Gel-forming structures and stages of red algal galactans of different sulfation levels

Sol-gel transition processes of algal galactans were studied using cryofixation method in combination with freeze-drying and scanning electron microscopy (SEM) techniques. The structures formed in successive stages of gelling process upon cooling were rapidly frozen at defined temperature points and viewed by SEM. It was established that in the case of both types of gelling galactans investigated, a fine honeycomb-like network exists for a wide range of solution temperatures. The formation and structure of this network depends on the structural type, gelling stage, and concentration of the galactan in solution. The honeycomb suprastructures exist also in carrageenan and agarose sols (at temperatures considerably exceeding the gelling temperatures). An additional helical network formed showed different behaviour in the case of carrageenan and agar-type polysaccharides. In the gel-formation process, tightening of the network takes place in both types of galactan gels; the honeycomb structures persist in carrageenan (furcellaran) but not in agarose gels.     

A novel long distance base-pairing interaction in human immunodeficiency virus type 1 RNA occludes the Gag start codon

The 5'-untranslated region (5'-UTR) is the most conserved part of the HIV-1 RNA genome, and it contains regulatory motifs that mediate various steps in the viral life cycle. Previous work showed that the 5'-terminal 290 nucleotides of HIV-1 RNA adopt two mutually exclusive secondary structures, long distance interaction (LDI) and branched multiple hairpin (BMH). BMH has multiple hairpins, including the dimer initiation signal (DIS) hairpin that mediates RNA dimerization. LDI contains a long distance base-pairing interaction that occludes the DIS region. Consequently, the two conformations differ in their ability to form RNA dimers. In this study, we have presented evidence that the full-length 5'-UTR also adopts the LDI and BMH conformations. The downstream 290-352 region, including the Gag start codon, folds differently in the context of the LDI and BMH structures. These nucleotides form an extended hairpin structure in the LDI conformation, but the same sequences create a novel long distance interaction with upstream U5 sequences in the BMH conformation. The presence of this U5-AUG duplex was confirmed by computer-assisted RNA structure prediction, biochemical analyses, and a phylogenetic survey of different virus isolates. The U5-AUG duplex may influence translation of the Gag protein because it occludes the start codon of the Gag open reading frame.     

The HIV-1 leader RNA conformational switch regulates RNA dimerization but does not regulate mRNA translation

The untranslated leader RNA is the most conserved part of the human immunodeficiency virus type I (HIV-1) genome. It contains many regulatory motifs that mediate a variety of steps in the viral life cycle. Previous work showed that the full-length leader RNA can adopt two alternative structures: a long distance interaction (LDI) and a branched multiple-hairpin (BMH) structure. The BMH structure exposes the dimer initiation site (DIS) hairpin, whereas this motif is occluded in the LDI structure. Consequently, these structures differ in their capacity to form RNA dimers in vitro. The BMH structure is dimerization-competent, due to DIS hairpin formation, but also presents the splice donor (SD) and RNA packaging (Psi) hairpins. In the LDI structure, an extended RNA packaging (Psi(E)) hairpin is folded, which includes the splice donor site and gag coding sequences. The gag initiation codon is engaged in a long distance base pairing interaction with sequences in the upstream U5 region in the BMH structure, thus forming the evolutionarily conserved U5-AUG duplex. Therefore, the LDI-BMH equilibrium may affect not only the process of RNA dimer formation but also translation initiation. In this study, we designed mutations in the 3'-terminal region of the leader RNA that alter the equilibrium of the LDI-BMH structures. The mutant leader RNAs are affected in RNA dimer formation, but not in their translation efficiency. These results indicate that the LDI-BMH status does not regulate HIV-1 RNA translation, despite the differential presentation of the gag initiation codon in both leader RNA structures.     

Preparative affinity electrophoresis of different glycoforms of serum glycoproteins: Application for the study of inflammation-induced expression of sialyl-Lewisx groups onα 1-acid glycoprotein (orosomucoid)

During acute inflammation, human ₁-acid glycoprotein (AGP) is subject to marked changes in branching of its glycans, its degree of fucosylation and the expression of sialyl-Lewis^x)(SLe^x) groups. To be able to study these changes in glycosylation in more detail, a procedure was developed to isolate the different glycoforms of AGP in milligram amounts by preparative affinity electrophoresis (AE) with a free lectin as fractionating agent. The method was applied to isolate differently fucosylated forms of AGP with the fucose-specific lectinAleuria aurantia (AAL). AGP was separated into one non-reactive (AO) and four reactive (A1-A4) fractions. It was found that, in particular, the highly fucosylated fractions A3 and A4 contained the inflammation-induced SLe^x groups of AGP. Analysis by crossed affinoimmunoelectrophoresis (CAIE) with concanavalin A (Con A) of these different glycoforms of AGP showed that the presence of tri-and/or tetraantennary glycans, instead of diantennary glycans, was associated with a higher degree of fucosylation. Identical results were obtained by subjecting Con A-fractionated forms of AGP to CAIE with AAL as the affinocomponent. It is expected that this method of preparative AE can generally be applied to other glycoproteins, which can be separated in different glycoforms by CAIE using lectins.Part of this work was published in abstract form,Glycoconjugate J 1993;10; 317.     

Structure and expression of DNA transferred to tobacco via transformation of protoplasts with Ti-plasmid DNA: co-transfer of T-DNA and non T-DNA sequences

Summary The T-DNA structure and organization in tissues obtained via transformation of tobacco protoplasts with Ti-plasmid DNA was found to be completely different from the T-DNA introduced via Agrobacterium tumefaciens. It is often fragmented. Overlapping copies of T-DNA, having various sizes, as well as separated fragments of T-DNA were detected. The border sequences of 23 basepairs (bp), flanking the T-region in the Ti-plasmid as direct repeats are not used as preferred sequences for integration. Similar results were obtained with a T-region clone lacking one of the T_L-borders. This clone, which carried the cytokinin locus and only the right border sequence of T_L and the left border sequence of T_R, still had the capacity to transform protoplasts. Also the Vir-region of the Ti-plasmid is not required for integration of foreign DNA via DNA transformation. This is demonstrated by the results with the T-region clone mentioned and by the transforming capacity of a Ti-plasmid carrying a mutated Vir-region. Nevertheless, in a number of Ti-plasmid DNA transformants Vir-region fragments were found to be stably integrated. Furthermore, it has been established that co-transformation can occur with plant cells. Besides the detection of Ti-plasmid fragments from outside the T-region also DNA sequences originating from two DNA sources, which were both independently present in transformation experiments, have been found in some DNA transformants, e.g. calf thymus DNA, which was used as carrier DNA. No expression of the co-transferred DNA was observed. In total three phenotypical classes of DNA transformants were isolated. Although the T-DNA was often scrambled, polyA⁺ mRNA studies indicated that the different phenotypes studied can be explained by the presence of active T-DNA genes with known functions.     

Plasma oxysterols and angiographically determined coronary atherosclerosis: a case control study

Several in vitro and in vivo experiments have implicated oxysterols in the aetiology and progression of atherosclerosis. Oxysterols may be formed endogenously by oxidation of cholesterol and thus may form a marker of LDL oxidation. They may also be obtained exogenously through dietary intake. We investigated the association of oxysterols with the degree of coronary stenosis in patients undergoing coronary angiography. Cases with severe coronary atherosclerosis 80 stenosis in one of the major coronary vessels, n =80 were compared with controls with no or minor stenosis 50 stenosis in all three major coronary vessels, n =79 . Cases and controls were prestratified on age, gender and smoking habits. Evaluated were plasma levels of unesterified 7 hydroxycholesterol, 7 hydroxycholesterol, 25 hydroxycholesterol, 7 ketocholesterol, cholestane triol and 5,6 epoxycholestanol. 7 Hydroxycholesterol made up 67 of the total amount of plasma oxysterol concentration and was the only one significantly higher in cases 1.53 mu g per 100 ml vs 1.27 mu g per 100 ml, p 0.05 . Further, cases had somewhat higher LDL cholesterol levels and significantly lower HDL cholesterol levels than controls. After multivariate adjustment to account for this difference in lipid levels and for the prestratification factors the mean difference between cases and controls for 7 hydroxycholesterol 0.14 mu g per 100 ml was no longer significant. Also the other oxysterols showed no significant association with the degree of coronary stenosis. Multiple logistic regression analyses showed an adjusted odds ratio of 1.07 95 CI, 0.45-2.59 in the highest tertile of total plasma oxysterol level. We conclude, that this study does not support the hypothesis that plasma oxysterols form an additional risk factor for coronary atherosclerosis.     

Activation of phospholipase D by calmodulin antagonists and mastoparan in carnation petals

An in vivo assay for phospholipase D (PLD; EC 3,1,4,4) activity,based on its transphosphatidylation property, is described indetail and was used to study putative post-translational regulationmechanisms of PLD activity in carnation (Dianthus caryophyllusL.) petals. A variety of agents was applied to petal discs.The calmodulin (CaM) antagonists propranolol, N-(6-aminohexyl)-5-chloro-1-naphthalenesulphonamide(W7) and N-(6-aminohexyl)-1-naphthalenesulphonamide (W5), stimulatedPLD activity in a dose-dependent manner. EGTA partially inhibitedthe stimulation by the CaM antagonists. Erythrosin B, an inhibitorof CaM-dependent P-type Ca^z+-ATPases, slightly stimulated PLDactivity. The results suggest that part of the stimulation ofPLD activity by CaM antagonists is due to an increased intracellularCa²⁺-concentration, PLD activity was stimulated by mastoparanin a dose- and time-dependent manner. The signal-like activationkinetics suggests that mastoparan activates PLD (in)directlyvia a G protein. Key words: Phospholipase D, CaM antagonists, mastoparan, Dianthus, calcium     

Retention of specific activity of muscle aldolase after its immobilization on odigos and odifil (ethylsulfo-activated agarose)

The effect of the number of active groups of new affinity supports--odigose and odifil (ethylsulfo-activated agarose) on the retention of the specific activity of muscle aldolase was investigated. The active center of the enzyme includes lysine able to react with activated supports. The aldolase completely retained the specific activity after immobilization on the abovementioned relatively high-substituted supports, on which other enzymes, e.g. phosphorylase B, NAD-kinase from pigeon heart, were partially or completely inactivated. The aldolase was inactivated when being immobilized on more substituted supports. The enzyme specific activity completely retained if the high substituted supports were preliminary incubated at 37 degrees to destroy some diazo-groups.