δN and δC analysis of a Posidonia sinuosa seagrass bed

Potential food sources and dominant invertebrates and fishes were collected for the examination of variability in ¹³C/¹²C and ¹⁵N/¹⁴N to determine the sources of carbon available to consumers within a Western Australian Posidonia sinuosa-dominated seagrass bed. Autotrophs showed a wide distribution of δ¹³C values, with P. sinuosa at −11.3 ± 0.8‰ and macroalgae ranging from −16.6 to −31.7‰. This variation allowed us to successfully identify macroalgae as the main contributor of carbon to the trophic structure, although no distinction could be made between epiphytic macroalgae on seagrass, or allochthonous macroalgal sources. The range in δ¹⁵N ratios among potential food items at the trophic base was too small to make it useful as tracer of nitrogen flow pathways, but it consistently increased from macrophytes and detritus (4.1–6.8‰), to invertebrates (5.7–7.4‰) located near the middle of the food web, to fishes (8.3–11.9‰), with piscivorous species such as Leviprora inops generally having a higher ¹⁵N. δ¹³C of seston (−12.8‰) and sedimentary organic matter (−8.7‰) indicate that seagrass material is the main contributor to these two carbon pools, and that very little of it contributes to animal biomass.     

Variability of stable isotope signatures (δC and δN) in two spider crab populations (Maja brachydactyla) in Western Europe

The ontogenic variations of nitrogen and carbon stable isotopic signatures (δ¹⁵N and δ¹³C) were investigated in two spider crab (Maja brachydactyla) populations inhabiting in different biotopes of Western Europe. The Iroise Sea population is localized in Western Brittany and characterized by a seasonal migration occurring on a large bathymetric and habitat gradient while the Seine Bay population, in the Eastern English Channel, remains in a more homogeneous environment during its migration. In the Iroise Sea population, δ¹³C values increased significantly both with body size and age, revealing a shift towards “benthic-component” prey with spider crab growth. On the contrary, neither body size nor ageing gave rise to a significant trophic level change (derived from the δ¹⁵N). In this M. brachydactyla population, the seasonal migrations from coastal waters in summer to offshore habitats in winter involved significant but slight differences in both δ¹³C and δ¹⁵N. In the Seine Bay population, low variations for both carbon and nitrogen were recorded related to either sex or size or seasonal migration. Thus, the δ¹³C and δ¹⁵N variability in the spider crab depends on the availability and diversity of prey in its different living habitats, as well as on the morphological aptitudes of individuals to feed on prey (individual's size).     

δO and δC of Permian brachiopods: A record of seawater evolution and continental glaciation

Two hundred sixty-four δ¹⁸O and δ¹³C values of Permian articulate brachiopod shells were analyzed and 81 of these values were characterized as well preserved and biostratigraphically well defined. These were then utilized for construction of baseline oxygen and carbon isotope curves for the Permian interval. In addition, 21 δ¹³C whole rock values are reported for the Wordian and Capitanian.The early Permian, Asselian to Artinskian, times are characterized by ∼ 2.5‰ decrease in oxygen isotope values, from ∼ − 0.7‰ to − 3.3‰ (V-PDB). This is attributed to a ∼ 4-7 °C increase in temperature in the Southern Urals, concomitant with the retreat of the Permo-Carboniferous ice sheets and return of the ¹⁸O-depleted melt water into the oceans. The Late Permian samples from Iran (Jolfa at Kuh-e-Ali-Bashi) and China (Meishan) yield δ¹⁸O values, and presumably temperatures, similar to those that followed the termination of the large-scale glaciation in the Lower Permian. In between, the upper Kungurian to Capitanian samples from the Delaware Basin (Guadalupe Mountains) are enriched in ¹⁸O, at − 1.5‰ to − 3‰. We have no definitive explanation for these data, but tentatively suggest that the “anomaly” can potentially be a result of evaporative enrichment of seawater in ¹⁸O, due to intracratonic arid setting of the basin. The ¹⁸O-enriched nature of the Zechstein samples (− 1.2‰ to + 2.5‰), on the other hand, is in all probability a reflection of the high evaporation rates in the Zechstein sea.The Permian interval is characterized by a relatively constant δ¹³C, at about 4‰. The exceptions are again the brachiopods from the Delaware Basin (Guadalupe Mountains), which show ∼ 1.6‰ increase in the Guadalupian, to values of up to 5.9‰ in the Wordian. A tentative explanation, as in the case of oxygen, is based on the proposition that the semi-enclosed Delaware Basin was likely stratified, with sequestration of the ¹³C-depleted carbon to the deeper water layers and a complementary ¹³C enrichment in the upper oxygenated layer. The coeval open ocean water DIC may have been similar to that of the remainder of the Permian interval, at ∼ 4‰, as indicated by whole rock carbonate samples from Oman, Sicily, and Iran. In the latest Permian, the trend mimics the well-known δ¹³C drop at the Permian/Triassic boundary.     

Effects of body size and environment on diet-tissue δN fractionation in fishes

Nitrogen stable isotope natural abundance data are often used in trophodynamic research. The assumed nitrogen diet-tissue fractionation (Δδ¹⁵N) determines conclusions about trophic level, potential food sources and ontogenetic diet shifts. Δδ¹⁵N is usually assumed to be 3.0-3.4‰ per trophic level and unaffected by the size or age of animals or their environment. To assess the effects of body size, experimental duration and environmental conditions on fish tissue Δδ¹⁵N, two populations of European sea bass (Dicentrarchus labrax) were reared on constant diets of dab (Limanda limanda) muscle or sandeel (Ammodytes marinus) for 2 years under natural light and temperature regimes. Bass were sampled at approximately monthly intervals to determine Δδ¹⁵N for muscle, heart and liver tissue. Mean values of Δδ¹⁵N were 3.83‰, 3.54‰, 2.05‰ (sandeel diet) and 3.98‰, 3.32‰, 1.95‰ (dab diet) for muscle, heart and liver tissue respectively. The assumption that fractionation was independent of body mass was upheld for muscle and heart tissue, but not for liver. Time effects on muscle Δδ¹⁵N were explainable by a sinusoidal function with a period of 1 year and wave height ∼ 0.3‰. Time resulted in increases in heart δ¹⁵N and decreases in liver δ¹⁵N which were small compared to background variation, equating to 1/6 of a trophic level over 2 years, and unlikely to have great significance in ecological studies. Heart and liver δ¹⁵N were also affected by temperature probably reflecting the metabolic functions of these tissues and their associated rates of turnover. However in heart the explanatory power of temperature appeared tied to that of time. Although the Δδ¹⁵N for bass muscle on both diets approached 4‰, the Δδ¹⁵N values from this study, when combined with those from the literature, suggest that where fish species specific data are not available, a mean Δδ¹⁵N for fish muscle of 3.2‰ should be applied (mean white muscle Δδ¹⁵N = 3.15). The literature based mean Δδ¹⁵N for whole fish was lower than that of white muscle suggesting that a separate Δδ¹⁵N (2.9‰) should be applied when sampling whole fish.     

Effects of body size and environment on diet-tissue δC fractionation in fishes

δ¹³C data are often used in trophodynamic research where diet-tissue fractionation (Δδ¹³C) is assumed to be 0-1‰ per trophic level and unaffected by the size of animals or their environment. Variation in Δδ¹³C will influence conclusions about food sources, energy pathways and trophic level. To assess the effects of body size, age and environmental conditions on Δδ¹³C, European sea bass (Dicentrarchus labrax) were reared on constant diets of dab (Limanda limanda) or (Ammodytes marinus) for 2years under natural environmental regimes. Bass were sampled approximately monthly to determine Δδ¹³C for muscle, heart and liver tissue and were 1.66‰, − 0.18‰, − 1.77‰ (sandeel diet) and 1.34‰, − 1.18‰, − 1.75‰ (dab diet) respectively. Arithmetic lipid correction increased Δδ¹³C to > 2‰ for muscle and liver. Δδ¹³C was dependent on body mass and experimental duration (age) and generally declined with weight or time even after correction for lipid content. For liver, increasing temperature increased Δδ¹³C. The Δδ¹³C estimates from this study were compared with all available published Δδ¹³C estimates for fish. Bass muscle Δδ¹³C was similar to previous estimates for fish white muscle Δδ¹³C (1.56 ± 1.10‰) and whole body Δδ¹³C (1.52 ± 1.13‰). Fractionations derived in this study, combined with those from the literature, support the use of diet-tissue fractionation values of between 1‰-2‰ for δ¹³C, rather than the commonly used 0‰ − 1‰. For muscle Δδ¹³C, 1.5‰ is appropriate.     

Biosynthetic origin of the saw-toothed profile in δC and δΗ of n-alkanes and systematic isotopic differences between n-, iso- and anteiso-alkanes in leaf waxes of land plants

The n-fatty acids containing an even number of carbons (ECN-n-FAs) in higher plants are biosynthesised by repetitive addition of a two carbon unit from malonyl-ACP. The n-alkanes containing an odd number of carbon atoms (OCN-n-alkanes) are generally formed by the decarboxylation of ECN-n-FAs, but it is unknown how the less abundant even-carbon-numbered alkanes (ECN-n-alkanes) are biosynthesised in higher plants.There is a distinctive compositional pattern of incorporation of stable carbon (¹³C) and hydrogen (²H) isotopes in co-existing ECN- and OCN-n-alkanes in leaves of higher plants, such that the OCN n-alkanes are relatively enriched in ¹³C but relatively depleted in ²H against the ECN-n-alkanes. This is consistent with the OCN-n-fatty acids having a propionate precursor which is derived from reduction of pyruvate. A tentative pathway is presented with propionate produced by enzymatic reduction of pyruvate which is then thio-esterified with CoSH (coenzyme A thiol) in the chloroplast to form the terminal precursor molecule propionyl-CoA. This is then repetitively extended/elongated with the 2-carbon unit from malonyl-ACP to form the long chain OCN-n-fatty acids.The anteiso- and iso-alkanes in Nicotiana tabacum leaf waxes have previously been found to be systematically enriched in ¹³C compared with the n-alkanes by Grice et al. (2008). This is consistent with the isotopic composition of their putative respective precursors (pyruvate as precursor for n-alkanes, valine for iso-alkanes and isoleucine for anteiso-alkanes). The current study complements that of Grice et al. (2008) and looks at the distribution of hydrogen isotopes. The n-alkanes were found to be more enriched in deuterium (²H) than the iso-alkanes which in turn were more enriched than the anteiso-alkanes. We propose therefore that the depletion of ²H in the iso-alkanes, relative to the n-alkanes is the consequence of accepting highly ²H-depleted hydrogen atoms from NADPH during their biosynthesis. The anteiso-alkanes are further depleted again because there are three NADPH-derived hydrogen atoms in their precursor isoleucine, as compared with only one NADPH-derived hydrogen in valine, the precursor of the iso-alkanes.     

巴郎山刺叶高山栎叶片δ13C对海拔高度的响应

在卧龙自然保护区,按海拔梯度选择了三个刺叶高山栎分布地点(2600m、3050m和3500m),对各研究地点刺叶高山栎进行了叶片d¹³C、光合、CO2扩散导度、养分以及形态等参数的测量,以期揭示刺叶高山栎叶片d¹³C随着海拔的响应规律及原因。结果表明：首先,随着海拔的升高,目标树种叶片d¹³C随之增加,且海拔每升高1000m,d¹³C增加2.0‰;其次,随着海拔升高,大气压强降低,因而导致的叶片扩散导度(包括气孔导度(gs)和叶肉细胞导度(gm))的降低是叶片d¹³C随着海拔升高而升高的主要原因;同时,随着海拔升高而增加的叶片厚度(LMA)也在一定程度上促进了这种响应趋势;最后,叶片N含量随着海拔升高而更多被分配给非光合系统的趋势促进了羧化效率及光合速率的降低,进而对刺叶高山栎叶片d¹³C海拔响应起到了一定的抑制作用,但程度不大;此外,光合氮利用效率(PNUE)在反映植物叶片的氮含量与其吸收和固定大气CO2能力之间的关系方面及对d¹³C的指示作用方面较单位面积氮含量(Narea)和单位重量氮含量(Nmass)更鲜明和准确。     

Thermodynamics of β-Sheet Formation in Polyglutamine

The role of β-sheets in the early stages of protein aggregation, specifically amyloid formation, remains unclear. Interpretations of kinetic data have led to a specific model for the role of β-sheets in polyglutamine aggregation. According to this model, monomeric polyglutamine, which is intrinsically disordered, goes through a rare conversion into an ordered, metastable, β-sheeted state that nucleates aggregation. It has also been proposed that the probability of forming the critical nucleus, a specific β-sheet conformation for the monomer, increases with increasing chain length. Here, we test this model using molecular simulations. We quantified free energy profiles in terms of β-content for monomeric polyglutamine as a function of chain length. In accord with estimates from experimental data, the free energy penalties for forming β-rich states are in the 10-20 kcal/mol range. However, the length dependence of these free energy penalties does not mirror interpretations of kinetic data. In addition, although homodimerization of disordered molecules is spontaneous, the imposition of conformational restraints on polyglutamine molecules does not enhance the spontaneity of intermolecular associations. Our data lead to the proposal that β-sheet formation is an attribute of peptide-rich phases such as high molecular weight aggregates rather than monomers or oligomers.     

Community structure and food web based on stable isotopes (δN and δC) analysis of a North Eastern Atlantic maerl bed

Maerl beds are highly biodiverse biogenic substrata that have been receiving increasing attention in the last decade. Although maerl beds represent important nursery areas for commercial fishes and molluscs, little is known on the trophic web of their communities. Community structure parameters of maerl bed of the Bay of Brest (species richness, abundance, biomass and dominating species) were studied in parallel with the carbon and nitrogen isotopic composition of their main benthic species (macrofaunal, and megafaunal organisms) in order to assess the trophic levels and differences in the potential food sources of maerl inhabitants. The major potential sources of energy were identified to originate either from epiphytic macroalgae and microphytobenthos both growing on maerl thalli, together with sedimenting (sedimentary) particulate organic matter (POM) originating from the water column. The majority of the macro- and megafaunal organisms investigated were filter feeders, selective-deposit feeders and predators/scavengers. Filter feeders fall into three different groups representing different trophic pathways (i) sponges feeding directly on POM (water column filter feeders I), (ii) ascidians and holothurians feeding on POM and probably captured pelagic preys (water column filter feeders II), and (iii) filter feeding molluscs and crustaceans were hypothesised to feed on microphytobenthos or on decaying sedimented POM (Interface filter feeders). Selective deposit feeders were also divided into two subgroups. Carnivores were also distinguished between those with scavenging habits and true predators. Coupling of the trophic levels observed with the community biomass structure revealed that most of the benthic biomass derives its food from detritic sedimented POM and/or microphytobenthos, with interface filter feeders (23% of the biomass), selective deposit feeders (12%). Carnivores made up to 14% of the total biomass. Generally stable isotopes ratio mean values overlap and cover a large range within feeding types, indicating a strong overlap in food sources and a high degree of complexity of the food web presumably due to the diversity of the potential food sources.     

中国东部亚热带地区树轮δ13C方位变化的谐波分析

对浙江天目山2株柳杉(Cryptomeria fortunei Hooibrenk ex Otto et Dietr,分别简称为CF-1,CF-3)及南京紫金山8株马尾松(Pinus massoniana Lamb.,分别简称为PM-1-PM-4,PM-7-PM-10)树轮δ¹³C平均值方位序列及2株柳杉树轮δ¹³C方位平均值年序列进行了谐波分析。分析结果及相关性检验表明,树轮δ¹³C值的方位变化有很强的谐波特征。第1次谐波与第2次谐波分量的方差贡献率占原序列总方差的百分比,除PM-8与PM-10低于70%外,其余均在70％以上,其中,CF-1与PM-9分别达到了93%和96.5％。第1次与第2次(或第3次)谐波的拟合序列与原序列的相关性极高,相关系数均在0.8以上,都通过了0.05的显著性检验,而且,两次谐波的拟合度均比较高,均在75％以上,拟合效果较好。分析结果表明,用2π与π(PM-1与PM-7为2π/3)两个主要谐波周期就可以较好地拟合各树轮δ¹³C序列的方位变化。初相位值的计算结果显示,第1、2次谐波的初相位值存在明显差异,这表明:不同树体2次谐波振幅的峰值出现的方位区域不同,即以2π及以π(PM-1与PM-7为2π/3)为周期的树轮δ¹³C方位变化的极大值并不出现在固定方位区。所以,两次谐波叠加的结果使树轮δ¹³C极值出现的方位区域更复杂。对天目山2株柳杉树轮δ¹³C各方位均值年序列的分析结果表明,2树轮δ¹³C极值均存在明显的年际漂移,其极大值出现频率较高的方位随树木生长坡向而发生转移。两树轮相比,多数年份其δ¹³C的主极大值出现的方位区基本发生45°的方位转移。而主、次极大值叠加的结果却使δ¹³C极值出现的方位基本发生90°的转移,这种极值转移的方向及转移度数与2株树所在坡向的变化和坡向变化度数正好相一致。     

Macromolecular Crowding Modulates Folding Mechanism of α/β Protein Apoflavodoxin

Protein dynamics in cells may be different from those in dilute solutions in vitro, because the environment in cells is highly concentrated with other macromolecules. This volume exclusion because of macromolecular crowding is predicted to affect both equilibrium and kinetic processes involving protein conformational changes. To quantify macromolecular crowding effects on protein folding mechanisms, we investigated the folding energy landscape of an α/β protein, apoflavodoxin, in the presence of inert macromolecular crowding agents, using in silico and in vitro approaches. By means of coarse-grained molecular simulations and topology-based potential interactions, we probed the effects of increased volume fractions of crowding agents (ϕ_c) as well as of crowding agent geometry (sphere or spherocylinder) at high ϕ_c. Parallel kinetic folding experiments with purified Desulfovibro desulfuricans apoflavodoxin in vitro were performed in the presence of Ficoll (sphere) and Dextran (spherocylinder) synthetic crowding agents. In conclusion, we identified the in silico crowding conditions that best enhance protein stability, and discovered that upon manipulation of the crowding conditions, folding routes experiencing topological frustrations can be either enhanced or relieved. Our test-tube experiments confirmed that apoflavodoxin''s time-resolved folding path is modulated by crowding agent geometry. Macromolecular crowding effects may be a tool for the manipulation of protein-folding and function in living cells.     

Crystal structure of α/β-galactoside α2,3-sialyltransferase from a luminous marine bacterium, Photobacterium phosphoreum

α/β-Galactoside α2,3-sialyltransferase produced by Photobacterium phosphoreum JT-ISH-467 is a unique enzyme that catalyzes the transfer of N-acetylneuraminic acid residue from cytidine monophosphate N-acetylneuraminic acid to acceptor carbohydrate groups. The enzyme recognizes both mono- and di-saccharides as acceptor substrates, and can transfer Neu5Ac to both α-galactoside and β-galactoside, efficiently. To elucidate the structural basis for the broad acceptor substrate specificity, we determined the crystal structure of the α2,3-sialyltransferase in complex with CMP. The overall structure belongs to the glycosyltransferase-B structural group. We could model a reasonable active conformation structure based on the crystal structure. The predicted structure suggested that the broad substrate specificity could be attributed to the wider entrance of the acceptor substrate binding site.     

Stable Polyglutamine Dimers Can Contain β-Hairpins with Interdigitated Side Chains—But Not α-Helices, β-Nanotubes, β-Pseudohelices,or Steric Zippers

A common thread connecting nine fatal neurodegenerative protein aggregation diseases is an abnormally expanded polyglutamine tract found in the respective proteins. Although the structure of this tract in the large mature aggregates is increasingly well described, its structure in the small early aggregates remains largely unknown. As experimental evidence suggests that the most toxic species along the aggregation pathway are the small early ones, developing strategies to alleviate disease pathology calls for understanding the structure of polyglutamine peptides in the early stages of aggregation. Here, we present a criterion, grounded in available experimental data, that allows for using kinetic stability of dimers to assess whether a given polyglutamine conformer can be on the aggregation path. We then demonstrate that this criterion can be assessed using present-day molecular dynamics simulations. We find that although the α-helical conformer of polyglutamine is very stable, dimers of α-helices lack the kinetic stability necessary to support further oligomerization. Dimers of steric zipper, β-nanotube, and β-pseudohelix conformers are also too short-lived to initiate aggregation. The β-hairpin-containing conformers, instead, invariably form very stable dimers when their side chains are interdigitated. Combining these findings with the implications of recent solid-state NMR data on mature fibrils, we propose a possible pathway for the initial stages of polyglutamine aggregation, in which β-hairpin-containing conformers act as templates for fibril formation.     

Heterotropic interactions in monomeric βSH chains from human hemoglobin

The O₂ affinity of β^SH chains is lowered by H⁺, inositol hexaphosphate (IHP), and CO₂. As the oxygen affinity of β^SH monomers (β₁^SH) is lower than that of β^SH tetramers (β₄^SH), it is possible that IHP and CO₂ exert their influence on the O₂ affinity of β^SH chains by increasing the dissociation constant of β₄^SH rather than by a direct effect on the molecule. In order to test for this hypothesis we have measured the O₂ affinity of β^SH chains as a function of protein concentration at various concentrations of IHP and inorganic phosphates in the absence and presence of CO₂. From these data association constants for the binding of IHP to β₁^SH and β₄^SH as well as for the equilibrium 4β₁^SH ? β₄^SH were calculated. We found that IHP and CO₂ influence the oxygen affinity of β₁^SH. It was furthermore established that inorganic phosphate enhances the stability of β₄^SH while IHP favors its dissociation in monomers.     

Probing α-310 Transitions in a Voltage-Sensing S4 Helix

The S4 helix of voltage sensor domains (VSDs) transfers its gating charges across the membrane electrical field in response to changes of the membrane potential. Recent studies suggest that this process may occur via the helical conversion of the entire S4 between α and 3₁₀ conformations. Here, using LRET and FRET, we tested this hypothesis by measuring dynamic changes in the transmembrane length of S4 from engineered VSDs expressed in Xenopus oocytes. Our results suggest that the native S4 from the Ciona intestinalis voltage-sensitive phosphatase (Ci-VSP) does not exhibit extended and long-lived 3₁₀ conformations and remains mostly α-helical. Although the S4 of NavAb displays a fully extended 3₁₀ conformation in x-ray structures, its transplantation in the Ci-VSP VSD scaffold yielded similar results as the native Ci-VSP S4. Taken together, our study does not support the presence of long-lived extended α-to-3₁₀ helical conversions of the S4 in Ci-VSP associated with voltage activation.     

Differences in β-strand Populations of Monomeric Aβ40 and Aβ42

Using homonuclear ¹H NOESY spectra, with chemical shifts, ³J_H^N_H^α scalar couplings, residual dipolar couplings, and ¹H-¹⁵N NOEs, we have optimized and validated the conformational ensembles of the amyloid-β 1–40 (Aβ40) and amyloid-β 1–42 (Aβ42) peptides generated by molecular dynamics simulations. We find that both peptides have a diverse set of secondary structure elements including turns, helices, and antiparallel and parallel β-strands. The most significant difference in the structural ensembles of the two peptides is the type of β-hairpins and β-strands they populate. We find that Aβ42 forms a major antiparallel β-hairpin involving the central hydrophobic cluster residues (16–21) with residues 29–36, compatible with known amyloid fibril forming regions, whereas Aβ40 forms an alternative but less populated antiparallel β-hairpin between the central hydrophobic cluster and residues 9–13, that sometimes forms a β-sheet by association with residues 35–37. Furthermore, we show that the two additional C-terminal residues of Aβ42, in particular Ile-41, directly control the differences in the β-strand content found between the Aβ40 and Aβ42 structural ensembles. Integrating the experimental and theoretical evidence accumulated over the last decade, it is now possible to present monomeric structural ensembles of Aβ40 and Aβ42 consistent with available information that produce a plausible molecular basis for why Aβ42 exhibits greater fibrillization rates than Aβ40.     

The Interaction of αB-Crystallin with Mature α-Synuclein Amyloid Fibrils Inhibits Their Elongation

αB-Crystallin is a small heat-shock protein (sHsp) that is colocalized with α-synuclein (αSyn) in Lewy bodies—the pathological hallmarks of Parkinson's disease—and is an inhibitor of αSyn amyloid fibril formation in an ATP-independent manner in vitro. We have investigated the mechanism underlying the inhibitory action of sHsps, and here we establish, by means of a variety of biophysical techniques including immunogold labeling and nuclear magnetic resonance spectroscopy, that αB-crystallin interacts with αSyn, binding along the length of mature amyloid fibrils. By measurement of seeded fibril elongation kinetics, both in solution and on a surface using a quartz crystal microbalance, this binding is shown to strongly inhibit further growth of the fibrils. The binding is also demonstrated to shift the monomer-fibril equilibrium in favor of dissociation. We believe that this mechanism, by which a sHsp interacts with mature amyloid fibrils, could represent an additional and potentially generic means by which at least some chaperones protect against amyloid aggregation and limit the onset of misfolding diseases.     

Synthesis and characterization of tetrairon-tungsten cluster complex containing a μ4, η-carbonyl ligand

Reaction of [(PPh₂C₅H₄)Cp₃Fe₄(CO)₄] (1) with (CO)₄W(CH₃CN)₂ at ambient temperature affords [(CO)₄W(PPh₂C₅H₄)Cp₃Fe₄(CO)₄] (2) as the major product, together with a small amount of [(CO)₅W(PPh₂C₅H₄)Cp₃Fe₄(CO)₄] (3). Compound 3 can be obtained in good yield by treating (CO)₅W(CH₃CN) with equal molar of 1, and reaction of 3 with Me₃NO in acetonitrile solvent produces 2 exclusively. The crystal structures of 2 and 3 have been determined by an X-ray diffraction study. Compound 2 contains an interesting μ₄, η²-CO ligand, where two electrons donated by the carbon atom are involved to bridge a Fe₃ face and two electrons from oxygen are donated to the tungsten(0) atom.     

β-catenin plays a central role in setting up the head organizer in hydra

In an adult hydra the head organizer, located in the hypostome, is constantly active in maintaining the structure of the animal in the context of its steady state tissue dynamics. Several Wnt genes, TCF, and elevated levels of β-catenin are expressed in the hypostome as well as during the formation of a new organizer region in developing buds suggesting they play a role in the organizer. Transgenic hydra were generated in which a modified hydra β-catenin gene driven by an actin promoter is continuously expressed at a high level throughout the animal. These animals formed heads and secondary axes in multiple locations along the body column. Transplantation experiments indicate they have a high and stable level of head organizer activity throughout the body columns. However, none of the Wnt genes are expressed in the body columns of these transgenic animals. Further, in alsterpaullone-treated animals, which results in a transient rise in head organizer activity throughout the body column, the time of expression of the Wnt genes is much shorter than the time of the elevated level of head inducing activity. These results for the first time provide direct functional evidence that β-catenin plays a crucial role in the maintenance and activity of the head organizer and suggest that Wnt ligands may be required only for the initiation but not in maintenance of the organizer in Hydra.