Biofuels for a sustainable future.

Rapid increases of energy consumption and human dependency on fossil fuels have led to the accumulation of greenhouse gases and consequently, climate change. As such, major efforts have been taken to develop, test, and adopt clean renewable fuel alternatives. Production of bioethanol and biodiesel from crops is well developed, while other feedstock resources and processes have also shown high potential to provide efficient and cost-effective alternatives, such as landfill and plastic waste conversion, algal photosynthesis, as well as electrochemical carbon fixation. In addition, the downstream microbial fermentation can be further engineered to not only increase the product yield but also expand the chemical space of biofuels through the rational design and fine-tuning of biosynthetic pathways toward the realization of "designer fuels" and diverse future applications.

Complete biosynthesis of QS-21 in engineered yeast.

QS-21 is a potent vaccine adjuvant and remains the only saponin-based adjuvant that has been clinically approved for use in humans1,2. However, owing to the complex structure of QS-21, its availability is limited. Today, the supply depends on laborious extraction from the Chilean soapbark tree or on low-yielding total chemical synthesis3,4. Here we demonstrate the complete biosynthesis of QS-21 and its precursors, as well as structural derivatives, in engineered yeast strains. The successful biosynthesis in yeast requires fine-tuning of the host's native pathway fluxes, as well as the functional and balanced expression of 38 heterologous enzymes. The required biosynthetic pathway spans seven enzyme families-a terpene synthase, P450s, nucleotide sugar synthases, glycosyltransferases, a coenzyme A ligase, acyl transferases and polyketide synthases-from six organisms, and mimics in yeast the subcellular compartmentalization of plants from the endoplasmic reticulum membrane to the cytosol. Finally, by taking advantage of the promiscuity of certain pathway enzymes, we produced structural analogues of QS-21 using this biosynthetic platform. This microbial production scheme will allow for the future establishment of a structure-activity relationship, and will thus enable the rational design of potent vaccine adjuvants.

Complete biosynthesis of the potent vaccine adjuvant QS-21.

QS-21 is a potent vaccine adjuvant currently sourced by extraction from the Chilean soapbark tree. It is a key component of human vaccines for shingles, malaria, coronavirus disease 2019 and others under development. The structure of QS-21 consists of a glycosylated triterpene scaffold coupled to a complex glycosylated 18-carbon acyl chain that is critical for immunostimulant activity. We previously identified the early pathway steps needed to make the triterpene glycoside scaffold; however, the biosynthetic route to the acyl chain, which is needed for stimulation of T cell proliferation, was unknown. Here, we report the biogenic origin of the acyl chain, characterize the series of enzymes required for its synthesis and addition and reconstitute the entire 20-step pathway in tobacco, thereby demonstrating the production of QS-21 in a heterologous expression system. This advance opens up unprecedented opportunities for bioengineering of vaccine adjuvants, investigating structure-activity relationships and understanding the mechanisms by which these compounds promote the human immune response.

Development of Corynebacterium glutamicum as a monoterpene production platform.

Monoterpenes are commonly known for their role in the flavors and fragrances industry and are also gaining attention for other uses like insect repellant and as potential renewable fuels for aviation. Corynebacterium glutamicum, a Generally Recognized as Safe microbe, has been a choice organism in industry for the annual million ton-scale bioproduction of amino acids for more than 50 years; however, efforts to produce monoterpenes in C. glutamicum have remained relatively limited. In this study, we report a further expansion of the C. glutamicum biosynthetic repertoire through the development and optimization of a mevalonate-based monoterpene platform. In the course of our plasmid design iterations, we increased flux through the mevalonate-based bypass pathway, measuring isoprenol production as a proxy for monoterpene precursor abundance and demonstrating the highest reported titers in C. glutamicum to date at 1504.6 mg/L. Our designs also evaluated the effects of backbone, promoter, and GPP synthase homolog origin on monoterpene product titers. Monoterpene production was further improved by disrupting competing pathways for isoprenoid precursor supply and by implementing a biphasic production system to prevent volatilization. With this platform, we achieved 321.1 mg/L of geranoids, 723.6 mg/L of 1,8-cineole, and 227.8 mg/L of linalool. Furthermore, we determined that C. glutamicum first oxidizes geraniol through an aldehyde intermediate before it is asymmetrically reduced to citronellol. Additionally, we demonstrate that the aldehyde reductase, AdhC, possesses additional substrate promiscuity for acyclic monoterpene aldehydes.

Expanding Extender Substrate Selection for Unnatural Polyketide Biosynthesis by Acyltransferase Domain Exchange within a Modular Polyketide Synthase.

Modular polyketide synthases (PKSs) are polymerases that employ α-carboxyacyl-CoAs as extender substrates. This enzyme family contains several catalytic modules, where each module is responsible for a single round of polyketide chain extension. Although PKS modules typically use malonyl-CoA or methylmalonyl-CoA for chain elongation, many other malonyl-CoA analogues are used to diversify polyketide structures in nature. Previously, we developed a method to alter an extension substrate of a given module by exchanging an acyltransferase (AT) domain while maintaining protein folding. Here, we report in vitro polyketide biosynthesis by 13 PKSs (the wild-type PKS and 12 AT-exchanged PKSs with unusual ATs) and 14 extender substrates. Our ∼200 in vitro reactions resulted in 13 structurally different polyketides, including several polyketides that have not been reported. In some cases, AT-exchanged PKSs produced target polyketides by >100-fold compared to the wild-type PKS. These data also indicate that most unusual AT domains do not incorporate malonyl-CoA and methylmalonyl-CoA but incorporate various rare extender substrates that are equal to in size or slightly larger than natural substrates. We developed a computational workflow to predict the approximate AT substrate range based on active site volumes to support the selection of ATs. These results greatly enhance our understanding of rare AT domains and demonstrate the benefit of using the proposed PKS engineering strategy to produce novel chemicals in vitro.

Chemoinformatic-Guided Engineering of Polyketide Synthases.

Polyketide synthase (PKS) engineering is an attractive method to generate new molecules such as commodity, fine and specialty chemicals. A significant challenge is re-engineering a partially reductive PKS module to produce a saturated ß-carbon through a reductive loop (RL) exchange. In this work, we sought to establish that chemoinformatics, a field traditionally used in drug discovery, offers a viable strategy for RL exchanges. We first introduced a set of donor RLs of diverse genetic origin and chemical substrates  into the first extension module of the lipomycin PKS (LipPKS1). Product titers of these engineered unimodular PKSs correlated with chemical structure similarity between the substrate of the donor RLs and recipient LipPKS1, reaching a titer of 165 mg/L of short-chain fatty acids produced by the host Streptomyces albus J1074. Expanding this method to larger intermediates that require bimodular communication, we introduced RLs of divergent chemosimilarity into LipPKS2 and determined triketide lactone production. Collectively, we observed a statistically significant correlation between atom pair chemosimilarity and production, establishing a new chemoinformatic method that may aid in the engineering of PKSs to produce desired, unnatural products.

Movement speed effects on beta-band oscillations in sensorimotor cortex during voluntary activity.

Beta-band oscillations are a dominant feature in the sensorimotor system, which includes movement-related beta desynchronization (MRBD) during the preparation and execution phases of movement and postmovement beta synchronization (PMBS) on movement cessation. Many studies have linked this rhythm to motor functions. However, its associations to the movement speed are still unclear. We make a hypothesis that PMBS will be modulated with increasing of movement speeds. We assessed the MRBD and PMBS during isotonic slower self-paced and ballistic movements with 15 healthy subjects. Furthermore, we conduct an additional control experiment with the isometric contraction with two levels of forces to match those in the isotonic slower self-paced and ballistic movements separately. We found that the amplitude of PMBS but not MRBD in motor cortex is modulated by the speed during voluntary movement. PMBS was positively correlated with movement speed and acceleration through the partial correlation analysis. However, there were no changes in the PMBS and MRBD during the isometric contraction with two levels of forces. These results demonstrate a different function of PMBS and MRBD to the movement speed during voluntary activity and suggest that the movement speed would affect the amplitude of PMBS.NEW & NOTEWORTHY Beta-band oscillations are a dominant feature in the sensorimotor system that associate to the motor function. We found that the movement-related postmovement beta synchronization (PMBS) over the contralateral sensorimotor cortex was positively correlated with the speed of a voluntary movement, but the movement-related beta desynchronization (MRBD) was not. Our results show a differential response of the PMBS and MRBD to the movement speed during voluntary movement.

Fatty Acid and Alcohol Metabolism in Pseudomonas putida: Functional Analysis Using Random Barcode Transposon Sequencing.

With its ability to catabolize a wide variety of carbon sources and a growing engineering toolkit, Pseudomonas putida KT2440 is emerging as an important chassis organism for metabolic engineering. Despite advances in our understanding of the organism, many gaps remain in our knowledge of the genetic basis of its metabolic capabilities. The gaps are particularly noticeable in our understanding of both fatty acid and alcohol catabolism, where many paralogs putatively coding for similar enzymes coexist, making biochemical assignment via sequence homology difficult. To rapidly assign function to the enzymes responsible for these metabolisms, we leveraged random barcode transposon sequencing (RB-Tn-Seq). Global fitness analyses of transposon libraries grown on 13 fatty acids and 10 alcohols produced strong phenotypes for hundreds of genes. Fitness data from mutant pools grown on fatty acids of varying chain lengths indicated specific enzyme substrate preferences and enabled us to hypothesize that DUF1302/DUF1329 family proteins potentially function as esterases. From the data, we also postulate catabolic routes for the two biogasoline molecules isoprenol and isopentanol, which are catabolized via leucine metabolism after initial oxidation and activation with coenzyme A (CoA). Because fatty acids and alcohols may serve as both feedstocks and final products of metabolic-engineering efforts, the fitness data presented here will help guide future genomic modifications toward higher titers, rates, and yields.IMPORTANCE To engineer novel metabolic pathways into P. putida, a comprehensive understanding of the genetic basis of its versatile metabolism is essential. Here, we provide functional evidence for the putative roles of hundreds of genes involved in the fatty acid and alcohol metabolism of the bacterium. These data provide a framework facilitating precise genetic changes to prevent product degradation and to channel the flux of specific pathway intermediates as desired.

Coordinative Alignment in the Pores of MOFs for the Structural Determination of N-, S-, and P-Containing Organic Compounds Including Complex Chiral Molecules.

Coordinative alignment of target small molecules onto a chiral metal-organic framework (MOF-520)provides a powerful method to determine the structures of small molecules through single-crystal X-ray diffraction (SXRD). In this work, the structures of 17 molecules with eight new coordinating functionalities and varying size have been determined by this method, four of which are complex molecules being crystallized for the first time. The chirality of the MOF backbone not only enables enantioselective crystallization of chiral small molecules from a racemic mixture but also imposes diastereoselective incorporation upon achiral molecules. Crystallographic studies assisted by density functional theory (DFT) calculations indicate that the stereoselectivity of MOF-520 not exclusively comes from the steric confinement of the chiral pore environment but also from asymmetric chemical bonding of the target molecules with the framework that is able to provide sufficient energy difference between possible coordination configurations.

3D Covalent Organic Frameworks of Interlocking 1D Square Ribbons.

A new mode of mechanical entanglement in extended structures is described where 1D organic ribbons of corner-sharing squares are mutually interlocked to form 3D woven covalent organic framework-500, COF-500. Reaction of aldehyde-functionalized tetrahedral Cu(PDB)2PO2Ph2 complexes (PDB = 4,4'-(1,10-phenanthroline-2,9-diyl)dibenzaldehyde) with rectangular tetratopic ETTBA (4',4‴,4''''',4''''‴-(ethene-1,1,2,2-tetrayl)tetrakis([1,1'-biphenyl]-4-amine)) linkers through imine condensation, yielded a crystalline porous metalated COF, COF-500-Cu, with pts topology. Upon removal of the Cu(I) ions, the individual 1D square ribbons in the demetalated form (COF-500) are held together only by mechanical interlocking of rings, which allows their collective movement to produce a narrow-pore form, as evidenced by nitrogen adsorption and solid-state photoluminescence studies. When exposed to tetrahydrofuran vapor, the interlocking ribbons can dynamically move away from each other to reopen up the structure. The structural integrity of COF-500 is maintained during its dynamics because the constituent square ribbons cannot part company due to spatial confinement imparted by their interlocking nature.

Publisher Correction: The role of reticular chemistry in the design of CO2 reduction catalysts.

In the version of this Perspective originally published, the titles of the references were missing; the online versions have now been amended to include them.

The role of reticular chemistry in the design of CO2 reduction catalysts.

The problem with current state-of-the-art catalysts for CO2 photo- or electroreduction is rooted in the notion that no single system can independently control, and thus optimize, the interplay between activity, selectivity and efficiency. At its core, reticular chemistry is recognized for its ability to control, with atomic precision, the chemical and structural features (activity and selectivity) as well as the output optoelectronic properties (efficiency) of porous, crystalline materials. The molecular building blocks that are in a reticular chemist's toolbox are chosen in such a way that the structures are rationally designed, framework chemistry is performed to integrate catalytically active components, and the manner in which these building blocks are connected endows the material with the desired optoelectronic properties. The fact that these aspects can be fine-tuned independently lends credence to the prospect of reticular chemistry contributing to the design of next-generation CO2 reduction catalysts.

The geometry of periodic knots, polycatenanes and weaving from a chemical perspective: a library for reticular chemistry.

The geometry of simple knots and catenanes is described using the concept of linear line segments (sticks) joined at corners. This is extended to include woven linear threads as members of the extended family of knots. The concept of transitivity that can be used as a measure of regularity is explained. Then a review is given of the simplest, most 'regular' 2- and 3-periodic patterns of polycatenanes and weavings. Occurrences in crystal structures are noted but most structures are believed to be new and ripe targets for designed synthesis.

Molecular Weaving of Covalent Organic Frameworks for Adaptive Guest Inclusion.

The synthesis of new isoreticular non-interpenetrated woven covalent organic frameworks (COFs) was achieved by linking aldehyde-functionalized copper(I) bisphenanthroline complexes with benzidine linkers in the presence of a bulky anion, diphenylphosphinate (PO2Ph2-) to give metalated COF-506-Cu and, upon removal of copper(I), the demetalated COF-506. The structures of these COFs were determined by a combination of powder X-ray diffraction and electron microscopy techniques. Guest-accessibility to the pores of the two frameworks was examined by vapor and dye inclusion studies and compared to the already reported doubly-interpenetrated COF-505-Cu.  Remarkably, COF-506 was found to take up guest molecules that exceed the size of the COF-506-Cu pores, thus giving credence to the notion of a novel mode of motional dynamics in solids we term 'adaptive inclusion'.

MicroRNA-221-5p Inhibits Porcine Epidemic Diarrhea Virus Replication by Targeting Genomic Viral RNA and Activating the NF-κB Pathway.

MicroRNAs (miRNAs) are a class of noncoding RNAs involved in posttranscriptional regulation of gene expression and many critical roles in numerous biological processes. Porcine epidemic diarrhea virus (PEDV), the etiological agent of porcine epidemic diarrhea, causes substantial economic loss in the swine industry worldwide. Previous studies reported miRNA involvement in viral infection; however, their role in regulating PEDV infection remains unknown. In this study, we investigated the regulatory relationship between miRNA-221-5p and PEDV infection, finding that miR-221-5p overexpression inhibited PEDV replication in a dose-dependent manner, and that silencing endogenous miR-221-5p enhanced viral replication. Our results showed that miR-221-5p directly targets the 3' untranslated region (UTR) of PEDV genomic RNA to inhibit PEDV replication, and that miR-221-5p overexpression activates nuclear factor (NF)-κB signaling via p65 nuclear translocation, thereby upregulating interferon (IFN)-ß, IFN-stimulated gene 15, and MX1 expression during CH/HBTS/2017 infection. We subsequently identified NF-κB-inhibitor α and suppressor of cytokine signaling 1, negative regulators of the NF-κB pathway, as miR-221-5p targets. These results demonstrated the ability of miR-221-5p to inhibit PEDV replication by targeting the 3' UTR of the viral genome and activating the NF-κB-signaling pathway. Our findings will aid the development of preventive and therapeutic strategies for PEDV infection.

[Cloning and expression analysis of pathogenesis-related protein 1 gene of Panax notoginseng].

By reverse transcription-polymerase chain reaction (RT-PCR), an open reading frame of pathogenesis-related protein 1 (PR1) was isolated from Panax notoginseng and named as PnPR1. Molecular and bioinformatic analyses of PnPR1 revealed that an open reading frame of 501 bp was predicted to encode a 166-amino acid protein with a deduced molecular mass of 18.1 kD. Homology analysis showed that the deduced amino acid sequence of PR1 protein of Panax notoginseng had a high similarity with other higher plants had the same conservative structure domain of cysteine-rich secretory protein (CAP). The recombinant expressed plasmid pET28a(+)-PnPR1 was expressed in Escherichia coli BL21. The expression conditions were optimized by induction at different times, different temperatures, different IPTG concentrations and different giving times. The optimum expression condition was 0.4 mmol.L-1 IPTG at 28 degrees C for 20 h. The successful expression of PnPR1 provides some basis for protein purification and preparation of the monoclonal antibody.

[Overexpression and RNAi vectors built for key secondary metabolic pathway genes PAL, HMGR, PGT of Arnebia euchroma].

Arnebia euchroma is the main source for medicinal herb Zicao. and its most important component shikonin compounds have high medicinal and industrial value. This research is aimed to build overexpression vectors and RNAi vectors for key secondary metabolism genes of A. euchroma, and bulid platform for constructions of related transgenic lines using GATEWAY technology. To build genetic material based genetic research platform is to provide a great convenience for digging and functional verification of the genes on secondary metabolic pathway, and also to fill the gaps in transgenic research of A. euchroma. This study is also important for the cultivation of shikonin high-yielding strains of A. euchroma.

[Construction of RNAi vectors for SmNAC1 transcription factors of Salvia miltiorrhiza using Gateway cloning technology].

NAC transcription factors involved in plant growth and development, as well as responses to biotic and abiotic stress. RNAi Vectors for SmNAC transcription factors of Salvia miltiorrhiza was constructed by using Gateway cloning technology, in order to further study the function of SmNAC1 transcription factor. According to Gateway cloning technology, the specific fragments of SmNAC1 containing attB adapter was amplified by PCR using ultra-fideling phusion polymerase of NEB. By the BP recombination reaction, the PCR product containing attB was transferred to an donor vector (pENTR/SD/D-TOPO). Finally, SmNACi specific gene was cloned into pK7GWIWG2D plant expression vectors by LR recombination reaction. Experimental results showed that Gateway cloning technology provide a rapid and highly efficient way to clone the interested gene.

[Optimization of expression and purification of recombinant Salvia miltiorrhiza WRKY1 protein in Escherichia coli].

WRKY transcription factor is one of the Zinc finger proteins which contains a highly conserved WRKY domain and is a family of the plant-specific transcription factor. The plasmid pET28a-SmWRKY1 harboring Salvia miltiorrhiza WRKY1 (SmWRKY1) gene was successfully transformed and expressed in Escherichia coli BL21 (DE3). The conditions on protein expression of SmWRKY1 in E. coli, including induction duration, temperature, IPTG concentration and the E. coli concentration were optimized. The results showed that the highest protein expression of SmWRKY1 was obtained at 24 hours after the E. coli was cultured in the presence of 0.2 mol x L(-1) IPTG at 20 degrees C with A600 values of 1.0-1.5. This recombinant histidine-tagged protein was expressed at 2.454 g x L(-1) as inclusion body, which was first extracted using urea, and then purified by Ni2+ affinity chromatography and identified by SDS-PAGE. The expression of SmWRKY1 in E. coli was further confirmed by western blotting analysis.

[Cloning and bioinformatics analysis of ent-kaurene oxidase synthase gene in Salvia miltiorrhiza].

Based on the transcriptome database of Salvia miltiorrhiza, specific primers were designed to clone a full-length cDNA of ent-kaurene oxidase synthase (SmKOL) using the RACE strategy. ORF Finder was used to find the open reading frame of SmKOL cDNA, and ClustalW has been performed to analysis the multiple amino acid sequence alignment. Phylogenetic tree has been constructed using MEGA 5.1. The transcription level of SmKOL from the hairy roots induced by elicitor methyl jasmonate (MeJA) was qualifiedby real-time quantitative PCR. The full length of SmKOL cDNA was of 1 884 bp nucleotides encoding 519 amino acids. The molecular weight of the SmKOL protein was about 58.88 kDa with isoelectric point (pI) of 7.62. Results of real-time quantitative PCR analyses indicated that the level of SmKOL mRNA expression in hairy roots was increased by elicitor oMeJA, and reached maximum in 36 h. The full-length cDNA of SmKOL was cloned from S. miltiorrhiza hairy root, which provides a target gene for further studies of its function, gibberellin biosynthesis and regulation of secondary metabolites.