Aldehyde Production in Crude Lysate- and Whole Cell-Based Biotransformation Using a Noncanonical Redox Cofactor System

Investigation of the catalytic mechanism of targeted adsorption and selective hydrogenation based on d-π conjugated derivatives

D-π conjugated coordination polymers (CCPs) are often widely used in photocatalysis and electrocatalysis due to their unique electronic conductivity and structural flexibility. However, it remains a challenge to overcome the self-degradation of d-π CCPs in thermal catalysis and to effectively utilize their excellent electron transfer properties. Here, we present a series of d-π CCPs derivative after calcination treatment. The derivatives were optimized for overall electron cloud density by constructing two-dimensional pyridinic-nitrogen (N) doped carbon carriers, which exhibited the inherent π-electron delocalization and charge transfer properties of d-π CCPs. The presence of electron transfer was confirmed by X-ray Photoelectron Spectroscopy (XPS), Raman and kinetic analysis, demonstrating that this d-π CCPs derivative possesses excellent electron conduction ability and low activation energies for the reaction. Density-functional theory (DFT) calculations further confirmed the modulation of the nickel nanoparticles (Ni NPs) electronic state by the carriers, which resulted in strong Ni NPs interactions with the high-electron-density π-bonds of the CC bond. This property significantly enhances the target adsorption and activation of the CC bond, leading to a substantial enhancement of the reaction performance. This strategy provides a new development direction for the application of d-π CCPs in thermal catalysis.

Engineering a newly identified alcohol dehydrogenase from Sphingobium Sp. for efficient utilization of nicotinamide cofactors biomimetics

Nicotinamide cofactor biomimetics (NCBs) serve as low-cost alternatives to the expensive NAD(P)+/NAD(P)H, holding significant potential for applications in oxidoreductases. In this study, an alcohol dehydrogenase (SpADH2) from Sphingobium sp. SYK-6 was identified for the utilization of synthetic NCBs. SpADH2 exhibited a catalytic activity of 11.55 U/g in oxidation of syringyl alcohol when utilizing para-3-carbamoyl-1-(4-carboxybenzyl)pyridin-1-ium (p-BANA+) as cofactor. Semi-rational engineering of SpADH2 led to identification of key variants (H43L, A290I, H43L/A290I) with enhanced catalytic efficiency and specificity using p-BANA+ as the cofactor. Compared with wild-type, variant H43L/A290I exhibited a 7-fold increase in activity and an astonishing 6750-fold improvement in cofactor specificity ratio. Enzymatic characterization reveals that the substrate spectrum of SpADH2 could change significantly when utilizing different totally synthetic NCBs (tsNCBs). Furthermore, interaction analysis demonstrates critical roles of residues 43 and 290 in anchoring and release of p-BANA+. This study identified a natural ADH capable of utilizing totally synthetic NCBs, which has never been reported. Importantly, our results provide valuable ADH candidates for potential synthetic biology and industrial developments, and offer valuable guidance for identification and engineering ADHs toward utilizing NCBs as cofactors with improved catalytic performance.

Carbon-conserving bioproduction of malate in an E. coli-based cell-free system

Formate, a biologically accessible form of CO2, has attracted interest as a renewable feedstock for bioproduction. However, approaches are needed to investigate efficient routes for biological formate assimilation due to its toxicity and limited utilization by microorganisms. Cell-free systems hold promise due to their potential for efficient use of carbon and energy sources and compatibility with diverse feedstocks. However, bioproduction using purified cell-free systems is limited by costly enzyme purification, whereas lysate-based systems must overcome loss of flux to background reactions in the cell extract. Here, we engineer an E. coli-based system for an eight-enzyme pathway from DNA and incorporate strategies to regenerate cofactors and minimize loss of flux through background reactions. We produce the industrial di-acid malate from glycine, bicarbonate, and formate by engineering the carbon-conserving reductive TCA and formate assimilation pathways. We show that in situ regeneration of NADH drives metabolic flux towards malate, improving titer by 15-fold. Background reactions can also be reduced 6-fold by diluting the lysate following expression and introducing chemical inhibitors of competing reactions. Together, these results establish a carbon-conserving, lysate-based cell-free platform for malate production, producing 64 μM malate after 8 h. This system conserves 43 % of carbon otherwise lost as CO2 through the TCA cycle and incorporates 0.13 mol CO2 equivalents/mol glycine fed. Finally, techno-economic analysis of cell-free malate production from formate revealed that the high cost of lysate is a key challenge to the economic feasibility of the process, even assuming efficient cofactor recycling. This work demonstrates the capabilities of cell-free expression systems for both the prototyping of carbon-conserving pathways and the sustainable bioproduction of platform chemicals.

Biological production of nicotinamide mononucleotide: a review

Nicotinamide mononucleotide (NMN) presents significant therapeutic potential against aging-related conditions, such as Alzheimer's disease, due to its consistent and strong pharmacological effects. Aside from its anti-aging effect, NMN is also an emerging noncanonical cofactor for orthogonal metabolic pathways in the field of biomanufacturing. This has significant advantages in the field of metabolic engineering, allowing cells to produce unnatural chemicals without disrupting the natural cellular processes. NMN is produced through both the chemical and biological methods, with the latter being more environmentally sustainable. The primary biological production pathway centers on the enzyme nicotinamide phosphoribosyltransferase, which transforms nicotinamide and phosphoribosyl pyrophosphate to NMN. Efforts to increase NMN production have been explored in microorganisms, such as: Escherichia coli, Bacillus subtilis, and yeast, serving as biocatalysts, by rewiring their metabolic processes. Although most researchers are focusing on genetically and metabolically manipulating microorganisms to act as biocatalysts, a growing number of studies on cell-free synthesis are emerging as a promising strategy for producing NMN. This review explores the different biological production techniques of NMN employing microorganisms. This article, in particular, is essential to those who are working on NMN production using microbial strain engineering and cell-free systems.

Harnessing noncanonical redox cofactors to advance synthetic assimilation of one-carbon feedstocks

One-carbon (C1) feedstocks, such as carbon monoxide (CO), formate (HCO2H), methanol (CH3OH), and methane (CH4), can be obtained either through stepwise electrochemical reduction of CO2 with renewable electricity or via processing of organic side streams. These C1 substrates are increasingly investigated in biotechnology as they can contribute to a circular carbon economy. In recent years, noncanonical redox cofactors (NCRCs) emerged as a tool to generate synthetic electron circuits in cell factories to maximize electron transfer within a pathway of interest. Here, we argue that expanding the use of NCRCs in the context of C1-driven bioprocesses will boost product yields and facilitate challenging redox transactions that are typically out of the scope of natural cofactors due to inherent thermodynamic constraints.

Shifting redox reaction equilibria on demand using an orthogonal redox cofactor

Nature's two redox cofactors, nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide phosphate (NADP+), are held at different reduction potentials, driving catabolism and anabolism in opposite directions. In biomanufacturing, there is a need to flexibly control redox reaction direction decoupled from catabolism and anabolism. We established nicotinamide mononucleotide (NMN+) as a noncanonical cofactor orthogonal to NAD(P)+. Here we present the development of Nox Ortho, a reduced NMN+ (NMNH)-specific oxidase, that completes the toolkit to modulate NMNH:NMN+ ratio together with an NMN+-specific glucose dehydrogenase (GDH Ortho). The design principle discovered from Nox Ortho engineering and modeling is facilely translated onto six different enzymes to create NMN(H)-orthogonal biocatalysts with a consistent ~103-106-fold cofactor specificity switch from NAD(P)+ to NMN+. We assemble these enzymes to produce stereo-pure 2,3-butanediol in cell-free systems and in Escherichia coli, enabled by NMN(H)'s distinct redox ratio firmly set by its designated driving forces, decoupled from both NAD(H) and NADP(H).

CRISPR Tools for Engineering Prokaryotic Systems: Recent Advances and New Applications

In the past decades, the broad selection of CRISPR-Cas systems has revolutionized biotechnology by enabling multimodal genetic manipulation in diverse organisms. Rooted in a molecular engineering perspective, we recapitulate the different CRISPR components and how they can be designed for specific genetic engineering applications. We first introduce the repertoire of Cas proteins and tethered effectors used to program new biological functions through gene editing and gene regulation. We review current guide RNA (gRNA) design strategies and computational tools and how CRISPR-based genetic circuits can be constructed through regulated gRNA expression. Then, we present recent advances in CRISPR-based biosensing, bioproduction, and biotherapeutics across in vitro and in vivo prokaryotic systems. Finally, we discuss forthcoming applications in prokaryotic CRISPR technology that will transform synthetic biology principles in the near future.

Recent developments in enzymatic and microbial biosynthesis of flavor and fragrance molecules

Flavors and fragrances are an important class of specialty chemicals for which interest in biomanufacturing has risen during recent years. These naturally occurring compounds are often amenable to biosynthesis using purified enzyme catalysts or metabolically engineered microbial cells in fermentation processes. In this review, we provide a brief overview of the categories of molecules that have received the greatest interest, both academically and industrially, by examining scholarly publications as well as patent literature. Overall, we seek to highlight innovations in the key reaction steps and microbial hosts used in flavor and fragrance manufacturing.

Utilizing a cell-free protein synthesis platform for the biosynthesis of a natural product, caffeine

Natural products are a valuable source of pharmaceuticals, providing a majority of the small-molecule drugs in use today. However, their production through organic synthesis or in heterologous hosts can be difficult and time-consuming. Therefore, to allow for easier screening and production of natural products, we demonstrated the use of a cell-free protein synthesis system to partially assemble natural products in vitro using S-Adenosyl Methionine (SAM)-dependent methyltransferase enzyme reactions. The tea caffeine synthase, TCS1, was utilized to synthesize caffeine within a cell-free protein synthesis system. Cell-free systems also provide the benefit of allowing the use of substrates that would normally be toxic in a cellular environment to synthesize novel products. However, TCS1 is unable to utilize a compound like S-adenosyl ethionine as a cofactor to create ethylated caffeine analogs. The automation and reduced metabolic engineering requirements of cell-free protein synthesis systems, in combination with other synthesis methods, may enable the more efficient generation of new compounds. Graphical Abstract.

Design, construction, and application of noncanonical redox cofactor infrastructures

Controlling the flow of carbon and reducing power in biological systems is a central theme in metabolic engineering. Often, trade-offs in pushing carbon flux through targeted pathways while operating in conditions agreeable to the host are required due to the central pools of the shared native redox cofactors NAD(P)/H. Noncanonical redox cofactors (NRCs) have emerged as promising tools to transform how engineers develop biotransformation systems. These new-to-Nature redox cofactors have been demonstrated to function orthogonally to the endogenous cofactors, support pathway thermodynamics optimization, and achieve product scopes previously difficult to reach due to endogenous pathway crosstalk. This review will discuss the development of NRC infrastructures, comprising NRC pools, cofactor reduction sources, and cofactor oxidation sinks, the (pool-source-sink) infrastructure.

Antimicrobial peptides in combination with citronellal efficiently kills multidrug resistance bacteria

BACKGROUND

Antimicrobial peptides (AMPs) are considered as the most potential alternatives to antibiotics, but they have several drawbacks, including high cost, medium antimicrobial efficacy, poor cell selectivity, which limit clinical application. To overcome the above problems, combination therapy of AMPs with adjuvants might maximize the effectiveness of AMPs. We found that citronellal can substantially potentiate the ZY4R peptide efficacy against Escherichia coli ATCC25922. However, it is unclear whether ZY4R/citronellal combination poses synergistic antimicrobial effects against most bacteria, and their synergy mechanism has not been elucidated.

PURPOSE

To investigate synergistic antimicrobial efficacies, biosafety, and synergy mechanism of ZY4R/citronellal combination.

METHOD

Checkerboard, time-kill curves, cytotoxicity assays, and in vivo animal models were conducted to assess synergistic antimicrobial effects and biosafety of the ZY4R/citronellal combination. To evaluate their synergy mechanism, a series of cell-based assays and transcriptome analysis were performed.

RESULTS

ZY4R/citronellal combination exhibited synergistic antimicrobial effects against 20 clinically significant pathogens, with the fractional inhibitory concentration index (FICI) ranging from 0.313 to 0.047. Meanwhile, ZY4R/citronellal combination enhanced antimicrobial efficacies without compromising cell selectivity, contributing to decreasing drug dosage and improving biosafety. Compared with ZY4R (4 mg/kg) and citronellal (25 mg/kg) alone, ZY4R (4 mg/kg)/citronellal (25 mg/kg) combination significantly decreased the bacterial load in peritoneal fluid, liver, and kidney (P < 0.05) and alleviated pathological damage of the organs of mice. Mechanistic studies showed that ZY4R allowed citronellal to pass through the outer membrane rapidly and acted on the inner membrane together with citronellal, causing more potent membrane damage. The membrane damage prompted the continuous accumulation of citronellal in cells, and citronellal further induced energy breakdown and inhibited exopolysaccharide (EPS) production, which aggravated ZY4R-induced outer membrane damage, thereby resulting in bacterial death.

CONCLUSIONS

ZY4R/citronellal combination exhibited broad-spectrum synergy with a low resistance development and high biosafety. Their synergy mechanism acted on two important cellular targets (energy metabolism and membrane integrity). Combination therapy of ZY4R with citronellal may be a promising mixture to combat bacterial infections facing an antibiotic-resistance crisis.

Shifting Redox Reaction Equilibria on Demand Using an Orthogonal Redox Cofactor

Natural metabolism relies on chemical compartmentalization of two redox cofactors, NAD+ and NADP+, to orchestrate life-essential redox reaction directions. However, in whole cells the reliance on these canonical cofactors limits flexible control of redox reaction direction as these reactions are permanently tied to catabolism or anabolism. In cell-free systems, NADP+ is too expensive in large scale. We have previously reported the use of nicotinamide mononucleotide, (NMN+) as a low-cost, noncanonical redox cofactor capable of specific electron delivery to diverse chemistries. Here, we present Nox Ortho, an NMNH-specific water-forming oxidase, that completes the toolkit to modulate NMNH/NMN+ ratio. This work uncovers an enzyme design principle that succeeds in parallel engineering of six butanediol dehydrogenases as NMN(H)-orthogonal biocatalysts consistently with a 103 - 106 -fold cofactor specificity switch from NAD(P)+ to NMN+. We combine these to produce chiral-pure 2,3-butanediol (Bdo) isomers without interference from NAD(H) or NADP(H) in vitro and in E. coli cells. We establish that NMN(H) can be held at a distinct redox ratio on demand, decoupled from both NAD(H) and NADP(H) redox ratios in vitro and in vivo.

Engineering Candida boidinii formate dehydrogenase for activity with the non-canonical cofactor 3'-NADP(H)

Oxidoreductases catalyze essential redox reactions, and many require a diffusible cofactor for electron transport, such as NAD(H). Non-canonical cofactor analogs have been explored as a means to create enzymatic reactions that operate orthogonally to existing metabolism. Here, we aimed to engineer the formate dehydrogenase from Candid boidinii (CbFDH) for activity with the non-canonical cofactor nicotinamide adenine dinucleotide 3'-phosphate (3'-NADP(H)). We used PyRosetta, the Cofactor Specificity Reversal Structural Analysis and Library Design (CSR-SALAD), and structure-guided saturation mutagenesis to identify mutations that enable CbFDH to use 3'-NADP+. Two single mutants, D195A and D195G, had the highest activities with 3'-NADP+, while the double mutant D195G/Y196S exhibited the highest cofactor selectivity reversal behavior. Steady state kinetic analyses were performed; the D195A mutant exhibited the highest KTS value with 3'-NADP+. This work compares the utility of computational approaches for cofactor specificity engineering while demonstrating the engineering of an important enzyme for novel non-canonical cofactor selectivity.

Orthogonal glycolytic pathway enables directed evolution of noncanonical cofactor oxidase

Noncanonical cofactor biomimetics (NCBs) such as nicotinamide mononucleotide (NMN+) provide enhanced scalability for biomanufacturing. However, engineering enzymes to accept NCBs is difficult. Here, we establish a growth selection platform to evolve enzymes to utilize NMN+-based reducing power. This is based on an orthogonal, NMN+-dependent glycolytic pathway in Escherichia coli which can be coupled to any reciprocal enzyme to recycle the ensuing reduced NMN+. With a throughput of >106 variants per iteration, the growth selection discovers a Lactobacillus pentosus NADH oxidase variant with ~10-fold increase in NMNH catalytic efficiency and enhanced activity for other NCBs. Molecular modeling and experimental validation suggest that instead of directly contacting NCBs, the mutations optimize the enzyme's global conformational dynamics to resemble the WT with the native cofactor bound. Restoring the enzyme's access to catalytically competent conformation states via deep navigation of protein sequence space with high-throughput evolution provides a universal route to engineer NCB-dependent enzymes.

Directed evolution of phosphite dehydrogenase to cycle noncanonical redox cofactors via universal growth selection platform

Noncanonical redox cofactors are attractive low-cost alternatives to nicotinamide adenine dinucleotide (phosphate) (NAD(P)+) in biotransformation. However, engineering enzymes to utilize them is challenging. Here, we present a high-throughput directed evolution platform which couples cell growth to the in vivo cycling of a noncanonical cofactor, nicotinamide mononucleotide (NMN+). We achieve this by engineering the life-essential glutathione reductase in Escherichia coli to exclusively rely on the reduced NMN+ (NMNH). Using this system, we develop a phosphite dehydrogenase (PTDH) to cycle NMN+ with ~147-fold improved catalytic efficiency, which translates to an industrially viable total turnover number of ~45,000 in cell-free biotransformation without requiring high cofactor concentrations. Moreover, the PTDH variants also exhibit improved activity with another structurally deviant noncanonical cofactor, 1-benzylnicotinamide (BNA+), showcasing their broad applications. Structural modeling prediction reveals a general design principle where the mutations and the smaller, noncanonical cofactors together mimic the steric interactions of the larger, natural cofactors NAD(P)+.

Engineering Embden-Meyerhof-Parnas Glycolysis to Generate Noncanonical Reducing Power

Noncanonical cofactors such as nicotinamide mononucleotide (NMN+) supplant the electron-transfer functionality of the natural cofactors, NAD(P)+, at a lower cost in cell-free biomanufacturing and enable orthogonal electron delivery in whole-cell metabolic engineering. Here, we redesign the high-flux Embden-Meyerhof-Parnas (EMP) glycolytic pathway to generate NMN+-based reducing power, by engineering Streptococcus mutans glyceraldehyde-3-phosphate dehydrogenase (Sm GapN) to utilize NMN+. Through iterative rounds of rational design, we discover the variant GapN Penta (P179K-F153S-S330R-I234E-G210Q) with high NMN+-dependent activity and GapN Ortho (P179K-F153S-S330R-I234E-G214E) with ~3.4 × 106-fold switch in cofactor specificity from its native cofactor NADP+ to NMN+. GapN Ortho is further demonstrated to function in Escherichia coli only in the presence of NMN+, enabling orthogonal control of glucose utilization. Molecular dynamics simulation and residue network connectivity analysis indicate that mutations altering cofactor specificity must be coordinated to maintain the appropriate degree of backbone flexibility to position the catalytic cysteine. These results provide a strategy to guide future designs of NMN+-dependent enzymes and establish the initial steps toward an orthogonal EMP pathway with biomanufacturing potential.

Enzymatic synthesis of high-titer nicotinamide mononucleotide with a new nicotinamide riboside kinase and an efficient ATP regeneration system

BACKGROUND

β-Nicotinamide mononucleotide (NMN) is the direct precursor of nicotinamide coenzymes such as NAD+ and NADP+, which are widely applied in industrial biocatalysis especially involving cofactor-dependent oxidoreductases. Moreover, NMN is a promising candidate for medical uses since it is considered to be beneficial for improving health of aged people who usually suffer from an insufficient level of NAD+. To date, various methods have been developed for the synthesis of NMN. Chemical phosphorylation of nicotinamide riboside (NR) to NMN depends on excessive phosphine oxychloride and delicate temperature control, while fermentation of NMN is limited by low product titers, making it unsuitable for industrial-scale NMN production. As a result, the more efficient synthesis process of NMN is still challenging.

AIM

This work attempted to construct an eco-friendly and cost-effective biocatalytic process for transforming the chemically synthesized NR into the highly value-added NMN.

RESULTS

A new nicotinamide riboside kinase (Klm-NRK) was identified from Kluyveromyces marxianus. The specific activity of purified Klm-NRK was 7.9 U·mg-1 protein, ranking the highest record among the reported NRKs. The optimal pH of Klm-NRK was 7.0 in potassium phosphate buffer. The purified Klm-NRK retained a half activity after 7.29 h at 50 °C. The catalytic efficiencies (kcat/KM) toward ATP and nicotinamide riboside (NR) were 57.4 s-1·mM-1 and 84.4 s-1·mM-1, respectively. In the presence of an external ATP regeneration system (AcK/AcP), as much as 100 g·L-1 of NR could be completely phosphorylated to NMN in 8 h with Klm-NRK, achieving a molar isolation yield of 84.2% and a space-time yield of 281 g·L-1·day-1. These inspiring results indicated that Klm-NRK is a promising biocatalyst which provides an efficient approach for the bio-manufacturing of NMN in a high titer.

Cell-Free Noncanonical Redox Cofactor Systems

Noncanonical redox cofactor systems utilize nicotinamide adenine dinucleotide (phosphate), NAD(P)H, mimics to perform biotransformation reactions. Compared to systems utilizing native NAD(P)H, these noncanonical redox cofactors can offer decreased cost of cofactor supply, improved system activities, and can even supply reducing power directly to targeted reactions in complex biological environments. When these systems are operated in cell-free settings, the high level of user control afforded by direct access to the reaction system enables specific tuning of cofactor parameters, enzyme activity, and reaction progression to maximize system productivity. In this chapter, we will describe methods for constructing these cell-free noncanonical redox cofactor systems. Specifically, methods, design concepts, and system adaptation will be discussed for applying noncanonical redox cofactors to both purified protein-based and crude lysate-based biotransformation systems.

LuxAB-Based Microbial Cell Factories for the Sensing, Manufacturing and Transformation of Industrial Aldehydes

The application of genetically encoded biosensors enables the detection of small molecules in living cells and has facilitated the characterization of enzymes, their directed evolution and the engineering of (natural) metabolic pathways. In this work, the LuxAB biosensor system from Photorhabdus luminescens was implemented in Escherichia coli to monitor the enzymatic production of aldehydes from primary alcohols and carboxylic acid substrates. A simple high-throughput assay utilized the bacterial luciferase—previously reported to only accept aliphatic long-chain aldehydes—to detect structurally diverse aldehydes, including aromatic and monoterpene aldehydes. LuxAB was used to screen the substrate scopes of three prokaryotic oxidoreductases: an alcohol dehydrogenase (Pseudomonas putida), a choline oxidase variant (Arthrobacter chlorophenolicus) and a carboxylic acid reductase (Mycobacterium marinum). Consequently, high-value aldehydes such as cinnamaldehyde, citral and citronellal could be produced in vivo in up to 80% yield. Furthermore, the dual role of LuxAB as sensor and monooxygenase, emitting bioluminescence through the oxidation of aldehydes to the corresponding carboxylates, promises implementation in artificial enzyme cascades for the synthesis of carboxylic acids. These findings advance the bio-based detection, preparation and transformation of industrially important aldehydes in living cells.

Cell-Free Total Biosynthesis of Plant Terpene Natural Products using an Orthogonal Cofactor Regeneration System

Here we report the one-pot, cell-free enzymatic synthesis of the plant monoterpene nepetalactol starting from the readily available geraniol. A pair of orthogonal cofactor regeneration systems permitted NAD⁺-dependent geraniol oxidation followed by NADPH-dependent reductive cyclization without isolation of intermediates. The orthogonal cofactor regeneration system maintained a high ratio of NAD⁺ to NADH and a low ratio of NADP⁺ to NADPH. The overall reaction contains four biosynthetic enzymes, including a soluble P450; and five accessory and cofactor regeneration enzymes. Furthermore, addition of a NAD⁺-dependent dehydrogenase to the one-pot mixture led to ~1 g/L of nepetalactone, the active cat- attractant in catnip.

Creating enzymes and self-sufficient cells for biosynthesis of the non-natural cofactor nicotinamide cytosine dinucleotide

Nicotinamide adenine dinucleotide (NAD) and its reduced form are indispensable cofactors in life. Diverse NAD mimics have been developed for applications in chemical and biological sciences. Nicotinamide cytosine dinucleotide (NCD) has emerged as a non-natural cofactor to mediate redox transformations, while cells are fed with chemically synthesized NCD. Here, we create NCD synthetase (NcdS) by reprograming the substrate binding pockets of nicotinic acid mononucleotide (NaMN) adenylyltransferase to favor cytidine triphosphate and nicotinamide mononucleotide over their regular substrates ATP and NaMN, respectively. Overexpression of NcdS alone in the model host Escherichia coli facilitated intracellular production of NCD, and higher NCD levels up to 5.0 mM were achieved upon further pathway regulation. Finally, the non-natural cofactor self-sufficiency was confirmed by mediating an NCD-linked metabolic circuit to convert L-malate into D-lactate. NcdS together with NCD-linked enzymes offer unique tools and opportunities for intriguing studies in chemical biology and synthetic biology.