寡聚脱氧核苷酸的结构与抗降解特性的研究

合成了４段具有不同高级结构或不同修饰的寡聚脱氧核苷酸,检查它们在２０％血清中的稳定性．发现：（１）寡核苷酸主要被血清中的３′外切核酸酶降解,未经修饰的线性寡核苷酸降解严重;（２）末端部分硫代修饰的寡核苷酸稳定性明显提高;（３）自身互补形成的配对结构可有效保护３′末端．具有４个以上（含４个）ＧＣ对的３′端发夹结构寡核苷酸,其抗核酸酶的能力几乎与硫代修饰的寡核苷酸相当．     

Dynamic and structural properties of glucose oxidase enzyme

The catalytic oxidation of β-D-glucose by the enzyme glucose oxidase involves a redox change of the flavin coenzyme. The structure and the dynamics of the two extreme glucose oxidase forms were studied by using infrared absorption spectroscopy of the amide I′ band, tryptophan fluorescence quenching and hydrogen isotopic exchange. The conversion of FAD to FADH₂ does not change the amount of α-helix present in the protein outer shell, but reorganises a fraction of random coil to β-sheet structure. The dynamics of the protein interior vary with the redox states of the flavin without affecting the motions of the structural elements near the protein surface. From the structure of glucose oxidase given by X-ray crystallography, these results suggest that the dynamics of the interface between the two monomers are involved in the catalytic mechanism. Received: 27 December 1996 / Accepted: 18 July 1997     

Early steps in plastid evolution: current ideas and controversies

Some nuclear‐encoded proteins are imported into higher plant plastids via the endomembrane (EM) system. Compared with multi‐protein Toc and Tic translocons required for most plastid protein import, the relatively uncomplicated nature of EM trafficking led to suggestions that it was the original transport mechanism for nuclear‐encoded endosymbiont proteins, and critical for the early stages of plastid evolution. Its apparent simplicity disappears, however, when EM transport is considered in light of selective constraints likely encountered during the conversion of stable endosymbionts into fully integrated organelles. From this perspective it is more parsimonious to presume the early evolution of post‐translational protein import via simpler, ancestral forms of modern Toc and Tic plastid translocons, with EM trafficking arising later to accommodate glycosylation and/or protein targeting to multiple cellular locations. This hypothesis is supported by both empirical and comparative data, and is consistent with the relative paucity of EM‐based transport to modern primary plastids.     

Posterior skeletal development and the segmentation clock period are sensitive to Lfng dosage during somitogenesis

The segmental structure of the axial skeleton is formed during somitogenesis. During this process, paired somites bud from the presomitic mesoderm (PSM), in a process regulated by a genetic clock called the segmentation clock. The Notch pathway and the Notch modulator Lunatic fringe (Lfng) play multiple roles during segmentation. Lfng oscillates in the posterior PSM as part of the segmentation clock, but is stably expressed in the anterior PSM during presomite patterning. We previously found that mice lacking overt oscillatory Lfng expression in the posterior PSM (Lfng^?FCE) exhibit abnormal anterior development but relatively normal posterior development. This suggests distinct requirements for segmentation clock activity during the formation of the anterior skeleton (primary body formation), compared to the posterior skeleton and tail (secondary body formation). To build on these findings, we created an allelic series that progressively lowers Lfng levels in the PSM. Interestingly, we find that further reduction of Lfng expression levels in the PSM does not increase disruption of anterior development. However tail development is increasingly compromised as Lfng levels are reduced, suggesting that primary body formation is more sensitive to Lfng dosage than is secondary body formation. Further, we find that while low levels of oscillatory Lfng in the posterior PSM are sufficient to support relatively normal posterior development, the period of the segmentation clock is increased when the amplitude of Lfng oscillations is low. These data support the hypothesis that there are differential requirements for oscillatory Lfng during primary and secondary body formation and that posterior development is less sensitive to overall Lfng levels. Further, they suggest that modulation of the Notch signaling by Lfng affects the clock period during development.     

Could a dysfunction of ferritin be a determinant factor in the aetiology of some neurodegenerative diseases?

Background

The concentration of iron in the brain increases with aging. Furthermore, it has also been observed that patients suffering from neurological diseases (e.g. Parkinson, Alzheimer…) accumulate iron in the brain regions affected by the disease. Nevertheless, it is still not clear whether this accumulation is the initial cause or a secondary consequence of the disease. Free iron excess may be an oxidative stress source causing cell damage if it is not correctly stored in ferritin cores as a ferric iron oxide redox-inert form.

Scope

Both, the composition of ferritin cores and their location at subcellular level have been studied using analytical transmission electron microscopy in brain tissues from progressive supranuclear palsy (PSP) and Alzheimer disease (AD) patients.

Major conclusions

Ferritin has been mainly found in oligodendrocytes and in dystrophic myelinated axons from the neuropili in AD. In relation to the biomineralization of iron inside the ferritin shell, several different crystalline structures have been observed in the study of physiological and pathological ferritin. Two cubic mixed ferric–ferrous iron oxides are the major components of pathological ferritins whereas ferrihydrite, a hexagonal ferric iron oxide, is the major component of physiological ferritin. We hypothesize a dysfunction of ferritin in its ferroxidase activity.

General significance

The different mineralization of iron inside ferritin may be related to oxidative stress in olygodendrocites, which could affect myelination processes with the consequent perturbation of information transference.     

Effect of low light intensity on growth and accumulation of secondary metabolites in roots of Glycyrrhiza uralensis Fisch

Effects of low light intensity on growth and accumulation of secondary metabolites of a medicinal plant Glycyrrhiza uralensis Fisch. were investigated. Hydroponic-cultivated one year-old rhizome seedlings were grown under three low irradiances, 200, 100, and 50 μmol m⁻² s⁻¹ for 135 days. Control plants were cultured under natural light conditions. Low light intensity stress decreased leaf thickness, photosynthesis and biomass, but increased leaf area and chlorophyll concentrations. Low light intensity also significantly increased accumulation of glycyrrhizic acid and liquiritin in the root, while the maximum values of both secondary metabolites were obtained under an irradiance of 100 μmol m⁻² s⁻¹. Concentrations of both secondary metabolites were negatively correlated with root biomass. The results suggested that G. uralensis could endure an environment with low light intensity and suitable light control might increase the secondary metabolite contents within agroforestry systems.     

The systematic position of Paraspathidium Noland, 1937 (Ciliophora,Litostomatea?) inferred from primary SSU rRNA gene sequences and predicted secondary rRNA structure

Traditionally the unusual ciliate Paraspathidium has been regarded as a gymnostome haptorid (Litostomatea) based on its morphological features. In order to test this placement, the small-subunit (SSU) rRNA gene was sequenced for two isolates of Paraspathidium apofuscum and phylogenetic trees were constructed. Furthermore, the putative structure of the variable regions 2 and 4 of the SSU rRNA gene were predicted and compared with those of other ciliates. Our analyses of SSU rRNA gene sequences revealed (i) a clear separation of Paraspathidium from the haptorids and indeed the class Litostomatea, rejecting its systematic position based on morphological characters and (ii) an equally clear association with the assemblage comprising the classes Plagiopylea and Prostomatea. Putative secondary structures of the variable regions 2 and 4 of Paraspathidium are similar to those of the plagiopyleans and prostomateans but differ from the hapotrids in Helix 10, Helix E10-1 and Helix E23-5. Taken together, these results support the placement of Paraspathidium close to prostomateans and plagiopyleans, or even as a distinct group possibly at ordinal rank, within the class Plagiopylea.     

Wood formation in Angiosperms

Wood formation is a complex biological process, involving five major developmental steps, including (1) cell division from a secondary meristem called the vascular cambium, (2) cell expansion (cell elongation and radial enlargement), (3) secondary cell wall deposition, (4) programmed cell death, and (5) heartwood formation. Thanks to the development of genomic studies in woody species, as well as genetic engineering, recent progress has been made in the understanding of the molecular mechanisms underlying wood formation. In this review, we will focus on two different aspects, the lignification process and the control of microfibril angle in the cell wall of wood fibres, as they are both key features of wood material properties.     

Reduction potential variations in azurin through secondary coordination sphere phenylalanine incorporations

Recent evidence has shown that the properties of metal binding sites can be tuned by more than the ligands in the primary coordination sphere. We investigated the incorporation of four phenylalanine residues into the secondary coordination sphere of the small soluble blue copper protein azurin. The locations for placement of these residues in azurin were based on the structure of the highly hydrophobic blue copper protein rusticyanin, which is known to have a significantly higher reduction potential than azurin. Using site-directed mutagenesis, these residues in close proximity to the copper binding site were mutated to large hydrophobic phenylalanine residues individually and in combination. We also added the Met121Leu mutation on top of the Phe mutations to construct a total of 13 variants. We found little change in the UV-visible absorption and EPR data for these proteins, however modest increases in reduction potential were observed with increases by as much as 30 mV per Phe residue. Furthermore, we observed the increases in potential to be additive.