Biosynthesis “debugged”: Novel bioproduction strategies

Development of an enzymatic cascade for semi de novo ATP production using thermophilic enzymes

Industrial production of ATP has mostly relied on extraction from living cells. Although microbial and enzymatic ATP production have also been developed, the former suffers from complexity in product separation, while the latter requires expensive substrates, making their practical use difficult. To tackle these problems, we newly developed an enzymatic cascade for ATP production, which does not use expensive substrates, by assembling 16 thermophilic enzymes prepared through a heat-purification from the crude extract of recombinant Escherichia coli. This cascade consists of two modules: an ATP regeneration module based on a non-oxidative glycolysis and an ADP supply module. The ATP regeneration module can provide the energy required for phosphorylation of AMP and ADP to ATP while simultaneously supplying ribose-5-phosphate, a building block of adenosine phosphates, from inexpensive starch and inorganic phosphate. Ribose-5-phosphate is then adenylated with exogenously supplied adenine in the ADP supply module and further phosphorylated to ATP. This ATP production cascade is not accompanied by CO2 emission and is expected to be a novel ATP manufacturing platform with less environmental impact. In the present study, ATP production with 100 % molar conversion yield was achieved from 1 mM adenine. However, increasing the initial adenine concentration resulted in lower yields. Enzyme characterization and docking simulations revealed that this decline was due to non-competitive inhibition of certain enzymes by ATP, which could potentially be mitigated through protein engineering.

EnzymeMap: curation, validation and data-driven prediction of enzymatic reactions

Enzymatic reactions are an ecofriendly, selective, and versatile addition, sometimes even alternative to organic reactions for the synthesis of chemical compounds such as pharmaceuticals or fine chemicals. To identify suitable reactions, computational models to predict the activity of enzymes on non-native substrates, to perform retrosynthetic pathway searches, or to predict the outcomes of reactions including regio- and stereoselectivity are becoming increasingly important. However, current approaches are substantially hindered by the limited amount of available data, especially if balanced and atom mapped reactions are needed and if the models feature machine learning components. We therefore constructed a high-quality dataset (EnzymeMap) by developing a large set of correction and validation algorithms for recorded reactions in the literature and showcase its significant positive impact on machine learning models of retrosynthesis, forward prediction, and regioselectivity prediction, outperforming previous approaches by a large margin. Our dataset allows for deep learning models of enzymatic reactions with unprecedented accuracy, and is freely available online.

EHreact: Extended Hasse Diagrams for the Extraction and Scoring of Enzymatic Reaction Templates

Data-driven computer-aided synthesis planning utilizing organic or biocatalyzed reactions from large databases has gained increasing interest in the last decade, sparking the development of numerous tools to extract, apply, and score general reaction templates. The generation of reaction rules for enzymatic reactions is especially challenging since substrate promiscuity varies between enzymes, causing the optimal levels of rule specificity and optimal number of included atoms to differ between enzymes. This complicates an automated extraction from databases and has promoted the creation of manually curated reaction rule sets. Here, we present EHreact, a purely data-driven open-source software tool, to extract and score reaction rules from sets of reactions known to be catalyzed by an enzyme at appropriate levels of specificity without expert knowledge. EHreact extracts and groups reaction rules into tree-like structures, Hasse diagrams, based on common substructures in the imaginary transition structures. Each diagram can be utilized to output a single or a set of reaction rules, as well as calculate the probability of a new substrate to be processed by the given enzyme by inferring information about the reactive site of the enzyme from the known reactions and their grouping in the template tree. EHreact heuristically predicts the activity of a given enzyme on a new substrate, outperforming current approaches in accuracy and functionality.

Status Update on Bioelectrochemical Systems: Prospects for Carbon Electrode Design and Scale-Up

Bioelectrochemical systems (BES) employ enzymes, subcellular structures or whole electroactive microorganisms as biocatalysts for energy conversion purposes, such as the electrosynthesis of value-added chemicals and power generation in biofuel cells. From a bioelectrode engineering viewpoint, customizable nanostructured carbonaceous matrices have recently received considerable scientific attention as promising electrode supports due to their unique properties attractive to bioelectronics devices. This review demonstrates the latest advances in the application of nano- and micro-structured carbon electrode assemblies in BES. Specifically, in view of the gradual increase in the commercial applicability of these systems, we aim to address the stability and scalability of different BES designs and to highlight their potential roles in a circular bioeconomy.

Enzymatic Bioreactors: An Electrochemical Perspective

Biocatalysts provide a number of advantages such as high selectivity, the ability to operate under mild reaction conditions and availability from renewable resources that are of interest in the development of bioreactors for applications in the pharmaceutical and other sectors. The use of oxidoreductases in biocatalytic reactors is primarily focused on the use of NAD(P)-dependent enzymes, with the recycling of the cofactor occurring via an additional enzymatic system. The use of electrochemically based systems has been limited. This review focuses on the development of electrochemically based biocatalytic reactors. The mechanisms of mediated and direct electron transfer together with methods of immobilising enzymes are briefly reviewed. The use of electrochemically based batch and flow reactors is reviewed in detail with a focus on recent developments in the use of high surface area electrodes, enzyme engineering and enzyme cascades. A future perspective on electrochemically based bioreactors is presented.

Characterization of highly active 2-keto-3-deoxy-L-arabinonate and 2-keto-3-deoxy-D-xylonate dehydratases in terms of the biotransformation of hemicellulose sugars to chemicals

2-keto-3-L-arabinonate dehydratase (L-KdpD) and 2-keto-3-D-xylonate dehydratase (D-KdpD) are the third enzymes in the Weimberg pathway catalyzing the dehydration of respective 2-keto-3-deoxy sugar acids (KDP) to α-ketoglutaric semialdehyde (KGSA). The Weimberg pathway has been explored recently with respect to the synthesis of chemicals from L-arabinose and D-xylose. However, only limited work has been done toward characterizing these two enzymes. In this work, several new L-KdpDs and D-KdpDs were cloned and heterologously expressed in Escherichia coli. Following kinetic characterizations and kinetic stability studies, the L-KdpD from Cupriavidus necator (CnL-KdpD) and D-KdpD from Pseudomonas putida (PpD-KdpD) appeared to be the most promising variants from each enzyme class. Magnesium had no effect on CnL-KdpD, whereas increased activity and stability were observed for PpD-KdpD in the presence of Mg2+. Furthermore, CnL-KdpD was not inhibited in the presence of L-arabinose and L-arabinonate, whereas PpD-KdpD was inhibited with D-xylonate (I50 of 75 mM), but not with D-xylose. Both enzymes were shown to be highly active in the one-step conversions of L-KDP and D-KDP. CnL-KdpD converted > 95% of 500 mM L-KDP to KGSA in the first 2 h while PpD-KdpD converted > 90% of 500 mM D-KDP after 4 h. Both enzymes in combination were able to convert 83% of a racemic mixture of D,L-KDP (500 mM) after 4 h, with both enzymes being specific toward the respective stereoisomer. Key points • L-KdpDs and D-KdpDs are specific toward L- and D-KDP, respectively. • Mg2+affected activity and stabilities of D-KdpDs, but not of L-KdpDs. • CnL-KdpD and PpD-KdpD converted 0.5 M of each KDP isomer reaching 95 and 90% yield. • Both enzymes in combination converted 0.5 M racemic D,L-KDP reaching 83% yield.

Cell-free biosynthesis of limonene using enzyme-enriched Escherichia coli lysates

Isoprenoids are an attractive class of metabolites for enzymatic synthesis from renewable substrates. However, metabolic engineering of microorganisms for monoterpenoid production is limited by the need for time-consuming, and often non-intuitive, combinatorial tuning of biosynthetic pathway variations to meet design criteria. Towards alleviating this limitation, the goal of this work was to build a modular, cell-free platform for construction and testing of monoterpenoid pathways, using the fragrance and flavoring molecule limonene as a model. In this platform, multiple Escherichia coli lysates, each enriched with a single overexpressed pathway enzyme, are mixed to construct the full biosynthetic pathway. First, we show the ability to synthesize limonene from six enriched lysates with mevalonate substrate, an adenosine triphosphate (ATP) source, and cofactors. Next, we extend the pathway to use glucose as a substrate, which relies on native metabolism in the extract to convert glucose to acetyl-CoA along with three additional enzymes to convert acetyl-CoA to mevalonate. We find that the native E. coli farnesyl diphosphate synthase (IspA) is active in the lysate and diverts flux from the pathway intermediate geranyl pyrophospahte to farnesyl pyrophsophate and the byproduct farnesol. By adjusting the relative levels of cofactors NAD+, ATP and CoA, the system can synthesize 0.66 mM (90.2 mg l-1) limonene over 24 h, a productivity of 3.8 mg l-1 h-1. Our results highlight the flexibility of crude lysates to sustain complex metabolism and, by activating a glucose-to-limonene pathway with 9 heterologous enzymes encompassing 20 biosynthetic steps, expands an approach of using enzyme-enriched lysates for constructing, characterizing and prototyping enzymatic pathways.

Characterization and application of chemical-resistant polyurethane-based enzyme and whole cell compartments

This study presents the preparation and physical-chemical characterization of chemical resistant polyurethane-based compartments for biocatalytic application. The artificial compartments were prepared from an emulsion of polymer precursor and an aqueous phase that includes a biocatalytic reaction system. After curing, highly dispersed aqueous domains were obtained, which still contain the entire biocatalytic reaction system and remain fixed in the solid polymer preparation. The tensile and compression behavior of the prepared polymeric material is not significantly affected by the incorporation and facilitates excellent stability against various organic solvents and acid solutions. Thereby, the compartments can be used not only for enantioselective alcohol-dehydrogenase catalyzed reduction but also for a whole cell catalyzed hydrolysis of esters. Moreover, the compartmented whole-cell system was considerably stable to allow multiple reuses without a noticeable loss of catalytic activity of the incorporated whole cell catalytic reaction system.

Identification of d-carbamoylase for biocatalytic cascade synthesis of d-tryptophan featuring high enantioselectivity

In this study, an enantioselective d-carbamoylase (AcHyuC) was identified from Arthrobacter crystallopoietes with optimum pH of 8.5, much more compatible with hydantoinase process than other reported d-N-carbamoylases. AcHyuC has a substrate preference for aromatic carbamoyl-compounds. The dynamic kinetic resolution (DKR) cascade was developed by combining this AcHyuC with hydantoin racemase from Arthrobacter aurescens (AaHyuA) and d-hydantoinase from Agrobacterium tumefaciens (AtHyuH) for enantioselective resolution of l-indolylmethylhydantoin into d-Trp. The optimum pH of DKR cascade reaction was determined to be 8.0, and PEG 400 could facilitate the reaction. As much as 80mM l-indolylmethylhydantoin could be fully converted to d-Trp within 12h at 0.5L scale, with 99.4% yield, >99.9% e.e. and productivity of 36.6gL^-1d^-1. This study provides a new d-carbamoylase compatible with the DKR cascade for efficient production of optically pure d-Trp from l-indolylmethylhydantoin.

Deacidification of grass silage press juice by continuous production of acetoin from its lactate via an immobilized enzymatic reaction cascade

An immobilized enzymatic reaction cascade was designed and optimized for the deacidification of grass silage press juice (SPJ), thus facilitating the production of bio-based chemicals. The cascade involves a three-step process using four enzymes immobilized in a Ca-alginate gel and uses lactic acid to form acetoin, a value-added product. The reaction is performed with a continuous, pH-dependent substrate feed under oxygenation. With titrated lactic acid yields of up to 91% and reaction times of ca. 6h was achieved. Using SPJ as titrant yields of 49% were obtained within 6h. In this deacidification process, with acetoin one value-added bio-based chemical is produced while simultaneously the remaining press juice can be used in applications that require a higher pH. Such, this system can be applied in a multi-product biorefinery concept to take full advantage of nutrient-rich SPJ, which is a widely available and easily storable renewable resource.

Preparation and Characterization of Enzyme Compartments in UV-Cured Polyurethane-Based Materials and Their Application in Enzymatic Reactions

The preparation and characterization of UV-cured polyurethane-based materials for the mild inclusion immobilization of enzymes was investigated. Full curing of the polymer precursor/enzyme solution mixture was realized by a short irradiation with UV-light at ambient temperatures. The included aqueous enzyme solution remains highly dispersed in the polymer material with an even size distribution throughout the polymer material. The presented concept provides stable enzyme compartments which were applied for an alcohol dehydrogenase-catalyzed reduction reaction in organic solvents. Cofactor regeneration was achieved by a substrate-coupled approach via 2-propanol or an enzyme-coupled approach by a glucose dehydrogenase. This reaction concept can also be used for a simultaneous application of contrary biocatalytic reaction conditions within an enzymatic cascade reaction. Independent polymer-based reaction compartments were provided for two incompatible enzymatic reaction systems (alcohol dehydrogenase and hydroxynitrile lyase), while the relevant reactants diffuse between the applied compartments.

Cell-Free Mixing of Escherichia coli Crude Extracts to Prototype and Rationally Engineer High-Titer Mevalonate Synthesis

Cell-free metabolic engineering (CFME) is advancing a powerful paradigm for accelerating the design and synthesis of biosynthetic pathways. However, as most cell-free biomolecule synthesis systems to date use purified enzymes, energy and cofactor balance can be limiting. To address this challenge, we report a new CFME framework for building biosynthetic pathways by mixing multiple crude lysates, or extracts. In our modular approach, cell-free lysates, each selectively enriched with an overexpressed enzyme, are generated in parallel and then combinatorically mixed to construct a full biosynthetic pathway. Endogenous enzymes in the cell-free extract fuel high-level energy and cofactor regeneration. As a model, we apply our framework to synthesize mevalonate, an intermediate in isoprenoid synthesis. We use our approach to rapidly screen enzyme variants, optimize enzyme ratios, and explore cofactor landscapes for improving pathway performance. Further, we show that genomic deletions in the source strain redirect metabolic flux in resultant lysates. In an optimized system, mevalonate was synthesized at 17.6 g·L^-1 (119 mM) over 20 h, resulting in a volumetric productivity of 0.88 g·L^-1·hr^-1. We also demonstrate that this system can be lyophilized and retain biosynthesis capability. Our system catalyzes ∼1250 turnover events for the cofactor NAD⁺ and demonstrates the ability to rapidly prototype and debug enzymatic pathways in vitro for compelling metabolic engineering and synthetic biology applications.

Forward design of a complex enzyme cascade reaction

Enzymatic reaction networks are unique in that one can operate a large number of reactions under the same set of conditions concomitantly in one pot, but the nonlinear kinetics of the enzymes and the resulting system complexity have so far defeated rational design processes for the construction of such complex cascade reactions. Here we demonstrate the forward design of an in vitro 10-membered system using enzymes from highly regulated biological processes such as glycolysis. For this, we adapt the characterization of the biochemical system to the needs of classical engineering systems theory: we combine online mass spectrometry and continuous system operation to apply standard system theory input functions and to use the detailed dynamic system responses to parameterize a model of sufficient quality for forward design. This allows the facile optimization of a 10-enzyme cascade reaction for fine chemical production purposes.

Building multi-component enzymatic processes in one pot is challenged by the inherent complexity of each biochemical system. Here, the authors use online mass spectroscopy and engineering systems theory to achieve forward design of a ten-membered reaction cascade.

Systems biocatalysis: para-alkenylation of unprotected phenols

Commercially available phenol derivatives were transformed with pyruvate to form a new C–C bond leading to the correspondingpara-coumaric acids and only one molecule of water as an innocent side product in buffer.

Crystallization behaviour of glyceraldehyde dehydrogenase from Thermoplasma acidophilum

The glyceraldehyde dehydrogenase from Thermoplasma acidophilum (TaAlDH) is a microbial enzyme that catalyzes the oxidation of D-glyceraldehyde to D-glycerate in the artificial enzyme cascade designed for the conversion of glucose to the organic solvents isobutanol and ethanol. Various mutants of TaAlDH were constructed by a random approach followed by site-directed and saturation mutagenesis in order to improve the properties of the enzyme that are essential for its functioning within the cascade. Two enzyme variants, wild-type TaAlDH (TaAlDHwt) and an F34M+S405N variant (TaAlDH F34M+S405N), were successfully crystallized. Crystals of TaAlDHwt belonged to the monoclinic space group P1211 with eight molecules per asymmetric unit and diffracted to a resolution of 1.95 Å. TaAlDH F34M+S405N crystallized in two different space groups: triclinic P1 with 16 molecules per asymmetric unit and monoclinic C121 with four molecules per asymmetric unit. These crystals diffracted to resolutions of 2.14 and 2.10 Å for the P1 and C121 crystals, respectively.

Cell-free metabolic engineering: biomanufacturing beyond the cell

Industrial biotechnology and microbial metabolic engineering are poised to help meet the growing demand for sustainable, low-cost commodity chemicals and natural products, yet the fraction of biochemicals amenable to commercial production remains limited. Common problems afflicting the current state-of-the-art include low volumetric productivities, build-up of toxic intermediates or products, and byproduct losses via competing pathways. To overcome these limitations, cell-free metabolic engineering (CFME) is expanding the scope of the traditional bioengineering model by using in vitro ensembles of catalytic proteins prepared from purified enzymes or crude lysates of cells for the production of target products. In recent years, the unprecedented level of control and freedom of design, relative to in vivo systems, has inspired the development of engineering foundations for cell-free systems. These efforts have led to activation of long enzymatic pathways (>8 enzymes), near theoretical conversion yields, productivities greater than 100 mg L(-1) h(-1) , reaction scales of >100 L, and new directions in protein purification, spatial organization, and enzyme stability. In the coming years, CFME will offer exciting opportunities to: (i) debug and optimize biosynthetic pathways; (ii) carry out design-build-test iterations without re-engineering organisms; and (iii) perform molecular transformations when bioconversion yields, productivities, or cellular toxicity limit commercial feasibility.

Synthetic biology outside the cell: linking computational tools to cell-free systems

As mathematical models become more commonly integrated into the study of biology, a common language for describing biological processes is manifesting. Many tools have emerged for the simulation of in vivo synthetic biological systems, with only a few examples of prominent work done on predicting the dynamics of cell-free synthetic systems. At the same time, experimental biologists have begun to study dynamics of in vitro systems encapsulated by amphiphilic molecules, opening the door for the development of a new generation of biomimetic systems. In this review, we explore both in vivo and in vitro models of biochemical networks with a special focus on tools that could be applied to the construction of cell-free expression systems. We believe that quantitative studies of complex cellular mechanisms and pathways in synthetic systems can yield important insights into what makes cells different from conventional chemical systems.

Improving the NADH-cofactor specificity of the highly active AdhZ3 and AdhZ2 from Escherichia coli K-12

Biocatalysis is a promising tool for the sustainable production of chemicals. When cofactor depending enzymatic reactions are involved the applicability of the right cofactor is a central issue. One important example in this regard is the production of alcohols by nicotinamide cofactor (NAD(P)(+)) depending alcohol dehydrogenases. AdhZ3 from Escherichia coli, which is important for the production of alcohols from biomass, has a preference for NADPH as cofactor. We used a structure guided site-specific random approach, to change the cofactor preference towards NADH and to deduce more general rules for redesigning the cofactor specificity. Transfer of a triplet motif from NADH preferring horse liver ADH to AdhZ3 showed an insufficient switch in the preference towards NADH. A combinatorial site saturation mutagenesis altering three residues at once was applied. Library screening with two different cofactor concentrations (0.1 and 0.3mM) resulted in nine improved variants with AdhZ3-LND having the highest vmax and AdhZ3-CND having the lowest K(m). Asparagine was the most frequent amino acid found in eight of nine triplet motifs. To verify the triplet-motif, two variants of E. coli AdhZ2 DIN and LND were designed and confirmed for improved activity with NADH.

Refolding of a thermostable glyceraldehyde dehydrogenase for application in synthetic cascade biomanufacturing

The production of chemicals from renewable resources is gaining importance in the light of limited fossil resources. One promising alternative to widespread fermentation based methods used here is Synthetic Cascade Biomanufacturing, the application of minimized biocatalytic reaction cascades in cell free processes. One recent example is the development of the phosphorylation independent conversion of glucose to ethanol and isobutanol using only 6 and 8 enzymes, respectively. A key enzyme for this pathway is aldehyde dehydrogenase from Thermoplasma acidophilum, which catalyzes the highly substrate specific oxidation of d-glyceraldehyde to d-glycerate. In this work the enzyme was recombinantly expressed in Escherichia coli. Using matrix-assisted refolding of inclusion bodies the yield of enzyme production was enhanced 43-fold and thus for the first time the enzyme was provided in substantial amounts. Characterization of structural stability verified correct refolding of the protein. The stability of the enzyme was determined by guanidinium chloride as well as isobutanol induced denaturation to be ca. -8 kJ/mol both at 25°C and 40°C. The aldehyde dehydrogenase is active at high temperatures and in the presence of small amounts of organic solvents. In contrast to previous publications, the enzyme was found to accept NAD(+) as cofactor making it suitable for application in the artificial glycolysis.

Improvement of thermostable aldehyde dehydrogenase by directed evolution for application in Synthetic Cascade Biomanufacturing

The aldehyde dehydrogenase from Thermoplasma acidophilum, which was previously implemented as a key enzyme in a synthetic cell-free reaction cascade for the production of alcohols, was optimized by directed evolution. Improvements have been made to enhance reaction velocity and solubility. Using a random approach followed by site-directed and saturation mutagenesis, three beneficial amino acid mutations were found after screening of ca. 20,000 variants. Mutation Y399C enhanced the protein solubility after recombinant expression in Escherichia coli 6-fold. Two further mutations, F34M and S405N, enhanced enzyme activity with the cofactor NAD(+) by a factor of eight. Impacts on enzyme stability and substrate specificity were negligible. Modeling of the enzyme structure did not reveal any direct interactions between the amino acid substitutions and residues of the active site or the enzyme's substrates. Thus, a directed evolution approach allowed for the generation of improved enzyme variants which were unlikely to be found by rational or semi-rational strategies.

Discovery and characterization of a novel ATP/polyphosphate xylulokinase from a hyperthermophilic bacterium Thermotoga maritima

Xylulokinase (XK, E.C. 2.7.1.17) is one of the key enzymes in xylose metabolism and it is essential for the activation of pentoses for the sustainable production of biocommodities from biomass sugars. The open reading frame (TM0116) from the hyperthermophilic bacterium Thermotoga maritima MSB8 encoding a putative xylulokinase were cloned and expressed in Escherichia coli BL21 Star (DE3) in the Luria-Bertani and auto-inducing high-cell-density media. The basic biochemical properties of this thermophilic XK were characterized. This XK has the optimal temperature of 85 °C. Under a suboptimal condition of 60 °C, the k cat was 83 s⁻¹, and the K(m) values for xylulose and ATP were 1.24 and 0.71 mM, respectively. We hypothesized that this XK could work on polyphosphate possibly because this ancestral thermophilic microorganism utilizes polyphosphate to regulate the Embden-Meyerhof pathway and its substrate-binding residues are somewhat similar to those of other ATP/polyphosphate-dependent kinases. This XK was found to work on low-cost polyphosphate, exhibiting 41 % of its specific activity on ATP. This first ATP/polyphosphate XK could have a great potential for xylose utilization in thermophilic ethanol-producing microorganisms and cell-free biosystems for low-cost biomanufacturing without the use of ATP.

Self-assembly of synthetic metabolons through synthetic protein scaffolds: one-step purification, co-immobilization, and substrate channeling

One-step purification of a multi-enzyme complex was developed based on a mixture of cell extracts containing three dockerin-containing enzymes and one family 3 cellulose-binding module (CBM3)-containing scaffoldin through high-affinity adsorption on low-cost solid regenerated amorphous cellulose (RAC). The three-enzyme complex, called synthetic metabolon, was self-assembled through the high-affinity interaction between the dockerin in each enzyme and three cohesins in the synthetic scaffoldin. The metabolons were either immobilized on the external surface of RAC or free when the scaffoldin contained an intein between the CBM3 and three cohesins. The immobilized and free metabolons containing triosephosphate isomerase, aldolase, and fructose 1,6-biphosphatase exhibited initial reaction rates 48 and 38 times, respectively, that of the non-complexed three-enzyme mixture at the same enzyme loading. Such reaction rate enhancements indicated strong substrate channeling among synthetic metabolons due to the close spatial organization among cascade enzymes. These results suggested that the construction of synthetic metabolons by using cohesins, dockerins, and cellulose-binding modules from cellulosomes not only decreased protein purification labor and cost for in vitro synthetic biology projects but also accelerated reaction rates by 1 order of magnitude compared to non-complexed enzymes. Synthetic metabolons would be an important biocatalytic module for in vitro and in vivo synthetic biology projects.

Cell-free Biosystems in the Production of Electricity and Bioenergy

: Increasing needs of green energy and concerns of climate change are motivating intensive R&D efforts toward the low-cost production of electricity and bioenergy, such as hydrogen, alcohols, and jet fuel, from renewable sugars. Cell-free biosystems for biomanufacturing (CFB2) have been suggested as an emerging platform to replace mainstream microbial fermentation for the cost-effective production of some biocommodities. As compared to whole-cell factories, cell-free biosystems comprised of synthetic enzymatic pathways have numerous advantages, such as high product yield, fast reaction rate, broad reaction condition, easy process control and regulation, tolerance of toxic compound/product, and an unmatched capability of performing unnatural reactions. However, issues pertaining to high costs and low stabilities of enzymes and cofactors as well as compromised optimal conditions for different source enzymes need to be solved before cell-free biosystems are scaled up for biomanufacturing. Here, we review the current status of cell-free technology, update recent advances, and focus on its applications in the production of electricity and bioenergy.