Uncovering the origin of Z-configured double bonds in polyketides: intermediate E-double bond formation during borrelidin biosynthesis

Formation of Z-configured double bonds in reduced polyketides is uncommon and their origins have not been extensively studied. To investigate the origin of the Z-configured double bond in the macrolide borrelidin, the recombinant dehydratase domains BorDH2 and B0rDH3 were assayed with a synthetic analogue of the predicted tetraketide substrate. The configuration of the dehydrated products was determined to be E in both cases by comparison to synthetic standards. Detailed NMR spectroscopic analysis of the biosynthetic intermediate pre-borrelidin confirmed the E,E-configuration of the fulllength polyketide synthase product. In contrast to a previously-proposed hypothesis, our results show that in this case the Z-configured double bond is not formed via dehydration from a 3 L-configured precursor, but rather as the result of a later isomerization process.Marie Curie programme of the European UnionEmmy Noether programme of the Deutsche ForschungsgemeinschaftDAA

Expanding the Substrate Scope of N- and O-Methyltransferases from Plants for Chemoselective Alkylation

Methylation reactions are of significant interest when generating pharmaceutically active molecules and building blocks for other applications. Synthetic methylating reagents are often toxic and unselective due to their high reactivity. S‐Adenosyl‐l‐methionine (SAM)‐dependent methyltransferases (MTs) present a chemoselective and environmentally friendly alternative. The anthranilate N‐MT from Ruta graveolens (RgANMT) is involved in acridone alkaloid biosynthesis, methylating anthranilate. Although it is known to methylate substrates only at the N‐position, the closest relatives with respect to amino acid sequence similarities of over 60 % are O‐MTs catalysing the methylation reaction of caffeate and derivatives containing only hydroxyl groups (CaOMTs). In this study, we investigated the substrate range of RgANMT and a CaOMT from Prunus persica (PpCaOMT) using compounds with both, an amino‐ and hydroxyl group (aminophenols) as possible methyl group acceptors. For both enzymes, the reaction was highly chemoselective. Furthermore, generating cofactor derivatives in situ enabled the transfer of other alkyl chains onto the aminophenols, leading to an enlarged pool of products. Selected MT reactions were performed at a preparative biocatalytic scale in in vitro and in vivo experiments resulting in yields of up to 62 %

Methyltransferases: Functions and Applications

In this review the current state of the art of S-adenosylmethionine (SAM)-dependent methyltransferases and SAM are evaluated. Their structural classification and diversity is introduced and key mechanistic aspects presented which are then detailed further. Then, catalytic SAM as a target for drugs and approaches to utilise SAM as a cofactor in synthesis is introduced with different recycling approaches evaluated. The use of SAM analogues are also described. Finally O-, N-, C- and S-MTs, their synthetic applications and potential for compound diversification is given

Multienzyme One‐Pot Cascades Incorporating Methyltransferases for the Strategic Diversification of Tetrahydroisoquinoline Alkaloids

The tetrahydroisoquinoline (THIQ) ring system is present in a large variety of structurally diverse natural products exhibiting a wide range of biological  activities. Routes  to mimic the biosynthetic pathways to such alkaloids, by building cascade reactions in vitro, represents a successful strategy and offers better stereoselectivities than traditional synthetic methods.  (S)-Adenosylmethionine (SAM)  dependent methyltransferases   are crucial in the biosynthesis and diversification of THIQs; however, their application is often limited in vitro by the high cost of SAM and low substrate scope. In this study, we describe  the use  of methyltransferases in vitro in multi-enzyme cascades,  including for the generation of SAM   in situ . Up to seven enzymes  were used  for the regioselective diversification of natural and non-natural THIQs on  an enzymatic  preparative scale.  Regioselectivites of the methyltransferases were dependent on the group at C-1 and presence of fluorine in the THIQs.   An interesting dual activity was also discovered for the catechol methyltransferases used, which were found to be able to regioselectively methylate two different catechols in a single molecule

Chorismate- and isochorismate converting enzymes: versatile catalysts acting on an important metabolic node

Chorismate and isochorismate represent an important branching point connecting primary and secondary metabolism in bacteria, fungi, archaea and plants. Chorismate- and isochorismate-converting enzymes are potential targets for new bioactive compounds, as well as valuable biocatalysts for the in vivo and in vitro synthesis of fine chemicals. The diversity of the products of chorismate- and isochorismate-converting enzymes is reflected in the enzymatic three-dimensional structures and molecular mechanisms. Due to the high reactivity of chorismate and its derivatives, these enzymes have evolved to be accurately tailored to their respective reaction; at the same time, many of them exhibit a fascinating flexibility regarding side reactions and acceptance of alternative substrates. Here, we give an overview of the different (sub)families of chorismate- and isochorismate-converting enzymes, their molecular mechanisms, and three-dimensional structures. In addition, we highlight important results of mutagenetic approaches that generate a broader understanding of the influence of distinct active site residues for product formation and the conversion of one subfamily into another. Based on this, we discuss to what extent the recent advances in the field might influence the general mechanistic understanding of chorismate- and isochorismate-converting enzymes. Recent discoveries of new chorismate-derived products and pathways, as well as biocatalytic conversions of non-physiological substrates, highlight how this vast field is expected to continue developing in the future.ISSN:1359-7345ISSN:1364-548

Catalytic alkylation using a cyclic S-adenosylmethionine regeneration system

S-Adenosylmethionine-dependent methyltransferases are versatile tools for the specific alkylation of many compounds, such as pharmaceuticals, but their biocatalytic application is severely limited owing to the lack of a cofactor regeneration system. We report a biomimetic, polyphosphate-based, cyclic cascade for methyltransferases. In addition to the substrate to be methylated, only methionine and polyphosphate have to be added in stoichiometric amounts. The system acts catalytically with respect to the cofactor precursor adenosine in methylation and ethylation reactions of selected substrates, as shown by HPLC analysis. Furthermore, 1H and 13CNMR measurements were performed to unequivocally identify methionine as the methyl donor and to gain insight into the selectivity of the reactions. This system constitutes a vital stage in the development of economical and environmentally friendly applications of methyltransferases

A Multi-Enzyme Cascade Reaction for the Production of 2′3′-cGAMP

Multi-enzyme cascade reactions for the synthesis of complex products have gained importance in recent decades. Their advantages compared to single biotransformations include the possibility to synthesize complex molecules without purification of reaction intermediates, easier handling of unstable intermediates, and dealing with unfavorable thermodynamics by coupled equilibria. In this study, a four-enzyme cascade consisting of ScADK, AjPPK2, and SmPPK2 for ATP synthesis from adenosine coupled to the cyclic GMP-AMP synthase (cGAS) catalyzing cyclic GMP-AMP (2′3′-cGAMP) formation was successfully developed. The 2′3′-cGAMP synthesis rates were comparable to the maximal reaction rate achieved in single-step reactions. An iterative optimization of substrate, cofactor, and enzyme concentrations led to an overall yield of 0.08 mole 2′3′-cGAMP per mole adenosine, which is comparable to chemical synthesis. The established enzyme cascade enabled the synthesis of 2′3′-cGAMP from GTP and inexpensive adenosine as well as polyphosphate in a biocatalytic one-pot reaction, demonstrating the performance capabilities of multi-enzyme cascades for the synthesis of pharmaceutically relevant products

Mechanistic Implications for the Chorismatase FkbO Based on the Crystal Structure

Chorismate-converting enzymes are involved in many biosynthetic pathways leading to natural products and can often be used as tools for the synthesis of chemical building blocks. Chorismatases such as FkbO from Streptomyces species catalyse the hydrolysis of chorismate yielding (dihydro)benzoic acid derivatives. In contrast to many other chorismate-converting enzymes, the structure and catalytic mechanism of a chorismatase had not been previously elucidated. Here we present the crystal structure of the chorismatase FkbO in complex with a competitive inhibitor at 1.08 Å resolution. FkbO is a monomer in solution and exhibits pseudo-3-fold symmetry; the structure of the individual domains indicates a possible connection to the trimeric RidA/YjgF family and related enzymes. The co-crystallised inhibitor led to the identification of FkbO's active site in the cleft between the central and the C-terminal domains. A mechanism for FkbO is proposed based on both interactions between the inhibitor and the surrounding amino acids and an FkbO structure with chorismate modelled in the active site. We suggest that the methylene group of the chorismate enol ether takes up a proton from an active-site glutamic acid residue, thereby initiating chorismate hydrolysis. A similar chemistry has been described for isochorismatases, albeit implemented in an entirely different protein scaffold. This reaction model is supported by kinetic data from active-site variants of FkbO derived by site-directed mutagenesis

Biosynthesis of Menaquinone in E. coli: Identification of an Elusive Isomer of SEPHCHC

In the biosynthesis of menaquinone in bacteria, the thiamine diphosphate-dependent enzyme MenD catalyzes the decarboxylative carboligation of alpha-ketoglutarate and isochorismate to (1R,2S,5S,6S)-2-succinyl-5-enolpyruvyl-6-hydroxycyclohex-3-ene-1-carboxylate (SEPHCHC). The regioisomer of SEPHCHC, namely (1R,5S,6S)-2-succinyl-5-enolpyruvyl-6-hydroxycyclohex-2-ene-1-carboxylate (iso-SEPHCHC), has been considered as a possible product, however, its existence has been doubtful due to a spontaneous elimination of pyruvate from SEPHCHC to 2-succinyl-6-hydroxy-2,4-cyclohexadiene-1-carboxylate (SHCHC). In this work, the regioisomer iso-SEPHCHC was distinguished from SEPHCHC by liquid chromatography-tandem mass spectrometry. Iso-SEPHCHC was purified and identified by NMR spectroscopy. Just as SEPHCHC remained hidden as a MenD product for more than two decades, its regioisomer iso-SEPHCHC has remained until now.ISSN:1439-4227ISSN:1439-763