Isoprenyl diphosphate synthases (IDSs) catalyze some of the most basic steps in terpene biosynthesis by producing the prenyl diphosphate precursors of each of the various terpenoid classes. Most plants investigated have distinct enzymes that produce the short‐chain all‐trans (E) prenyl diphosphates geranyl diphosphate (GDP, C10), farnesyl diphosphate (FDP, C15) or geranylgeranyl diphosphate (GGDP, C20). In the genome of Arabidopsis thaliana, 15 trans‐product‐forming IDSs are present. Ten of these have recently been shown to produce GGDP by genetic complementation of a carotenoid pathway engineered into Escherichia coli. When verifying the product pattern of IDSs producing GGDP by a new LC‐MS/MS procedure, we found that five of these IDSs produce geranylfarnesyl diphosphate (GFDP, C25) instead of GGDP as their major product in enzyme assays performed in vitro. Over‐expression of one of the GFDP synthases in A. thaliana confirmed the production of GFDP in vivo. Enzyme assays with A. thaliana protein extracts from roots but not other organs showed formation of GFDP. Furthermore, GFDP itself was detected in root extracts. Subcellular localization studies in leaves indicated that four of the GFDP synthases were targeted to the plastoglobules of the chloroplast and one was targeted to the mitochondria. Sequence comparison and mutational studies showed that the size of the R group of the 5th amino acid residue N‐terminal to the first aspartate‐rich motif is responsible for C25 versus C20 product formation, with smaller R groups (Ala and Ser) resulting in GGDP (C20) as a product and a larger R group (Met) resulting in GFDP (C25).

BackgroundHelichrysum species are used extensively for stress-related ailments and as dressings for wounds normally encountered in circumcision rites, bruises, cuts and sores. It has been reported that Helichysum species are used to relief abdominal pain, heart burn, cough, cold, wounds, female sterility, menstrual pain.ResultsFrom the extracts of Helichrysum foetidum (L.) Moench, six known compounds were isolated and identified. They were 7, 4′-dihydroxy-5-methoxy-flavanone (1), 6′-methoxy-2′,4, 4′-trihydroxychalcone (2), 6′-methoxy-2′,4-dihydroxychalcone -4′-O-β-D-glucoside (3), apigenin (4), apigenin-7-O-β-D-glucoside (5), kaur-16-en-18-oic acid (6) while two known compounds 3,5,7-trihydroxy-8-methoxyflavone (12), 4,5-dicaffeoyl quinic acid (13) together with a mixture of phytosterol were isolated from the methanol extract of Helichrysum mechowianum Klatt. All the compounds were characterized by spectroscopic and mass spectrometric methods, and by comparison with literature data. Both extracts and all the isolates were screened for the protease inhibition, antibacterial and antifungal activities. In addition, the phytochemical profiles of both species were investigated by ESI-MS experiments.ConclusionsThese results showed that the protease inhibition assay of H. foetidum could be mainly attributed to the constituents of flavonoids glycosides (3, 5) while the compound (13) from H. mechowianum contributes to the stomach protecting effects. In addition, among the antibacterial and antifungal activities of all the isolates, compound (6) was found to possess a potent inhibitor effect against the tested microorganisms. The heterogeneity of the genus is also reflected in its phytochemical diversity. The differential bioactivities and determined constituents support the traditional use of the species. Molecular modelling was carried out by computing selected descriptors related to drug absorption, distribution, metabolism, excretion and toxicity (ADMET).

Antimicrobial peptides form part of the first line of defense against pathogens for many organisms. Current treatments for fungal infections are limited by drug toxicity and pathogen resistance. Cm-p5 (SRSELIVHQRLF), a peptide derived from the marine mollusk Cenchritis muricatus peptide Cm-p1, has a significantly increased fungistatic activity against pathogenic Candida albicans (minimal inhibitory concentration, 10 µg/ml; EC50, 1.146 µg/ml) while exhibiting low toxic effects against a cultured mammalian cell line. Cm-p5 as characterized by circular dichroism and nuclear magnetic resonance revealed an α-helical structure in membrane-mimetic conditions and a tendency to random coil folding in aqueous solutions. Additional studies modeling Cm-p5 binding to a phosphatidylserine bilayer in silico and isothermal titration calorimetry using lipid monophases demonstrated that Cm-p5 has a high affinity for the phospholipids of fungal membranes (phosphatidylserine and phosphatidylethanolamine), only moderate interactions with a mammalian membrane phospholipid, low interaction with ergosterol, and no interaction with chitin. Adhesion of Cm-p5 to living C. albicans cells was confirmed by fluorescence microscopy with FITC-labeled peptide. In a systemic candidiasis model in mice, intraperitoneal administration of Cm-p5 was unable to control the fungal kidney burden, although its low amphiphaticity could be modified to generate new derivatives with improved fungicidal activity and stability.

Alzheimer´s disease (AD) is the most common form of dementia affecting predominantly elderly people from developed countries. One aspect of the illness is that patients suffer from an impaired memory due to deposition of aggregated A-peptides forming amyloid plaques. According to the glutaminyl cyclase (QC) hypothesis this enzyme plays a key role in generating neurotoxic amyloid peptides (amyloid-β or Aβ) by modifying the N-terminus of peptides to N-pyroglutamated derivatives. These modified proteins are resistant to degradation and are at the same time “seeds” for the formation of toxic A-oligomers in the brain. In order to screen for natural inhibitors of QC, strains of different species of algae belonging to Chlorophyceae and Eustigmatophyceae were cultivated in 100 L tubular photobioreactors. The resulting crude extracts of algae from exponential and stationary growth phases were tested for their inhibition properties of glutaminyl cyclase (QC). Here 27 of the 72 tested extracts inhibited the QC. Fractions separated by Sephadex G-15 column chromatography also showed QC inhibition activity.

The interaction between floral oil secreting plants and oil-collecting bees is one of the most specialized of all pollination mutualisms. Yet, the specific stimuli used by the bees to locate their host flowers have remained elusive. This study identifies diacetin, a volatile acetylated glycerol, as a floral signal compound shared by unrelated oil plants from around the globe. Electrophysiological measurements of antennae and behavioural assays identified diacetin as the key volatile used by oil-collecting bees to locate their host flowers. Furthermore, electrophysiological measurements indicate that only oil-collecting bees are capable of detecting diacetin. The structural and obvious biosynthetic similarity between diacetin and associated floral oils make it a reliable cue for oil-collecting bees. It is easily perceived by oil bees, but can’t be detected by other potential pollinators. Therefore, diacetin represents the first demonstrated private communication channel in a pollination system.

Four new 11‐mer peptaibols, named albupeptins A–D (1–4), were isolated from cultures of the fungus Gliocladium album. Their structures were elucidated on the basis of 1D and 2D NMR spectroscopy, as well as ESI‐HRMSn analysis. The sequence of albupeptin A (1) was thus identified as Ac‐Aib1‐Aib2‐Val3‐Leu4‐Aib5‐Pro6‐Iva7‐Leu8‐Gln9‐Aib10‐Leuol11. Albupeptins B (2) and C (3) feature an exchange of Aib5 by Iva5 and of Aib1 by Iva1, respectively, and albupeptin D (4) contains both Iva1 and Iva5 residues. The stereochemistry of the isolated peptaibols 1–4 was unambiguously assigned by 1H NMR chemical shift analysis in conjunction with solid‐phase peptide synthesis. By using this approach, the absolute configuration of the Iva residues in albupeptins A (1) and C (3) was determined to be D, whereas albupeptins B (2) and D (4) feature an additional Iva5 residue with an L configuration. Thus, albupeptins B (2) and D (4) belong to the rare class of peptaibols that have both stereoisomers of Iva in the same sequence.

The hitherto unknown natural formation of hygrophorones, antibacterial and antifungal cyclopentenone derivatives from mushrooms, was investigated for hygrophorone B12 in Hygrophorus abieticola Krieglst. ex Gröger & Bresinsky by feeding experiments in the field using 13C labelled samples of d-glucose and sodium acetate. The incorporation of 13C isotopes was extensively studied using 1D and 2D NMR spectroscopy as well as ESI-HRMS analyses. In the experiment with [U-13C6]-glucose, six different 13C2 labelled isotopomers were observed in the 2D INADEQUATE spectrum due to incorporation of [1,2-13C2]-acetyl-CoA. This labelling pattern demonstrated that hygrophorone B12 is derived from a fatty acid-polyketide route instead of a 1,4-α-d-glucan derived anhydrofructose pathway. The experiment with [2-13C]-acetate revealed an unexpected incorporation pattern in the cyclopentenone functionality of hygrophorone B12. Four single-labelled isotopomers, in particular [1-13C]-, [2-13C]-, [3-13C]-, and [4-13C]-hygrophorone B12, were detected that showed only half enrichment in comparison to the respective labelled alkyl side chain carbons. This labelling pattern indicates the formation of a symmetrical intermediate during hygrophorone B12 biosynthesis. Based on these observations, a biogenetic route via a 4-oxo fatty acid and a chrysotrione B homologue is discussed.

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Hygrophorone B12, a new antifungal constituent from the fruiting bodies of Hygrophorus abieticola, has been isolated and subsquently synthesized in enantiomerically pure form. The total synthesis includes a Sharpless asymmetric dihydroxylation protocol as the stereodifferentiating step, followed by two diastereoselective aldol‐type reactions. The approach allows the unambiguous control of all three stereogenic centres, and, furthermore, unequivocal determination of the relative and absolute configuration of antibiotic hygrophorones B for the first time.

Despite recent advances in studies on trade‐offs between plant defence traits, little is known about whether trade‐offs reflect (i) evolutionary constraints at the species level or (ii) allocation constraints at the individual level. Here, we asked to which degree physical and chemical carbon‐based leaf defence traits covary within and across species.We assessed leaf toughness, leaf total phenolic and tannin concentrations for 51 subtropical tree species. Species trait means, sample‐specific values and phylogenetically independent contrasts were used in regression analyses. Phylogenetic signals and trait evolution were assessed along the phylogeny.Analyses of species‐level trait means revealed significant negative trait covariations between physical and chemical defence traits in analyses over all species. These covariations were inconsistent at the within‐species level. All three defence aspects showed strong phylogenetic signals, but differed in the degree of conservatism along the phylogeny. Inclusion of intraspecific trait variability significantly decreased the strength of these covariations. Strong negative covariations were detected between physical and chemical defence traits when phylogenetic non‐independence was accounted for.Synthesis. We addressed two sources of variation (allocation and evolution) independently from each other in the context of trait interrelationships. The observed negative covariations hint at the existence of a trade‐off between physical and chemical defence traits. The finding that intraspecific trait variation contributed less to this relationship suggests that the trade‐off is dominated by evolutionary constraints rather than by carbon allocation constraints.