Herbal remedies for the management of seed-borne fungal pathogens by an edible plant Decalepis hamiltonii (Wight & Arn)

Abstract

Antifungal activity-guided assay of solvent extracts of Decalepis hamiltonii (Wight & Arn) (Asclepiadaceae) against important phytopathogenic fungi, known to cause diseases in sorghum, maize and paddy proved to be highly significant. Among the five solvent extracts tested, Petroleum ether extract showed highly significant antifungal activity. Phytochemical analysis revealed that the antifungal active principle is a phenolic compound. TLC separation of the phenolic fraction using chloroform as an eluting solvent revealed the presence of seven bands but the antifungal activity was observed only in band five with R_f value 0.77. The antifungal active compound is identified as 2-hydroxy-4-methoxybenzaldehyde based on Nuclear Magnetic Resonance (NMR) and mass spectral analysis. The Minimal inhibitory concentration (MIC) varied between 200 μg ml^?1 and 700 μg ml^?1 depending on the fungal species. Seed treatment of the active principle significantly increased seed germination and seed vigour with a corresponding decrease in seed mycoflora. The antifungal active compound was effective against all the 24 fungal species tested suggesting broad-spectrum antifungal activity. Comparative evaluation of the active principle with the synthetic fungicides revealed that the antifungal activity of the active principle obtained from the plant is better than that of synthetic fungicide. This plant being an edible one can be exploited in the management of seed-borne pathogenic fungi and the prevention of biodeterioration of grains and mycotoxin elaboration during storage.     

Chemical modification of ascorbic acid and evaluation of its lipophilic derivatives as inhibitors of secretory phospholipase A2 with anti-inflammatory activity

This investigation aims to evaluate the antitumor and antioxidant potential of Chrysaora quinquecirrha (sea nettle) nematocyst venom on Ehrlich ascites carcinoma (EAC) tumor model. Tumor was induced in mice by intraperitoneal injection of EAC cells. The antitumor effect of sea nettle nematocyst venom (SNV) peptide was evaluated by assessing in vitro cytotoxicity, survival time, hematological, and antioxidant parameters. Intraperitoneal injection of SNV peptide increased the survival time of the EAC-bearing mice. The SNV peptide brought back the altered levels of the hematological and antioxidant parameters in a dose dependent manner in EAC-bearing mice. The results were comparable to that of the result obtained from the animals treated with the standard drug 5-fluorouracil (20 mg/kg bw). Thus, present study revealed that SNV peptide possessed significant antitumor and antioxidant activity.     

Dimeric core structure of modular stator subunit E of archaeal H+ -ATPase

Archaeal H(+)-ATPase (A-ATPase) is composed of an A(1) region that hydrolyzes ATP and an integral membrane part A(0) that conducts protons. Subunit E is a component of peripheral stator(s) that physically links A(1) and A(0) parts of the A-ATPase. Here we report the first crystal structure of subunit E of A-ATPase from Pyrococcus horikoshii OT3 at 1.85 A resolution. The protomer structure of subunit E represents a novel fold. The quaternary structure of subunit E is a homodimer, which may constitute the core part of the stator. To investigate the relationship with other stator subunit H, the complex of subunits EH was prepared and characterized using electrophoresis, mass spectrometry, N-terminal sequencing and circular dichroism spectroscopy, which revealed the polymeric and highly helical nature of the EH complex with equimolar stoichiometry of both the subunits. On the basis of the modular architecture of stator subunits, it is suggested that both cytoplasm and membrane sides of the EH complex may interact with other subunits to link A(1) and A(0) parts.     

Structures of dimeric nonstandard nucleotide triphosphate pyrophosphatase from Pyrococcus horikoshii OT3: functional significance of interprotomer conformational changes

Nonstandard nucleotide triphosphate pyrophosphatase (NTPase) can efficiently hydrolyze nonstandard purine nucleotides in the presence of divalent cations. The crystal structures of the NTPase from Pyrococcus horikoshii OT3 (PhNTPase) have been determined in two unliganded forms and in three liganded forms with inosine 5′-monophosphate (IMP), ITP and Mn²⁺, which visualize the recognition of these ligands unambiguously. The overall structure of PhNTPase is similar to that of previously reported crystal structures of the NTPase from Methanococcus jannaschii and the human ITPase. They share a similar protomer folding with two domains and a similar homodimeric quaternary structure. The dimeric interface of NTPase is well conserved, and the dimeric state might be important to constitute the active site of this enzyme. A conformational analysis of the five snapshots of PhNTPase structures using the multiple superposition method reveals that IMP, ITP and Mn²⁺ bind to the active site without inducing large local conformational changes, indicating that a combination of interdomain and interprotomer rigid-body shifts mainly describes the conformational change of PhNTPase. The interdomain and interprotomer conformations of the ITP liganded form are essentially the same as those observed in the unliganded form 1, indicating that ITP binding to PhNTPase in solution may follow the selection mode in which ITP binds to the subunit that happens to be in the conformation observed in the unliganded form 1. In contrast to the human ITPase inducing a large domain closure upon ITP binding, the interdomain active site cleft is generally closed in PhNTPase and only the IMP binding form shows a remarkable domain opening by 14° only in the B subunit. The interprotomer rigid-body rotation of PhNTPase has a tendency to keep the dimeric 2-fold symmetry, which is also true in human ITPase, thereby suggesting its relevance to the positive cooperativity of the dimeric NTPases. The exception of this rule is observed in the IMP liganded form in which the dimeric 2-fold symmetry is broken by a 3° interprotomer rotation in an unusual direction. A combination of the exceptional interdomain and interprotomer relocations is most likely the reason for the observed asymmetric IMP binding that might be necessary for PhNTPase to release the reaction product IMP.     

Crystal structure of the protease domain of a heat-shock protein HtrA from Thermotoga maritima

HtrA (high temperature requirement A), a periplasmic heat-shock protein, functions as a molecular chaperone at low temperatures, and its proteolytic activity is turned on at elevated temperatures. To investigate the mechanism of functional switch to protease, we determined the crystal structure of the NH(2)-terminal protease domain (PD) of HtrA from Thermotoga maritima, which was shown to retain both proteolytic and chaperone-like activities. Three subunits of HtrA PD compose a trimer, and multimerization architecture is similar to that found in the crystal structures of intact HtrA hexamer from Escherichia coli and human HtrA2 trimer. HtrA PD shares the same fold with chymotrypsin-like serine proteases, but it contains an additional lid that blocks access the of substrates to the active site. A corresponding lid found in E. coli HtrA is a long loop that also blocks the active site of another subunit. These results suggest that the activation of the proteolytic function of HtrA at elevated temperatures might occur by a conformational change, which includes the opening of the helical lid to expose the active site and subsequent rearrangement of a catalytic triad and an oxyanion hole.     

Spectrophotometric determination with a chromogenic reagent of lead in vegetables

A method was developed for the simple, selective, and sensitive spectrophotometric determination of lead in vegetables with synthesized chromogenic reagent 3-[(2,6-dibromo-4-methylphenyl)diazenyl]-4,5-dihydroxy-6-[(2,4,6-tribromophenyl)diazenyl]naphthalene-2,7-disulfonic acid (DBMTBA; 1). In 0.25 M phosphoric acid medium, which greatly increases the selectivity, lead reacts with DBMTBA to form a 1:2 blue complex, which shows maximum absorption at 646 nm. Under optimal conditions, Beer's law is obeyed over the range from 0.09 to 0.8 microg ml(-1) Pb2+, and the apparent molar absorptivity is 1.024x10(5) l mol(-1) cm(-1). The detection limit and the variation coefficient were found to be 2.09 microg ml(-1) and 1.0%, resp. The proposed method has been applied successfully for the determination of lead in vegetables (Solanum melongena fruits, tomato fruits, Ablemoschus esculentus leaves, and Daucous carota leaves) with satisfactory results.     

Crystal structure of novel NADP-dependent 3-hydroxyisobutyrate dehydrogenase from Thermus thermophilus HB8

3-Hydroxyisobutyrate, a central metabolite in the valine catabolic pathway, is reversibly oxidized to methylmalonate semialdehyde by a specific dehydrogenase belonging to the 3-hydroxyacid dehydrogenase family. To gain insight into the function of this enzyme at the atomic level, we have determined the first crystal structures of the 3-hydroxyisobutyrate dehydrogenase from Thermus thermophilus HB8: holo enzyme and sulfate ion complex. The crystal structures reveal a unique tetrameric oligomerization and a bound cofactor NADP+. This bacterial enzyme may adopt a novel cofactor-dependence on NADP, whereas NAD is preferred in eukaryotic enzymes. The protomer folds into two distinct domains with open/closed interdomain conformations. The cofactor NADP+ with syn nicotinamide and the sulfate ion are bound to distinct sites located at the interdomain cleft of the protomer through an induced-fit domain closure upon cofactor binding. From the structural comparison with the crystal structure of 6-phosphogluconate dehydrogenase, another member of the 3-hydroxyacid dehydrogenase family, it is suggested that the observed sulfate ion and the substrate 3-hydroxyisobutyrate share the same binding pocket. The observed oligomeric state might be important for the catalytic function through forming the active site involving two adjacent subunits, which seems to be conserved in the 3-hydroxyacid dehydrogenases. A kinetic study confirms that this enzyme has strict substrate specificity for 3-hydroxyisobutyrate and serine, but it cannot distinguish the chirality of the substrates. Lys165 is likely the catalytic residue of the enzyme.     

Molecular docking studies of benzimidazopyrimidine and coumarin substituted benzimidazopyrimidine derivatives: As potential human Aurora A kinase inhibitors

Protein kinases are important drug targets in human cancers, inflammation and metabolic diseases. Docking studies was performed for all the benzimidazopyrimidine and coumarin substituted benzimidazopyridimine derivatives with human Aurora A kinase target (3FDN) employing flexible ligand docking approach by using AutoDock 4.2. All the compounds were found to have minimum binding energy ranging from -6.26 to -9.29 kJ/mol. Among the molecules tested for docking study, 10-(6-Bromo-2-oxo- 2H-chromen-4-ylmethyl)-2-isopropyl-10H-benzo[4,5]imidazo[1,2-a]pyrimidin-4-one (2k) showed minimum binding energy (-9.29 kJ/mol) with ligand efficiency of -0.31. All the ligands were docked deeply within the binding pocket region of 3FDN showing hydrogen bonds with Ala 213 and Asn 261. The docking study results showed that these derivatives are excellent inhibitor of human Aurora A kinase target; and also all these docked compounds have good inhibition constant, vdW + Hbond + desolv energy with best RMSD value.     

Structural basis for the reaction mechanism of UDP-glucose pyrophosphorylase

UDP-glucose pyrophosphorylases (UGPase; EC 2.7.7.9) catalyze the conversion of UTP and glucose-1-phosphate to UDP-glucose and pyrophosphate and vice versa. Prokaryotic UGPases are distinct from their eukaryotic counterparts and are considered appropriate targets for the development of novel antibacterial agents since their product, UDP-glucose, is indispensable for the biosynthesis of virulence factors such as lipopolysaccharides and capsular polysaccharides. In this study, the crystal structures of UGPase from Helicobacter pylori (HpUGPase) were determined in apo- and UDP-glucose/Mg²⁺-bound forms at 2.9 Å and 2.3 Å resolutions, respectively. HpUGPase is a homotetramer and its active site is located in a deep pocket of each subunit. Magnesium ion is coordinated by Asp130, two oxygen atoms of phosphoryl groups, and three water molecules with octahedral geometry. Isothermal titration calorimetry analyses demonstrated that Mg²⁺ ion plays a key role in the enzymatic activity of UGPase by enhancing the binding of UGPase to UTP or UDP-glucose, suggesting that this reaction is catalyzed by an ordered sequential Bi Bi mechanism. Furthermore, the crystal structure explains the specificity for uracil bases. The current structural study combined with functional analyses provides essential information for understanding the reaction mechanism of bacterial UGPases, as well as a platform for the development of novel antibacterial agents.