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G A Strobel

Publications and source records attributed to G A Strobel.

At least 19 recordsLinked to original sources
PubMed2001

Characterization of stereochemistry and molecular conformation using solid-state NMR tensors.

A solid-state NMR technique is described for establishing stereochemistry using the natural product terrein as a model compound. This method involves comparison of experimental (13)C tensor principal values with ab initio computed values for all possible computer-generated stereoisomers. In terrein the relative stereochemistry is confirmed by NMR to be 2R*,3S with high statistical probability (>99.5%). The proposed approach also simultaneously verifies the molecular conformation of the two hydroxy groups in terrein established by X-ray data. It is sufficient to use only shift tensor values at carbons 2 and 3, the stereocenters, to characterize both the stereochemistry and molecular conformations. The solid-state NMR method appears to be especially useful for determining relative stereochemistry of compounds or their derivatives that are difficult to crystallize.

Carbon Isotopes↗
PubMed2001

Ambuic acid, a highly functionalized cyclohexenone with antifungal activity from Pestalotiopsis spp. and Monochaetia sp.

Ambuic acid, a highly functionalized cyclohexenone, was isolated and characterized from Pestalotiopsis spp. and Monochaetia sp. these being biologically related endophytic fungi associated with many tropical plant species. This compound was found in representative isolates of these fungal species obtained from rainforest plants located on several continents. The relevance of ambuic acid to the biology of the association of these fungi to their host plants is also discussed.

Antifungal Agents↗
PubMed2001

Jesterone and hydroxy-jesterone antioomycete cyclohexenone epoxides from the endophytic fungus Pestalotiopsis jesteri.

Jesterone and hydroxy-jesterone are novel highly functionalized cyclohexenone epoxides isolated from a newly described endophytic fungal species--Pestalotiopsis jesteri. They were purified from cultures of the fungus by bioassay guided fractionation using Pythium ultimum as the indicator organism. Jesterone, in particular, displays selective antimycotic activity against the oomycetous fungi which are some of the most plant pathogenic of all disease causing fungi. The possible importance of these cyclohexenones to the biology of the endophytic fungus-host plant relationship is also discussed.

Alkenes↗
PubMed2001

Two telomerase reverse transcriptases (TERTs) expressed in Candida albicans.

The human pathogenic yeast Candida albicans contains two telomerase reverse transcriptase (TERT) genes. CaTERT1 and CaTERT2 appear either to be two alleles of the same gene or two entirely different genes that encode 867-residue proteins that differ by five amino acids. Both TERTs have a calculated pI of 9.5 and a M(r) of 100.9 kDa and are the smallest TERTs identified to date. Both genes appear to be expressed. Based on sequence similarity between CaTERT1 and the Saccharomyces cerevisiae orthologue Est2p, we suggest a revised alignment for motif E of Est2p. The identification of these TERT genes provides the first opportunity to study telomerase in an important human pathogen.

Alleles↗
PubMed2001

Evidence for paclitaxel from three new endophytic fungi of Himalayan yew of Nepal.

Taxus wallichiana, collected from the Himalayan region of Nepal, yielded, among others, three different endophytic fungi including Sporormia minima, Trichothecium sp., and an unidentified dimorphic fungus. Each was shown to produce paclitaxel in a culture medium. Each of these fungi represents a new report as a paclitaxel producer. The production of paclitaxel was confirmed by an immunoassay that utilized monoclonal antibodies, TLC chromatography as well as high performance liquid chromatography combined with on-line mass spectrometry.

Antibodies, Monoclonal↗
PubMed2001

Volatile antimicrobials from Muscodor albus, a novel endophytic fungus.

Muscodor albus is a recently described endophytic fungus obtained from small limbs of Cinnamomum zeylanicum (cinnamon tree). This xylariaceaous fungus effectively inhibits and kills certain other fungi, and bacteria, by virtue of a mixture of volatile compounds that it produces. The majority of these compounds were identified by gas chromatography/mass spectrometry and then made into an artificial mixture that mimicked the antibiotic effects of the mixture of volatile compounds given off by the fungus. Each of the five classes of volatile compounds produced by the fungus (alcohols, esters, ketones, acids and lipids) had some inhibitory effect against the test fungi and bacteria, but none was lethal. However, collectively they acted synergistically to kill a broad range of plant- and human-pathogenic fungi and bacteria. The most effective class of inhibitory compounds was the esters, of which 1-butanol, 3-methyl-, acetate was the most active biologically. This report describes the ecological implications and potential practical benefits of the 'mycofumigation' effects of M. albus.

Aldehydes↗
PubMed1999

Seimatoantlerium tepuiense gen. nov., a unique epiphytic fungus producing taxol from the Venezuelan Guyana.

Seimatoantlerium gen. nov., type species, S. tepuiense sp. nov. is proposed for an acervular fungus producing 4-septate, holoblastic conidia with 6-8 unbranched, apical appendages that dehisce as an appendage apparatus and also commonly possessing one or two exogenous basal appendages as well as a pedicel. It is compared with Seimatosporium, Seimatosporiopsis, and other genera. It is epiphytic on Maguireothamnus speciosus, a rubiaceous plant endemic to the tepuis of southeastern Venezuela. It produces the anti-oomycetous anticancer compound, taxol, as shown by immunological and spectroscopic methods. Taxol production is discussed relative to the ability of this fungus to exist in an extremely moist ecosystem, as well as to its relationship to other plant associated fungi.

Antineoplastic Agents, Phytogenic↗
PubMed1998

In vivo addition of telomeric repeats to foreign DNA generates extrachromosomal DNAs in the taxol-producing fungus Pestalotiopsis microspora.

Transformation of the taxol-producing filamentous fungus Pestalotiopsis microspora with a plasmid containing the bacterial hygromycin resistance gene fused to Aspergillus regulatory sequences resulted in the in vivo formation of extrachromosomal DNAs with telomeric repeats in the majority of transformants. Repeats of the telomeric sequence 5'-TTAGGG-3' were appended to nontelomeric transforming DNA termini. No fungal sequences other than telomeric repeats were detected in extrachromosomal DNAs. Transformants contained three to six different sizes or conformational forms of extrachromosomal DNAs. The DNAs showed no change in size or internal structure during 6 months of growth with selection, but were lost after 20 days of growth without selection. Transformation of wild-type P. microspora with a PCR-amplified extrachromosomal DNA having terminal telomeric repeats produced up to 50-fold more transformants than the original transformation vector. The addition of telomeric repeats to foreign DNA is unusual among fungi and may have important adaptive or developmental implications.

Aspergillus nidulans↗
PubMed1998

Ecomycins, unique antimycotics from Pseudomonas viridiflava.

A novel family of peptide antimycotics, termed ecomycins, is described from Pseudomonas viridiflava, a plant-associated bacterium. Ecomycins B and C have molecular masses of 1153 and 1181. They contain equimolar amounts of a beta hydroxyaspartic acid, homoserine, threonine, serine, alanine, glycine and one unknown amino acid. Fatty acids were detectable after hydrolysis, methylation and gas chromatography and mass spectroscopy. The ecomycins have significant bioactivities against a wide range of human and plant pathogenic fungi. The minimum inhibitory concentration values for ecomycin B were 4.0 micrograms ml-1 against Cryptococcus neoformans and 31 micrograms ml-1 against Candida albicans. Pseudomonas viridiflava also produces what appears to be syringotoxin, an antifungal lipopeptide previously described from Ps. syringae.

Amino Acids↗
PubMed1997

Glucosylation of the peptide leucinostatin A, produced by an endophytic fungus of European yew, may protect the host from leucinostatin toxicity.

BACKGROUND: Yew species (Taxus spp.) throughout the world are hosts to hundreds, or perhaps thousands, of endophytic organisms. Most commonly, these organisms are fungi, living in a commensal or a symbiotic relationship with their host plant, so the plants exhibit little or no outward evidence that they are supporting these microorganisms. Little is known about any of the biochemical mechanisms that mediate the interactions between the yew host and its associated microbes. We feel that such information may not only contribute to our understanding of endophyte-tree biology, but also may provide novel pharmaceutical leads, because some of the compounds produced by these endophytes have demonstrated pharmacological activities. RESULTS: Acremonium sp. was isolated as an endophytic fungus of the European yew, Taxus baccata. Entry of Acremonium sp. into the plant may proceed via invasion of natural openings such as stomata. The relationship between Acremonium sp. and T. baccata may be a symbiotic one, because no symptoms are seen when Taxus media p.v. Hicksii is inoculated with this fungus. In culture, the fungus makes leucinostatin A, a peptide with phytotoxic, anticancer and antifungal properties. Although this peptide causes necrotic symptoms in many non-host plants and other cell types, it causes no visible symptoms in the host plant. T. baccata and several other plants have a UDP glucose; leucinostatin A glucosyl transferase that catalyzes the production of leucinostatin A beta di-O-glucoside from leucinostatin A. This glucoside, also made by the fungus, has a lower bioactivity against plants, fungi and a breast cancer cell line, BT-20, than leucinostatin A. CONCLUSIONS: Leucinostatin A may be one of several potentially toxic peptides produced by Acremonium sp. that contribute to the defense of the host, thereby preserving the fungus' own biological niche. The host plant is relatively immune to leucinostatin A because it has an enzyme which transfers two glycosyl residues to leucinostatin A, markedly reducing the peptide's bioactivity. Our results suggest that glucosylation reactions may play a more general role in plant defenses, especially against toxin-mediated disease development.

Acremonium↗
PubMed1996

A scanning electron microscopy study of Taxus leaves as related to taxonomy.

Scanning electron microscopy, when applied to the surfaces of the needles of Taxus spp. (yew) revealed features that appear useful in the taxonomy of this tree species which yields the important anticancer drug, taxol. For instance, all of the four North American species have 3-5 rows of stomata on one-half of the abaxial leaf surface, whereas all of the others, including those from Europe and Asia, have 7-10 rows of stomata. The appearance of individual or fused papilliform epidermal cells and their arrangement on the leaf surface also is a feature that varies between species. Patterns of wax formation appeared on all species of yew examined but none could characteristically be assigned to a given species. Wax pattern variation was dependent upon age, environment, and probably to some extent, species differences. This study may provide some additional useful and reliable indicators in Taxus taxonomy.

Microscopy, Electron, Scanning↗
PubMed1994

Novel bioactive lipodepsipeptides from Pseudomonas syringae: the pseudomycins.

The covalent structure and most of the stereochemistry of the pseudomycins, bioactive metabolites of a transposon-generated mutant of a Pseudomonas syringae wild-type strain proposed for the biological control of Dutch elm disease, have been determined. While two pseudomycins are identical to the known syringopeptins 25-A and 25-B, pseudomycins A, B, C, C' are new lipodepsinonapeptides. For all of these the peptide moiety corresponds to L-Ser-D-Dab-L-Asp-L-Lys-L-Dab-L-aThr-Z-Dhb-L-Asp(3-OH) -L-Thr (4-Cl) with the terminal carboxyl group closing a macrocyclic ring on the OH group of the N-terminal Ser. This is in turn N-acylated by 3,4-dihydroxytetradecanoate in pseudomycin A, by 3-hydroxytetradecanoate in pseudomycin B, by 3,4-dihydroxyhexadecanoate in pseudomycin C, and by 3-hydroxyhexadecanoate in pseudomycin C'. Some preliminary data on the biological activity of pseudomycin A are reported.

Amino Acid Sequence↗
PubMed1994

Cellular protein receptors of maculosin, a host specific phytotoxin of spotted knapweed (Centaurea maculosa L.).

Maculosin (the diketopiperazine, cyclo (L-Pro-L-Tyr)) is a host specific phytotoxin produced by Alternaria alternata on spotted knapweed (Centaurea maculosa L.). Receptors for this phytotoxin have been isolated from spotted knapweed. Knapweed leaves possess most of the maculosin-binding activity in the cytosolic fraction. However, activity was also observed in the whole membrane fraction of the leaf. The binding component of the cytosolic fraction was identified as a protein(s) because of its heat-lability and sensitivity to proteases. A 16-fold purification of a toxin-binding protein was carried out by ammonium sulfate fractionation, and Sephadex G-200, and maculosin-affinity column chromatography. The affinity column was prepared with epoxy activated Sepharose 6B to which the phenolic group of maculosin was attached. The receptor was estimated to contain more than one binding protein by native and SDS-PAGE. At least one of the maculosin-binding proteins was identified as ribulose-1,5-biphosphate carboxylase (RuBPcase).

Binding Sites↗
PubMed1982

Phytotoxins.

Explore the source record for details and available documents.

Alternaria↗
PubMed1980

Inverse relationship of protein concentration and binding activity of alpha-galactoside receptors from sugarcane membranes.

1. The binding activity of purified alpha-galactoside receptor proteins from a number of plant species decreases when the protein concentration is increased from 2 ng/ml to 100 micrograms/ml. 2. The apparent loss of binding activity at high protein concentrations corresonds to the formation of high molecular weight multimers. 3. Raffinose and melibiose cause a ligant-dependent increase in binding activity and a corresponding decrease in the relative abundance of multimers at any give protein concentration. 4. The self-inhibition of binding activity at high protein concentrations arises from a competition between ligant binding by oligomers and self-association of these oligomers into multimeric species which have little or no binding acitivity.

Binding, Competitive↗
PubMed1979

The relationship between membrane ATPase activity in sugarcane and heat-induced resistance to helminthosporoside.

1. Heating of susceptible sugarcane leaves (4 h at 35 degrees C) renders them resistant, for 24 h, to the effects of helminthosporoside. Membrane ATPase activity is reduced by 50% as a result of the heat treatment. When the leaves again become susceptible (after 24 h), membrane. ATPase activity is fully restored. 2. Inhibitors of membrane ATPase activity protect susceptible leaves from the effects of helminthosporoside (KF, EDTA, and octylguanidine). 3. Helminthosporoside activates (30%) membrane ATPase in microsomes from susceptible, but not heat-treated (resistant) leaves. Once heat-treated leaves again become susceptible, helminthosporoside activation of membrane ATPase activity resumes. 4. A plot of the production of helminthosporoside-induced symptoms, and membrane ATPase activity as a function of the reciprocal of the absolute temperature reveals that both have sharp breaks at 32 degrees C. 5. Protoplasts of susceptible cane are rendered insensitivity to the effects of the toxin in a medium deficient in K+ and Mg2+. When these ions are added, cell sensitivity to the toxin is restored. Since K+ uptake in plants is mediated by membrane ATPase, a connection with this enzyme activity can be made to cell sensitivity to the toxin.

Adenosine Triphosphatases↗
PubMed1977

Bacterial phytotoxins.

Representatives of all of the major genera of plant disease-causing bacteria have been shown to produce one or more phytotoxins. Toxicological studies on the bacterial diseases of the major food crops have not been extensive. Bacterial phytotoxins belong to a number of classes of organic substances, including peptide, derivatized amino acid, polysaccharide, and glycopeptide. The mechanism of action of these compounds is largely unknown, as is their origin and importance in the disease syndrome. Nevertheless, some progress has been made in these areas in isolated cases. There is a tremendous potential in the future for studies on the bacterial phytotoxins.

Bacterial Proteins↗