation of invaginated archenteron roof.
The present experiments suggest that the cranio-caudal and dorso-ventral axis formations of amphibian mesoderm are finally determined by sequential and reciprocal interactions between the mesodermal anlage and the overlying ectoderm. It should be also shown that lower DMZ acts to trigger a series of the sequential interactions during primary embryonic induction.     

Evolution of the primary and secondary structures of the E1a mRNAs of the adenovirus

In this paper we investigate and compare (evolutionary) patterns in the primary and secondary structure of four homologous E1a mRNAs of the adenovirus. Our main results are as follows: (1) The similarity of the coding regions of the mRNA sequences reflects both similarity in function (i.e., oncogenicity) and evolutionary divergence. (2) The similarity of the leader and the trailer regions reflects host specificity (i.e., human or simian) and must therefore arise from convergence. (3) Minimal energy foldings of the mRNAs show similar secondary structures (in particular around the splice sites). The conservation of pre-mRNA secondary structure shows that mRNAs are subject to selection constraints in addition to those associated with proteins. (4) The conserved secondary (helical) structures consist of nonhomologous subsequences, i.e., shifts have occurred. The observed shifts near the splice sites seem to be the simplest way of dealing with the dual constraints.