Silencing of ZFP36L2 increases sensitivity to temozolomide through G2/M cell cycle arrest and BAX mediated apoptosis in GBM cells

Molecular Biology Reports - Despite the advancements in primary brain tumour diagnoses and treatments, the mortality rate remains high, particularly in glioblastoma (GBM). Chemoresistance,...     

Structural studies on a low oxygen affinity hemoglobin from mammalian species: Sheep (Ovis aries)

Hemoglobin (Hb) is in equilibrium between low affinity Tense (T) and high affinity Relaxed (R) states associated with its unliganded and liganded forms, respectively. Mammalian species can be classified into two groups on the basis of whether they express ‘high’ and ‘low’ oxygen affinity Hbs. Although Hbs from former group have been studied extensively, a limited number of structural studies have been performed for the low oxygen affinity Hbs. Here, the crystal structure of low oxygen affinity sheep methemoglobin (metHb) has been determined to 2.7 Å resolution. Even though sheep metHb adopts classical R state like quaternary structure, it shows localized quaternary and tertiary structural differences compared with other liganded Hb. The critical group of residues in the “joint region”, shown as a major source of quaternary constraint on deoxyHb, formed unique interactions in the α1β2/α2β1 interfaces of sheep metHb structure. In addition, the constrained β subunits heme environment and the contraction of N-termini and A-helices of β subunits towards the molecular dyad are observed for sheep metHb structure. These observations provide the structural basis for a low oxygen affinity and blunt response to allosteric effector of sheep Hb.     

Evidence of foliar aluminium accumulation in local, regional and global datasets of wild plants

? High foliar concentrations of aluminium (Al) have been reported in numerous plant species, but progress on the understanding of the functional significance of this trait is constrained by the absence of a quantitative analysis of its distribution among plant lineages and across biomes. ? We constructed a global dataset of foliar Al and nutrient concentrations for 1044 plant species from literature sources and new data collections in Brunei Darussalam. ? Our results provide statistical support for the existence of Al accumulators and non-Al accumulators in global, regional and local floras based on foliar Al concentrations. A value of 1 mg Al g(-1) leaf dry mass is a suitable threshold to distinguish between these two groups in a sample of species that lacks any geographical reference. However, a higher threshold foliar Al concentration is required to distinguish between Al accumulators in tropical (2.3-3.9 mg Al g(-1) leaf dry mass) than in temperate (1.1 mg Al g(-1) leaf dry mass) floras. There was a phylogenetic signal in the foliar concentrations of Al, but phylogeny did not explain the difference in the mean foliar Al concentration between tropical and temperate floras in a phylogenetically controlled analysis. ? Phylogeny and soil chemistry are potential factors driving Al accumulation in certain groups of plants.     

Effects of cold exposure and shear stress on endothelial nitric oxide synthase activation

Endothelial nitric oxide synthase (eNOS) is the primary enzyme that produces nitric oxide (NO), which plays an important role in blood vessel relaxation. eNOS activation is stimulated by various mechanical forces, such as shear stress. Several studies have shown that local cooling of the human finger causes strong vasoconstriction, followed after several minutes by cold-induced vasodilation (CIVD). However, the role played by endothelial cells (ECs) in blood vessel regulation in respond to cold temperatures is not fully understood. In this study, we found that low temperature alone does not significantly increase or decrease eNOS activation in ECs. We further found that the combination of shear stress with temperature change leads to a significant increase in eNOS activation at 37 °C and 28 °C, and a decrease at 4 °C. These results show that ECs play an important role in blood vessel regulation under shear stress and low temperature.     

Key roles of the Escherichia coli AhpC C-terminus in assembly and catalysis of alkylhydroperoxide reductase,an enzyme essential for the alleviation of oxidative stress

2-Cys peroxiredoxins (Prxs) are a large family of peroxidases, responsible for antioxidant function and regulation in cell signaling, apoptosis and differentiation. The Escherichia coli alkylhydroperoxide reductase (AhpR) is a prototype of the Prxs-family, and is composed of an NADH-dependent AhpF reductase (57 kDa) and AhpC (21 kDa), catalyzing the reduction of H₂O₂. We show that the E. coli AhpC (EcAhpC, 187 residues) forms a decameric ring structure under reduced and close to physiological conditions, composed of five catalytic dimers. Single particle analysis of cryo-electron micrographs of C-terminal truncated (EcAhpC_1 -172 and EcAhpC_1 -182) and mutated forms of EcAhpC reveals the loss of decamer formation, indicating the importance of the very C-terminus of AhpC in dimer to decamer transition. The crystallographic structures of the truncated EcAhpC_1 -172 and EcAhpC_1 -182 demonstrate for the first time that, in contrast to the reduced form, the very C-terminus of the oxidized EcAhpC is oriented away from the AhpC dimer interface and away from the catalytic redox-center, reflecting structural rearrangements during redox-modulation and -oligomerization. Furthermore, using an ensemble of different truncated and mutated EcAhpC protein constructs the importance of the very C-terminus in AhpC activity and in AhpC–AhpF assembly has been demonstrated.     

Habitat Associations and Community Structure of Dipterocarps in Response to Environment and Soil Conditions in Brunei Darussalam,Northwest Borneo

Plant habitat associations are well documented in Bornean lowland tropical forests, but few studies contrast the prevalence of associations across sites. We examined habitat associations and community composition of Dipterocarpaceae trees in two contrasting Bornean lowland mixed dipterocarp forests separated by approximately 100 km: Andulau (uniform topography, lower altitudinal range, sandy soils) and Belalong (highly dissected topography, higher altitudinal range, clay‐rich soils). Dipterocarpaceae trees ≥ 1 cm diameter at breast height (dbh) were censused in 20‐m wide belt transects established along topographic gradients at each site. Dipterocarp density, evenness, species richness, and diversity were significantly higher at Andulau than Belalong. Significant site associations (with either Andulau or Belalong) were detected for 19 (52%) of the 37 dipterocarp species tested. Dipterocarpaceae community composition at Belalong correlated with soil nutrient concentrations as well as measures of vegetation and topographic structure, but community composition at Andulau correlated with fewer habitat variables. Within each site, dipterocarp density, species richness, and diversity were consistently higher on ridges than in slopes and valleys. Significant within‐site associations to topographic habitats were less common at Andulau (10% of species tested) than at Belalong (15%). We conclude that edaphic and other environmental factors influence dipterocarp community composition at a local scale, and are more important drivers of community structure in the more variable environment at Belalong. Species richness and diversity of dipterocarps on small plots, however, were higher at Andulau, suggesting that factors other than environmental heterogeneity contribute to contrasts in dipterocarp tree species richness at small scales.     

Structural insight into the glycosylphosphatidylinositol transamidase subunits PIG-K and PIG-S from yeast

The addition of glycosylphosphatidylinositol (GPI) anchors to eukaryotic proteins in the lumen of the endoplasmic reticulum is catalyzed by the transamidase complex, composed of at least five subunits (PIG-K, PIG-S, PIG-T, PIG-U and GPAA1). Here PIG-K(24-337) and PIG-S(38-467) from yeast, including the residues 24-337 and 38-467 of the entire 411 and 534 residue protein, respectively, was produced in Escherichia coli and purified to homogeneity. Analysis of secondary structure by circular dichroism spectroscopy showed that yPIG-K(24-377) comprises 52% α-helix and 12% β-sheet, whereas yPIG-S(38-467) involves 58% α-helix and 18% β-sheet. The radius of gyration (R(g)) and the maximum size (D(max)) of both proteins have been analyzed by small angle X-ray scattering (SAXS) and determined to be 2.64±0.3 and 10.3±0.1 nm (yPIG-K(24-377)) as well as 3.06±0.02 nm (R(g)) and 16.9±0.4 nm (D(max)) in the case of yPIG-S(38-467), respectively. Using an ab initio approach, the first low-resolution solution structures of both proteins were restored. yPIG-K(24-377) is an elongated particle consisting of an egg-like portion and a small globular segment linked together by an 1.9 nm long stalk. yPIG-S(38-467) forms an elongated molecule in solution with a larger domain of 10.1 nm in length, a diameter of 9.1 nm and a smaller domain of 6.7 nm in length and 3.4 nm in width. The two domains of yPIG-S(38-467) are tilted relative to each other. Finally, the arrangements of PIG-K and PIG-S inside the ensemble of the transamidase complex are discussed.     

Assessing calibration uncertainty in molecular dating: the assignment of fossils to alternative calibration points

Although recent methodological advances have allowed the incorporation of rate variation in molecular dating analyses, the calibration procedure, performed mainly through fossils, remains resistant to improvements. One source of uncertainty pertains to the assignment of fossils to specific nodes in a phylogeny, especially when alternative possibilities exist that can be equally justified on morphological grounds. Here we expand on a recently developed fossil cross-validation method to evaluate whether alternative nodal assignments of multiple fossils produce calibration sets that differ in their internal consistency. We use an enlarged Crypteroniaceae-centered phylogeny of Myrtales, six fossils, and 72 combinations of calibration points, termed calibration sets, to identify (i) the fossil assignments that produce the most internally consistent calibration sets and (ii) the mean ages, derived from these calibration sets, for the split of the Southeast Asian Crypteroniaceae from their West Gondwanan sister clade (node X). We found that a correlation exists between s values, devised to measure the consistency among the calibration points of a calibration set (Near and Sanderson, 2004), and nodal distances among calibration points. By ranking all sets according to the percent deviation of s from the regression line with nodal distance, we identified the sets with the highest level of corrected calibration-set consistency. These sets generated lower standard deviations associated with the ages of node X than sets characterized by lower corrected consistency. The three calibration sets with the highest corrected consistencies produced mean age estimates for node X of 79.70, 79.14, and 78.15 My. These timeframes are most compatible with the hypothesis that the Crypteroniaceae stem lineage dispersed from Africa to the Deccan plate as it drifted northward during the Late Cretaceous.