γ-Glutamyl transpeptidase: catalytic,structural and functional aspects

Summary -Glutamyl transpeptidase catalyzes transfer of the -glutamyl moiety of glutathione to amino acids, dipeptides, and to glutathione itself; the enzyme also catalyzes the hydrolysis of glutathione to glutamate and cysteinyl-glycine. This review deals with the tissue distribution and localization of the enzyme in mammals, the catalytic properties of the enzyme (including its inhibition by reversible and irreversible inhibitors), structural studies on the enzyme, and new findings about its physiological function.     

Functional diversity,functional composition and functional β diversity drive aboveground biomass across different bioclimatic rangelands

There has been a growing interest in understanding how biodiversity affects the functioning of ecosystems, while, it is still unclear how and to what extent different aspects of biodiversity are related to ecosystems function. We tested the relationship between aboveground biomass (AGB) and various aspects of functional diversity (functional richness (FRic), functional evenness (FEve) and functional divergence (FDiv)), functional β diversity and functional composition. Our study areas were located in four different bioclimatic regions including desert-steppe, steppe, semi-steppe, and Mediterranean rangelands extending along a productivity gradient created by the elevational-rainfall variations in the central Zagros Mountains of Iran.The results showed that FDiv positively predicted AGB in more productive (i.e., Mediterranean) and negatively in less productive rangelands of desert-steppe, steppe and semi-steppe. Functional β diversity predicted AGB only in more productive regions in semi-steppe and Mediterranean rangelands. Functional β diversity decomposed into turnover and nestedness, with turnover being more important in more productive and nestedness being more important in less productive ecosystems. The results also showed that the effects of FD and functional β diversity on AGB are generally directed by animal grazing through homogenizing community-wide trait composition in less productive ecosystems and inducing shifting mosaics across locations in more productive ecosystem.The results indicate that different components of FD were significantly related to AGB and the strength and direction of these effects vary with the different components studied and the bioclimatic regions under the study. In higher productive ecosystems, both functional diversity and functional β diversity are likely to contribute more to AGB through the complementary use of the resources. In less productive ecosystems, however, the functional identity of dominant species and traits would drive AGB.     

17β-hydroxysteroid dehydrogenase from the fungus Cochlioboluslunatus: structural and functional aspects

17β-Hydroxysteroid dehydrogenase (17β-HSD) activity has been described in all filamentous fungi tested, but until now only one 17β-HSD from Cochlioboluslunatus (17β-HSDcl) was sequenced. We examined the evolutionary relationship among 17β-HSDcl, fungal reductases, versicolorin reductase (Ver1), trihydroxynaphthalene reductase (THNR), and other homologous proteins. In the phylogenetic tree 17β-HSDcl formed a separate branch with Ver1, while THNRs reside in another branch, indicating that 17β-HSDcl could have similar function as Ver1. The structural relationship was investigated by comparing a model structure of 17β-HSDcl to several known crystal structures of the short chain dehydrogenase/reductase (SDR) family. A similarity was observed to structures of bacterial 7α-HSD and plant tropinone reductase (TR). Additionally, substrate specificity revealed that among the substrates tested the 17β-HSDcl preferentially catalyzed reductions of steroid substrates with a 3-keto group, Δ⁴ or 5α, such as: 4-estrene-3,17-dione and 5α-androstane-3,17-dione.     

Metabolism of 3α, 7α-dihydrexy-7β-methyl-5β-cholanoic acid and 3α,7β-dihydroxy-7α-methyi-5β-cholanoic acid in hamsters

The metabolic fate of the bile add analogs, 3α,7α-dihydroxy-7β-methyl-5β-cholanoic acid and 3α,7β-dihydroxy-7α-methyl-5β-cholanoic acid, was investigated and compared with that of chenodeoxycholic acid in hamsters. Both bile acid analogs were absorbed rapidly from the intestine and excreted into bile at similar to that of chenodeoxycholic acid. In the strain of hamster studied, the biliary bile were conjugated with both glycine and taurine. After continuous intravenous infusion, chenodeoxycholic acid the analogs became the major bile acid constituents in bile. After oral administration of a single dose of these compounds, fecal analysis revealed the existence of unchanged material (25–35%) as well as considerable amounts of metabolites (65–75%). The major metabolites excreted into feces were more polar than the starting material and were tentatively identified as trifaydroxy-7-methyl compounds by radioactive thin-layer chromatography. However, monohydroxy compounds were also found in the fecal extracts. These results show that chenodeoxycholic acid and ursodeoxycholic acid with a methyl group at the 7-position are resistant to bacterial 7-dehydroxylation than the normally occurring bile acids and that a certain proportion of these analogs is hydroxylated to give the corespondiag trihydroxy compound(s), In a control experiment, about 5% of administered chenodeoxychoulic acid was metabolized to a trihydroxy feile acid, but most of the compound (95%) was transformed into lithocholic acid.     

α-Amino acid containing degradable polymers as functional biomaterials: rational design, synthetic pathway, and biomedical applications

Currently, biomedical engineering is rapidly expanding, especially in the areas of drug delivery, gene transfer, tissue engineering, and regenerative medicine. A prerequisite for further development is the design and synthesis of novel multifunctional biomaterials that are biocompatible and biologically active, are biodegradable with a controlled degradation rate, and have tunable mechanical properties. In the past decades, different types of α-amino acid-containing degradable polymers have been actively developed with the aim to obtain biomimicking functional biomaterials. The use of α-amino acids as building units for degradable polymers may offer several advantages: (i) imparting chemical functionality, such as hydroxyl, amine, carboxyl, and thiol groups, which not only results in improved hydrophilicity and possible interactions with proteins and genes, but also facilitates further modification with bioactive molecules (e.g., drugs or biological cues); (ii) possibly improving materials biological properties, including cell-materials interactions (e.g., cell adhesion, migration) and degradability; (iii) enhancing thermal and mechanical properties; and (iv) providing metabolizable building units/blocks. In this paper, recent developments in the field of α-amino acid-containing degradable polymers are reviewed. First, synthetic approaches to prepare α-amino acid-containing degradable polymers will be discussed. Subsequently, the biomedical applications of these polymers in areas such as drug delivery, gene delivery and tissue engineering will be reviewed. Finally, the future perspectives of α-amino acid-containing degradable polymers will be evaluated.     

Cation-π interactions in lipocalins: structural and functional implications

The cation-π interaction impacts protein folding, structural stability, specificity, and molecular recognition. Cation-π interactions have been overlooked in the lipocalin family. To fill this gap, these interactions were analyzed in the 113 crystal and solution structures from the lipocalin family. The cation-π interactions link previously identified structurally conserved regions and reveal new motifs, which are beyond the reach of a sequence alignment algorithm. Functional and structural significance of the interactions were tested experimentally in human tear lipocalin (TL). TL, a prominent and promiscuous lipocalin, has a key role in lipid binding at the ocular surface. Ligand binding modulation through the loop AB at the "open" end of the barrel has been erroneously attributed solely to electrostatic interactions. Data revealed that the interloop cation-π interaction in the pair Phe28-Lys108 contributes significantly to stabilize the holo-conformation of the loop AB. Numerous energetically significant and conserved cation-π interactions were uncovered in TL and throughout the lipocalin family. Cation-π interactions, such as the highly conserved Trp17-Arg118 pair in TL, were educed in low temperature experiments of mutants with Trp to Tyr substitutions.     

α-Pyrones,secondary metabolites from fungus Cephalotrichum microsporum and their bioactivities

Cephalotrichum microsporum (SYP-F 7763) was a fungus isolated from the rhizosphere soil of traditional Chinese medicine Panax notoginseng. The EtOAc extract of Cephalotrichum microsporum cultivated on sterilized moistened-rice medium was separated by various chromatographic techniques, which yielded 11 metabolites (1–11) of this fungus. On the basis of the widely spectroscopic data, the chemical structures of isolated metabolites were determined, most of which were α-pyrones, including 5 compounds (4–7, and 10) unreported. In the anti-bacterial bioassay, compound 1 displayed significant inhibitory effects on three pathogenic bacteria, MR S. aureus, S. aureus, and B. cereus. α-Pyrones 2, 3, and 5–7 also displayed moderate inhibitory effects on MR S. aureus, S. aureus, and B. subtilis, which could be the major anti-bacterial constituents of Cephalotrichum microsporum. Additionally, compounds 1, 4, and 5 displayed significant cytotoxicity on five human cancer cell lines, with the IC₅₀ values < 20 μM, which are more effective than positive control 5-fluorouracil. Therefore, α-pyrones were important secondary metabolites of Cephalotrichum microsporum, which displayed anti-bacterial and anti-tumor activities.     

2β-3,4-Unsaturated sialic acid derivatives: Synthesis optimization,and biological evaluation as Newcastle disease virus hemagglutinin-neuraminidase inhibitors

The optimization of the synthetic protocol to obtain the 3,4-unsaturated sialic acid derivatives, through the fine-tuning of both the Ferrier glycosylation conditions and the subsequent hydrolysis work-up, is herein reported. The accomplishment of the desired β-anomers and some selected α-ones, in pure form, led us to evaluate their specific inhibitory activity towards NDV-HN and human sialidase NEU3. Importantly, the resulting data allowed the identification, for the first time, of three active 3,4-unsaturated sialic acid analogs, showing IC₅₀ values against NDV-HN in the micromolar range.     

Efficient synthesis, structural characterization and anti-microbial activity of chiral aryl boronate esters of 1,2-O-isopropylidene-α-D-xylofuranose

A simple and efficient synthetic approach toward a series of chiral aryl boronate esters, starting from d-xylose, as anti-microbial agents, is described herein. Minimum inhibitory concentration and zone of inhibition revealed that these derivatives exhibit potent anti-bacterial and anti-fungal properties. Herein, we report the first anti-microbial activity of this class of compounds. All products have been characterized by NMR (¹H, ¹³C and ¹¹B), IR, elemental and mass spectral study.     

Fromβ-lactams toα- andβ-amino acid derived peptides

Summary The potential of-lactams as intermediates for the access to- and-amino acid-derived peptides is shortly reviewed, with major focus on the technologies developed in our group. The two general strategies lie, on one side, in the oxidative ring expansion of 3-hydroxy-lactams toN-carboxy-amino acid anhydrides or Leuch's anhydrides and subsequent coupling with-amino acid esters and, on the other side, in the nucleophilic ring opening ofN-Boc--lactams. Both approaches have been successfully applied to the synthesis of,-diamino acid,-amino--hydroxy acid, polyhydroxylated-amino acid,,-disubstituted-amino acid,-amino acid,-amino--hydroxy acid and,-disubstituted-amino acid derived peptides. Because of the mild reaction conditions needed for the above transformations and the highly stereoselective procedures employed for the construction of the starting-lactam ring, the whole process allows the production of optically pure final products.     

β-glucosyl esters of 19α-hydroxyursolic acid derivatives in leaves of Rubus species

β-Glucosyl esters of A-ring oxygenated 19α-hydroxyursolic acids were isolated from the leaves of Rubus microphyllus, R. koehneanus, R. trifidus and R. medius. Comparisons of the glycoside fractions of the leaves of 39 Rubus species were conducted, indicating the chemotaxonomic significance of this type of glucosyl ester in this genus.     

TGF-β singaling and cancer: structural and functional consequences of mutations in Smads

Transforming growth factor-β (TGF-β) and related cytokines control the development and homeostasis of many tissues by regulating the expression of genes that determine cell phenotype. Recent progress has elucidated the way in which members of the TGF-β family initiate their signal through transmembrane receptors and transmit it to target genes via the Smad family of signal-transducing proteins. This review describes TGF-β signaling pathways as currently understood and mutations of the genes that encode Smads that disrupt the function of these proteins and cause various forms of cancer.     

γ-amino butyric acid and glutamic acid in Manduca sexta: Proposed roles in insect development

1. In the tobacco hornworm, Manduca sexta, the haemolymph titres of γ-amino butyruc acid (GABA) and glutamic acid range from 0.03–0.40 × 10⁻³ M and 0.1–7.8 × 10⁻³ M, respectively, during the last larval instar.2. Glutamic acid in hemolymph does not appear to be derived from haemocytes.3. Increases in GABA and glutamate haemolymph titres occur sequentially and independently of changes in the titres of ecdysone and juvenile hormone.4. A single injection of GABA sufficient to initially raise the haemolymph titre to 4 mM on each day of the larval-pupal transformation causes a 12–18 hr delay in the time of the larval-pupal ecdysis.5. A single injection of glutamate sufficient to initially raise the haemolymph titre by 2 mM on each day of the larval-pupal transformation was without apparent effect on co-ordinated body movements or on the time of the larval-pupil ecdysis.6. When GABAase is injected into hornworms whose GABA titres are rising (pink stripe + 1 day, through pink stripe + 3 days), haemolymph GABA titres decline, rates of haemolymph GABA turnover increase and the time of the larval-pupil ecdysis is advanced significantly.7. When hornworms are administered GABAase at the pink stripe stage in development, a time when the titre of haemolymph GABA is minimal, the time of ecdysis is normal.8. A possible role for GABA during the larval-pupal transformation may be in preventing premature initiation of pre-ecdysial behavior, while a proposed role for glutamic acid is to potentiate those coordinated neuro-muscular activities necessary for successful ecdysis which had been inhibited by GABA.     

Coral–macroalgal phase shifts or reef resilience: links with diversity and functional roles of herbivorous fishes on the Great Barrier Reef

Changes from coral to macroalgal dominance following disturbances to corals symbolize the global degradation of coral reefs. The development of effective conservation measures depends on understanding the causes of such phase shifts. The prevailing view that coral–macroalgal phase shifts commonly occur due to insufficient grazing by fishes is based on correlation with overfishing and inferences from models and small-scale experiments rather than on long-term quantitative field studies of fish communities at affected and resilient sites. Consequently, the specific characteristics of herbivorous fish communities that most promote reef resilience under natural conditions are not known, though this information is critical for identifying vulnerable ecosystems. In this study, 11 years of field surveys recorded the development of the most persistent coral–macroalgal phase shift (>7 years) yet observed on Australia’s Great Barrier Reef (GBR). This shift followed extensive coral mortality caused by thermal stress (coral bleaching) and damaging storms. Comparisons with two similar reefs that suffered similar disturbances but recovered relatively rapidly demonstrated that the phase shift occurred despite high abundances of one herbivore functional group (scraping/excavating parrotfishes: Labridae). However, the shift was strongly associated with low fish herbivore diversity and low abundances of algal browsers (predominantly Siganidae) and grazers/detritivores (Acanthuridae), suggesting that one or more of these factors underpin reef resilience and so deserve particular protection. Herbivorous fishes are not harvested on the GBR, and the phase shift was not enhanced by unusually high nutrient levels. This shows that unexploited populations of herbivorous fishes cannot ensure reef resilience even under benign conditions and suggests that reefs could lose resilience under relatively low fishing pressure. Predictions of more severe and widespread coral mortality due to global climate change emphasize the need for more effective identification and protection of ecosystem components that are critical for the prevention of coral reef phase shifts.     

Synthesis, aggregation behavior and cholesterol solubilization studies of 16-epi-pythocholic acid (3α,12α,16β-trihydroxy-5β-cholan-24-oic acid)

Synthesis, aggregation behavior and in vitro cholesterol solubilization studies of 16-epi-pythocholic acid (3α,12α,16β-trihydroxy-5β-cholan-24-oic acid, EPCA) are reported. The synthesis of this unnatural epimer of pythocholic acid (3α,12α,16α-trihydroxy-5β-cholan-24-oic acid, PCA) involves a series of simple and selective chemical transformations with an overall yield of 21% starting from readily available cholic acid (CA). The critical micellar concentration (CMC) of 16-epi-pythocholate in aqueous media was determined using pyrene as a fluorescent probe. In vitro cholesterol solubilization ability was evaluated using anhydrous cholesterol and results were compared with those of other natural di- and trihydroxy bile acids. These studies showed that 16-epi-pythocholic acid (16β-hydroxy-deoxycholic acid) behaves similar to cholic acid (CA) and avicholic acid (3α,7α,16α-trihydroxy-5β-cholan-24-oic acid, ACA) in its aggregation behavior and cholesterol dissolution properties.     

Synthesis,structural characterization,and biological properties of pentyl- and isopentyl-α-D-glucosides

The study was devoted to the synthesis of pentyl glucosides (PenG_n) and isopentyl glucosides (Iso-PenG_n) by transglycosylation using recombinant cyclodextrin glycosyltransferase from Bacillus circulans A11, β-cyclodextrin as a glucosyl donor and 1-pentanol and isopentanol as acceptors. TLC and MS analysis indicated at least 3 products which were in accordance with PenG_n and IsoPenG_n having glucose, maltose and maltotriose attached to the alkyl groups of both alcohols. Two products of each glucoside were purified by preparative TLC and their structures were identified by NMR technique to be pentyl-α-D-glucopyranoside (PenG₁), pentyl-α-D-maltopyranoside (PenG₂), isopentyl-α-D-glucopyranoside (IsoPenG1) and isopentyl- α-D-maltopyranoside (IsoPenG₂). The effect of water-in-hexadecane emulsion on emulsion-forming properties showed that PenG₂ had the highest emulsifying activity. Adding PenG₂ to the insoluble Corynebacterium glutamicum amylomaltase from Escherichia coli transformants (A406R), helped to perform it to more soluble conformation. Moreover, it was found that PenG_1,2 exhibited a higher antibacterial activity against E. coli ATCC 25922 than that of IsoPenG_1,2. Hence, the biological properties of the synthesized products may be useful for their applications as emulsifying, solubilizing and antibacterial agents.     

Cα-Methyl, Cα-phenylglycine peptides: A structural study

Summary In order to obtain further information on the role played by phenyl ring position in the C^α-methylated α-amino acid side chain on peptide preferred conformation, the crystal-state structural preferences of C^α-methyl, C^α-phenylglycine peptides have been determined by X-ray diffraction. This study shows that either the fully extended conformation or the β-bend/3₁₀-helical structures are adopted by peptides characterized by this C^α-methylated, β-branched, aromatic α-amino acid.