Fusion of Ferredoxin and Cytochrome P450 Enables Direct Light-Driven Biosynthesis

Efficient sex hormone biosensors in Saccharomyces cerevisiae cells to evaluate human aromatase activity and inhibition

Yeast sex-hormone whole-cell biosensors are analytical tools characterized by long-time storage and low production cost. We engineered compact β-estradiol biosensors in S. cerevisiae cells by leveraging short (20-nt long) operators bound by the fusion protein LexA-ER-VP64-where ER is the human estrogen receptor and VP64 a strong viral activation domain. Our best biosensors showed high accuracy since their recovery concentration ranged between 97.13% and 104.69%. As a novelty, we built on top of them testosterone biosensors that exploit the conversion of testosterone into β-estradiol by the human aromatase enzyme-expressed in S. cerevisiae together with its co-factor CPR. We used our engineered yeast strains to evaluate aromatase activity through fluorescence measurements without the need for protein purification. Besides, we set up an aromatase-inhibitors evaluation assay to measure the IC50 (half-maximal inhibitory concentration) of candidate inhibitory compounds and developed a screening assay for enzymes that metabolize β-estradiol that demands only to measure fluorescence. These two assays allow the screening of a large number of chemicals and proteins in a fast and economic fashion. We think that our work will facilitate considerably high throughput screening for the discovery of new drugs and unknown metabolic processes.

A Convenient Route to Large-Scale Chemical Synthesis of p-Hydroxyphenylacetaldehyde Oxime and Its p-β-d-Glucopyranoside: Key Intermediates and Products in Plant Specialized Metabolism

Oximes are unrecognized chameleons in general and specialized plant metabolism. E- and Z-p-hydroxyphenylacetaldehyde oxime are key intermediates in the biosynthesis of the cyanogenic glucoside dhurrin produced in sorghum. Nevertheless, none of the geometrical oxime isomers accumulate in the plant. Herein, we report a convenient route to the chemical synthesis of E- and Z-p-hydroxyphenylacetaldehyde oxime and its biologically produced p-β-d-glucopyranoside using p-hydroxyphenylacetic acid as a starting material. This starting material is also available in radiolabeled forms. All reaction steps proceeded with excellent yield under mild conditions, operational facility, and scalability.

Strong heterologous electron sink outcompetes alternative electron transport pathways in photosynthesis

Improvement of photosynthesis requires a thorough understanding of electron partitioning under both natural and strong electron sink conditions. We applied a wide array of state-of-the-art biophysical and biochemical techniques to thoroughly investigate the fate of photosynthetic electrons in the engineered cyanobacterium Synechocystis sp. PCC 6803, a blueprint for photosynthetic biotechnology, expressing the heterologous gene for ene-reductase, YqjM. This recombinant enzyme catalyses the reduction of an exogenously added substrate into the desired product by utilising photosynthetically produced NAD(P)H, enabling whole-cell biotransformation. Through coupling the biotransformation reaction with biophysical measurements, we demonstrated that the strong artificial electron sink, outcompetes the natural electron valves, the flavodiiron protein-driven Mehler-like reaction and cyclic electron transport. These results show that ferredoxin-NAD(P)H-oxidoreductase is the preferred route for delivering photosynthetic electrons from reduced ferredoxin and the cellular NADPH/NADP+ ratio as a key factor in orchestrating photosynthetic electron flux. These insights are crucial for understanding molecular mechanisms of photosynthetic electron transport and harnessing photosynthesis for sustainable bioproduction by engineering the cellular source/sink balance. Furthermore, we conclude that identifying the bioenergetic bottleneck of a heterologous electron sink is a crucial prerequisite for targeted engineering of photosynthetic biotransformation platforms.

Source leaves are regulated by sink strengths through non-coding RNAs and alternative polyadenylation in cucumber (Cucumis sativus L.)

BACKGROUND

The yield of major crops is generally limited by sink capacity and source strength. Cucumber is a typical raffinose family oligosaccharides (RFOs)-transporting crop. Non-coding RNAs and alternative polyadenylation (APA) play important roles in the regulation of growth process in plants. However, their roles on the sink‒source regulation have not been demonstrated in RFOs-translocating species.

RESULTS

Here, whole-transcriptome sequencing was applied to compare the leaves of cucumber under different sink strength, that is, no fruit-carrying leaves (NFNLs) and fruit-carrying leaves (FNLs) at 12th node from the bottom. The results show that 1101 differentially expressed (DE) mRNAs, 79 DE long non-coding RNAs (lncRNAs) and 23 DE miRNAs were identified, which were enriched in photosynthesis, energy production and conversion, plant hormone signal transduction, starch and carbohydrate metabolism and protein synthesis pathways. Potential co-expression networks like, DE lncRNAs-DE mRNAs/ DE miRNAs-DE mRNAs, and competing endogenous RNA (ceRNA) regulation models (DE lncRNAs-DE miRNAs-DE mRNAs) associated with sink‒source allocation, were constructed. Furthermore, 37 and 48 DE genes, which enriched in MAPK signaling and plant hormone signal transduction pathway, exist differentially APA, and SPS (CsaV3_2G033300), GBSS1 (CsaV3_5G001560), ERS1 (CsaV3_7G029600), PNO1 (CsaV3_3G003950) and Myb (CsaV3_3G022290) may be regulated by both ncRNAs and APA between FNLs and NFNLs, speculating that ncRNAs and APA are involved in the regulation of gene expression of cucumber sink‒source carbon partitioning.

CONCLUSIONS

These results reveal a comprehensive network among mRNAs, ncRNAs, and APA in cucumber sink-source relationships. Our findings also provide valuable information for further research on the molecular mechanism of ncRNA and APA to enhance cucumber yield.

Photosynthesis: Genetic Strategies Adopted to Gain Higher Efficiency

The global challenge of feeding an ever-increasing population to maintain food security requires novel approaches to increase crop yields. Photosynthesis, the fundamental energy and material basis for plant life on Earth, is highly responsive to environmental conditions. Evaluating the operational status of the photosynthetic mechanism provides insights into plants' capacity to adapt to their surroundings. Despite immense effort, photosynthesis still falls short of its theoretical maximum efficiency, indicating significant potential for improvement. In this review, we provide background information on the various genetic aspects of photosynthesis, explain its complexity, and survey relevant genetic engineering approaches employed to improve the efficiency of photosynthesis. We discuss the latest success stories of gene-editing tools like CRISPR-Cas9 and synthetic biology in achieving precise refinements in targeted photosynthesis pathways, such as the Calvin-Benson cycle, electron transport chain, and photorespiration. We also discuss the genetic markers crucial for mitigating the impact of rapidly changing environmental conditions, such as extreme temperatures or drought, on photosynthesis and growth. This review aims to pinpoint optimization opportunities for photosynthesis, discuss recent advancements, and address the challenges in improving this critical process, fostering a globally food-secure future through sustainable food crop production.

Enlighting Electron Routes In Oxyfunctionalizing Synechocystis sp. PCC 6803

Phototrophic microorganisms, like cyanobacteria, are gaining attention as host organisms for biocatalytic processes with light as energy source and water as electron source. Redox enzymes, especially oxygenases, can profit from in-situ supply of co-substrates, i. e., reduction equivalents and O2 , by the photosynthetic light reaction. The electron transfer downstream of PS I to heterologous electron consuming enzymes in principle can involve NADPH, NADH, and/or ferredoxin, whereas most direct and efficient transfer is desirable. Here, we use the model organism Synechocystis sp. PCC 6803 to investigate, to what extent host and/or heterologous constituents are involved in electron transfer to a heterologous cytochrome P450 monooxygenase from Acidovorax sp. CHX100. Interestingly, in this highly active light-fueled cycloalkane hydroxylating biocatalyst, host-intrinsic enzymes were found capable of completely substituting the function of the Acidovorax ferredoxin reductase. To a certain extent (20 %), this also was true for the Acidovorax ferredoxin. These results indicate the presence of a versatile set of electron carriers in cyanobacteria, enabling efficient and direct coupling of electron consuming reactions to photosynthetic water oxidation. This will both simplify and promote the use of phototrophic microorganisms for sustainable production processes.

Production of Gibberellins via a Non-Natural Pathway Using Steviol as a Substrate

Gibberellins (GAs) are plant hormones widely used in agriculture. At present, GAs are produced by fermentation of the fungus Fusarium fujikuroi. However, fungal growth is too slow, resulting in slow fungal fermentation and a low yield. Here, to develop an alternative production source of GAs, an artificial pathway was engineered in Escherichia coli. By selecting and combining enzymes derived from plants and bacteria, a novel 4-enzyme pathway was successfully constructed to produce GAs using steviol, a readily available and less valuable byproduct during enzymatic refining of rebaudioside A, as a feedstock. Whole-cell biotransformation with E. coli strain expressing the novel pathway produced 71.17 ± 2.00 mg/L GA1 and a trace amount of GA3 from steviol in 48 h. This report presents a significant advancement in the fast production of GAs and establishes a method for the metabolism of terpenoids to produce target products in microbial hosts.

Solar-powered P450 catalysis: Engineering electron transfer pathways from photosynthesis to P450s

With the increasing focus on green chemistry, biocatalysis is becoming more widely used in the pharmaceutical and other chemical industries for sustainable production of high value and structurally complex chemicals. Cytochrome P450 monooxygenases (P450s) are attractive biocatalysts for industrial application due to their ability to transform a huge range of substrates in a stereo- and regiospecific manner. However, despite their appeal, the industrial application of P450s is limited by their dependence on costly reduced nicotinamide adenine dinucleotide phosphate (NADPH) and one or more auxiliary redox partner proteins. Coupling P450s to the photosynthetic machinery of a plant allows photosynthetically-generated electrons to be used to drive catalysis, overcoming this cofactor dependency. Thus, photosynthetic organisms could serve as photobioreactors with the capability to produce value-added chemicals using only light, water, CO2 and an appropriate chemical as substrate for the reaction/s of choice, yielding new opportunities for producing commodity and high-value chemicals in a carbon-negative and sustainable manner. This review will discuss recent progress in using photosynthesis for light-driven P450 biocatalysis and explore the potential for further development of such systems.

Electrochemical transformations catalyzed by cytochrome P450s and peroxidases

Cytochrome P450s (Cyt P450s) and peroxidases are enzymes featuring iron heme cofactors that have wide applicability as biocatalysts in chemical syntheses. Cyt P450s are a family of monooxygenases that oxidize fatty acids, steroids, and xenobiotics, synthesize hormones, and convert drugs and other chemicals to metabolites. Peroxidases are involved in breaking down hydrogen peroxide and can oxidize organic compounds during this process. Both heme-containing enzymes utilize active Fe^IVO intermediates to oxidize reactants. By incorporating these enzymes in stable thin films on electrodes, Cyt P450s and peroxidases can accept electrons from an electrode, albeit by different mechanisms, and catalyze organic transformations in a feasible and cost-effective way. This is an advantageous approach, often called bioelectrocatalysis, compared to their biological pathways in solution that require expensive biochemical reductants such as NADPH or additional enzymes to recycle NADPH for Cyt P450s. Bioelectrocatalysis also serves as an ex situ platform to investigate metabolism of drugs and bio-relevant chemicals. In this paper we review biocatalytic electrochemical reactions using Cyt P450s including C-H activation, S-oxidation, epoxidation, N-hydroxylation, and oxidative N-, and O-dealkylation; as well as reactions catalyzed by peroxidases including synthetically important oxidations of organic compounds. Design aspects of these bioelectrocatalytic reactions are presented and discussed, including enzyme film formation on electrodes, temperature, pH, solvents, and activation of the enzymes. Finally, we discuss challenges and future perspective of these two important bioelectrocatalytic systems.

Yeast-based system for in vivo evaluation of alleles of the anthocyanin production pathway

Plants produce anthocyanins to incite the pollination and seed dispersion performed by pigment-attracted animals. These natural blue-to-red-coloured pigments can be used as food colourants and antioxidants. For this purpose, microbial bioproduction of anthocyanins has become of industrial interest in recent years. 20 new alleles of anthocyanin production pathway genes were extracted and characterised for protein expression level and stability using a developed single-PCR product gene-entry system for tagged protein synthesis in yeast S. cerevisiae. Enzymatic activities of these proteins in the episomally complemented in vivo systems were compared by HPLC-MS analysis. Results show that the codon optimisation of the anthocyanin pathway genes is not essential for the effective heterologous expression in yeast. Elevating the cellular abundance of CHS and F3H enzymes can increase anthocyanidin production from supplemented precursors. New alleles VmF3Hv1 and VuCHS were shown to have the best performance in the analysed system. System complementation with flavonoid 3',5'-hydroxylase substantially increases total anthocyanidin production. The described single-entry yeast episomal complementation system is a convenient and rapid tool for the complex evaluation of new alleles in vivo.

Cytochrome P450s in plant terpenoid biosynthesis: discovery, characterization and metabolic engineering

As the largest family of natural products, terpenoids play valuable roles in medicine, agriculture, cosmetics and food. However, the traditional methods that rely on direct extraction from the original plants not only produce low yields, but also result in waste of resources, and are not applicable at all to endangered species. Modern heterologous biosynthesis is considered a promising, efficient, and sustainable production method, but it relies on the premise of a complete analysis of the biosynthetic pathway of terpenoids, especially the functionalization processes involving downstream cytochrome P450s. In this review, we systematically introduce the biotech approaches used to discover and characterize plant terpenoid-related P450s in recent years. In addition, we propose corresponding metabolic engineering approaches to increase the effective expression of P450 and improve the yield of terpenoids, and also elaborate on metabolic engineering strategies and examples of heterologous biosynthesis of terpenoids in Saccharomyces cerevisiae and plant hosts. Finally, we provide perspectives for the biotech approaches to be developed for future research on terpenoid-related P450.

Exploiting photosynthesis-driven P450 activity to produce indican in tobacco chloroplasts

Photosynthetic organelles offer attractive features for engineering small molecule bioproduction by their ability to convert solar energy into chemical energy required for metabolism. The possibility to couple biochemical production directly to photosynthetic assimilation as a source of energy and substrates has intrigued metabolic engineers. Specifically, the chemical diversity found in plants often relies on cytochrome P450-mediated hydroxylations that depend on reductant supply for catalysis and which often lead to metabolic bottlenecks for heterologous production of complex molecules. By directing P450 enzymes to plant chloroplasts one can elegantly deal with such redox prerequisites. In this study, we explore the capacity of the plant photosynthetic machinery to drive P450-dependent formation of the indigo precursor indoxyl-β-D-glucoside (indican) by targeting an engineered indican biosynthetic pathway to tobacco (Nicotiana benthamiana) chloroplasts. We show that both native and engineered variants belonging to the human CYP2 family are catalytically active in chloroplasts when driven by photosynthetic reducing power and optimize construct designs to improve productivity. However, while increasing supply of tryptophan leads to an increase in indole accumulation, it does not improve indican productivity, suggesting that P450 activity limits overall productivity. Co-expression of different redox partners also does not improve productivity, indicating that supply of reducing power is not a bottleneck. Finally, in vitro kinetic measurements showed that the different redox partners were efficiently reduced by photosystem I but plant ferredoxin provided the highest light-dependent P450 activity. This study demonstrates the inherent ability of photosynthesis to support P450-dependent metabolic pathways. Plants and photosynthetic microbes are therefore uniquely suited for engineering P450-dependent metabolic pathways regardless of enzyme origin. Our findings have implications for metabolic engineering in photosynthetic hosts for production of high-value chemicals or drug metabolites for pharmacological studies.

Use of engineered cytochromes P450 for accelerating drug discovery and development

Numerous steps in drug development, including the generation of authentic metabolites and late-stage functionalization of candidates, necessitate the modification of often complex molecules, such as natural products. While it can be challenging to make the required regio- and stereoselective alterations to a molecule using purely chemical catalysis, enzymes can introduce changes to complex molecules with a high degree of stereo- and regioselectivity. Cytochrome P450 enzymes are biocatalysts of unequalled versatility, capable of regio- and stereoselective functionalization of unactivated CH bonds by monooxygenation. Collectively they catalyze over 60 different biotransformations on structurally and functionally diverse organic molecules, including natural products, drugs, steroids, organic acids and other lipophilic molecules. This catalytic versatility and substrate range makes them likely candidates for application as potential biocatalysts for industrial chemistry. However, several aspects of the P450 catalytic cycle and other characteristics have limited their implementation to date in industry, including: their lability at elevated temperature, in the presence of solvents, and over lengthy incubation times; the typically low efficiency with which they metabolize non-natural substrates; and their lack of specificity for a single metabolic pathway. Protein engineering by rational design or directed evolution provides a way to engineer P450s for industrial use. Here we review the progress made to date toward engineering the properties of P450s, especially eukaryotic forms, for industrial application, and including the recent expansion of their catalytic repertoire to include non-natural reactions.

Circular biomanufacturing through harvesting solar energy and CO2

Using synthetic biology, it is now time to expand the biosynthetic repertoire of plants and microalgae by utilizing the chloroplast to augment the production of desired high-value compounds and of oil-, carbohydrate-, or protein-enriched biomass based on direct harvesting of solar energy and the consumption of CO₂. Multistream product lines based on separate commercialization of the isolated high-value compounds and of the improved bulk products increase the economic potential of the light-driven production system and accelerate commercial scale up. Here we outline the scientific basis for the establishment of such green circular biomanufacturing systems and highlight recent results that make this a realistic option based on cross-disciplinary basic and applied research to advance long-term solutions.

Cytochrome P450s in algae: Bioactive natural product biosynthesis and light-driven bioproduction

Algae are a large group of photosynthetic organisms responsible for approximately half of the earth's total photosynthesis. In addition to their fundamental ecological roles as oxygen producers and as the food base for almost all aquatic life, algae are also a rich source of bioactive natural products, including several clinical drugs. Cytochrome P450 enzymes (P450s) are a superfamily of biocatalysts that are extensively involved in natural product biosynthesis by mediating various types of reactions. In the post-genome era, a growing number of P450 genes have been discovered from algae, indicating their important roles in algal life-cycle. However, the functional studies of algal P450s remain limited. Benefitting from the recent technical advances in algae cultivation and genetic manipulation, the researches on P450s in algal natural product biosynthesis have been approaching to a new stage. Moreover, some photoautotrophic algae have been developed into “photo-bioreactors” for heterologous P450s to produce high-value added pharmaceuticals and chemicals in a carbon-neutral or carbon-negative manner. Here, we comprehensively review these advances of P450 studies in algae from 2000 to 2021.

Potential of Producing Flavonoids Using Cyanobacteria As a Sustainable Chassis

Numerous plant secondary metabolites have remarkable impacts on both food supplements and pharmaceuticals for human health improvement. However, higher plants can only generate small amounts of these chemicals with specific temporal and spatial arrangements, which are unable to satisfy the expanding market demands. Cyanobacteria can directly utilize CO₂, light energy, and inorganic nutrients to synthesize versatile plant-specific photosynthetic intermediates and organic compounds in large-scale photobioreactors with outstanding economic merit. Thus, they have been rapidly developed as a "green" chassis for the synthesis of bioproducts. Flavonoids, chemical compounds based on aromatic amino acids, are considered to be indispensable components in a variety of nutraceutical, pharmaceutical, and cosmetic applications. In contrast to heterotrophic metabolic engineering pioneers, such as yeast and Escherichia coli, information about the biosynthesis flavonoids and their derivatives is less comprehensive than that of their photosynthetic counterparts. Here, we review both benefits and challenges to promote cyanobacterial cell factories for flavonoid biosynthesis. With increasing concerns about global environmental issues and food security, we are confident that energy self-supporting cyanobacteria will attract increasing attention for the generation of different kinds of bioproducts. We hope that the work presented here will serve as an index and encourage more scientists to join in the relevant research area.

Synthetic biology of plant natural products: From pathway elucidation to engineered biosynthesis in plant cells

Plant natural products (PNPs) are the main sources of drugs, food additives, and new biofuels and have become a hotspot in synthetic biology. In the past two decades, the engineered biosynthesis of many PNPs has been achieved through the construction of microbial cell factories. Alongside the rapid development of plant physiology, genetics, and plant genetic modification techniques, hosts have now expanded from single-celled microbes to complex plant systems. Plant synthetic biology is an emerging field that combines engineering principles with plant biology. In this review, we introduce recent advances in the biosynthetic pathway elucidation of PNPs and summarize the progress of engineered PNP biosynthesis in plant cells. Furthermore, a future vision of plant synthetic biology is proposed. Although we are still a long way from overcoming all the bottlenecks in plant synthetic biology, the ascent of this field is expected to provide a huge opportunity for future agriculture and industry.

Improved photosynthetic capacity and photosystem I oxidation via heterologous metabolism engineering in cyanobacteria

Cyanobacteria have been increasingly explored as a biotechnological platform, although their economic feasibility relies in part on the capacity to maximize their photosynthetic, solar-to-biomass energy conversion efficiency. Here we show that cyanobacterial photosynthetic capacity can be increased by diverting cellular resources toward heterologous, energy-storing metabolic pathways and by reducing electron flow to photoprotective, but energy-dissipating, oxygen reduction reactions. We further show that these heterologous sinks can partially contribute to photosystem I (PSI) oxidation, suggesting an engineering strategy to improve both energy storage capacity and robustness by selective diversion of excess photosynthetic capacity to productive processes.

Cyanobacteria must prevent imbalances between absorbed light energy (source) and the metabolic capacity (sink) to utilize it to protect their photosynthetic apparatus against damage. A number of photoprotective mechanisms assist in dissipating excess absorbed energy, including respiratory terminal oxidases and flavodiiron proteins, but inherently reduce photosynthetic efficiency. Recently, it has been hypothesized that some engineered metabolic pathways may improve photosynthetic performance by correcting source/sink imbalances. In the context of this subject, we explored the interconnectivity between endogenous electron valves, and the activation of one or more heterologous metabolic sinks. We coexpressed two heterologous metabolic pathways that have been previously shown to positively impact photosynthetic activity in cyanobacteria, a sucrose production pathway (consuming ATP and reductant) and a reductant-only consuming cytochrome P450. Sucrose export was associated with improved quantum yield of phtotosystem II (PSII) and enhanced electron transport chain flux, especially at lower illumination levels, while cytochrome P450 activity led to photosynthetic enhancements primarily observed under high light. Moreover, coexpression of these two heterologous sinks showed additive impacts on photosynthesis, indicating that neither sink alone was capable of utilizing the full “overcapacity” of the electron transport chain. We find that heterologous sinks may partially compensate for the loss of photosystem I (PSI) oxidizing mechanisms even under rapid illumination changes, although this compensation is incomplete. Our results provide support for the theory that heterologous metabolism can act as a photosynthetic sink and exhibit some overlapping functionality with photoprotective mechanisms, while potentially conserving energy within useful metabolic products that might otherwise be “lost.”

A new twist of rubredoxin function in M. tuberculosis

Electron transfer mediated by metalloproteins drives many biological processes. Rubredoxins are a ubiquitous [1Fe-0S] class of electron carriers that play an important role in bacterial adaptation to changing environmental conditions. In Mycobacterium tuberculosis, oxidative and acidic stresses as well as iron starvation induce rubredoxins expression. However, their functions during M. tuberculosis infection are unknown. In the present work, we show that rubredoxin B (RubB) is able to efficiently shuttle electrons from cognate reductases, FprA and FdR to support catalytic activity of cytochrome P450s, CYP124, CYP125, and CYP142, which are important for bacterial viability and pathogenicity. We solved the crystal structure of RubB and characterized the interaction between RubB and CYPs using site-directed mutagenesis. Mutations that not only neutralize single charge but also change the specific residues on the surface of RubB did not dramatically decrease activity of studied CYPs. Together with isothermal calorimetry (ITC) experiments, the obtained results suggest that interactions are transient and not highly specific. The redox potential of RubB is -264 mV vs. Ag/AgCl and the measured extinction coefficients are 9931 M^-1cm^-1 and 8371 M^-1cm^-1 at 380 nm and 490 nm, respectively. Characteristic parameters of RubB along with the discovered function might be useful for biotechnological applications. Our findings suggest that a switch from ferredoxins to rubredoxins might be crucial for M. tuberculosis to support CYPs activity during the infection.

Ru(II)-diimine complexes and cytochrome P450 working hand-in-hand

With a growing interest in utilizing visible light to drive biocatalytic processes, several light-harvesting units and approaches have been employed to harness the synthetic potential of heme monooxygenases and carry out selective oxyfunctionalization of a wide range of substrates. While the fields of cytochrome P450 and Ru(II) photochemistry have separately been prolific, it is not until the turn of the 21st century that they converged. Non-covalent and subsequently covalently attached Ru(II) complexes were used to promote rapid intramolecular electron transfer in bacterial P450 enzymes. Photocatalytic activity with Ru(II)-modified P450 enzymes was achieved under reductive conditions with a judicious choice of a sacrificial electron donor. The initial concept of Ru(II)-modified P450 enzymes was further improved using protein engineering, photosensitizer functionalization and was successfully applied to other P450 enzymes. In this review, we wish to present the recent contributions from our group and others in utilizing Ru(II) complexes coupled with P450 enzymes in the broad context of photobiocatalysis, protein assemblies and chemoenzymatic reactions. The merging of chemical catalysts with the synthetic potential of P450 enzymes has led to the development of several chemoenzymatic approaches. Moreover, strained Ru(II) compounds have been shown to selectively inhibit P450 enzymes by releasing aromatic heterocycle containing molecules upon visible light excitation taking advantage of the rapid ligand loss feature in those complexes.

Influence of Size and Phase on the Biodegradation, Excretion, and Phytotoxicity Persistence of Single-Layer Molybdenum Disulfide

The increasing applications of single-layer molybdenum disulfide (SLMoS₂) pose great potential risks associated with environmental exposure. This study found that metallic-phase SLMoS₂ with nanoscale (N-1T-SLMoS₂, ∼400 nm) and microscale (M-1T-SLMoS₂, ∼3.6 μm) diameters at 10-25 mg/L induced significant algal growth inhibition (maximum 72.7 and 74.6%, respectively), plasmolysis, and oxidative damage, but these alterations were recoverable. Nevertheless, membrane permeability, chloroplast damage, and chlorophyll biosynthesis reduction were persistent. By contrast, the growth inhibition (maximum 55.3%) and adverse effects of nano-sized semiconductive-phase SLMoS₂ (N-2H-SLMoS₂, ∼400 nm) were weak and easily alleviated after 96 h of recovery. N-1T-SLMoS₂ (0.011 μg/h) and N-2H-SLMoS₂ (0.008 μg/h) were quickly biodegraded to soluble Mo compared with M-1T-SLMoS₂ (0.004 μg/h) and excreted by algae. Incomplete biodegradation of SLMoS₂ (26.8-43.9%) did not significantly mitigate its toxicity. Proteomics and metabolomics indicated that the downregulation of proteins (50.7-99.2%) related to antioxidants and photosynthesis and inhibition of carbon fixation and carbohydrate metabolism contributed to the persistent phytotoxicity. These findings highlight the roles and mechanisms of the size and phase in the persistent phytotoxicity of SLMoS₂, which has potential implications for risk assessment and environmental applications of nanomaterials.

Light-driven catalysis with engineered enzymes and biomimetic systems

Efforts to drive catalytic reactions with light, inspired by natural processes like photosynthesis, have a long history and have seen significant recent growth. Successfully engineering systems using biomolecular and bioinspired catalysts to carry out light-driven chemical reactions capitalizes on advantages offered from the fields of biocatalysis and photocatalysis. In particular, driving reactions under mild conditions and in water, in which enzymes are operative, using sunlight as a renewable energy source yield environmentally friendly systems. Furthermore, using enzymes and bioinspired systems can take advantage of the high efficiency and specificity of biocatalysts. There are many challenges to overcome to fully capitalize on the potential of light-driven biocatalysis. In this mini-review, we discuss examples of enzymes and engineered biomolecular catalysts that are activated via electron transfer from a photosensitizer in a photocatalytic system. We place an emphasis on selected forefront chemical reactions of high interest, including CH oxidation, proton reduction, water oxidation, CO2 reduction, and N2 reduction.

Protein Engineering for Improving and Diversifying Natural Product Biosynthesis

Proteins found in nature have traditionally been the most frequently used biocatalysts to produce numerous natural products ranging from commodity chemicals to pharmaceuticals. Protein engineering has emerged as a powerful biotechnological toolbox in the development of metabolic engineering, particularly for the biosynthesis of natural products. Recently, protein engineering has become a favored method to improve enzymatic activity, increase enzyme stability, and expand product spectra in natural product biosynthesis. This review summarizes recent advances and typical strategies in protein engineering, highlighting the paramount role of protein engineering in improving and diversifying the biosynthesis of natural products. Future prospects and research directions are also discussed.

Natural Compounds as Pharmaceuticals: The Key Role of Cytochromes P450 Reactivity

The design of drugs from natural products is a re-emerging area due to the need for bioactive compounds. The exploitation of natural products and their derivatives obtained by biocatalysis is in line with the higher attention given today to new sustainable technologies that better preserve the environment (green chemistry). The research field of cytochromes P450 (CYPs) is continuously providing new enzymes and mutants that produce metabolites suitable for late-stage functionalization for new potential drugs. This review provides an overview of the exploitation of CYPs as biocatalysts in drug synthesis. Additionally, recent progress in protein and metabolic engineering is provided to show how these enzymes offer a toolbox that can be combined with other biocatalytic or chemical processes to build new platforms for the green production of new drugs.

Engineering Improved Photosynthesis in the Era of Synthetic Biology

Much attention has been given to the enhancement of photosynthesis as a strategy for the optimization of crop productivity. As traditional plant breeding is most likely reaching a plateau, there is a timely need to accelerate improvements in photosynthetic efficiency by means of novel tools and biotechnological solutions. The emerging field of synthetic biology offers the potential for building completely novel pathways in predictable directions and, thus, addresses the global requirements for higher yields expected to occur in the 21st century. Here, we discuss recent advances and current challenges of engineering improved photosynthesis in the era of synthetic biology toward optimized utilization of solar energy and carbon sources to optimize the production of food, fiber, and fuel.

Ecotoxicological effects of sulfonamide on and its removal by the submerged plant Vallisneria natans (Lour.) Hara

The extensive application of sulfonamides (SAs) raises concern regarding its negative environmental effects. In aquatic environments, macrophytes may not only be affected by various pollutants, they may also help to reduce the concentrations in the surrounding environment. We studied both the ecotoxicological effects of sulfonamide (SN) on and its removal by Vallisneria natans (Lour.) Hara, an important submerged macrophyte in Chinese lakes and rivers. The toxic effect and oxidative stress caused by SN resulted in a reduction of total chlorophyll (chl.a and b) and autofluorescence of chloroplast. Meanwhile, the levels of reactive oxygen species (ROS, including O₂^- and H₂O₂) and peroxidase (POD) increased with increasing SN concentration and duration of exposure. After 20 days' exposure, a reduction in the relative growth rate (RGR) and leaf length of V. natans was found under SN stress, but SN had only a weak effect on root length. Although high SN concentrations had toxic effects on the growth of V. natans, the plant was overall resistant to the SN doses that we used. We studied the effect of V. natans on sulfonamide removal in an additional 13-day exposure experiment with focus on the dynamics of dissolved oxygen (DO), the oxidation-reduction potential (ORP) and microbial communities in the water column, as well as in the periphyton on V. natans surfaces. The results show that presence of V. natans significantly improved the SN removal efficiency likely by increasing DO, ORP and bacterial diversity in the water column. The presence of V. natans led to higher relative abundances of Saccharimonadales and Rhizoniales. Lefse analysis showed that Saccharimonadales, Micrococcales, Sphingobacteriales, Bacteroidales, Obscuribacterales, Flavobacteriales, Pseudomonadaceae and Myxococcales, which are considered to be SN-resistant bacteria, increased significantly in the V + S+ (V. natans and SN) treatment compared with the V + S- (V. natans and no SN) treatment and V-S+ (no V. natans and SN) treatment. As far as we know, ours is the first study of the ecotoxicological effects of sulfonamide and its removal by submerged vascular plants (here V. natans). Thus, our results add to the understanding of the antibiotic removal mechanism of macrophytes in freshwater systems and help to clarify the linkages between antibiotics and macrophyte-microbe systems; thereby providing new insight into ecological-based removal of antibiotics in aquatic systems.

Engineering cytochrome P450 enzyme systems for biomedical and biotechnological applications

Cytochrome P450 enzymes (P450s) are broadly distributed among living organisms and play crucial roles in natural product biosynthesis, degradation of xenobiotics, steroid biosynthesis, and drug metabolism. P450s are considered as the most versatile biocatalysts in nature because of the vast variety of substrate structures and the types of reactions they catalyze. In particular, P450s can catalyze regio- and stereoselective oxidations of nonactivated C-H bonds in complex organic molecules under mild conditions, making P450s useful biocatalysts in the production of commodity pharmaceuticals, fine or bulk chemicals, bioremediation agents, flavors, and fragrances. Major efforts have been made in engineering improved P450 systems that overcome the inherent limitations of the native enzymes. In this review, we focus on recent progress of different strategies, including protein engineering, redox-partner engineering, substrate engineering, electron source engineering, and P450-mediated metabolic engineering, in efforts to more efficiently produce pharmaceuticals and other chemicals. We also discuss future opportunities for engineering and applications of the P450 systems.

Defining optimal electron transfer partners for light-driven cytochrome P450 reactions

Plants and cyanobacteria are promising heterologous hosts for metabolic engineering, and particularly suited for expression of cytochrome P450 (P450s), enzymes that catalyse key steps in biosynthetic pathways leading to valuable natural products such as alkaloids, terpenoids and phenylpropanoids. P450s are often difficult to express and require a membrane-bound NADPH-dependent reductase, complicating their use in metabolic engineering and bio-production. We previously demonstrated targeting of heterologous P450s to thylakoid membranes both in N. benthamiana chloroplasts and cyanobacteria, and functional substitution of their native reductases with the photosynthetic apparatus via the endogenous soluble electron carrier ferredoxin. However, because ferredoxin acts as a sorting hub for photosynthetic reducing power, there is fierce competition for reducing equivalents, which limits photosynthesis-driven P450 output. This study compares the ability of four electron carriers to increase photosynthesis-driven P450 activity. These carriers, three plant ferredoxins and a flavodoxin-like engineered protein derived from cytochrome P450 reductase, show only modest differences in their electron transfer to our model P450, CYP79A1 in vitro. However, only the flavodoxin-like carrier supplies appreciable reducing power in the presence of competition for reduced ferredoxin, because it possesses a redox potential that renders delivery of reducing equivalents to endogenous processes inefficient. We further investigate the efficacy of these electron carrier proteins in vivo by expressing them transiently in N. benthamiana fused to CYP79A1. All but one of the fusion enzymes show improved sequestration of photosynthetic reducing power. Fusion with the flavodoxin-like carrier offers the greatest improvement in this comparison - nearly 25-fold on a per protein basis. Thus, this study demonstrates that synthetic electron transfer pathways with optimal redox potentials can alleviate the problem of endogenous competition for reduced ferredoxin and sets out a new metabolic engineering strategy useful for producing valuable natural products.

Phenotypic Variation and Genetic Architecture for Photosynthesis and Water Use Efficiency in Soybean (Glycine max L. Merr)

Photosynthesis (A) and intrinsic water use efficiency (WUE) are physiological traits directly influencing biomass production, conversion efficiency, and grain yield. Though the influence of physiological process on yield is widely known, studies assessing improvement strategies are rare due to laborious phenotyping and specialized equipment needs. This is one of the first studies to assess the genetic architecture underlying A and intrinsic WUE, as well as to evaluate the feasibility of implementing genomic prediction. A panel of 383 soybean recombinant inbred lines were evaluated in a multi-environment yield trial that included measurements of A and intrinsic WUE, using an infrared gas analyzer during R4-R5 growth stages. Genetic variability was found to support the possibility of genetic improvement through breeding. High genetic correlation between grain yield (GY) and A (0.80) was observed, suggesting increases in GY can be achieved through the improvement of A. Genome-wide association analysis revealed quantitative trait loci (QTLs) for these physiological traits. Cross-validation studies indicated high predictive ability (>0.65) for the implementation of genomic prediction as a viable strategy to improve physiological efficiency while reducing field phenotyping. This work provides core knowledge to develop new soybean cultivars with enhanced photosynthesis and water use efficiency through conventional breeding and genomic techniques.

A force awakens: exploiting solar energy beyond photosynthesis

In recent years, efforts to exploit sunlight, a free and abundant energy source, have sped up dramatically. Oxygenic photosynthetic organisms, such as higher plants, algae, and cyanobacteria, can convert solar energy into chemical energy very efficiently using water as an electron donor. By providing organic building blocks for life in this way, photosynthesis is undoubtedly one of the most important processes on Earth. The aim of light-driven catalysis is to harness solar energy, in the form of reducing power, to drive enzymatic reactions requiring electrons for their catalytic cycle. Light-driven enzymes have been shown to have a large number of biotechnological applications, ranging from the production of high-value secondary metabolites to the development of green chemistry processes. Here, we highlight recent key developments in the field of light-driven catalysis using biological components. We will also discuss strategies to design and optimize light-driven systems in order to develop the next generation of sustainable solutions in biotechnology.

Expansion of Redox Chemistry in Designer Metalloenzymes

Many artificial enzymes that catalyze redox reactions have important energy, environmental, and medical applications. Native metalloenzymes use a set of redox-active amino acids and cofactors as redox centers, with a potential range between -700 and +800 mV versus standard hydrogen electrode (SHE, all reduction potentials are versus SHE). The redox potentials and the orientation of redox centers in native metalloproteins are optimal for their redox chemistry. However, the limited number and potential range of native redox centers challenge the design and optimization of novel redox chemistry in metalloenzymes. Artificial metalloenzymes use non-native redox centers and could go far beyond the natural range of redox potentials for novel redox chemistry. In addition to designing protein monomers, strategies for increasing the electron transfer rate in self-assembled protein complexes and protein-electrode or -nanomaterial interfaces will be discussed. Redox reactions in proteins occur on redox active amino acid residues (Tyr, Trp, Met, Cys, etc.) and cofactors (iron sulfur clusters, flavin, heme, etc.). The redox potential of these redox centers cover a ∼1.5 V range and is optimized for their specific functions. Despite recent progress, tuning the redox potential for amino acid residues or cofactors remains challenging. Many redox-active unnatural amino acids (UAAs) can be incorporated into protein via genetic codon expansion. Their redox potentials extend the range of physiologically relevant potentials. Indeed, installing new redox cofactors with fined-tuned redox potentials is essential for designing novel redox enzymes. By combining UAA and redox cofactor incorporation, we harnessed light energy to reduce CO₂ in a fluorescent protein, mimicking photosynthetic apparatus in nature. Manipulating the position and reduction potential of redox centers inside proteins is important for optimizing the electron transfer rate and the activity of artificial enzymes. Learning from the native electron transfer complex, protein-protein interactions can be enhanced by increasing the electrostatic interaction between proteins. An artificial oxidase showed close to native enzyme activity with optimized interaction with electron transfer partner and increased electron transfer efficiency. In addition to the de novo design of protein-protein interaction, protein self-assembly methods using scaffolds, such as proliferating cell nuclear antigen, to efficiently anchor enzymes and their redox partners. The self-assembly process enhances electron transfer efficiency and enzyme activity by bringing redox centers into close proximity of each other. In addition to protein self-assembly, protein-electrode or protein-nanomaterial self-assembly can also promote efficient electron transfer from inorganic materials to enzyme active sites. Such hybrid systems combine the efficiency of enzyme reactions and the robustness of electrodes or nanomaterials, often with advantageous catalytic activities. By combining these strategies, we can not only mimic some of nature's most fascinating reactions, such as photosynthesis and aerobic respiration, but also transcend nature toward environmental, energy, and health applications.

Genetic Engineering, Synthetic Biology and the Light Reactions of Photosynthesis

Applications of synthetic biology to photosynthesis currently range from exchanging photosynthetic proteins to the utilization of photosynthesis as a source of electrons for entirely unrelated reactions.

Cytochrome P450 Monooxygenases in Biotechnology and Synthetic Biology

Cytochromes P450 (P450 or CYP) are heme-containing enzymes that catalyze the introduction of one atom of molecular oxygen into nonactivated C-H bonds, often in a regio- and stereoselective manner. This ability, combined with a tremendous number of accepted substrates, makes P450s powerful biocatalysts. Sixty years after their discovery, P450 systems are recognized as essential bio-bricks in synthetic biology approaches to enable production of high-value complex molecules in recombinant hosts. Recent impressive results in protein engineering led to P450s with tailored properties that are even able to catalyze abiotic reactions. The introduction of P450s in artificial multi-enzymatic cascades reactions and chemo-enzymatic processes offers exciting future perspectives to access novel compounds that cannot be synthesized by nature or by chemical routes.

Metalloprotein switches that display chemical-dependent electron transfer in cells

Biological electron transfer is challenging to directly regulate using environmental conditions. To enable dynamic, protein-level control over energy flow in metabolic systems for synthetic biology and bioelectronics, we created ferredoxin logic gates that utilize transcriptional and post-translational inputs to control energy flow through a synthetic electron transfer pathway that is required for bacterial growth. These logic gates were created by subjecting a thermostable, plant-type ferredoxin to backbone fission and fusing the resulting fragments to a pair of proteins that self-associate, a pair of proteins whose association is stabilized by a small molecule, and to the termini of a ligand-binding domain. We show that the latter domain insertion design strategy yields an allosteric ferredoxin switch that acquires an oxygen-tolerant [2Fe-2S] cluster and can use different chemicals, including a therapeutic drug and an environmental pollutant, to control the production of a reduced metabolite in Escherichia coli and cell lysates.

Green Algal Hydrogenase Activity Is Outcompeted by Carbon Fixation before Inactivation by Oxygen Takes Place

Photoproduction of hydrogen by green algae is considered a transitory release valve of excess reducing power and a potential carbon-free source of sustainable energy. It is generally accepted that the transitory production of hydrogen is governed by fast inactivation of hydrogenase by oxygen. However, our data suggest that photosynthetic electron loss to competing processes, mainly carbon fixation, stops hydrogen production, supports hydrogen uptake, and precedes the inevitable inactivation by oxygen. Here, we show that when transitioning from dark anaerobiosis to light, hydrogen production ceases within 2 min, regardless of the presence of oxygen. Simultaneous monitoring of the active hydrogenase pool size shows that it remains entirely intact up to 4 min after illumination and is inactivated only later. Thus, our data reveal a window of 4 min in which the hydrogenase pool is not being degraded by oxygen. Furthermore, we show that electron loss, prominently to carbon fixation, outcompetes hydrogen production and leads to hydrogen uptake. Indeed, supplying additional reducing power to hydrogenase at the cessation point regenerates the accumulation of hydrogen. Our results imply the fast cessation of hydrogen production is governed by electron loss rather than oxygen inactivation, which takes place minutes later.

Rational engineering of photosynthetic electron flux enhances light-powered cytochrome P450 activity

In this study, we exploited a modified photosynthetic electron transfer chain (PET) in the model cyanobacterium Synechococcus PCC 7002, where electrons derived from water-splitting are used to power reactions catalyzed by a heterologous cytochrome P450 (CYP1A1). A simple in vivo fluorescent assay for CYP1A1 activity was employed to determine the impact of rationally engineering of photosynthetic electron flow. This showed that knocking out a subunit of the type I NADH dehydrogenase complex (NDH-1), suggested to be involved in cyclic photosynthetic electron flow (ΔndhD2), can double the activity of CYP1A1, with a concomitant increase in the flux of electrons from photosynthesis. This also resulted in an increase in cellular adenosine triphosphate (ATP) and the ATP/nicotinamide adenine dinucleotide phosphate (NADPH) ratio, suggesting that expression of a heterologous electron sink in photosynthetic organisms can be used to modify the bioenergetic landscape of the cell. We therefore demonstrate that CYP1A1 is limited by electron supply and that photosynthesis can be re-engineered to increase heterologous P450 activity for the production of high-value bioproducts. The increase in cellular ATP achieved could be harnessed to support metabolically demanding heterologous processes. Furthermore, this experimental system could provide valuable insights into the mechanisms of photosynthesis.

Photosynthetic fuel for heterologous enzymes: the role of electron carrier proteins

Plants, cyanobacteria, and algae generate a surplus of redox power through photosynthesis, which makes them attractive for biotechnological exploitations. While central metabolism consumes most of the energy, pathways introduced through metabolic engineering can also tap into this source of reducing power. Recent work on the metabolic engineering of photosynthetic organisms has shown that the electron carriers such as ferredoxin and flavodoxin can be used to couple heterologous enzymes to photosynthetic reducing power. Because these proteins have a plethora of interaction partners and rely on electrostatically steered complex formation, they form productive electron transfer complexes with non-native enzymes. A handful of examples demonstrate channeling of photosynthetic electrons to drive the activity of heterologous enzymes, and these focus mainly on hydrogenases and cytochrome P450s. However, competition from native pathways and inefficient electron transfer rates present major obstacles, which limit the productivity of heterologous reactions coupled to photosynthesis. We discuss specific approaches to address these bottlenecks and ensure high productivity of such enzymes in a photosynthetic context.

Tat proteins as novel thylakoid membrane anchors organize a biosynthetic pathway in chloroplasts and increase product yield 5-fold

Photosynthesis drives the production of ATP and NADPH, and acts as a source of carbon for primary metabolism. NADPH is also used in the production of many natural bioactive compounds. These are usually synthesized in low quantities and are often difficult to produce by chemical synthesis due to their complex structures. Some of the crucial enzymes catalyzing their biosynthesis are the cytochromes P450 (P450s) situated in the endoplasmic reticulum (ER), powered by electron transfers from NADPH. Dhurrin is a cyanogenic glucoside and its biosynthesis involves a dynamic metabolon formed by two P450s, a UDP-glucosyltransferase (UGT) and a P450 oxidoreductase (POR). Its biosynthetic pathway has been relocated to the chloroplast where ferredoxin, reduced through the photosynthetic electron transport chain, serves as an efficient electron donor to the P450s, bypassing the involvement of POR. Nevertheless, translocation of the pathway from the ER to the chloroplast creates other difficulties, such as the loss of metabolon formation and intermediate diversion into other metabolic pathways. We show here that co-localization of these enzymes in the thylakoid membrane leads to a significant increase in product formation, with a concomitant decrease in off-pathway intermediates. This was achieved by exchanging the membrane anchors of the dhurrin pathway enzymes to components of the Twin-arginine translocation pathway, TatB and TatC, which have self-assembly properties. Consequently, we show 5-fold increased titers of dhurrin and a decrease in the amounts of intermediates and side products in Nicotiana benthamiana. Further, results suggest that targeting the UGT to the membrane is a key factor to achieve efficient substrate channeling.

Determinants of thermostability in the cytochrome P450 fold

Cytochromes P450 are found throughout the biosphere in a wide range of environments, serving a multitude of physiological functions. The ubiquity of the P450 fold suggests that it has been co-opted by evolution many times, and likely presents a useful compromise between structural stability and conformational flexibility. The diversity of substrates metabolized and reactions catalyzed by P450s makes them attractive starting materials for use as biocatalysts of commercially useful reactions. However, process conditions impose different requirements on enzymes to those in which they have evolved naturally. Most natural environments are relatively mild, and therefore most P450s have not been selected in Nature for the ability to withstand temperatures above ~40°C, yet industrial processes frequently require extended incubations at much higher temperatures. Thus, there has been considerable interest and effort invested in finding or engineering thermostable P450 systems. Numerous P450s have now been identified in thermophilic organisms and analysis of their structures provides information as to mechanisms by which the P450 fold can be stabilized. In addition, protein engineering, particularly by directed or artificial evolution, has revealed mutations that serve to stabilize particular mesophilic enzymes of interest. Here we review the current understanding of thermostability as it applies to the P450 fold, gleaned from the analysis of P450s characterized from thermophilic organisms and the parallel engineering of mesophilic forms for greater thermostability. We then present a perspective on how this information might be used to design stable P450 enzymes for industrial application. This article is part of a Special Issue entitled: Cytochrome P450 biodiversity and biotechnology, edited by Erika Plettner, Gianfranco Gilardi, Luet Wong, Vlada Urlacher, Jared Goldstone.

Keeping the spotlight on cytochrome P450

This review describes the recent advances utilizing photosensitizers and visible light to harness the synthetic potential of P450 enzymes. The structures of the photosensitizers investigated to date are first presented along with their photophysical and redox properties. Functional photosensitizers range from organic and inorganic complexes to nanomaterials as well as the biological photosystem I complex. The focus is then on the three distinct approaches that have emerged for the activation of P450 enzymes. The first approach utilizes the in situ generation of reactive oxygen species entering the P450 mechanism via the peroxide shunt pathway. The other two approaches are sustained by electron injections into catalytically competent heme domains either facilitated by redox partners or through direct heme domain reduction. Achievements as well as pitfalls of each approach are briefly summarized. This article is part of a Special Issue entitled: Cytochrome P450 biodiversity and biotechnology, edited by Erika Plettner, Gianfranco Gilardi, Luet Wong, Vlada Urlacher, Jared Goldstone.

Expanding the substrates for a bacterial hydrogenlyase reaction

Escherichia coli produces enzymes dedicated to hydrogen metabolism under anaerobic conditions. In particular, a formate hydrogenlyase (FHL) enzyme is responsible for the majority of hydrogen gas produced under fermentative conditions. FHL comprises a formate dehydrogenase (encoded by fdhF) linked directly to [NiFe]-hydrogenase-3 (Hyd-3), and formate is the only natural substrate known for proton reduction by this hydrogenase. In this work, the possibility of engineering an alternative electron donor for hydrogen production has been explored. Rational design and genetic engineering led to the construction of a fusion between Thermotoga maritima ferredoxin (Fd) and Hyd-3. The Fd-Hyd-3 fusion was found to evolve hydrogen when co-produced with T. maritima pyruvate :: ferredoxin oxidoreductase (PFOR), which links pyruvate oxidation to the reduction of ferredoxin. Analysis of the key organic acids produced during fermentation suggested that the PFOR/Fd-Hyd-3 fusion system successfully diverted pyruvate onto a new pathway towards hydrogen production.

Improving artificial metalloenzymes' activity by optimizing electron transfer

This feature article discusses the strategies to optimize electron transfer efficiency, towards enhancing the activity of artificial metalloenzymes.

Tapping the Unused Potential of Photosynthesis with a Heterologous Electron Sink

Increasing the efficiency of the conversion of light energy to products by photosynthesis represents a grand challenge in biotechnology. Photosynthesis is limited by the carbon-fixing enzyme Rubisco resulting in much of the absorbed energy being wasted as heat or fluorescence or lost as excess reductant via alternative electron dissipation pathways. To harness this wasted reductant, we engineered the model cyanobacterium Synechococcus PCC 7002 to express the mammalian cytochrome P450 CYP1A1 to serve as an artificial electron sink for excess electrons derived from light-catalyzed water-splitting. This improved photosynthetic efficiency by increasing the maximum rate of photosynthetic electron flow by 31.3%. A simple fluorescent assay for CYP1A1 activity demonstrated that the P450 was functional in the absence of its native reductase, that activity was light-dependent and scaled with irradiance. We show for the first time in live cells that photosynthetic reductant can be redirected to power a heterologous cytochrome P450. Furthermore, Synechococcus PCC 7002 expressing CYP1A1 degraded the herbicide atrazine, which is a widespread environmental pollutant.