Peniphenone and Penilactone Formation in Penicillium crustosum via 1,4-Michael Additions of ortho-Quinone Methide from Hydroxyclavatol to γ-Butyrolactones from Crustosic Acid

Genomics- and Transcriptomics-Guided Discovery of Clavatols from Arctic Fungi Penicillium sp. MYA5

Clavatols exhibit a wide range of biological activities due to their diverse structures. A genome mining strategy identified an A5cla cluster from Penicillium sp. MYA5, derived from the Arctic plant Dryas octopetala, is responsible for clavatol biosynthesis. Seven clavatols, including one new clavatol derivate named penicophenone F (1) and six known clavatols (2-7), were isolated from Penicillium sp. MYA5 using a transcriptome mining strategy. These structures were elucidated by comprehensive spectroscopic analysis. Antibacterial, aldose reductase inhibition, and siderophore-producing ability assays were conducted on compounds 1-7. Compounds 1 and 2 demonstrated inhibitory effects on the ALR2 enzyme with inhibition rates of 75.3% and 71.6% at a concentration of 10 μM, respectively. Compound 6 exhibited antibacterial activity against Staphylococcus aureus and Escherichia coli with MIC values of 4.0 μg/mL and 4.0 μg/mL, respectively. Additionally, compounds 1, 5, and 6 also showed potential iron-binding ability.

One-step Bio-guided Isolation of Secondary Metabolites from the Endophytic Fungus Penicillium crustosum Using High-resolution Semi-preparative HPLC

BACKGROUND

An endophytic fungal strain Penicillium crustosum was isolated from the seagrass Posidonia oceanica and investigated to identify its antimicrobial constituents and characterize its metabolome composition. The ethyl acetate extract of this fungus exhibited antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA) as well as an anti-quorum sensing effect against Pseudomonas aeruginosa.

METHODS

The crude extract was profiled by UHPLC-HRMS/MS, and the dereplication was assisted by feature-based molecular networking. As a result, more than twenty compounds were annotated in this fungus. To rapidly identify the active compounds, the enriched extract was fractionated by semipreparative HPLC-UV applying a chromatographic gradient transfer and dry load sample introduction to maximise resolution. The collected fractions were profiled by 1H-NMR and UHPLC-HRMS.

RESULTS

The use of molecular networking-assisted UHPLC-HRMS/MS dereplication allowed preliminary identification of over 20 compounds present in the ethyl acetate extract of P. crustosum. The chromatographic approach significantly accelerated the isolation of the majority of compounds present in the active extract. The one-step fractionation allowed the isolation and identification of eight compounds (1-8).

CONCLUSION

This study led to the unambiguous identification of eight known secondary metabolites as well as the determination of their antibacterial properties.

Formation of the Fungal Indole Alkaloid Speradine F Implies Multiple Nonenzymatic Oxidation Steps

The highly oxygenated indole alkaloid speradine F (4) with a 6/5/6/5/5/5 hexacyclic skeleton was isolated from a culture of Penicillium palitans, together with its precursors β-cyclopiazonic acid (β-CPA, 5) and cyclopiazonic acid (CPA, 1). Gene deletion and heterologous expression led to the identification of the responsible five-gene spe cluster for the speradine skeleton formation. Precursor supply experiments proved that 1 was enzymatically converted, via 2-oxoCPA (2), to speradine A (3), which subsequently undergoes multistep nonenzymatic hydroxylations to 4.

p-Quinone Methide-Mediated Nonenzymatic Formation of Chalcane-Containing Dimers in Dragon's Blood

Chalcane-containing dimers are major compounds identified from dragon's blood, the red resin that accumulates in Dracaena trees after injury. The key step for the formation of these dimers was a p-quinone methide (p-QM, 3) mediated nonenzymatic Michael addition. Compound 3 is derived from the spontaneous dehydration of chalcane alcohol-M274 (2). Two dihydroflavonol-4-reductases, discovered in D. cambodiana, reduce dihydrochalcone-M272 (7) to 2. Moreover, the application potential of p-QMs was demonstrated using a 3-like p-QM to synthesize diverse dimeric derivatives.

Quantitative characterization of filamentous fungal promoters on a single-cell resolution to discover cryptic natural products

Characterization of filamentous fungal regulatory elements remains challenging because of time-consuming transformation technologies and limited quantitative methods. Here we established a method for quantitative assessment of filamentous fungal promoters based on flow cytometry detection of the superfolder green fluorescent protein at single-cell resolution. Using this quantitative method, we acquired a library of 93 native promoter elements from Aspergillus nidulans in a high-throughput format. The strengths of identified promoters covered a 37-fold range by flow cytometry. P_zipA and P_sltA were identified as the strongest promoters, which were 2.9- and 1.5-fold higher than that of the commonly used constitutive promoter P_gpdA. Thus, we applied P_zipA and P_sltA to activate the silent nonribosomal peptide synthetase gene Afpes1 from Aspergillus fumigatus in its native host and the heterologous host A. nidulans. The metabolic products of Afpes1 were identified as new cyclic tetrapeptide derivatives, namely, fumiganins A and B. Our method provides an innovative strategy for natural product discovery in fungi.

Biosynthesis of Annullatin D in Penicillium roqueforti Implies Oxidative Lactonization between Two Hydroxyl Groups Catalyzed by a BBE-like Enzyme

Annullatins from Cordyceps annullata are alkylated aromatic polyketides including annullatin D with a fused dihydrobenzofuran lactone ring system. Here, we report the identification of a silent biosynthetic gene cluster for annullatins from Penicillium roqueforti by heterologous expression in Aspergillus nidulans, gene deletion, and feeding experiments as well as by biochemical characterization. The polyketide core structure is consecutively modified by hydroxylation and prenylation. A berberine bridge enzyme-like protein catalyzes the final step, an oxidative lactonization between two hydroxyl groups, to form (2S, 9S)-annullatin D.

Biosynthesis of Xylariolide D in Penicillium crustosum Implies a Chain Branching Reaction Catalyzed by a Highly Reducing Polyketide Synthase

Fungi are important sources for the discovery of natural products. During the last decades, technological progress and the increasing number of sequenced genomes facilitated the exploration of new secondary metabolites. Among those, polyketides represent a structurally diverse group with manifold biological activities. In this study, we successfully used genome mining and genetic manipulation for functional proof of a polyketide biosynthetic gene cluster from the filamentous fungus Penicillium crustosum. Gene activation in the native host and heterologous expression in Aspergillus nidulans led to the identification of the xil cluster, being responsible for the formation of the 6-methyl-2-pyrone derivative xylariolide D. Feeding with ¹³C-labeled precursors supported the hypothesis of chain branching during the backbone formation catalyzed by a highly reducing fungal polyketide synthase. A cytochrome P450-catalyzed hydroxylation converts the PKS product to the final metabolite. This proved that just two enzymes are required for the biosynthesis of xylariolide D.

Harnessing ortho-Quinone Methides in Natural Product Biosynthesis and Biocatalysis

The implementation of ortho-quinone methide (o-QM) intermediates in complex molecule assembly represents a remarkably efficient strategy designed by Nature and utilized by synthetic chemists. o-QMs have been taken advantage of in biomimetic syntheses for decades, yet relatively few examples of o-QM-generating enzymes in natural product biosynthetic pathways have been reported. The biosynthetic enzymes that have been discovered thus far exhibit tremendous potential for biocatalytic applications, enabling the selective production of desirable compounds that are otherwise intractable or inherently difficult to achieve by traditional synthetic methods. Characterization of this biosynthetic machinery has the potential to shine a light on new enzymes capable of similar chemistry on diverse substrates, thus expanding our knowledge of Nature's catalytic repertoire. The presently known o-QM-generating enzymes include flavin-dependent oxidases, hetero-Diels-Alderases, S-adenosyl-l-methionine-dependent pericyclases, and α-ketoglutarate-dependent nonheme iron enzymes. In this review, we discuss their diverse enzymatic mechanisms and potential as biocatalysts in constructing natural product molecules such as cannabinoids.

Biosynthesis of Fungal Natural Products Involving Two Separate Pathway Crosstalk

Fungal natural products (NPs) usually possess complicated structures, exhibit satisfactory bioactivities, and are an outstanding source of drug leads, such as the cholesterol-lowering drug lovastatin and the immunosuppressive drug mycophenolic acid. The fungal NPs biosynthetic genes are always arranged within one single biosynthetic gene cluster (BGC). However, a rare but fascinating phenomenon that a crosstalk between two separate BGCs is indispensable to some fungal dimeric NPs biosynthesis has attracted increasing attention. The hybridization of two separate BGCs not only increases the structural complexity and chemical diversity of fungal NPs, but also expands the scope of bioactivities. More importantly, the underlying mechanism for this hybridization process is poorly understood and needs further exploration, especially the determination of BGCs for each building block construction and the identification of enzyme(s) catalyzing the two biosynthetic precursors coupling processes such as Diels–Alder cycloaddition and Michael addition. In this review, we summarized the fungal NPs produced by functional crosstalk of two discrete BGCs, and highlighted their biosynthetic processes, which might shed new light on genome mining for fungal NPs with unprecedented frameworks, and provide valuable insights into the investigation of mysterious biosynthetic mechanisms of fungal dimeric NPs which are constructed by collaboration of two separate BGCs.

A novel chemical marker of tremorgenic mycotoxicosis detected by gas-chromatography/mass-spectrometry

Tremorgenic mycotoxicosis can arise from dietary exposure to secondary metabolite products of various fungal species, particularly those from the Penicillium genus. Although general toxin screens often rely on gas chromatography-mass spectrometry (GC/MS) and well-developed mass spectral library databases, two principal representative Penicillium mycotoxins, roquefortine and penitrem A, are unamenable to GC/MS owing to high molecular weights, low volatilities and/or high thermal instabilities. Reliance on GC/MS screens alone could therefore inadvertently result in failure to collect evidence of exposure to such tremorgenic mycotoxins. In this report we describe a newly discovered tremorgenic marker compound (TMC), the presence of which correlates highly with conclusive exposure to Penicillium toxins in explanation of clinical manifestations of tremorgenic mycotoxicosis. According to detailed mass spectral deconvolution, the compound is 210.0892 molecular weight, and amenable to GC/MS whether chemically underivatized or derivatized by methylation or trimethylsilylation. 1D and 2D NMR (nuclear magnetic resonance) studies on the isolated compound determined the TMC to be the Penicillium product terrestric acid, C11H14O4, which matches the molecular formula determined by high resolution mass spectrometry and thus provides an excellent target for assessment of mycotoxicosis by GC/MS.

Conversion of viridicatic acid to crustosic acid by cytochrome P450 enzyme-catalysed hydroxylation and spontaneous cyclisation

Cytochrome P450 monooxygenases (P450s) are considered nature's most versatile catalysts and play a crucial role in regio- and stereoselective oxidation reactions on a broad range of organic molecules. The oxyfunctionalisation of unactivated carbon-hydrogen (C-H) bonds, in particular, represents a key step in the biosynthesis of many natural products as it provides substrates with increased reactivity for tailoring reactions. In this study, we investigated the function of the P450 enzyme TraB in the terrestric acid biosynthetic pathway. We firstly deleted the gene coding for the DNA repair subunit protein Ku70 by using split marker-based deletion plasmids for convenient recycling of the selection marker to improve gene targeting in Penicillium crustosum. Hereby, we reduced ectopic DNA integration and facilitated genetic manipulation in P. crustosum. Afterward, gene deletion in the Δku70 mutant of the native producer P. crustosum and heterologous expression in Aspergillus nidulans with precursor feeding proved the involvement of TraB in the formation of crustosic acid by catalysing the essential hydroxylation reaction of viridicatic acid. KEY POINTS: •Deletion of Ku70 by using split marker approach for selection marker recycling. •Functional identification of the cytochrome P450 enzyme TraB. •Fulfilling the reaction steps in the terrestric acid biosynthesis.

Fungal quinones: diversity, producers, and applications of quinones from Aspergillus, Penicillium, Talaromyces, Fusarium, and Arthrinium

Quinones represent an important group of highly structurally diverse, mainly polyketide-derived secondary metabolites widely distributed among filamentous fungi. Many quinones have been reported to have important biological functions such as inhibition of bacteria or repression of the immune response in insects. Other quinones, such as ubiquinones are known to be essential molecules in cellular respiration, and many quinones are known to protect their producing organisms from exposure to sunlight. Most recently, quinones have also attracted a lot of industrial interest since their electron-donating and -accepting properties make them good candidates as electrolytes in redox flow batteries, like their often highly conjugated double bond systems make them attractive as pigments. On an industrial level, quinones are mainly synthesized from raw components in coal tar. However, the possibility of producing quinones by fungal cultivation has great prospects since fungi can often be grown in industrially scaled bioreactors, producing valuable metabolites on cheap substrates. In order to give a better overview of the secondary metabolite quinones produced by and shared between various fungi, mainly belonging to the genera Aspergillus, Penicillium, Talaromyces, Fusarium, and Arthrinium, this review categorizes quinones into families such as emodins, fumigatins, sorbicillinoids, yanuthones, and xanthomegnins, depending on structural similarities and information about the biosynthetic pathway from which they are derived, whenever applicable. The production of these quinone families is compared between the different genera, based on recently revised taxonomy. KEY POINTS: • Quinones represent an important group of secondary metabolites widely distributed in important fungal genera such as Aspergillus, Penicillium, Talaromyces, Fusarium, and Arthrinium. • Quinones are of industrial interest and can be used in pharmacology, as colorants and pigments, and as electrolytes in redox flow batteries. • Quinones are grouped into families and compared between genera according to the revised taxonomy.

Precursor Supply Increases the Accumulation of 4-Hydroxy-6-(4-hydroxyphenyl)-α-pyrone after NRPS-PKS Gene Expression

Expression of a nonribosomal peptide synthetase-nonreducing polyketide synthase hybrid gene pcr10109 from Penicillium crustosum PRB-2 in Aspergillus nidulans led to the accumulation of 4-hydroxy-6-(4-hydroxyphenyl)-α-pyrone (1). Adding para-hydroxybenzoic acid into the medium in which the overexpressing mutant is growing increased the product yield up to 5-fold. This strategy could be helpful for heterologous gene expression experiments requiring special substrates for product formation.

Chemoenzymatic Total Synthesis of Natural Products

The total synthesis of structurally complex natural products has challenged and inspired generations of chemists and remains an exciting area of active research. Despite their history as privileged bioactivity-rich scaffolds, the use of natural products in drug discovery has waned. This shift is driven by their relatively low abundance hindering isolation from natural sources and the challenges presented by their synthesis. Recent developments in biocatalysis have resulted in the application of enzymes for the construction of complex molecules. From the inception of the Narayan lab in 2015, we have focused on harnessing the exquisite selectivity of enzymes alongside contemporary small molecule-based approaches to enable concise chemoenzymatic routes to natural products.We have focused on enzymes from various families that perform selective oxidation reactions. For example, we have targeted xyloketal natural products through a strategy that relies on a chemo- and site-selective biocatalytic hydroxylation. Members of the xyloketal family are characterized by polycyclic ketal cores and demonstrate potent neurological activity. We envisioned assembling a representative xyloketal natural product (xyloketal D) involving a biocatalytically generated ortho-quinone methide intermediate. The non-heme iron (NHI) dependent monooxygenase ClaD was used to perform the benzylic hydroxylation of a resorcinol precursor, the product of which can undergo spontaneous loss of water to form an ortho-quinone methide under mild conditions. This intermediate was trapped using a chiral dienophile to complete the total synthesis of xyloketal D.A second class of biocatalytic oxidation that we have employed in synthesis is the hydroxylative dearomatization of resorcinol compounds using flavin-dependent monooxygenases (FDMOs). We anticipated that the catalyst-controlled site- and stereoselectivity of FDMOs would enable the total synthesis of azaphilone natural products. Azaphilones are bioactive compounds characterized by a pyranoquinone bicyclic core and a fully substituted chiral carbon atom. We leveraged the stereodivergent reactivity of FDMOs AzaH and AfoD to achieve the enantioselective synthesis of trichoflectin enantiomers, deflectin 1a, and lunatoic acid. We also leveraged FDMOs to construct tropolone and sorbicillinoid natural products. Tropolones are a structurally diverse class of bioactive molecules characterized by an aromatic cycloheptatriene core bearing an α-hydroxyketone moiety. We developed a two-step biocatalytic cascade to the tropolone natural product stipitatic aldehyde using the FDMO TropB and a NHI monooxygenase TropC. The FDMO SorbC obtained from the sorbicillin biosynthetic pathway was used in the concise total synthesis of a urea sorbicillinoid natural product.Our long-standing interest in using enzymes to carry out C-H hydroxylation reactions has also been channeled for the late-stage diversification of complex scaffolds. For example, we have used Rieske oxygenases to hydroxylate the tricyclic core common to paralytic shellfish toxins. The systemic toxicity of these compounds can be reduced by adding hydroxyl and sulfate groups, which improves their properties and potential as therapeutic agents. The enzymes SxtT, GxtA, SxtN, and SxtSUL were used to carry out selective C-H hydroxylation and O-sulfation in saxitoxin and related structures. We conclude this Account with a discussion of existing challenges in biocatalysis and ways we can currently address them.

Enzymatic dimerization in the biosynthetic pathway of microbial natural products

Covering: up to August 2020The dramatic increase in the identification of dimeric natural products generated by microorganisms and plants has played a significant role in drug discovery. The biosynthetic pathways of these products feature inherent dimerization reactions, which are valuable for biosynthetic applications and chemical transformations. The extraordinary mechanisms of the dimerization of secondary metabolites should advance our understanding of the uncommon chemical rules for natural product biosynthesis, which will, in turn, accelerate the discovery of dimeric reactions and molecules in nature and provide promising strategies for the total synthesis of natural products through dimerization. This review focuses on the enzymes involved in the dimerization in the biosynthetic pathway of microbial natural products, with an emphasis on cytochrome P450s, laccases, and intermolecular [4 + 2] cyclases, along with other atypical enzymes. The identification, characterization, and catalytic landscapes of these enzymes are also introduced.

Oxepinamide F biosynthesis involves enzymatic D-aminoacyl epimerization, 3H-oxepin formation, and hydroxylation induced double bond migration

Oxepinamides are derivatives of anthranilyl-containing tripeptides and share an oxepin ring and a fused pyrimidinone moiety. To the best of our knowledge, no studies have been reported on the elucidation of an oxepinamide biosynthetic pathway and conversion of a quinazolinone to a pyrimidinone-fused 1H-oxepin framework by a cytochrome P450 enzyme in fungal natural product biosynthesis. Here we report the isolation of oxepinamide F from Aspergillus ustus and identification of its biosynthetic pathway by gene deletion, heterologous expression, feeding experiments, and enzyme assays. The nonribosomal peptide synthase (NRPS) OpaA assembles the quinazolinone core with D-Phe incorporation. The cytochrome P450 enzyme OpaB catalyzes alone the oxepin ring formation. The flavoenzyme OpaC installs subsequently one hydroxyl group at the oxepin ring, accompanied by double bond migration. The epimerase OpaE changes the D-Phe residue back to L-form, which is essential for the final methylation by OpaF.

Hunzeylanines A-E, Five Bisindole Alkaloids Tethered with a Methylene Group from the Roots of Hunteria zeylanica

Five novel bisindole alkaloids, hunzeylanines A-E (1-5), with an unprecedented skeleton were isolated from the roots of Hunteria zeylanica. Compounds 1-5 represent the first examples of akuammine-pleioarpamine-type bisindole alkaloids fused with a dihydropyran unit. Their structures including absolute configurations were established through comprehensive spectroscopic data analyses and computational calculation methods. The plausible biogenetic pathway of 1 was also proposed. Alkaloids 1 and 2 displayed moderate cytotoxicity toward three human cancer cell lines (MDA-MB-231, AV3, and Huh7).

Harnessing the biocatalytic potential of iron- and α-ketoglutarate-dependent dioxygenases in natural product total synthesis

Covering: up to the end of 2019Iron- and α-ketoglutarate-dependent dioxygenases (Fe/αKGs) represent a versatile and intriguing enzyme family by virtue of their ability to directly functionalize unactivated C-H bonds at the cost of αKG and O2. Fe/αKGs play an important role in the biosynthesis of natural products, valuable biologically active secondary metabolites frequently pursued as drug leads. The field of natural product total synthesis seeks to contruct these molecules as effeciently as possible, although natural products continue to challenge chemists due to their intricate structural complexity. Chemoenzymatic approaches seek to remedy the shortcomings of traditional synthetic methodology by combining Nature's biosynthetic machinery with traditional chemical methods to efficiently construct natural products. Although other oxygenase families have been widely employed for this purpose, Fe/αKGs remain underutilized. The following review will cover recent chemoenzymatic total syntheses involving Fe/αKG enzymes. Additionally, related information involving natural product biosynthesis, methods development, and non-chemoenzymatic total syntheses will be discussed to inform retrosynthetic logic and synthetic design.

Chemoreactive-Inspired Discovery of Influenza A Virus Dual Inhibitor to Block Hemagglutinin-Mediated Adsorption and Membrane Fusion

Owing to the emergence of drug resistance and high morbidity and mortality, the need for novel anti-influenza A virus (IAV) drugs with divergent targets is highly sought after. Herein, we reveal the discovery of an anti-IAV agent as a dual inhibitor to block hemagglutinin-mediated adsorption and membrane fusion using a chemoreactive ortho-quinone methide (o-QM) equivalent. Based on the o-QM equivalent nonenzymatically multipotent behavior, we created a series of clavatol-derived pseudo-natural products and found that penindolone (PND), a new diclavatol indole adduct, exhibited potent and broad-spectrum anti-IAV activities with low risk of inducing drug resistance. Distinct from current anti-IAV drugs, PND possesses a novel scaffold and is the first IAV inhibitor targeting both HA1 and HA2 subunits of virus hemagglutinin to dually block the IAV adsorption and membrane fusion process. More importantly, intranasal and oral administration of PND can protect mice against IAV-induced death and weight loss, superior to the effects of the clinical drug oseltamivir. Thus, the use of chemoreactive intermediates could expand our understanding of chemical diversity and aid in the development of anti-IAV drugs with novel targets.

Synthetic utility of one-pot chemoenzymatic reaction sequences

In recent years, there has been a rapid and sustained increase in the development and use of one-pot chemoenzymatic reaction processes for the efficient synthesis of high-value molecules. This strategy can provide a number of advantages over traditional synthetic methods, including high levels of selectivity in reactions, mild and sustainable reaction conditions, and the ability to rapidly build molecular complexity in a single reaction vessel. Here, we present several examples of chemoenzymatic one-pot reaction sequences that demonstrate the diversity of transformations that can be incorporated in these processes.

Increasing Structural Diversity of Natural Products by Michael Addition with ortho-Quinone Methide as the Acceptor

The active form of clavatol, ortho-quinone methide, can be generated from hydroxyclavatol in an aqueous system and used as a highly reactive intermediate for coupling with diverse natural products under very mild conditions. These include flavonoids, hydroxynaphthalenes, coumarins, xanthones, anthraquinones, phloroglucinols, phenolic acids, indole derivatives, tyrosine analogues, and quinolines. The clavatol moiety was mainly attached via C-C bonds to the ortho- or para-positions of phenolic hydroxyl/amino groups and the C2-position of the indole ring.

Isocoumarin formation by heterologous gene expression and modification by host enzymes

The polyketide synthase product was converted to its methylated and hydroxylated derivatives by host endogenous enzymes.

Amplisins A–E, chromone methide polymers with hypoglycemic activity from a new fungicolous fungus Amplistroma fungicola

Five new non-enzymatic 1,4-Michael addition of chromone methide polymers, (±)-amplisins A–D (1–4) and amplisin E (5), with hypoglycemic and anti-inflammatory activities, were isolated from a new fungicolous fungus Amplistroma fungicola.

Chemoenzymatic o-Quinone Methide Formation

Generation of reactive intermediates and interception of these fleeting species under physiological conditions is a common strategy employed by Nature to build molecular complexity. However, selective formation of these species under mild conditions using classical synthetic techniques is an outstanding challenge. Here, we demonstrate the utility of biocatalysis in generating o-quinone methide intermediates with precise chemoselectivity under mild, aqueous conditions. Specifically, α-ketoglutarate-dependent non-heme iron enzymes, CitB and ClaD, are employed to selectively modify benzylic C-H bonds of o-cresol substrates. In this transformation, biocatalytic hydroxylation of a benzylic C-H bond affords a benzylic alcohol product which, under the aqueous reaction conditions, is in equilibrium with the corresponding o-quinone methide. o-Quinone methide interception by a nucleophile or a dienophile allows for one-pot conversion of benzylic C-H bonds into C-C, C-N, C-O, and C-S bonds in chemoenzymatic cascades on preparative scale. The chemoselectivity and mild nature of this platform is showcased here by the selective modification of peptides and chemoenzymatic synthesis of the chroman natural product (-)-xyloketal D.

An Ugi-like Biosynthetic Pathway Encodes Bombesin Receptor Subtype-3 Agonists

Isocyanide functional groups can be found in a variety of natural products. Rhabduscin is one such isocyanide-functionalized immunosuppressant produced in Xenorhabdus and Photorhabdus gammaproteobacterial pathogens, and deletion of its biosynthetic gene cluster inhibits virulence in an invertebrate animal infection model. Here, we characterized the first "opine-glycopeptide" class of natural products termed rhabdoplanins, and strikingly, these molecules are spontaneously produced from rhabduscin via an unprecedented multicomponent "Ugi-like" reaction sequence in nature. The rhabdoplanins also represent new lead G protein-coupled receptor (GPCR) agonists, stimulating the bombesin receptor subtype-3 (BB3) GPCR.

Secondary Metabolites Produced by Combined Culture of Penicillium crustosum and a Xylaria sp

Four new alkyl aromatics, penixylarins A-D (1-4), along with the known biogenetically related 1,3-dihydroxy-5-(12-hydroxyheptadecyl)benzene (5) and 1,3-dihydroxy-5-(12-sulfoxyheptadecyl)benzene (6), were isolated from a mixed culture of the Antarctic deep-sea-derived fungus Penicillium crustosum PRB-2 and the mangrove-derived fungus Xylaria sp. HDN13-249. UPLC-MS data and an analysis of structural features showed that compounds 1 and 2 were produced by collaboration of the two fungi, while compounds 3-6 could be produced by Xylaria sp. HDN13-249 alone, but in noticeably increased quantities by cocultivation. Compounds 2, 3, 5, and 6 showed antibacterial activity against a panel of strains, and compound 3 possessed potential antituberculosis effects (MIC = 6.25 μM against Mycobacterium phlei).

Genomic Locus of a Penicillium crustosum Pigment as an Integration Site for Secondary Metabolite Gene Expression

Heterologous expression of secondary metabolite genes and gene clusters has been proven to be a successful strategy for identification of new natural products of cryptic or silent genes hidden in the genome sequences. It is also a useful tool to produce designed compounds by synthetic biology approaches. In this study, we demonstrate the potential usage of the gene locus pcr4401 in the fast-growing filamentous fungus Penicillium crustosum as an integration site for heterologous gene expression. The deduced polyketide synthase (PKS) Pcr4401 is involved in the dihydroxynaphthalene (DHN)-melanin pigment formation, and its deletion in P. crustosum PRB-2 led to an albino phenotype. Heterologous expression of pcr4401 in Aspergillus nidulans proved its function as the melanin precursor YWA1 synthase. To ensure gene expression after genomic integration and to easily identify the potential transformants by visualization, the gene locus of pcr4401 was chosen as an integration site. For heterologous expression in P. crustosum, the expression constructs were created by ligation-independent homologous recombination in Escherichia coli or Saccharomyces cerevisiae. A pyrG deficient strain was also created, so that both the pyrG and hph resistance gene can be used as selection markers. Successful expression in P. crustosum was demonstrated by using one uncharacterized PKS gene from Aspergillus and two from Penicillium strains. All three genes were successfully introduced, heterologously expressed, and their biosynthetic products elucidated. The results presented in this study demonstrated that P. crustosum can be used as a suitable host for heterologous expression of secondary metabolite genes.