Karen E. Lebe

Bio: Karen E. Lebe is an academic researcher from Leibniz University of Hanover. The author has contributed to research in topics: Polyketide synthase & Gene cluster. The author has an hindex of 3, co-authored 5 publications receiving 59 citations.

Strobilurin biosynthesis in Basidiomycete fungi

Abstract: Strobilurins from fungi are the inspiration for the creation of the β-methoxyacrylate class of agricultural fungicides However, molecular details of the biosynthesis of strobilurins have remained cryptic Here we report the sequence of genomes of two fungi that produce strobilurins and show that each contains a biosynthetic gene cluster, which encodes a highly reducing polyketide synthase with very unusual C-terminal hydrolase and methyltransferase domains Expression of stpks1 in Aspergillus oryzae leads to the production of prestrobilurin A when the fermentation is supplemented with a benzoyl coenzyme A (CoA) analogue This enables the discovery of a previously unobserved route to benzoyl CoA Reconstruction of the gene cluster in A oryzae leads to the formation of prestrobilurin A, and addition of the gene str9 encoding an FAD-dependent oxygenase leads to the key oxidative rearrangement responsible for the creation of the β-methoxyacrylate toxophore Finally, two methyltransferases are required to complete the synthesis

Oxidative steps during the biosynthesis of squalestatin S1.

Abstract: The squalestatins are a class of highly complex fungal metabolites which are potent inhibitors of squalene synthase with potential use in the control of cholesterol biosynthesis. Little is known of the chemical steps involved in the construction of the 4,8-dioxa-bicyclo[3.2.1]octane core. Here, using a combination of directed gene knockout and heterologous expression experiments, we show that two putative non-heme-iron-dependent enzymes appear to catalyse a remarkable series of six consecutive oxidations which set up the bioactive core of the squalestatins. This is followed by the action of an unusual copper-dependent oxygenase which introduces a hydroxyl required for later acetylation.

An Unusual Fatty Acyl:Adenylate Ligase (FAAL)–Acyl Carrier Protein (ACP) Didomain in Ambruticin Biosynthesis

Abstract: The divinylcyclopropane (DVC) fragment of the ambruticins is proposed to be formed by a unique polyene cyclisation mechanism, in which the unusual didomain AmbG plays a key role. It is proposed to activate the branched thioester carboxylic acid resulting from polyene cyclisation and to transfer it to its associated acyl carrier protein (ACP). After oxidative decarboxylation, the intermediate is channelled back into polyketide synthase (PKS) processing. AmbG was previously annotated as an adenylation-thiolation didomain with a very unusual substrate selectivity code but has not yet been biochemically studied. On the basis of sequence and homology model analysis, we reannotate AmbG as a fatty acyl:adenylate ligase (FAAL)-acyl carrier protein didomain with unusual substrate specificity. The expected adenylate-forming activity on fatty acids was confirmed by in vitro studies. AmbG also adenylates a number of structurally diverse carboxylic acids, including functionalised fatty acids and unsaturated and aromatic carboxylic acids. HPLC-MS analysis and competition experiments show that AmbG preferentially acylates its ACP with long-chain hydrophobic acids and tolerates a π system and a branch near the carboxylic acid. AmbG is the first characterised example of a FAAL-ACP didomain that is centrally located in a PKS and apparently activates a polyketidic intermediate. This is an important step towards deeper biosynthetic studies such as partial reconstitution of the ambruticin pathway to elucidate DVC formation.

O-Methylation steps during strobilurin and bolineol biosynthesis

Abstract: Strobilurins are potent antifungal polyketides produced by basidiomycete fungi. Two genes encoding O-methyltransferases (O-MeT) are present in the biosynthetic gene cluster of strobilurin A 1. In previous studies, the two O-MeT enzymes Str2 and Str3 were found to catalyse the final steps of the biosynthesis of 1. Here, we show by in vivo expression experiments, that O-methylation during strobilurin biosynthesis is regiospecific. O-MeT Str2 acts first and selectively catalyses the methylation of the carboxyl group of strobilurin and bolineol precursors. Str3 catalyses the subsequent methyl transfer to the enol group to form strobilurin A 1, but cannot methylate bolineol 4. Toxicity tests showed increasing antifungal activity of intermediates through the pathway and that bolineol 4 shows antifungal activity against A. oryzae NSAR1 with an MIC of 0.1 mg ml−1.

Investigating the biosynthesis of Sch-642305 in the fungus Phomopsis sp. CMU-LMA

Abstract: Sch-642305 is an unusual bicyclic 10-membered macrolide produced by the filamentous fungus Phomopsis sp. CMU-LMA for which no biosynthetic evidence exists. Here, we generate a draft genome sequence of the producing organism and discover the biosynthetic gene cluster responsible for formation of Sch-642305. Targeted gene disruptions together with reconstitution of the pathway in the heterologous host Aspergillus oryzae dissect key chemical steps and shed light on a series of oxidoreductions occuring in the pathway.

The amazing potential of fungi: 50 ways we can exploit fungi industrially

Abstract: Fungi are an understudied, biotechnologically valuable group of organisms. Due to the immense range of habitats that fungi inhabit, and the consequent need to compete against a diverse array of other fungi, bacteria, and animals, fungi have developed numerous survival mechanisms. The unique attributes of fungi thus herald great promise for their application in biotechnology and industry. Moreover, fungi can be grown with relative ease, making production at scale viable. The search for fungal biodiversity, and the construction of a living fungi collection, both have incredible economic potential in locating organisms with novel industrial uses that will lead to novel products. This manuscript reviews fifty ways in which fungi can potentially be utilized as biotechnology. We provide notes and examples for each potential exploitation and give examples from our own work and the work of other notable researchers. We also provide a flow chart that can be used to convince funding bodies of the importance of fungi for biotechnological research and as potential products. Fungi have provided the world with penicillin, lovastatin, and other globally significant medicines, and they remain an untapped resource with enormous industrial potential.

Catalytic Reactions and Energy Conservation in the Cytochrome bc1 and b6f Complexes of Energy-Transducing Membranes.

Abstract: This review focuses on key components of respiratory and photosynthetic energy-transduction systems: the cytochrome bc1 and b6f (Cytbc1/b6f) membranous multisubunit homodimeric complexes. These remarkable molecular machines catalyze electron transfer from membranous quinones to water-soluble electron carriers (such as cytochromes c or plastocyanin), coupling electron flow to proton translocation across the energy-transducing membrane and contributing to the generation of a transmembrane electrochemical potential gradient, which powers cellular metabolism in the majority of living organisms. Cytsbc1/b6f share many similarities but also have significant differences. While decades of research have provided extensive knowledge on these enzymes, several important aspects of their molecular mechanisms remain to be elucidated. We summarize a broad range of structural, mechanistic, and physiological aspects required for function of Cytbc1/b6f, combining textbook fundamentals with new intriguing concepts that have emerged from more recent studies. The discussion covers but is not limited to (i) mechanisms of energy-conserving bifurcation of electron pathway and energy-wasting superoxide generation at the quinol oxidation site, (ii) the mechanism by which semiquinone is stabilized at the quinone reduction site, (iii) interactions with substrates and specific inhibitors, (iv) intermonomer electron transfer and the role of a dimeric complex, and (v) higher levels of organization and regulation that involve Cytsbc1/b6f. In addressing these topics, we point out existing uncertainties and controversies, which, as suggested, will drive further research in this field.

Diels–Alder Reactions During the Biosynthesis of Sorbicillinoids

Abstract: The sorbicillinoids are a class of biologically active and structurally diverse fungal polyketides arising from sorbicillin. Through co-expression of sorA, sorB, sorC, and sorD from Trichoderma reesei QM6a, the biosynthetic pathway to epoxysorbicillinol and dimeric sorbicillinoids, which resemble Diels-Alder-like and Michael-addition-like products, was reconstituted in Aspergillus oryzae NSAR1. Expression and feeding experiments demonstrated the crucial requirement of the flavin-dependent monooxygenase SorD for the formation of dimeric sorbicillinoids, hybrid sorbicillinoids, and epoxysorbicillinol in vivo. In contrast to prior reports, SorD catalyses neither the oxidation of 2',3'-dihydrosorbicillin to sorbicillin nor the oxidation of sorbicillinol to oxosorbicillinol. This is the first report that both the intermolecular Diels-Alder and Michael dimerization reactions, as well as the epoxidation of sorbicillinol are catalysed in vivo by SorD.

Efficient Reconstitution of Basidiomycota Diterpene Erinacine Gene Cluster in Ascomycota Host Aspergillus oryzae Based on Genomic DNA Sequences.

Abstract: To develop the versatile methodology for genome mining of mushroom metabolites, we examined the production of bioactive diterpenes erinacines using genomic DNA sequences. In this report, we initially identified high expression loci (hot spots) in Aspergillus oryzae by sequencing the genomic DNAs from highly yielding transformants which were obtained in our previous biosynthetic studies. Genome editing knock-in of all erinacine biosynthetic genes directly to the hot spot showed that A. oryzae correctly spliced more than 90% of the introns in the mushroom genomic DNA gene sequences. Then, we reconstituted the erinacine biosynthetic gene cluster using two rounds of knock-in of the cDNAs and newly developed repeatable genetic engineering by plasmid recycling. At 100% transformation rate, we obtained a transformant that successfully produced erinacine Q and its intermediates. In this study, we elucidated a biosynthetic pathway of erinacines involving functionally unique hydroxylation supported by dehydrogenase EriH and xylose-specific glycosylation by introducing plant genes for supplying UDP-xylose. Our newly developed hot spot knock-in and plasmid recycling allowed us to avoid a time-consuming screening process and to use unlimited introduction of biosynthetic genes due to marker-free genome editing.