Chemoenzymatic Synthesis of an Unnatural Deazaflavin Cofactor That Can Fuel F420-Dependent Enzymes

F420-dependent transformations in biosynthesis of secondary metabolites

Cofactor F420 has been historically known as the "methanogenic redox cofactor". It is now recognised that F420 has essential roles in the primary and secondary metabolism of archaea and bacteria. Recent discoveries highlight the role of F420 as a redox cofactor in the biosynthesis of various natural products, including ribosomally synthesised and post-translationally modified peptides, and a new class of nicotinamide adenine dinucleotide-based secondary metabolites. With the vast availability of (meta)genomic data, the identification of uncharacterised F420-dependent enzymes offers the potential for discovering novel secondary metabolites, presenting valuable prospects for clinical and biotechnological applications.

Equipping Saccharomyces cerevisiae with an Additional Redox Cofactor Allows F420-Dependent Bioconversions in Yeast

Industrial application of the natural deazaflavin cofactor F420 has high potential for the enzymatic synthesis of high value compounds. It can offer an additional range of chemistry to the use of well-explored redox cofactors such as FAD and their respective enzymes. Its limited access through organisms that are rather difficult to grow has urged research on the heterologous production of F420 using more industrially relevant microorganisms such as Escherichia coli. In this study, we demonstrate the possibility of producing this cofactor in a robust and widely used industrial organism, Saccharomyces cerevisiae, by the heterologous expression of the F420 pathway. Through careful selection of involved enzymes and some optimization, we achieved an F420 yield of ∼1.3 μmol/L, which is comparable to the yield of natural F420 producers. Furthermore, we showed the potential use of F420-producing S. cerevisiae for F420-dependent bioconversions by carrying out the whole-cell conversion of tetracycline. As the first demonstration of F420 synthesis and use for bioconversion in a eukaryotic organism, this study contributes to the development of versatile bioconversion platforms.

Asymmetric Ene-Reduction by F420 -Dependent Oxidoreductases B (FDOR-B) from Mycobacterium smegmatis

Asymmetric reduction by ene-reductases has received considerable attention in recent decades. While several enzyme families possess ene-reductase activity, the Old Yellow Enzyme (OYE) family has received the most scientific and industrial attention. However, there is a limited substrate range and few stereocomplementary pairs of current ene-reductases, necessitating the development of a complementary class. Flavin/deazaflavin oxidoreductases (FDORs) that use the uncommon cofactor F₄₂₀ have recently gained attention as ene-reductases for use in biocatalysis due to their stereocomplementarity with OYEs. Although the enzymes of the FDOR-As sub-group have been characterized in this context and reported to catalyse ene-reductions enantioselectively, enzymes from the similarly large, but more diverse, FDOR-B sub-group have not been investigated in this context. In this study, we investigated the activity of eight FDOR-B enzymes distributed across this sub-group, evaluating their specific activity, kinetic properties, and stereoselectivity against α,β-unsaturated compounds. The stereochemical outcomes of the FDOR-Bs are compared with enzymes of the FDOR-A sub-group and OYE family. Computational modelling and induced-fit docking are used to rationalize the observed catalytic behaviour and proposed a catalytic mechanism.

Functionalised Cofactor Mimics for Interactome Discovery and Beyond

Cofactors are required for almost half of all enzyme reactions, but their functions and binding partners are not fully understood even after decades of research. Functionalised cofactor mimics that bind in place of the unmodified cofactor can provide answers, as well as expand the scope of cofactor activity. Through chemical proteomics approaches such as activity-based protein profiling, the interactome and localisation of the native cofactor in its physiological environment can be deciphered and previously uncharacterised proteins annotated. Furthermore, cofactors that supply functional groups to substrate biomolecules can be hijacked by mimics to site-specifically label targets and unravel the complex biology of post-translational protein modification. The diverse activity of cofactors has inspired the design of mimics for use as inhibitors, antibiotic therapeutics, and chemo- and biosensors, and cofactor conjugates have enabled the generation of novel enzymes and artificial DNAzymes.

High-yield production of coenzyme F420 in Escherichia coli by fluorescence-based screening of multi-dimensional gene expression space

Coenzyme F₄₂₀ is involved in bioprocesses such as biosynthesis of antibiotics by streptomycetes, prodrug activation in Mycobacterium tuberculosis, and methanogenesis in archaea. F₄₂₀-dependent enzymes also attract interest as biocatalysts in organic chemistry. However, as only low F₄₂₀ levels are produced in microorganisms, F₄₂₀ availability is a serious bottleneck for research and application. Recent advances in our understanding of the F₄₂₀ biosynthesis enabled heterologous overproduction of F₄₂₀ in Escherichia coli, but the yields remained moderate. To address this issue, we rationally designed a synthetic operon for F₄₂₀ biosynthesis in E. coli. However, it still led to the production of low amounts of F₄₂₀ and undesired side-products. In order to strongly improve yield and purity, a screening approach was chosen to interrogate the gene expression-space of a combinatorial library based on diversified promotors and ribosome binding sites. The whole pathway was encoded by a two-operon construct. The first module ("core") addressed parts of the riboflavin biosynthesis pathway and F_O synthase for the conversion of GTP to the stable F₄₂₀ intermediate F_O. The enzymes of the second module ("decoration") were chosen to turn F_O into F₄₂₀. The final construct included variations of T7 promoter strengths and ribosome binding site activity to vary the expression ratio for the eight genes involved in the pathway. Fluorescence-activated cell sorting was used to isolate clones of this library displaying strong F₄₂₀-derived fluorescence. This approach yielded the highest titer of coenzyme F₄₂₀ produced in the widely used organism E. coli so far. Production in standard LB medium offers a highly effective and simple production process that will facilitate basic research into unexplored F₄₂₀-dependent bioprocesses as well as applications of F₄₂₀-dependent enzymes in biocatalysis.

Chemoenzymatic Synthesis of the Most Pleasant Stereoisomer of Jessemal

We describe the asymmetric synthesis of the most pleasant enantiomer of Jessemal fragrance. The key steps are (i) the one-pot reduction of an α-chloro-tetrasubstituted cyclohexenone to give the chlorohydrin, catalyzed by two stereoselective redox enzymes (an ene-reductase and an alcohol dehydrogenase); (ii) the regioselective epoxide ring-opening with organocuprate or organolithium nucleophiles. Density functional theory calculations together with the Curtin–Hammett principle allowed the rationalization of the regioselectivity.

Broadening the scope of the Flavin-tag method by improving flavin incorporation and incorporating flavin analogs

Methods for facile site-selective modifications of proteins are in high demand. We have recently shown that a flavin transferase can be used for site-specific covalent attachment of a chromo- and fluorogenic flavin (FMN) to any targeted protein. Although this Flavin-tag method resulted in efficient labeling of proteins in vitro , labelling in E. coli cells resulted in partial flavin incorporation. It was also restricted in the type of installed label with only type of flavin, FMN, being incorporated. Here, we report on an extension of the Flavin-tag method that addresses previous limitations. We demonstrate that coexpression of FAD synthetase improves the flavin incorporation efficiency, allowing complete flavin-labeling of a target protein in E. coli cells. Furthermore, we have found that various flavin derivatives and even a nicotinamide can be covalently attached to a target protein, rendering this method even more versatile and valuable.

Cofactor F420, an emerging redox power in biosynthesis of secondary metabolites

Cofactor F420 is a low-potential hydride-transfer deazaflavin that mediates important oxidoreductive reactions in the primary metabolism of archaea and a wide range of bacteria. Over the past decade, biochemical studies have demonstrated another essential role for F420 in the biosynthesis of various classes of natural products. These studies have substantiated reports predating the structural determination of F420 that suggested a potential role for F420 in the biosynthesis of several antibiotics produced by Streptomyces. In this article, we focus on this exciting and emerging role of F420 in catalyzing the oxidoreductive transformation of various imine, ketone and enoate moieties in secondary metabolites. Given the extensive and increasing availability of genomic and metagenomic data, these F420-dependent transformations may lead to the discovery of novel secondary metabolites, providing an invaluable and untapped resource in various biotechnological applications.

Diversification by CofC and Control by CofD Govern Biosynthesis and Evolution of Coenzyme F420 and Its Derivative 3PG-F420

Coenzyme F₄₂₀ is a microbial redox cofactor that mediates diverse physiological functions and is increasingly used for biocatalytic applications. Recently, diversified biosynthetic routes to F₄₂₀ and the discovery of a derivative, 3PG-F₄₂₀, were reported. 3PG-F₄₂₀ is formed via activation of 3-phospho-d-glycerate (3-PG) by CofC, but the structural basis of substrate binding, its evolution, as well as the role of CofD in substrate selection remained elusive. Here, we present a crystal structure of the 3-PG-activating CofC from Mycetohabitans sp. B3 and define amino acids governing substrate specificity. Site-directed mutagenesis enabled bidirectional switching of specificity and thereby revealed the short evolutionary trajectory to 3PG-F₄₂₀ formation. Furthermore, CofC stabilized its product, thus confirming the structure of the unstable molecule and revealing its binding mode. The CofD enzyme was shown to significantly contribute to the selection of related intermediates to control the specificity of the combined biosynthetic CofC/D step. These results imply the need to change the design of combined CofC/D activity assays. Taken together, this work presents novel mechanistic and structural insights into 3PG-F₄₂₀ biosynthesis and evolution and opens perspectives for the discovery and enhanced biotechnological production of coenzyme F₄₂₀ derivatives in the future. IMPORTANCE The microbial cofactor F₄₂₀ is crucial for processes like methanogenesis, antibiotics biosynthesis, drug resistance, and biocatalysis. Recently, a novel derivative of F₄₂₀ (3PG-F₄₂₀) was discovered, enabling the production and use of F₄₂₀ in heterologous hosts. By analyzing the crystal structure of a CofC homolog whose substrate choice leads to formation of 3PG-F₄₂₀, we defined amino acid residues governing the special substrate selectivity. A diagnostic residue enabled reprogramming of the substrate specificity, thus mimicking the evolution of the novel cofactor derivative. Furthermore, a labile reaction product of CofC was revealed that has not been directly detected so far. CofD was shown to provide another layer of specificity of the combined CofC/D reaction, thus controlling the initial substrate choice of CofC. The latter finding resolves a current debate in the literature about the starting point of F₄₂₀ biosynthesis in various organisms.

Introducing an Artificial Deazaflavin Cofactor in Escherichia coli and Saccharomyces cerevisiae

Deazaflavin-dependent whole-cell conversions in well-studied and industrially relevant microorganisms such as Escherichia coli and Saccharomyces cerevisiae have high potential for the biocatalytic production of valuable compounds. The artificial deazaflavin FOP (FO-5′-phosphate) can functionally substitute the natural deazaflavin F₄₂₀ and can be synthesized in fewer steps, offering a solution to the limited availability of the latter due to its complex (bio)synthesis. Herein we set out to produce FOP in vivo as a scalable FOP production method and as a means for FOP-mediated whole-cell conversions. Heterologous expression of the riboflavin kinase from Schizosaccharomyces pombe enabled in vivo phosphorylation of FO, which was supplied by either organic synthesis ex vivo, or by a coexpressed FO synthase in vivo, producing FOP in E. coli as well as in S. cerevisiae. Through combined approaches of enzyme engineering as well as optimization of expression systems and growth media, we further improved the in vivo FOP production in both organisms. The improved FOP production yield in E. coli is comparable to the F₄₂₀ yield of native F₄₂₀-producing organisms such as Mycobacterium smegmatis, but the former can be achieved in a significantly shorter time frame. Our E. coli expression system has an estimated production rate of 0.078 μmol L^–1 h^–1 and results in an intracellular FOP concentration of about 40 μM, which is high enough to support catalysis. In fact, we demonstrate the successful FOP-mediated whole-cell conversion of ketoisophorone using E. coli cells. In S. cerevisiae, in vivo FOP production by SpRFK using supplied FO was improved through media optimization and enzyme engineering. Through structure-guided enzyme engineering, a SpRFK variant with 7-fold increased catalytic efficiency compared to the wild type was discovered. By using this variant in optimized media conditions, FOP production yield in S. cerevisiae was 20-fold increased compared to the very low initial yield of 0.24 ± 0.04 nmol per g dry biomass. The results show that bacterial and eukaryotic hosts can be engineered to produce the functional deazaflavin cofactor mimic FOP.

Improved production of the non-native cofactor F420 in Escherichia coli

The deazaflavin cofactor F₄₂₀ is a low-potential, two-electron redox cofactor produced by some Archaea and Eubacteria that is involved in methanogenesis and methanotrophy, antibiotic biosynthesis, and xenobiotic metabolism. However, it is not produced by bacterial strains commonly used for industrial biocatalysis or recombinant protein production, such as Escherichia coli, limiting our ability to exploit it as an enzymatic cofactor and produce it in high yield. Here we have utilized a genome-scale metabolic model of E. coli and constraint-based metabolic modelling of cofactor F₄₂₀ biosynthesis to optimize F₄₂₀ production in E. coli. This analysis identified phospho-enol pyruvate (PEP) as a limiting precursor for F₄₂₀ biosynthesis, explaining carbon source-dependent differences in productivity. PEP availability was improved by using gluconeogenic carbon sources and overexpression of PEP synthase. By improving PEP availability, we were able to achieve a ~ 40-fold increase in the space–time yield of F₄₂₀ compared with the widely used recombinant Mycobacterium smegmatis expression system. This study establishes E. coli as an industrial F₄₂₀-production system and will allow the recombinant in vivo use of F₄₂₀-dependent enzymes for biocatalysis and protein engineering applications.

A Tailor-Made Deazaflavin-Mediated Recycling System for Artificial Nicotinamide Cofactor Biomimetics

Nicotinamide adenine dinucleotide (NAD) and its 2'-phosphorylated form NADP are crucial cofactors for a large array of biocatalytically important redox enzymes. Their high cost and relatively poor stability, however, make them less attractive electron mediators for industrial processes. Nicotinamide cofactor biomimetics (NCBs) are easily synthesized, are inexpensive, and are also generally more stable than their natural counterparts. A bottleneck for the application of these artificial hydride carriers is the lack of efficient cofactor recycling methods. Therefore, we engineered the thermostable F420:NADPH oxidoreductase from Thermobifida fusca (Tfu-FNO), by structure-inspired site-directed mutagenesis, to accommodate the unnatural N1 substituents of eight NCBs. The extraordinarily low redox potential of the natural cofactor F420H2 was then exploited to reduce these NCBs. Wild-type enzyme had detectable activity toward all selected NCBs, with K m values in the millimolar range and k cat values ranging from 0.09 to 1.4 min-1. Saturation mutagenesis at positions Gly-29 and Pro-89 resulted in mutants with up to 139 times higher catalytic efficiencies. Mutant G29W showed a k cat value of 4.2 s-1 toward 1-benzyl-3-acetylpyridine (BAP+), which is similar to the k cat value for the natural substrate NADP+. The best Tfu-FNO variants for a specific NCB were then used for the recycling of catalytic amounts of these nicotinamides in conversion experiments with the thermostable ene-reductase from Thermus scotoductus (TsOYE). We were able to fully convert 10 mM ketoisophorone with BAP+ within 16 h, using F420 or its artificial biomimetic FOP (FO-2'-phosphate) as an efficient electron mediator and glucose-6-phosphate as an electron donor. The generated toolbox of thermostable and NCB-dependent Tfu-FNO variants offers powerful cofactor regeneration biocatalysts for the reduction of several artificial nicotinamide biomimetics at both ambient and high temperatures. In fact, to our knowledge, this enzymatic method seems to be the best-performing NCB-recycling system for BNAH and BAPH thus far.

Cofactor F420: an expanded view of its distribution, biosynthesis and roles in bacteria and archaea

Many bacteria and archaea produce the redox cofactor F420. F420 is structurally similar to the cofactors FAD and FMN but is catalytically more similar to NAD and NADP. These properties allow F420 to catalyze challenging redox reactions, including key steps in methanogenesis, antibiotic biosynthesis and xenobiotic biodegradation. In the last 5 years, there has been much progress in understanding its distribution, biosynthesis, role and applications. Whereas F420 was previously thought to be confined to Actinobacteria and Euryarchaeota, new evidence indicates it is synthesized across the bacterial and archaeal domains, as a result of extensive horizontal and vertical biosynthetic gene transfer. F420 was thought to be synthesized through one biosynthetic pathway; however, recent advances have revealed variants of this pathway and have resolved their key biosynthetic steps. In parallel, new F420-dependent biosynthetic and metabolic processes have been discovered. These advances have enabled the heterologous production of F420 and identified enantioselective F420H2-dependent reductases for biocatalysis. New research has also helped resolve how microorganisms use F420 to influence human and environmental health, providing opportunities for tuberculosis treatment and methane mitigation. A total of 50 years since its discovery, multiple paradigms associated with F420 have shifted, and new F420-dependent organisms and processes continue to be discovered.

Facile Stereoselective Reduction of Prochiral Ketones by using an F420 -dependent Alcohol Dehydrogenase

Effective procedures for the synthesis of optically pure alcohols are highly valuable. A commonly employed method involves the biocatalytic reduction of prochiral ketones. This is typically achieved by using nicotinamide cofactor-dependent reductases. In this work, we demonstrate that a rather unexplored class of enzymes can also be used for this. We used an F420 -dependent alcohol dehydrogenase (ADF) from Methanoculleus thermophilicus that was found to reduce various ketones to enantiopure alcohols. The respective (S) alcohols were obtained in excellent enantiopurity (>99 % ee). Furthermore, we discovered that the deazaflavoenzyme can be used as a self-sufficient system by merely using a sacrificial cosubstrate (isopropanol) and a catalytic amount of cofactor F420 or the unnatural cofactor FOP to achieve full conversion. This study reveals that deazaflavoenzymes complement the biocatalytic toolbox for enantioselective ketone reductions.

Biocatalytic in Vitro and in Vivo FMN Prenylation and (De)carboxylase Activation

Reversible UbiD-like (de)carboxylases represent a large family of mostly uncharacterized enzymes, which require the recently discovered prenylated FMN (prFMN) cofactor for activity. Functional characterization of novel UbiDs is hampered by a lack of robust protocols for prFMN generation and UbiD activation. Here, we report two systems for in vitro and in vivo FMN prenylation and UbiD activation under aerobic conditions. The in vitro one-pot prFMN cascade includes five enzymes: FMN prenyltransferase (UbiX), prenol kinase, polyphosphate kinase, formate dehydrogenase, and FMN reductase, which use prenol, polyphosphate, formate, ATP, NAD⁺, and FMN as substrates and cofactors. Under aerobic conditions, this cascade produced prFMN from FMN with over 98% conversion and activated purified ferulic acid decarboxylase Fdc1 from Aspergillus niger and protocatechuic acid decarboxylase ENC0058 from Enterobacter cloaceae. The in vivo system for FMN prenylation and UbiD activation is based on the coexpression of Fdc1 and UbiX in Escherichia coli cells under aerobic conditions in the presence of prenol. The in vitro and in vivo FMN prenylation cascades will facilitate functional characterization of novel UbiDs and their applications.

Convergent pathways to biosynthesis of the versatile cofactor F420

Cofactor F₄₂₀ is historically known as the methanogenic redox cofactor, having a key role in the central metabolism of methanogens, and archaea in general. Over the past decade, however, it has become evident this cofactor is more widely distributed across archaeal and bacterial taxa, suggesting a broader role for F₄₂₀ in various metabolic and ecological capacities. In this article, we focus on the recent findings that have led to a deeper understanding of F₄₂₀ biosynthetic enzymes and metabolites across microorganisms.

Redox Coenzyme F420 Biosynthesis in Thermomicrobia Involves Reduction by Stand-Alone Nitroreductase Superfamily Enzymes

Coenzyme F₄₂₀ is a redox cofactor involved in hydride transfer reactions in archaea and bacteria. Since F₄₂₀-dependent enzymes are attracting increasing interest as tools in biocatalysis, F₄₂₀ biosynthesis is being revisited. While it was commonly accepted for a long time that the 2-phospho-l-lactate (2-PL) moiety of F₄₂₀ is formed from free 2-PL, it was recently shown that phosphoenolpyruvate is incorporated in Actinobacteria and that the C-terminal domain of the FbiB protein, a member of the nitroreductase (NTR) superfamily, converts dehydro-F₄₂₀ into saturated F₄₂₀ Outside the Actinobacteria, however, the situation is still unclear because FbiB is missing in these organisms and enzymes of the NTR family are highly diversified. Here, we show by heterologous expression and in vitro assays that stand-alone NTR enzymes from Thermomicrobia exhibit dehydro-F₄₂₀ reductase activity. Metabolome analysis and proteomics studies confirmed the proposed biosynthetic pathway in Thermomicrobium roseum These results clarify the biosynthetic route of coenzyme F₄₂₀ in a class of Gram-negative bacteria, redefine functional subgroups of the NTR superfamily, and offer an alternative for large-scale production of F₄₂₀ in Escherichia coli in the future.IMPORTANCE Coenzyme F₄₂₀ is a redox cofactor of Archaea and Actinobacteria, as well as some Gram-negative bacteria. Its involvement in processes such as the biosynthesis of antibiotics, the degradation of xenobiotics, and asymmetric enzymatic reductions renders F₄₂₀ of great relevance for biotechnology. Recently, a new biosynthetic step during the formation of F₄₂₀ in Actinobacteria was discovered, involving an enzyme domain belonging to the versatile nitroreductase (NTR) superfamily, while this process remained blurred in Gram-negative bacteria. Here, we show that a similar biosynthetic route exists in Thermomicrobia, although key biosynthetic enzymes show different domain architectures and are only distantly related. Our results shed light on the biosynthesis of F₄₂₀ in Gram-negative bacteria and refine the knowledge about sequence-function relationships within the NTR superfamily of enzymes. Appreciably, these results offer an alternative route to produce F₄₂₀ in Gram-negative model organisms and unveil yet another biochemical facet of this pathway to be explored by synthetic microbiologists.

A High-Throughput Method for Directed Evolution of NAD(P)+-Dependent Dehydrogenases for the Reduction of Biomimetic Nicotinamide Analogues

Engineering flavin-free NAD(P)⁺-dependent dehydrogenases to reduce biomimetic nicotinamide analogues (mNAD⁺s) is of importance for eliminating the need for costly NAD(P)⁺ in coenzyme regeneration systems. Current redox dye-based screening methods for engineering the mNAD⁺ specificity of dehydrogenases are frequently encumbered by a background signal from endogenous NAD(P) and intracellular reducing compounds, making the detection of low mNAD⁺-based activities a limiting factor for directed evolution. Here, we develop a high-throughput screening method, NAD(P)-eliminated solid-phase assay (NESPA), which can reliably identify mNAD⁺-active mutants of dehydrogenases with a minimal background signal. This method involves (1) heat lysis of colonies to permeabilize the cell membrane, (2) colony transfer onto filter paper, (3) washing to remove endogenous NAD(P) and reducing compounds, (4) enzyme-coupled assay for mNADH-dependent color production, and (5) digital imaging of colonies to identify mNAD⁺-active mutants. This method was used to improve the activity of 6-phosphogluconate dehydrogenase on nicotinamide mononucleotide (NMN⁺). The best mutant obtained after six rounds of directed evolution exhibits a 50-fold enhancement in catalytic efficiency (k _cat/K _M) and a specific activity of 17.7 U/mg on NMN⁺, which is comparable to the wild-type enzyme on its natural coenzyme, NADP⁺. The engineered dehydrogenase was then used to construct an NMNH regeneration system to drive an ene-reductase catalysis. A comparable level of turnover frequency and product yield was observed using the engineered system relative to NADPH regeneration by using the wild-type dehydrogenase. NESPA provides a simple and accurate readout of mNAD⁺-based activities and the screening at high-throughput levels (approximately tens of thousands per round), thus opening up an avenue for the evolution of dehydrogenases with specific activities on mNAD⁺s similar to the levels of natural enzyme/coenzyme pairs.

Cofactor F420-Dependent Enzymes: An Under-Explored Resource for Asymmetric Redox Biocatalysis

The asymmetric reduction of enoates, imines and ketones are among the most important reactions in biocatalysis. These reactions are routinely conducted using enzymes that use nicotinamide cofactors as reductants. The deazaflavin cofactor F420 also has electrochemical properties that make it suitable as an alternative to nicotinamide cofactors for use in asymmetric reduction reactions. However, cofactor F420-dependent enzymes remain under-explored as a resource for biocatalysis. This review considers the cofactor F420-dependent enzyme families with the greatest potential for the discovery of new biocatalysts: the flavin/deazaflavin-dependent oxidoreductases (FDORs) and the luciferase-like hydride transferases (LLHTs). The characterized F420-dependent reductions that have the potential for adaptation for biocatalysis are discussed, and the enzymes best suited for use in the reduction of oxidized cofactor F420 to allow cofactor recycling in situ are considered. Further discussed are the recent advances in the production of cofactor F420 and its functional analog FO-5′-phosphate, which remains an impediment to the adoption of this family of enzymes for industrial biocatalytic processes. Finally, the prospects for the use of this cofactor and dependent enzymes as a resource for industrial biocatalysis are discussed.

Metabolic Pathway Rerouting in Paraburkholderia rhizoxinica Evolved Long-Overlooked Derivatives of Coenzyme F420

Coenzyme F₄₂₀ is a specialized redox cofactor with a negative redox potential. It supports biochemical processes like methanogenesis, degradation of xenobiotics, and the biosynthesis of antibiotics. Although well-studied in methanogenic archaea and actinobacteria, not much is known about F₄₂₀ in Gram-negative bacteria. Genome sequencing revealed F₄₂₀ biosynthetic genes in the Gram-negative, endofungal bacterium Paraburkholderia rhizoxinica, a symbiont of phytopathogenic fungi. Fluorescence microscopy, high-resolution LC-MS, and structure elucidation by NMR demonstrated that the encoded pathway is active and yields unexpected derivatives of F₄₂₀ (3PG-F₄₂₀). Further analyses of a biogas-producing microbial community showed that these derivatives are more widespread in nature. Genetic and biochemical studies of their biosynthesis established that a specificity switch in the guanylyltransferase CofC reprogrammed the pathway to start from 3-phospho-d-glycerate, suggesting a rerouting event during the evolution of F₄₂₀ biosynthesis. Furthermore, the cofactor activity of 3PG-F₄₂₀ was validated, thus opening up perspectives for its use in biocatalysis. The 3PG-F₄₂₀ biosynthetic gene cluster is fully functional in Escherichia coli, enabling convenient production of the cofactor by fermentation.