Tenasogenin,a pregnane ester from Marsdenia tenacissima

A new polyhydroxy pregnane ester named tenasogenin was isolated from the seeds of Marsdenia tenacissima. On the basis of chemical and spectroscopic evidence and identification of its hydrolysis products, its structure has been established as 11α-O-β,β-dimethylacryloyl-3β,12β,14β,20R-tetrahydroxypregn-5-ene.     

Structure of tigmobiose

A new, nonreducing disaccharide, tigmobiose, has been isolated from the dried twigs of Sarcostemma brevistigma. On the basis of chemical and spectroscopic evidence, and identification of its sole hydrolysis product, its structure has been established as 2,6-dideoxy-β-d-ribo-hexopyranosyl 2,6-dideoxy-β-d-ribo-hexopyranoside (β-d- digitoxopyranosyl β-d-digitoxopyranoside).     

Flavonoid glycosides from needles of Pinus massoniana

Seven flavonoids have been isolated from Pinus massoniana needles and identified as taxifolin and its 3′-O-β-D-glucopyranoside, (+)-catechin, naringenin-7-O-β-D-glucopyranoside and three new flavonoid glycosides, 6-C-methylaromadendrin 7-O-β-D-glucopyranoside, taxifolin 3′-O-β-D-(6″-O-phenylacetyl)-glucopyranoside and eriodictyol 3′-O-β-D-glucopyranoside.     

Stereoselective hydrogenation of methyl dideoxy- and trideoxy-β-D-hex-5-enopyranosides

Hydrogenation, severally, of methyl 3-azido-2,3,6-trideoxy-β-D-erythro-hex-5-enopyranoside, its 3-benzamido analogue, and methyl 2,6-dideoxy-β-D-threo-hex-5-enopyranoside in the presence of palladium-on-barium sulphate gave the corresponding 6-deoxy-β-D-hexopyranoside derivatives. Stereoselective addition of hydrogen was observed in each case. Methyl 2,6-dideoxy-β-D-arabino-hexopyranoside was also prepared by reductive dehalogenation of methyl 3,4-di-O-benzoyl-6-bromo-2,6-dideoxy-β-D-arabino-hexopyranoside.     

Amyloid-β Fibrillogenesis Seeded by Interface-Induced Peptide Misfolding and Self-Assembly

The amphipathicity of the natively unstructured amyloid-β (Aβ40) peptide may play an important role in its aggregation into β-sheet rich fibrils, which is linked to the pathogenesis of Alzheimer's disease. Using the air/subphase interface as a model interface, we characterized Aβ's surface activity and its conformation, assembly, and morphology at the interface. Aβ readily adsorbed to the air/subphase interface to form a 20 Å thick film and showed a critical micelle concentration of ∼120 nM. Aβ adsorbed at the air/subphase exhibited in-plane ordering that gave rise to Bragg peaks in grazing-incidence x-ray diffraction measurements. Analysis of the peaks showed that the air/subphase interface induced Aβ to fold into a β-sheet conformation and to self-assemble into ∼100 Å-sized ordered clusters. The formation of these clusters at the air/subphase interface was not affected by pH, salts, or the presence of sucrose or urea, which are known to stabilize or denature native proteins, suggesting that interface-driven Aβ misfolding and assembly are strongly favored. Furthermore, Aβ at the interface seeded the growth of fibrils in the bulk with a distinct morphology compared to those formed by homogeneous nucleation. Our results indicate that interface-induced Aβ misfolding may serve as a heterogeneous, nucleation-controlled aggregation mechanism for Aβ fibrillogenesis in vivo.     

Vein Patterning 1-encoded progesterone 5β-reductase: Activity-guided improvement of catalytic efficiency

Progesterone 5β-reductases (P5βR; EC 1.3.99.6) encoded by Vein Patterning 1 (VEP1) genes are capable of reducing the CC double-bond of a variety of enones enantioselectively. Sequence and activity data of orthologous P5βRs were used to define a set of residues possibly responsible for the large differences in enzyme activity seen between rAtSt5βR and rDlP5βR, recombinant forms of P5βRs from Arabidopsis thaliana and Digitalis lanata, respectively. Tyrosine-156, asparagine-205 and serine-248 were identified as hot spots in the rDlP5βR responsible for its low catalytic efficiency. These positions were individually substituted for amino acids found in the strong rAtSt5βR in the corresponding sites. Kinetic constants were determined for rDlP5βR and its mutants as well as for rAtSt5βR using progesterone and 2-cyclohexen-1-one as substrates. Enzyme mutants in which asparagine-205 was substituted for methionine or alanine showed considerably lower km and higher K_cat/k_m values than the wild-type DlP5βR, approaching the catalytic efficiency of strong P5βRs. The introduced mutations not only lead to an improved capability to reduce progesterone but also to altered substrate preference. Our findings provided structural insights into the differences seen among the natural P5βRs with regard to their substrate preferences and catalytic efficiencies.     

3β-hydroxy-21β-e-cinnamoyloxyolean-12-en-28-oic acid,a triterpenoid from enterolobium contorstisiliquum

The triterpenes 3β-hydroxy-21β-E-cinnamoyloxyolean-12-en-20-oic acid, 3β,21β-dihydroxyolean-12-en-28-oic acid (machaerinic acid) and its lactone (3β-hydroxyolean-12-en-21β→28-lactone) were isolated from the fruits of Enterolobium contorstisiliquum. Methyl and ethyl esters of 3β,21β-dihydroxyolean-12-en-oic acid were isolated and characterized as artifacts. The structures of these triterpenes have been established by a study of their chemical and spectroscopic (IR, MS and NMR) data.     

Costusoside-I and costusoside-J,two new furostanol saponins from the seeds of Costus speciosus

The structure of costusoside I and costusoside J have been established as 3-O-{β-d-glucopyranosyl (1 → 2)-α-l-rhamnopyranosyl (1 → 2) [α-l-rhamnopyranosyl (1 → 4)]-β-d-glucopyranosyl}-26-O-(β-d-glucopyranosyl)-22α-methoxy 25 R)-furost-5-en-3β, 26-diol and its 22-hydroxy compound respectively, isolated fron the seeds of Costus speciosus.     

Analysing the impact of nucleo-cytoplasmic shuttling of β-catenin and its antagonists APC,Axin and GSK3 on Wnt/β-catenin signalling

The canonical Wnt signalling pathway plays a critical role in development and disease. The key player of the pathway is β-catenin. Its activity is mainly regulated by the destruction complex consisting of APC, Axin and GSK3. In the nucleus, the complex formation of β-catenin and TCF initiates target gene expression. Our study provides a comprehensive analysis of the role of nucleo-cytoplasmic shuttling of APC, Axin, and GSK3 and the inactivation of β-catenin by the destruction complex in Wnt/β-catenin signalling.We address the following questions: Can nucleo-cytoplasmic shuttling of APC, Axin and GSK3 increase the [β-catenin/TCF] concentration? And, how is the [β-catenin/TCF] concentration influenced by phosphorylation and subsequent degradation of nuclear β-catenin?Based on experimental findings, we develop a compartmental model and conduct several simulation experiments. Our analysis reveals the following key findings: 1) nucleo-cytoplasmic shuttling of β-catenin and its antagonists can yield a spatial separation between the said proteins, which results in a breakdown of β-catenin degradation, followed by an accumulation of β-catenin and hence leads to an increase of the [β-catenin/TCF] concentration. Our results strongly suggest that Wnt signalling can benefit from nucleo-cytoplasmic shuttling of APC, Axin and GSK3, although they are in general β-catenin antagonising proteins. 2) The total robustness of the [β-catenin/TCF] output is closely linked to its absolute concentration levels. We demonstrate that the compartmental separation of β-catenin and the destruction complex does not only lead to a maximization, but additionally to an increased robustness of [β-catenin/TCF] signalling against perturbations in the cellular environment. 3) A nuclear accumulation of the destruction complex renders the pathway robust against fluctuations in Wnt signalling and against changes in the compartmental distribution of β-catenin. 4) Elucidating the impact of destruction complex inhibition, we show that the [β-catenin/TCF] concentration is more effectively enhanced by inhibition of the kinase GSK3 rather than the binding of β-catenin to the destruction complex.     

Two terpenoids activates close mating behavior and enhances trap efficiency of sex pheromone of Grapholita molesta

Grapholita molesta (Busck) (Lepidoptera: Tortricidae) is a notorious pest of many Rosaceae crops worldwide. Enhancement of trap efficiency of its sex pheromone was devised by addition of E-β-ocimene and E-β-farnesene. The addition of E-β-ocimene or E-β-farnesene to sex pheromone increased electroantennogram response of male G. molesta compared to sex pheromone alone. Blend of pheromone and E-β-ocimene or E-β-farnesene in 1:0.1 increased the upwind flight and landing behaviors. Furthermore, field experiments showed that sex lures with E-β-ocimene, or /and E-β-farnesene, enhanced trapping efficiency compared to sex pheromone alone. These results may provide the basis for the development of efficient pest management systems against G. molesta using plant volatiles and insect sex pheromones.     

Triterpene saponins of Genista ulicina Spach

From the n-BuOH extract of the aerial parts of Genista ulicina, six triterpene saponins, 3-O-β-d-glucopyranosyl-olean-12-ene-3β,27,28,30-tetraol, 3-O-β-d-glucopyranosyl-olean-12-ene-3β,27,28,29-tetraol, 3,29-di-O-β-d-glucopyranosyl-olean-12-ene-3β,27,28,29-tetraol, 3-O-β-d-glucopyranosyl-olean-12-ene-3β,28,29-triol-27-oic acid, 3-O-β-d-glucopyranosyl-olean-12-ene-3β,27,28-triol-29-oic acid, and 3-O-β-d-glucopyranosyl-14-H-27-nor-olean-12-ene-3β,28,29-triol, were isolated together with eight known triterpene saponins and six flavonoids. Their structures were established mainly by means of spectroscopic methods (1D and 2D-NMR as well as HR-ESI-MS). The n-BuOH extract, investigated for its antitumor growth inhibition of human colon cancer HT-29 cells, presented no significant activity (IC₅₀ > 100 μg).     

Glycosylation of sesamol by cultured plant cells

The glycosylation of sesamol was investigated using cultured cells of Nicotiana tabacum and Eucalyptus perriniana. The cultured suspension cells of N. tabacum converted sesamol into its β-glucoside (7%) as well as the disaccharide, sesamyl 6-O-(β-D-glucopyranosyl)-β-D-glucopyranoside (β-gentiobioside, 30%). On the other hand, sesamyl 6-O-(α-L-rhamnopyranosyl)-β-D-glucopyranoside (β-rutinoside, 56%), together with the β-glucoside (3%), was produced when sesamol was incubated with suspension cells of E. perriniana.     

Thermodynamic Characterization of the Interaction between Prefoldin and Group II Chaperonin

Prefoldin (PFD) is a hexameric chaperone that captures a protein substrate and transfers it to a group II chaperonin (CPN) to complete protein folding. We have studied the interaction between PFD and CPN using those from a hyperthermophilic archaeon, Thermococcus strain KS-1 (T. KS-1). In this study, we determined the crystal structure of the T. KS-1 PFDβ2 subunit and characterized the interactions between T. KS-1 CPNs (CPNα and CPNβ) and T. KS-1 PFDs (PFDα1-β1 and PFDα2-β2). As predicted from its amino acid sequence, the PFDβ2 subunit conforms to a structure similar to those of the PFDβ1 subunit and the Pyrococcus horikoshii OT3 PFDβ subunit, with the exception of the tip of its coiled-coil domain, which is thought to be the CPN interaction site. The interactions between T. KS-1 CPNs and PFDs (CPNα and PFDα1-β1; CPNα and PFDα2-β2; CPNβ and PFDα1-β1; and CPNβ and PFDα2-β2) were analyzed using the Biacore T100 system at various temperatures ranging from 20 to 45 ºC. The affinities between PFDs and CPNs increased with an increase in temperature. The thermodynamic parameters calculated from association constants showed that the interaction between PFD and CPN is entropy driven. Among the four combinations of PFD-CPN interactions, the entropy difference in binding between CPNβ and PFDα2-β2 was the largest, and affinity significantly increased at higher temperatures. Considering that expression of PFDα2-β2 and CPNβ subunit is induced upon heat shock, our results suggest that PFDα1-β1 is a general PFD for T. KS-1 CPNs, whereas PFDα2-β2 is specific for CPNβ.     

C-glycosylflavones from Oryza sativa

Eight flavone C-glycosides isolated from rice plant were found to act as probing stimulants for planthoppers. They have been identified as the known compounds schaftoside, neoschaftoside, carlinoside, isoorientin 2″-glucoside and the new constituents neocarlinoside (6-C-β-D-glucopyranosyl-8-C-β-L-arabinopyranosylluteolin), isoscoparin 2″-glucoside (chrysoeriol 6-C-β-D-(2-O-β-D-glucopyranosyl)glucopyranoside) and its 6?-p-coumaric and ferulic acid esters.     

The amyloid precursor protein forms plasmalemmal clusters via its pathogenic amyloid-β domain

The amyloid precursor protein (APP) is a large, ubiquitous integral membrane protein with a small amyloid-β (Aβ) domain. In the human brain, endosomal processing of APP produces neurotoxic Aβ-peptides, which are involved in Alzheimer's disease. Here, we show that the Aβ sequence exerts a physiological function when still present in the unprocessed APP molecule. From the extracellular site, Aβ concentrates APP molecules into plasmalemmal membrane protein clusters. Moreover, Aβ stabilization of clusters is a prerequisite for their targeting to endocytic clathrin structures. Therefore, we conclude that the Aβ domain directly mediates a central step in APP trafficking, driving its own conversion into neurotoxic peptides.     

Molecular Modeling of the Misfolded Insulin Subunit and Amyloid Fibril

Insulin, a small hormone protein comprising 51 residues in two disulfide-linked polypeptide chains, adopts a predominantly α-helical conformation in its native state. It readily undergoes protein misfolding and aggregates into amyloid fibrils under a variety of conditions. Insulin is a unique model system in which to study protein fibrillization, since its three disulfide bridges are retained in the fibrillar state and thus limit the conformational space available to the polypeptide chains during misfolding and fibrillization. Taking into account this unique conformational restriction, we modeled possible monomeric subunits of the insulin amyloid fibrils using β-solenoid folds, namely, the β-helix and β-roll. Both models agreed with currently available biophysical data. We performed molecular dynamics simulations, which allowed some limited insights into the relative structural stability, suggesting that the β-roll subunit model may be more stable than the β-helix subunit model. We also constructed β-solenoid-based insulin fibril models and conducted fiber diffraction simulation to identify plausible fibril architectures of insulin amyloid. A comparison of simulated fiber diffraction patterns of the fibril models to the experimental insulin x-ray fiber diffraction data suggests that the model fibers composed of six twisted β-roll protofilaments provide the most reasonable fit to available experimental diffraction patterns and previous biophysical studies.     

Two steroidal alkaloids from fritillaria harelinii

Two new steroidal alkaloids named harepermine and hareperminside have been isolated from the bulbs of Fritillaria harelinii together with a known alkaloid, peiminine. The structure of the alkaloids were found to be 3β, 6β-dihydroxy-5α, 14α,17β-cevanine and its 3-O-glucoside on the basis of spectroscopic evidence.     

Anthraquinone,anthrone and phenylpyrone components of Aloe nyeriensis var. kedongensis leaf exudate

The leaf exudate of Aloe nyeriensis var. kedongensis yielded six compounds which were identified on the basis of spectral data and inter-conversions as two groups of three allied compounds. These were (a) 4-methoxy-6(2′,4′-dihydroxy-6′- methylphenyl)-pyran-2-one, its 2′-O-β-D-glucopyranoside (aloenin) and the 2″-O-p-coumaroyl ester of aloenin, (b) the anthracene derivatives l,2,8-trihydroxy- 6-methylanthraquinone (nataloe-emodin), its 2-O-β-D-glucopyranosyl ester and the corresponding 10-C -β-D-glucopyranoside nataloin.     

A 24β-ethyl-Δ7-steryl glucopyranoside from Cucurbita pepo seeds

In the seeds of Cucurbita pepo three closely related 24-ethyl-Δ⁷-steryl glucosides were identified by hydrolytic studies and spectral analysis as spinasteryl-β-D-glucopyranoside, the new 3-O-(β-D-glucopyranosyl)-24β-ethyl-5α-cholesta-7,25(27)-dien-3β-ol and the corresponding Δ^22E,25,(27)-trienol. Except for its occurrence in cucumber seeds the latter is so far unknown as a natural product.