Neutralization of mobile antiviral small RNA through peroxisomal import.

In animals, certain viral proteins are targeted to peroxisomes to dampen the antiviral immune response mediated by these organelles1-3. In plants, RNA interference (RNAi) mediated by small interfering (si)RNA is the main antiviral defence mechanism. To protect themselves against the cell- and non-cell autonomous effects of RNAi, viruses produce viral suppressors of RNA silencing (VSR)4, whose study is crucial to properly understand the biological cycle of plant viruses and potentially find new solutions to control these pathogens. By combining biochemical approaches, cell-specific inhibition of RNAi movement and peroxisome isolation, we show here that one such VSR, the peanut clump virus (PCV)-encoded P15, isolates siRNA from the symplasm by delivering them into the peroxisomal matrix. Infection with PCV lacking this ability reveals that piggybacking of these VSR-bound nucleic acids into peroxisomes potentiates viral systemic movement by preventing the spread of antiviral siRNA. Collectively, these results highlight organellar confinement of antiviral molecules as a novel pathogenic strategy that may have its direct counterpart in other plant and animal viruses.

The chemical structure of mumbaistatin, a novel glucose-6-phosphate translocase inhibitor produced by Streptomyces sp. DSM 11641.

The characterization of the structure of mumbaistatin (1), an effective inhibitor of the glucose-6-phosphatase system (EC 3.1.3.9), is reported. Isolation of mumbaistatin from cultures of Streptomyces sp. DSM 11641 was achieved by anion-exchange and reversed-phase chromatography. The acid-labile inhibitor was methylated for the structure determination. Single-crystal X-ray structure analysis of a triply methylated dehydration product, C31H24O11, revealed the structure of an aromatic dispirodiketal (2), a compound containing a previously undescribed ring system. Extensive 2D-NMR experiments with mumbaistatin and with the methylation products showed that mumbaistatin itself possesses the hydroxydiketodicarboxylic acid structure 1, C28H20O12, which, in the presence of acid or upon activation through methyl ester formation, undergoes self-condensation with loss of water to the dispirodiketal form (2). Mumbaistatin is an anthraquinone derivative, whose open-chain diketo form acts as a specific and powerful inhibitor of glucose-6-phosphate translocase: IC50=5 nM. The activity towards the same enzyme of the cyclized dispirodiketal derivatives is roughly one thousand times lower.

Friulimicins: novel lipopeptide antibiotics with peptidoglycan synthesis inhibiting activity from Actinoplanes friuliensis sp. nov. II. Isolation and structural characterization.

Four novel lipopeptide antibiotics, friulimicins A, B, C, and D, were isolated from cultures of Actinoplanes friuliensis HAG 010964 after fermentation in different nutrient media. The new compounds were separated by ion-exchange chromatography from the acidic lipopeptides of the amphomycin type also present in the culture fluid, compounds A-1437 A, B, E, and G. The principal constituent friulimicin B, C59H94N14O19, was structurally characterized by mass spectrometric investigations of its hydrolysis and partial degradation products and by sequencing of the cyclic acyl peptide. The NMR data of friulimycin B and the amphomycin constituent A-1437 B were completely assigned by a variety of 2-D experiments, and confirmed the structures determined by mass spectrometry. All 8 lipopeptides possess an identical peptide macrocycle as their central element, linked via a diaminobutyric acid N-terminal either to an acylated asparagine residue or, in the case of the amphomycin series, to an acylated aspartic acid residue. The structures of the amphomycins have now been revised to take account of the peptide framework described herein and the determined cis-configuration of the exocyclic double bond. As a consequence of their higher isoelectric points, the new compounds friulimicin A, B, C, and D have different properties than the amphomycins.

Kodaistatins, novel inhibitors of glucose-6-phosphate translocase T1 from Aspergillus terreus thom DSM 11247. Isolation and structural elucidation.

Two novel compounds, kodaistatin A, C35H34O11, molecular weight 630, and kodaistatin C, C35H34O12, molecular weight 646, have been isolated from cultures of Aspergillus terreus Thom DSM 11247 by solid-phase extraction, size-exclusion chromatography, and various preparative HPLC steps. The use of a range of 2D NMR measurements, in particular 13C-13C correlation measurements, has led to the clarification of the structure of kodaistatin A. Kodaistatin C is a hydroxylated derivative of kodaistatin A. Both natural products contain hydroxylated aspulvinones and identical highly substituted polyketide units. An X-ray single crystal structure analysis of aspulvinon E demonstrated the z-configuration at the central double bond. The kodaistatins are effective inhibitors of the glucose-6-phosphate translocase component of the glucose-6-phosphatase system (EC 3.1.3.9), an enzyme system which is important for the control of blood glucose levels. The IC50 is 80 nM for kodaistatin A and 130 nM for kodaistatin C.

Sequence and functional analysis of the left-hand part of the T-region from the nopaline-type Ti plasmid, pTiC58.

The Agrobacterium tumefaciens nopaline strain C58 transfers a large, 29 kb T-DNA into plant cells during infection. Part of this DNA (the 'common DNA') is also found on the T-DNA of octopine strains, the remaining DNA is nopaline strain-specific. Up to now, only parts of the C58 T-DNA and related T37 T-DNA have been sequenced. We have sequenced the remainder of the nopaline-specific T-DNA (containing genes a to d) and acs to iaaM. Gene c codes for a new unknown T-DNA protein. Gene a is homologous to the agrocinopine synthase gene. Genes b, c', d and e are part of a larger family: they are related to the T-DNA genes 5, rolB, lso and 3'. Genes 5, rolB and lso induce or modify plant growth and have been called T-DNA oncogenes. Our studies show that gene 3' (located on the TR-DNA of octopine strains) is also oncogenic. Although the b-e T-DNA fragment from C58 and its individual genes lack growth-inducing activity, an a-acs deletion mutant was distinctly less virulent on Kalanchoe daigremontiana and showed reduced shoot formation on Kalanchoe tubiflora. Shoot formation could be restored by genes c and c' in co-infection experiments. Contrary to an earlier report, a C58 e gene deletion mutant was fully virulent on all plants tested.

Secondary metabolites by chemical screening. 17. Nigericinol derivatives: synthesis, biological activities, and modeling studies.

The synthesis and the biological activity of C-1-reduced nigericin derivatives (nigericinols) are described and discussed. The dichloronigericinol 7 impressively demonstrated that the C-1 carboxylic acid moiety was not required for a distinct activity against bacteria and viruses. Based on the correlation between K+/H+ antiport activities and antibacterial activities it was deduced that the mode of action of the described nigericinols are related to their ionophoric properties. Molecular modeling studies showed that the efficiency of the nigericinols as ionophores correlates, qualitatively, with the probability of forming a cyclic structure, with the exception of 7.

Secondary metabolites by chemical screening. 7. I. Elaiophylin derivatives and their biological activities.

The synthesis and the biological activity of 34 acyl derivatives of elaiophylin (1) and 6 deglycosidation products were described. Especially the unsymmetric deglycosidation products 33, 38 and 40 and dimethyloctahydroelaiophylin (21) exhibited an activity against nematodes.

Secondary metabolites by chemical screening: II. Amycins A and B two novel niphimycin analogs isolated from a high producer strain of elaiophylin and nigericin.

Two novel natural niphimycin analogs, amycins A (5) and B (3) were isolated from the culture broth of the Streptomyces sp. DSM 3816 by chemical screening methods. In addition this strain produces the antibiotics niphimycin (4), elaiophylin (2) and nigericin (1). Fermentation, isolation, structure elucidation and biological activity of the amycins are described.

The influence of structural modification on progesterone and androgen receptor binding of norethisterone. Correlation with nuclear magnetic resonance signals.

The relative binding affinities (RBA) of eight progestogens structurally derived from 17 alpha-ethinyl-19-nortestosterone (norethisterone) have been estimated a) for the progesterone receptor from human premenopausal endometrium and b) for the androgen receptor in human mammary carcinoma in vitro. Introduction of a methylene group at C-11, a methyl group at C-18, or a double bond between C-15 and C-16 of the norethisterone molecule increases the RBA to the progesterone receptor. As a rough approximation, the substituent effects seem to be additive. RBA to the androgen receptor follows a more complex pattern when norethisterone is structurally modified. An additional methyl at C-18 enhances affinity to the androgen receptor. The double bond between C-15 and C-16 has no effect except when introduced into desogestrel, where it reduces RBA to the lowest value in the study. The methylene group at C-11 increases androgen RBA when present as the only substituent, but reduces androgen RBA when together with any other substituent. The complete assignment of 13C-NMR signals has been achieved for all 8 steroids investigated. The 13C-resonance signal of C-17 shows a correlation with the RBA to the progesterone receptor, and with the progestogen/androgen RBA ratios.