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At least 757 records · Page 42Linked to original sources
PubMed1992

Indonesian medicinal plants. I. Chemical structures of calotroposides A and B, two new oxypregnane-oligoglycosides from the root of Calotropis gigantea (Asclepiadaceae).

Two new oxypregnane-oligoglycosides named calotroposides A (1) and B (2) have been isolated from the root of Calotropis gigantea (Asclepiadaceae), an Indonesian medicinal plant, and their chemical structures have been elucidated by chemical and spectroscopic methods as 12-O-benzoyllineolon 3-O-beta-D-cymaropyranosyl(1----4)-beta-D-oleandropyranosyl( 1----4)- beta-D-oleandropyranosyl(1----4)-beta-D-cymaropyranosyl(1--- -4)-beta-D- cymaropyranoside and 12-O-benzoyldeacetylmetaplexigenin 3-O-beta-D-cymaropyranosyl(1---4)-beta-D-oleandropyranosyl(- ---4)- beta-D-oleandropyranosyl(1----4)-beta-D-cymaropyranosyl(1--- -4)- beta-D-cymaropyranoside, respectively.

Parasympathomimetics↗
PubMed2002

Nitric oxide formation and corresponding relaxation of porcine coronary arteries induced by plant phenols: essential structural features.

The high intake of polyphenols is thought to contribute to the beneficial cardiovascular effects of plant-centered diets. A putative mechanism underlying the cardioprotective activity is thought to be a plant phenol-induced increase of nitric oxide formation by the constitutive endothelial nitric oxide synthase. Twenty-eight phenols of different classes commonly occurring in plant foods were examined for their capability of enhancing the endothelial nitric oxide release of isolated porcine coronary arteries by direct real-time measurement of the luminal surface nitric oxide concentration with an amperometric microsensor. Additionally, the relaxing activity of the phenols was measured on porcine coronary rings. Quercetin, myricetin, leucocyanidol, and oligomeric proanthocyanidins induced the highest increases in nitric oxide release (delta[NO] > 8.5 nM ); caffeic acid, fisetin, hyperosid, and isoquercitrin were moderately active (5 nM < delta[NO] < 8.5 nM ); the other phenolic compounds caused only marginal increases of the nitric oxide levels (delta[NO] < 5 nM). The nitric oxide-stimulating activity of the phenols was uniformly positively correlated with their vasorelaxing activity. However, endothelium-dependent vasorelaxations were limited to phenols inducing nitric oxide elevations > 5 nM (= Km value of the soluble guanylate cyclase). Analysis of structure-activity relations revealed that a high nitric oxide activity was confined to a flavan-moiety with free hydroxyl-residues at C3, C3', C4', C5, and C7 and a hydroxyl-, oxo-, or phenolic substituent at C4, whereas the caffeic acid scaffolding emerged as the minimally essential motif for the nitric oxide-dependent vasorelaxation.

Animals↗
PubMed1991

Application of a nuclease from rye nucleus for structural studies of plant ribonucleic acids.

A new nuclease (Rn) isolated from rye nucleus was applied for the structural studies of methionine initiator transfer ribonucleic acid and ribosomal 5S rRNA from yellow lupin seeds. The enzyme shows high specificity for some regions of both RNAs. The dihydrouridine and ribothymidine loops which are supposed to be involved in the tertiary interactions of the methionine initiator tRNA were hydrolysed. The anticodon loop is not digested at all. 5S rRNA was digested in single stranded regions (loops). The cleavage pattern of the tRNA and 5S rRNA obtained with Rn enzyme, suggests not only the high specificity toward single stranded regions, but also some dependence on their tertiary structure.

Base Sequence↗
PubMed2004

Plant acetyl-CoA carboxylase: structure, biosynthesis, regulation, and gene manipulation for plant breeding.

Acetyl-CoA carboxylase (ACCase) catalyzes the first committed step of fatty acid synthesis, the carboxylation of acetyl-CoA to malonyl-CoA. Two physically distinct types of enzymes are found in nature. Heteromeric ACCase composed of four subunits is usually found in prokaryotes, and homomeric ACCase composed of a single large polypeptide is found in eukaryotes. Most plants have both forms, the heteromeric form in plastids, in which de novo fatty acids are synthesized, and the homomeric form in cytosol. This review focuses on the structure and regulation of plant heteromeric ACCase and its manipulation for plant breeding.

Acetyl-CoA Carboxylase↗
PubMed2000

Crystal structure of a plant ribonuclease, RNase LE.

Ribonuclease LE (RNase LE) from cultured tomato (Lycopersicon esculentum) cells is a member of the RNase T(2) family showing broad base specificity. The crystal structure of RNase LE has been determined at 1.65 A resolution. The structure consists of seven alpha-helices and seven beta-strands, belonging to an alpha+beta type structure. Comparison of the structure of RNase LE with that of RNase Rh, a microbial RNase belonging to the RNase T(2) family, reveals that while the overall folding topologies are similar to each other, major insertions and deletions are found at the N-terminal regions. The structural comparison, an amino acid sequence alignment of the RNase T(2) enzymes, and comparison of the disulfide-bonding pattern of these enzymes show that the structure of RNase LE shown here is the basic framework of the animal/plant subfamily of RNase T(2) enzymes (including a self-incompatibility protein called S-RNase), and the structure of RNase Rh is that of the fungal subfamily of RNase T(2) enzymes (including RNase T(2)). Subsequently, we superposed the active-site of the RNase LE with that of RNase Rh and found that (1) His39, Trp42, His92, Glu93, Lys96, and His97 of RNase LE coincided exactly with His46, Trp49, His104, Glu105, Lys108, and His109, respectively, of RNase Rh, and (2) two conserved water molecules were found at the putative P(1) sites of both enzymes. These facts suggest that plant RNase LE has a very similar hydrolysis mechanism to that of fungal RNase Rh, and almost all the RNase T(2) enzymes widely distributed in various species share a common catalytic mechanism. A cluster of hydrophobic residues was found on the active-site face of the RNase LE molecule and two large hydrophobic pockets exist. These hydrophobic pockets appear to be base binding sites mainly by hydrophobic interactions and are responsible for the base non-specificity of RNase LE.

Amino Acid Sequence↗
PubMed1995

Structural classification of plant chitinases: two subclasses in class I and class II chitinases.

For the classification of plant chitinases, phylogenetic relationships were analyzed besides the established classification of domain structure and C-terminal extension sequences. Two genetically different subclasses (high and low molecular weight) were found for the main structure of class I and class II chitinases in their phylogenetic trees. The genetic distance of these subclasses showed that the high molecular weight subclass may be an ancestral molecule.

Amino Acid Sequence↗
PubMed2005

Structural determinants for plant annexin-membrane interactions.

The interactions of two plant annexins, annexin 24(Ca32) from Capsicum annuum and annexin Gh1 from Gossypium hirsutum, with phospholipid membranes have been characterized using liposome-based assays and adsorption to monolayers. These two plant annexins show a preference for phosphatidylserine-containing membranes and display a membrane binding behavior with a half-maximum calcium concentration in the sub-millimolar range. Surprisingly, the two plant annexins also display calcium-independent membrane binding at levels of 10-20% at neutral pH. This binding is regulated by three conserved surface-exposed residues on the convex side of the proteins that play a pivotal role in membrane binding. Due to quantitative differences in the membrane binding behavior of N-terminally His-tagged and wild-type annexin 24(Ca32), we conclude that the N-terminal domain of plant annexins plays an important role, reminiscent of the findings in their mammalian counterparts. Experiments elucidating plant annexin-mediated membrane aggregation and fusion, as well as the effect of these proteins on membrane surface hydrophobicity, agree with findings from the membrane binding experiments. Results from electron microscopy reveal elongated rodlike assemblies of plant annexins in the membrane-bound state. It is possible that these structures consist of protein molecules directly interacting with the membrane surface and molecules that are membrane-associated but not in direct contact with the phospholipids. The rodlike structures would also agree with the complex data from intrinsic protein fluorescence. The tubular lipid extensions suggest a role in the membrane cytoskeleton scaffolding or exocytotic processes. Overall, this study demonstrates the importance of subtle changes in an otherwise conserved annexin fold where these two plant annexins possess distinct modalities compared to mammalian and other nonplant annexins.

Animals↗
PubMed1996

Isolation of a cDNA for a phosphoenolpyruvate carboxylase from a monocot CAM-plant, Aloe arborescens: structure and its gene expression.

A phosphoenolpyruvate carboxylase (PEPCase) cDNA was isolated from Aloe arborescens, a monocot CAM plant. Northern analysis of the PEPCase transcript indicated that it is specifically expressed in green leaves, strongly suggesting its involvement in CAM photosynthesis. No diurnal change in expression level was evident. Western blot analysis also showed no alteration of the amount of the PEPCase protein. These results suggest that circadian rhythm in PEPCase activity may be regulated post-translationally. The representative cDNA clone contained an ORF encoding 964 amino acid residues. Deduced amino acid sequence of the aloe PEPCase is highly conserved as compared with other PEPCases. The phosphorylation site which may be modified by PEPC-kinase was conserved. An evolutional map with known PEPCases suggested that CAM-type PEPCases were located between C4 and housekeeping PEPCases.

Aloe↗
PubMed1998

Rapid molecular mass and structural determination of plant cell wall-derived oligosaccharides using off-line high-performance anion-exchange chromatography/mass spectrometry.

A method has been developed for the rapid molecular mass determination and structural elucidation of mixtures of oligosaccharides derived from plant cell walls. The oligosaccharides were fractionated using gel permeation chromatography and 'analytical' high-performance anion-exchange chromatography (HPAEC), neutralized, dried and the mixtures of eluent salt and oligosaccharides were per-O-acetylated directly. The derivatized oligosaccharides were isolated by dissolution in dichloromethane and the salts were removed by aqueous partitioning. The per-O-acetylated oligosaccharides were analysed using electrospray (ES) and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MS). Exploiting the fact that acid-catalysed per-O-acetylation of oligosaccharides can be achieved even under the extremely salty conditions that are found in post-column neutralized HPAEC fractions, and combining this derivatization step with off-line ESMS, allow rapid screening for molecular mass and thus yield information on the composition of the various oligosaccharides in these complex mixtures. Subsequent per-O-methylation of the per-O-acetylated, salt-free fractions and collision-induced dissociation tandem mass spectrometric analysis was used for additional sequence and branching determination of the oligosaccharides.

Carbohydrate Sequence↗
PubMed2001

Structure of the plant alternative oxidase. Site-directed mutagenesis provides new information on the active site and membrane topology.

All higher plants and many fungi contain an alternative oxidase (AOX), which branches from the cytochrome pathway at the level of the quinone pool. In an attempt, first, to distinguish between two proposed structural models of this di-iron protein, and, second, to examine the roles of two highly conserved tyrosine residues, we have expressed an array of site-specific mutants in Schizosaccharomyces pombe. Mitochondrial respiratory analysis reveals that S. pombe cells expressing AOX proteins in which Glu-217 or Glu-270 were mutated, no longer exhibit antimycin-resistant oxygen uptake, indicating that these residues are essential for AOX activity. Although such data corroborate a model that describes the AOX as an interfacial membrane protein, they are not in full agreement with the most recently proposed ligation sphere of its di-iron center. We furthermore show that upon mutation of Tyr-253 and Tyr-275 to phenylalanines, AOX activity is fully maintained or abolished, respectively. These data are discussed in reference to the importance of both residues in the catalytic cycle of the AOX.

Antifungal Agents↗
PubMed2006

The crystal structure of a plant 3-ketoacyl-CoA thiolase reveals the potential for redox control of peroxisomal fatty acid beta-oxidation.

Crystal structures of peroxisomal Arabidopsis thaliana 3-ketoacyl-CoA thiolase (AtKAT), an enzyme of fatty acid beta-oxidation, are reported. The subunit, a typical thiolase, is a combination of two similar alpha/beta domains capped with a loop domain. The comparison of AtKAT with the Saccharomyces cerevisiae homologue (ScKAT) structure reveals a different placement of subunits within the functional dimers and that a polypeptide segment forming an extended loop around the open catalytic pocket of ScKAT converts to alpha-helix in AtKAT, and occludes the active site. A disulfide is formed between Cys192, on this helix, and Cys138, a catalytic residue. Access to Cys138 is determined by the structure of this polypeptide segment. AtKAT represents an oxidized, previously unknown inactive form, whilst ScKAT is the reduced and active enzyme. A high level of sequence conservation is observed, including Cys192, in eukaryotic peroxisomal, but not mitochondrial or prokaryotic KAT sequences, for this labile loop/helix segment. This indicates that KAT activity in peroxisomes is influenced by a disulfide/dithiol change linking fatty acid beta-oxidation with redox regulation.

Acetyl-CoA C-Acyltransferase↗
PubMed1994

Indonesian medicinal plants. IX. Chemical structures of gongganosides A, B, and C, three new quinovic acid glycosides from the bark of Bhesa paniculata (Celastraceae).

Three new quinovic acid glycosides, named gongganosides A (1), B (2), and C (3), were isolated from the bark of Bhesa paniculata (Celastraceae), an Indonesian medicinal plant collected in Sumatra Island. The chemical structures have been elucidated on the basis of chemical and physicochemical evidence as quinovic acid 3-O-beta-D-xylopyranosyl(1-->3)-alpha-L- rhamnopyranoside for 1,28-O-beta-D-glucopyranosylquinovic acid 3-O-alpha-L-rhamnopyranoside for 2, and 28-O-beta-D-glucopyranosyl-quinovic acid 3-O-beta-D-xylopyranosyl(1-->3)-alpha-L-rhamnopyranoside for 3.

Carbohydrate Sequence↗
PubMed1992

Cap structure of U3 small nucleolar RNA in animal and plant cells is different. gamma-Monomethyl phosphate cap structure in plant RNA.

U3 small nucleolar RNA (snoRNA) is an abundant small RNA involved in the processing of pre-ribosomal RNA of eukaryotic cells. U3 snoRNA has been previously characterized from several sources, including human, rat, mouse, frog, fruit fly, dinoflagellates, slime mold, and yeast; in all these organisms, U3 snoRNA contains trimethylguanosine cap structure. In all instances where investigated, the trimethylguanosine-capped snRNAs including U3 snoRNA, are synthesized by RNA polymerase II. However, in higher plants, the U3 snoRNA is synthesized by RNA polymerase III and contains a cap structure different from trimethylguanosine (Kiss, T., and Solymosy, F. (1990) Nucleic Acids Res. 18, 1941-1949; Marshallsay, C., Kiss, T., and Filipowicz, W. (1990) Nucleic Acids Res. 18, 3451-3458; Kiss, T., Marshallsay, C., and Filipowicz, W. (1991) Cell 65, 517-526). In this study, we present evidence that cowpea and, most likely, tomato plant U3 snoRNA contains a methyl-pppA cap structure. These data show that the same U3 snoRNA contains different cap structures in different species and suggest that the kind of cap structure that an uridylic acid-rich small nuclear RNA contains is dependent on the RNA polymerase responsible for its synthesis. In vitro synthesized plant U3 snoRNA, with pppA or pppG as its 5' end, was converted to methyl-pppA/G cap structure in vitro when incubated with extracts prepared from wheat germ or HeLa cells. These data show that the capping machinery is conserved in organisms as evolutionarily distant as plants and mammals. Nucleotides 1-45 of tomato U3 snoRNA, which are capable of forming a stem-loop structure, are sufficient to direct the methyl cap formation in vitro.

Animals↗
PubMed1994

Indonesian medicinal plants. X. Chemical structures of four new triterpene-glycosides, gongganosides D, E, F, and G, and two secoiridoid-glucosides from the bark of Bhesa paniculata (Celastraceae).

Four new triterpene-glycosides, named gongganosides D (4), E (5), F (6), and G (7), and two new secoiridoid-glucosides, (7R)-7-caffeoyloxysweroside (8) and (7S)-7-caffeoyloxysweroside (9), were isolated from the bark of the Indonesian medicinal plant Bhesa paniculata (Celastraceae). The chemical structures have been elucidated on the bases of their chemical and physiocochemical properties.

Carbohydrate Sequence↗
PubMed1999

Induction of a protective antibody response to foot and mouth disease virus in mice following oral or parenteral immunization with alfalfa transgenic plants expressing the viral structural protein VP1.

The utilization of transgenic plants expressing recombinant antigens to be used in the formulation of experimental immunogens has been recently communicated. We report here the development of transgenic plants of alfalfa expressing the structural protein VP1 of foot and mouth disease virus (FMDV). The presence of the transgenes in the plants was confirmed by PCR and their specific transcription was demonstrated by RT-PCR. Mice parenterally immunized using leaf extracts or receiving in their diet freshly harvested leaves from the transgenic plants developed a virus-specific immune response. Animals immunized by either method elicited a specific antibody response to a synthetic peptide representing amino acid residues 135-160 of VP1, to the structural protein VP1, and to intact FMDV particles. Additionally, the immunized mice were protected against experimental challenge with the virus. We believe this is the first report demonstrating the induction of a protective systemic antibody response in animals fed transgenic plants expressing a viral antigen. These results support the feasibility of producing edible vaccines in transgenic forage plants, such as alfalfa, commonly used in the diet of domestic animals even for those antigens for which a systemic immune response is required.

Administration, Oral↗