Sea Cucumbers Triterpene Glycosides, the Recent Progress in Structural Elucidation and Chemotaxonomy

Triterpene glycosides are characteristic metabolites of sea cucumbers (Holothurioidea, Echinodermata). Majority of the glycosides belong to holostane type (lanostane derivatives with 18(20)-lactone). Carbohydrate chains of these glycosides contain xylose, glucose, quinovose, 3-O-methylglucose and 3-O-methyl sylose. During the last 5 years, main investigations were focused on holothurians belonging to the order Dendrochirotida collected in the North Pacific, North Atlantic, Antarctic and in subtropical waters. The glycosides of holothurians belonging to the order Aspidochirotida have also been studied. The most uncommon structural features of carbohydrate chains of new glycosides were: (1) the presence of quinovose as fifth terminal monosaccharide unit and the presence of two quinovose residues; (2) the presence of glucose instead of common xylose as fifth terminal monosaccharide unit; (3) trisaccharide carbohydrate chain; (4) the presence of two 3-O-methylxylose terminal monosaccharide units; (5) the presence of sulfate group at C-3 of quinovose residue. New glycosides without lactone or with 18(16)-lactone and having shortened side chains have also been isolated. The presence of 17α and 12α-hydroxyls, which are characteristic for glycosides from holothurians belonging to the family Holothuriidae (Aspidochirotida) in glycosides of dendrochirotids confirms parallel and relatively independent character of evolution of glycosides. All three families belonging to the order Aspidochirotida: Holothuriidae, Stichopodidae and Synallactidae have similar and parallel trends in evolution of the glycosides carbohydrate chains, namely from non-sulfated hexaosides to sulfated tetraosides. Sets of aglycones in glycosides from holothurians belonging to the genus Cucumaria (Cucumariidae, Dendrochirotida) are specific for each species. The carbohydrate chains are similar in all representatives of the genus Cucumaria.     

Predicting Calendar Aging in Lithium Metal Secondary Batteries: The Impacts of Solid Electrolyte Interphase Composition and Stability

Calendar aging of lithium metal batteries, in which cells' components degrade internally due to chemical reactions while no current is being applied, is a relatively unstudied field. In this work, a model to predict calendar aging of lithium metal cells is developed using two sets of readily obtainable data: solid electrolyte interphase (SEI) layer composition (measured via X‐ray photoelectron spectroscopy) and SEI stability (measured as a degradation rate using a simple constant current–constant voltage charging protocol). Electrolyte properties such as volume and salt concentration are varied in order to determine their effect on SEI stability and composition, with subsequent impacts to calendar aging. Lower salt concentrations produce a solvent‐based, more soluble SEI, while the highest concentration produces a salt‐based, less soluble SEI. Higher electrolyte volumes promote dissolution of the SEI and thus decrease its stability. The model predicts that lithium metal would be the limiting factor in calendar aging, depleting long before the electrolyte does. Additionally, the relative composition of the electrolyte during aging is modeled and found to eventually converge to the same value independent of initial salt concentration.     

Specific Inter-residue Interactions as Determinants of Human Monoacylglycerol Lipase Catalytic Competency: A ROLE FOR GLOBAL CONFORMATIONAL CHANGES*

The serine hydrolase monoacylglycerol lipase (MGL) functions as the main metabolizing enzyme of 2-arachidonoyl glycerol, an endocannabinoid signaling lipid whose elevation through genetic or pharmacological MGL ablation exerts therapeutic effects in various preclinical disease models. To inform structure-based MGL inhibitor design, we report the direct NMR detection of a reversible equilibrium between active and inactive states of human MGL (hMGL) that is slow on the NMR time scale and can be modulated in a controlled manner by pH, temperature, and select point mutations. Kinetic measurements revealed that hMGL substrate turnover is rate-limited across this equilibrium. We identify a network of aromatic interactions and hydrogen bonds that regulates hMGL active-inactive state interconversion. The data highlight specific inter-residue interactions within hMGL modulating the enzymes function and implicate transitions between active (open) and inactive (closed) states of the hMGL lid domain in controlling substrate access to the enzymes active site.     

Thiamine deficiency caused by thiamine antagonists triggers upregulation of apoptosis inducing factor gene expression and leads to caspase 3-mediated apoptosis in neuronally differentiated rat PC-12 cells

Recent evidence suggests that alterations in oxidative metabolism induced by thiamine deficiency lead to neuronal cell death. However, the molecular mechanisms underlying this process are still under extensive investigation. Here, we report that rat pheochromocytoma PC-12 cells differentiated in the presence of NGF into neurons undergo apoptosis due to thiamine deficiency caused by antagonists of thiamine - amprolium, pyrithiamine and oxythiamine. Confocal laser scanning fluorescence microscopy revealed that annexin V binds to PC-12 cells in presence of thiamine antagonists after 72 h incubation. Results also show that thiamine antagonists trigger upregulation of gene expression of mitochondrial-derived apoptosis inducing factor, DNA fragmentation, cleavage of caspase 3 and translocation of active product to the nucleus. We therefore propose that apoptosis induced by amprolium, pyrithiamine or oxythiamine occurs via the mitochondria-dependent caspase 3-mediated signaling pathway. In addition, our data indicate that pyrithiamine and oxythiamine are more potent inducers of apoptosis than amprolium.     

CO<Subscript>2</Subscript> fluxes at south taiga bog in the European part of Russia in summer

This paper estimates CO₂ emission and net ecosystem exchange (NEE) between the atmosphere and the surface of bog in the south taiga of the European part of Russia for the summer periods of 2013–2015. Flux measurements are carried out by the static chamber method every 7–10 days in three experimental sites with homogenous conditions of soil moisture and vegetation type. Statistically significant differences in CO₂ fluxes and NEE are found between different experimental sites. It is shown that an assessment of the significance of bogs in CO₂ balance with the atmosphere must be made with consideration for the spatial heterogeneity of bogs.     

Neurogenesis directed by Sirt1

Differentiation of neuronal stem cells into astrocytes or neurons is important in maintaining brain function. Oxidative stress and inflammation are now shown to bias differentiation toward astrocytes by modulating activity of the anti-ageing gene Sirt1. These findings link a longevity gene to the activity of neuronal stem cells and their response to stress.     

Defensin promoters as potential tools for engineering disease resistance in cereal grains

Engineering of plant protection in cereals requires well characterized tissue-specific and wounding/pathogen-inducible promoters for targeted expression of pathogen responsive and resistance genes. We describe the isolation of seven wheat and rice defensin genes expressed in early developing grain and during grain germination, two developmental stages that are particularly vulnerable to pathogens and insects. Comparison of three-dimensional (3D) models of these rice and wheat PRPI defensins indicated variations in spatial architectures that could reflect their functional diversities. Wheat and rice were stably transformed with promoter–GUS fusion constructs and the spatial and temporal activities of four promoters were studied using whole-mount and histological assays. PRPI promoters were active before and at anthesis in both transgenic wheat and rice with activity mainly in the ovary. In rice, GUS activity was also observed in vascular tissue of the lemma, palea and anthers. After fertilization, GUS was strongly expressed in the outer cell layers of the pericarp and in the main vascular bundle of the grain. During, and a short time after, seed germination, wheat promoters were active in transgenic rice embryos, roots and/or coleoptiles. All wheat and rice promoters were strongly induced by wounding in leaf, stem and grain of transgenic rice plants. These results suggest that PRPI promoters will be useful for specific targeting and accumulation of proteins conferring resistance to pathogens in vulnerable tissues of developing and germinating grain.     

Estrogenic activity of triterpene glycosides in yeast two-hybrid assay

Estrogenic potency of six triterpene glycosides, Holothurin A, Holotoxin A₁, Frondoside A, Cucumarioside A₂-2 and Cauloside C, that are natural products and semi-synthesized Ginsenoside-Rh₂, were examined with yeast two-hybrid system, including expressed genes of human estrogen receptor, hER, the co-activator TIF2 and lacZ as a reporter gene. Only Ginsenoside-Rh₂ exhibited significant moderate estrogenic activity in the concentration range of 10⁻⁷ to 10⁻⁶ M. Its effect was approximately 30% of the activity of 17β-estradiol applied at half-effective concentration. This indicates Ginsenosides-Rh₂ is a weak phytoestrogen. The sea cucumber triterpene glycosides, Holothurin A, Holotoxin A₁, Cucumarioside A₂-2 and Frondoside A, and plant glycoside Cauloside C had no appreciable estrogenic activity. Data obtained by yeast two-hybrid assay reflect structure–activity relationship between tested compounds and 17β-estradiol. Only Ginsenoside-Rh₂ has some similarity in chemical structure with 17β-estradiol that might explain affinity of this glycoside to the hER receptor.     

Integrin alphaIIbbeta3:ligand interactions are linked to binding-site remodeling

This study tested the hypothesis that high-affinity binding of macromolecular ligands to the alphaIIbbeta3 integrin is tightly coupled to binding-site remodeling, an induced-fit process that shifts a conformational equilibrium from a resting toward an open receptor. Interactions between alphaIIbbeta3 and two model ligands-echistatin, a 6-kDa recombinant protein with an RGD integrin-targeting sequence, and fibrinogen's gamma-module, a 30-kDa recombinant protein with a KQAGDV integrin binding site-were measured by sedimentation velocity, fluorescence anisotropy, and a solid-phase binding assay, and modeled by molecular graphics. Studying echistatin variants (R24A, R24K, D26A, D26E, D27W, D27F), we found that electrostatic contacts with charged residues at the alphaIIb/beta3 interface, rather than nonpolar contacts, perturb the conformation of the resting integrin. Aspartate 26, which interacts with the nearby MIDAS cation, was essential for binding, as D26A and D26E were inactive. In contrast, R24K was fully and R24A partly active, indicating that the positively charged arginine 24 contributes to, but is not required for, integrin recognition. Moreover, we demonstrated that priming--i.e., ectodomain conformational changes and oligomerization induced by incubation at 35 degrees C with the ligand-mimetic peptide cHarGD--promotes complex formation with fibrinogen's gamma-module. We also observed that the gamma-module's flexible carboxy terminus was not required for alphaIIbbeta3 integrin binding. Our studies differentiate priming ligands, which bind to the resting receptor and perturb its conformation, from regulated ligands, where binding-site remodeling must first occur. Echistatin's binding energy is sufficient to rearrange the subunit interface, but regulated ligands like fibrinogen must rely on priming to overcome conformational barriers.