Isolation & characterization of malformin

Calm Before the Storm: A Glimpse into the Secondary Metabolism of Aspergillus welwitschiae, the Etiologic Agent of the Sisal Bole Rot

Aspergillus welwitschiae is a species of the Nigri section of the genus Aspergillus. In nature, it is usually a saprotroph, decomposing plant material. However, it causes the bole rot disease of Agave sisalana (sisal), a plant species used for the extraction of hard natural fibers, causing great economic loss to this culture. In this study, we isolated and sequenced one genome of A. welwitschiae (isolate CCMB 674 (Collection of Cultures of Microorganisms of Bahia)) from the stem tissues of sisal and performed in silico and wet lab experimental strategies to describe its ability to produce mycotoxins. CCMB 674 possesses 64 secondary metabolite gene clusters (SMGCs) and, under normal conditions, it produces secondary metabolism compounds that could disturb the cellular cycle of sisal or induce abnormalities in plant growth, such as malformin C. This isolate also produces a pigment that might explain the characteristic red color of the affected tissues. Additionally, this isolate is defective for the production of fumonisin B1, and, despite bearing the full cluster for the synthesis of this compound, it did not produce ochratoxin A. Altogether, these results provide new information on possible strategies used by the fungi during the sisal bole rot, helping to better understand this disease and how to control it.

Genome-Scale CRISPR/Cas9 Screening Reveals Squalene Epoxidase as a Susceptibility Factor for Cytotoxicity of Malformin A1

Malformin A1 (MA1) is a fungus-produced cyclic pentapeptide. MA1 exhibits teratogenicity to plants, fibrinolysis-enhancing activity, and cytotoxicity to mammalian cells. To clarify the cytotoxic mechanism of MA1, we screened for the genes involved in the cytotoxicity of MA1 in monocytoid U937 cells by using a CRISPR/Cas9-based genome-wide knockout library. Screening was performed by positive selection for cells that were resistant to MA1 treatment, and single guide RNAs (sgRNAs) integrated into MA1-resistant cells were analyzed by high-throughput sequencing. As a result of the evaluation of sgRNAs that were enriched in MA1-resistant cells, SQLE, which encodes squalene epoxidase, was identified as a candidate gene. SQLE-depleted U937 cells were viable in the presence of MA1, and squalene epoxidase inhibitor conferred MA1 resistance to wild-type cells. These results indicate that squalene epoxidase is implicated in the cytotoxicity of MA1. This finding represents a new insight into applications of MA1 for treating ischemic diseases.

Involvement of RSK1 activation in malformin-enhanced cellular fibrinolytic activity

Pharmacological interventions to enhance fibrinolysis are effective for treating thrombotic disorders. Utilizing the in vitro U937 cell line-based fibrin degradation assay, we had previously found a cyclic pentapeptide malformin A₁ (MA₁) as a novel activating compound for cellular fibrinolytic activity. The mechanism by which MA₁ enhances cellular fibrinolytic activity remains unknown. In the present study, we show that RSK1 is a crucial mediator of MA₁-induced cellular fibrinolysis. Treatment with rhodamine-conjugated MA₁ showed that MA₁ localizes mainly in the cytoplasm of U937 cells. Screening with an antibody macroarray revealed that MA₁ induces the phosphorylation of RSK1 at Ser380 in U937 cells. SL0101, an inhibitor of RSK, inhibited MA₁-induced fibrinolytic activity, and CRISPR/Cas9-mediated knockout of RSK1 but not RSK2 suppressed MA₁-enhanced fibrinolysis in U937 cells. Synthetic active MA₁ derivatives also induced the phosphorylation of RSK1. Furthermore, MA₁ treatment stimulated phosphorylation of ERK1/2 and MEK1/2. PD98059, an inhibitor of MEK1/2, inhibited MA₁-induced phosphorylation of RSK1 and ERK1/2, indicating that MA₁ induces the activation of the MEK-ERK-RSK pathway. Moreover, MA₁ upregulated the expression of urokinase-type plasminogen activator (uPA) and increased uPA secretion. These inductions were abrogated in RSK1 knockout cells. These results indicate that RSK1 is a key regulator of MA₁-induced extracellular fibrinolytic activity.

Structure-activity relationship of cyclic pentapeptide malformins as fibrinolysis enhancers

The formation of blood clots in blood vessels causes severe ischemic diseases such as cerebral infarction and myocardial infarction. While searching for microbial products that increase fibrinolytic activity using an in vitro fibrin degradation assay, we found malformin A1, a disulfide form of cyclo(-d-Cys-d-Cys-l-Val-d-Leu-l-Ile-), as an active compound. In this study, we synthesized malformin derivatives using a solid-phase peptide synthesis method and evaluated their fibrinolytic activity and cytotoxicity. Reduction of the disulfide bond and linearization of the cyclic peptide frame decreased the pro-fibrinolytic activity. Substitution of a branched-chain amino acid with lysine resulted in loss of activity. However, protection of the amino group in the lysine derivatives by the tert-butoxycarbonyl (Boc) group rescued the inactivity. Furthermore, the phenylalanine derivatives also exhibited a similar pro-fibrinolytic effect compared to malformin A1. These results suggest that the disulfide bond, the cyclic peptide frame, and the bulky hydrophobic side chains play a crucial role in the pro-fibrinolytic activity of malformin. The effective dose of the active derivatives for the in vitro fibrin degradation showed similar ranges (1-5μM), while the order of cytotoxic potency for the active derivatives was as follows: Phe-derivatives>BocLys-derivatives>malformin A1>reduced form. These results showed no correlation between pro-fibrinolytic activity and cytotoxicity, suggesting the possibility of the synthesis for non-toxic malformin derivatives possessing the activity.

Malformin A1 promotes cell death through induction of apoptosis, necrosis and autophagy in prostate cancer cells

PURPOSE

Malformin A1 (MA1), a cyclopentapeptide isolated from fungal origin, has been identified to induce varieties of intriguing biological activities. Here, we reported the mode of mechanism underlying MA1-mediated cytotoxicity through induction of apoptosis, necrosis and autophagy in prostate cancer (PCa) cells.

METHODS

Human PCa cells PC3 and LNCaP were treated with MA1, and cell viability, apoptosis, necrosis, mitochondrial damage, oxidative stress and autophagy were analyzed, respectively. Pharmacological inhibitors, transient transfection of plasmids and siRNAs were then used to identify the roles of oxidative stress and autophagy in MA1-triggered cell death.

RESULTS

In both PC3 and LNCaP cells, MA1 inhibited cell proliferation and triggered oxidative stress via the rapid accumulation of reactive oxygen species and a decrease in mitochondrial transmembrane potential. Mitochondrial damage by MA1 triggered caspase activation and intracellular ATP deletion, leading to apoptosis and necrosis, respectively. Meanwhile, MA1 activated autophagy as indicated by conversion of LC3BI to LC3BII and increased GFP-tagged LC3B punctate dots. Pharmacological inhibition of autophagy or knocking down LC3B attenuated MA1-mediated cell death. Excessive oxidative stress and decreased ATP stimulated AMPK/mTOR pathway, which led to induction of MA1-mediated autophagy.

CONCLUSIONS

Coaction of apoptotic, necrotic and autophagic cell death induced by mitochondrial damage defines a novel mechanism contributing to the growth suppression of MA1 in prostate cancer cells, and activation of autophagy might be a potential strategy for improving its chemotherapeutic effects.

Macrocycles as potential therapeutic agents in neglected diseases

Macrocycles possess desirable properties that make them promising candidates for the discovery of novel drugs. They present structural features to favor bioactive conformations, selectivity to the receptors, cell permeability and metabolic stability. More effective and nontoxic drugs to cure human African trypanosomiasis, Leishmaniasis and Chagas disease are needed, especially because resistance has been detected. Therefore, major efforts should be made for investigation in new bioactive compounds exhibiting different mechanisms of action. Macrocycles might fulfill the expectations for the development of new drugs to treat those diseases. In the current review, we focus on macrocycles exhibiting biological activities as antitrypanosomal and/or antileishmanial. The isolation, synthetic and biological studies of this class of compounds published from 2005 to 2014 are summarized.

Disulfide-bridged peptide macrobicycles from nature

This review highlights known disulfide-bridged peptide bicycles and the studies on their unique structural and biological features.

Solid-phase synthesis and biological activity of malformin C and its derivatives

We accomplished the solid-phase total synthesis of malformin C, which is adaptable for the easy preparation of various derivatives. A solid-phase total synthesis of malformin C was achieved by on-resin macrolactamization and disulfide bond formation, with concurrent cleavage from the resin. Antimalarial and antitrypanosomal activities were examined, which helped elucidate partial structure-activity relationships. Results indicate that the disulfide bond is essential and branched amino acids are also crucial components if the compound is to exhibit potent antimalarial and antitrypanosomal properties.

Review of secondary metabolites and mycotoxins from the Aspergillus niger group

Filamentous fungi in the Aspergillus section Nigri (the black aspergilli) represent some of the most widespread food and feed contaminants known but they are also some of the most important workhorses used by the biotechnological industry. The Nigri section consists of six commonly found species (excluding A. aculeatus and its close relatives) from which currently 145 different secondary metabolites have been isolated and/or detected. From a human and animal safety point of view, the mycotoxins ochratoxin A (from A. carbonarius and less frequently A. niger) and fumonisin B(2) (from A. niger) are currently the most problematic compounds. Especially in foods and feeds such as coffee, nuts, dried fruits, and grape-based products where fumonisin-producing fusaria are not a problem, fumonisins pose a risk. Moreover, compounds such as malformins, naptho-gamma-pyrones, and bicoumarins (kotanins) call for monitoring in food, feed, and biotechnology products as well as for a better toxicological evaluation, since they are often produced in large amounts by the black aspergilli. For chemical differentiation/identification of the less toxic species the diketopiperazine asperazine can be used as a positive marker since it is consistently produced by A. tubingensis (177 of 177 strains tested) and A. acidus (47 of 47 strains tested) but never by A. niger (140 strains tested). Naptho-gamma-pyrones are the compounds produced in the highest quantities and are produced by all six common species in the group (A. niger 134 of 140; A. tubingensis 169 of 177; A. acidus 44 of 47; A. carbonarius 40 of 40, A. brasiliensis 18 of 18; and A. ibericus three of three).

Production of toxic metabolites in Aspergillus niger, Aspergillus oryzae, and Trichoderma reesei: justification of mycotoxin testing in food grade enzyme preparations derived from the three fungi

Aspergillus niger, Aspergillus oryzae, and Trichoderma reesei are three important production organisms used in industrial fermentations. Several of the fungal secondary metabolites produced by selected strains of these three fungi are capable of eliciting toxicity in animals. Among those toxic substances are the well-known mycotoxins 3-nitropropionic acid and ochratoxin A. However, many others, such as kojic acid, may not be true mycotoxins. The production, extraction, chemical structure, and the toxicity (expressed as LD(50)) of these substances are reviewed. Production of toxic secondary metabolites in A. niger, A. oryzae, and T. reesei is strain-specific and environment-dependent. Considering all of the safety measures taken in the industrial production process, these three fungal species are safe to use. The recently revised JECFA specification for mycotoxins in food enzyme preparations is also discussed. The extent of mycotoxin tests in food enzyme preparations should be judged on a case-by-case basis, through a careful evaluation based on knowledge of taxonomy, biochemistry, and genetics. In many cases, the testing scope at the level of genus should be sufficient. In other cases, the scope can even be further narrowed based on scientific knowledge and assessment.

Induction of resistance to dark abscission by malformin in white light

When cuttings or seedlings of Phaseolus aureus were treated proximally with malformin for 2 days in continuous white light, resistance to subsequent leaf abscission in the dark resulted. The amount of resistance diminished as the concentration of malformin decreased from 10 to 0.1 micromolar. Resistance to dark abscission persisted for 7 days in continuous light. Little resistance was obtained when cuttings were taken from seedlings grown under low irradiance and short photoperiods, but resistance gradually increased as the photoperiod increased. Resistance to dark abscission induced by malformin in light differs from inhibition of abscission by indoleacetic acid because when malformin is applied in the dark it stimulates abscission after distal or proximal application. Malformin induces resistance only in conjunction with light treatment.

Phytochrome involvement in the induction of resistance to dark abscission by malformin

The active portion of the visible spectrum which is required for malformin to produce leaves which are resistant to dark abscission from cuttings of Phaseolus aureus is red light. Abscission resistance was partially to almost completely lost by far irradiation prior to dark incubation. Although Ethrel, an ethylene releasing compound, stimulated dark abscission of resistant and control leaves, resistance was not lost because control leaves always abscised at a greater rate. The participation of phytochrome in the induction of abscission resistance by malformin is indicated.

Phytochrome involvement in stimulation and alleviation of inhibition of plant growth by malformin

Stimulation of stem elongation on green cuttings of Phaseolus aureus by malformin occurred only in red light and was specifically reversible by subsequent treatment with far red radiation. Inhibition of stem elongation of etiolated cuttings by malformin in the dark was alleviated by red light and was repeatedly reversible with far red irradiation. A direct or indirect effect of malformin on phytochrome action was suggested.

White light requirements for stimulation of plant growth by malformin

Over a 3-day period, the minimum white fluorescent light intensity required for malformin-induced growth stimulation of etiolated and green cuttings of Phaseolus aureus was approximately 2.6 x 10(3) and 0.4 x 10(3) ergs/cm(2) . sec, respectively. High light intensities were unable to inhibit the ability of malformin to stimulate growth. Over 3 days, the minimum photoperiod for malformin-induced growth stimulation using etiolated and green cuttings and a light intensity of 13.5 x 10(3) ergs/cm(2) . sec was 4 hours and 1 hour, respectively. Malformin must be present in the area of growth stimulation during the time of light treatment. Those changes induced by light and required for malformin-induced growth stimulation were estimated to undergo almost complete decay within 1 hour in the dark. By manipulating the experimental technique, it was possible to stimulate the growth of green cuttings with malformin with a 10-min light treatment (13.5 x 10(3) ergs/cm(2) . sec). Although low light intensities and short photoperiods did not allow growth stimulation by malformin using etiolated cuttings, they prevented or alleviated growth inhibition induced by malformin in the dark.

Production and antibacterial activity of malforming C, a toxic metabolite of Aspergillus niger

The production of the new mycotoxin malformin C by a solid substrate fermentation is described. Malformin C is highly toxic (mean lethal dose = 0.9 mg/kg) and exerts antibacterial activity against a variety of gram-positive and gram-negative organisms.

Products of soil microorganisms in relation to plant growth

A survey has been made of the range and activity of the organic products of soil microorganisms which have a direct influence on plant growth. Microbial metabolites which effect plants indirectly by the modification of the soil environment are also reviewed. The sources of substrates for the production of metabolites in soil and the farming practices which give rise to them are considered. It is stressed that an interdisciplinary approach is needed in the manipulation of microbiological activity in soil.

A Mung Bean Assay for Malformin-induced Growth Stimulation

A bioassay employing green or etiolated cuttings of Phaseolus aureus Roxb. was developed for determining malformin-induced growth stimulation in light. Growth enhancement of green cuttings was more rapid and relatively greater than that of etiolated cuttings. Cuttings from green seedlings responded less as seedlings aged; those from etiolated seedlings responded more. Malformin also stimulated the growth of green or etiolated seedlings in light. Most growth enhancement induced by malformin occurred in the upper 1 cm of the stem. Using green cuttings, malformin stimulated stem elongation relatively more when cotyledons, leaves, or especially apical buds were removed. Although malformin failed to stimulate elongation of 2-cm stem sections "floated" on solutions in Petri dishes, it stimulated elongation of sections when they were upright. High concentrations of indoleacetic acid inhibited growth enhancement by malformin. When gibberellin and malformin were combined, growth enhancement was nearly additive.

Malformin in Aspergillus niger-infected onion bulbs (Allium cepa)

Malformin was identified, by its biological activity and chromatography, in acetone extracts of the outer scales of onion bulbs infected with Aspergillus niger. Malformin was not detected in tissue underlying the infected areas or in the central portions of the bulbs, nor was malformein liberated from extracts or extracted tissues after reduction with zinc in acetic acid. This is the first report of naturally occurring malformin.

The structure and synthesis of malformin A

A structure (the disulfide form of cyclo-D-cysteinyl-L-valyl-D-cysteinyl-D-leucyl-L-isoleucyl), previously proposed for malformin A, was reexamined. On the basis of chemical degradations, a different structure (the disulfide form of cyclo-D-cysteinyl-D-cysteinyl-L-valyl-D-leucyl-L-isoleucyl) was established. Accordingly, a compound with this structure was synthesized and was found to be identical with malformin A. The synthetic product causes curvatures on corn roots; maximum effect was seen at a concentration of 0.1 mug/ml, the optimal concentration for malformin A.

Potentiation and inhibition of the effects of 2-chloroethylphosphonic Acid by malformin

Malformin completely inhibited Ethrel-induced swelling and fresh weight increase on the basal stem portion of Phaseolus vulgaris L. cuttings, but markedly potentiated Ethrel- or ethylene-induced abscission. With regard to abscission, malformin reacted synergistically with ethylene and dark aging, and in a manner which appeared to differ from that of ethylene and dark aging. The numerous effects of malformin on plant growth and development cannot be explained in simple terms of enhanced ethylene production.

Mediation of a plant response to malformin by ethylene

Malformin and ethylene stimulate abscission of the primary leaves of Phaseolus aureus Roxb. in the dark, and abscission stimulation by both compounds is inhibited by indeleacetic acid and CO(2). Ethylene production by malformin-treated buds is stimulated within 4 hours. and up to 8 days, after treatment. Malformin-induced growth disturbances in P. vulgaris L. and abscission in P. aureus are considered mediated by ethylene. Although root curvatures of Zea mays L. are induced by both malformin and ethylene, and malformin is inhibited by CO(2), ethylene production is not stimulated by malformin. A role of ethylene in root curvatures induced by malformin is neither proposed nor disproved.

PHYTOTOXIC SUBSTANCES FROM SOIL MICROORGANISMS AND CROP RESIDUES

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Studies on response of bean seedlings & corn roots to malformin

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