Poly(3-hydroxypropionate): Biosynthesis Pathways and Malonyl-CoA Biosensor Material Properties

Kinetic characterization of the C-terminal domain of Malonyl-CoA reductase

Malonyl-CoA reductase utilizes two equivalents of NADPH to catalyze the reduction of malonyl-CoA to 3-hydroxypropionic acid (3HP). This reaction is part of the carbon fixation pathway in the phototrophic bacterium Chloroflexus aurantiacus. The enzyme is composed of two domains. The C-terminal domain catalyzes the reduction of malonyl-CoA to malonic semialdehyde, while the N-terminal domain catalyzes the reduction of the aldehyde to 3HP. The two domains can be produced independently and retain their enzymatic activity. This report focuses on the kinetic characterization of the C-terminal domain. Initial velocity patterns and inhibition studies showed the kinetic mechanism is ordered with NADPH binding first followed by malonyl-CoA. Malonic semialdehyde is released first, while CoA and NADP+ are released randomly. Analogs of malonyl-CoA showed that the thioester carbon is reduced, while the carboxyl group is needed for proper positioning. The enzyme transfers the pro-S hydrogen of NADPH to malonyl-CoA and pH rate profiles revealed that a residue with a pKa value of about 8.8 must be protonated for activity. Kinetic isotope effects indicated that NADPH is not sticky (that is, NADPH dissociates from the enzyme faster than the rate of product formation) and product release is partially rate-limiting. Moreover, the mechanism is stepwise with the pH dependent step occurring before or after hydride transfer. The findings from this study will aid in the development of an eco-friendly biosynthesis of 3HP which is an industrial chemical used in the production of plastics and adhesives.

Conductive/Insulating Bioinks with Multitechnology Compatibility and Adjustable Performance

Conducting/insulating inks have received significant attention for the fabrication of a wide range of additive manufacturing technology. However, current inks often demonstrate poor biocompatibility and face trade-offs between conductivity and mechanical stiffness under physiological conditions. Here, conductive/insulating bioinks based on two-dimensional materials are proposed. The conductive bioink, graphene (GR)-poly(lactic-co-glycolic acid) (PLGA), is prepared by introducing conductive GR into a degradable polymer matrix, PLGA, while the insulating bioink, boron nitride (BN)-PLGA, is synthesized by adding insulating BN. By optimizing the material ratios, this work achieves precise control of the electromechanical properties of the bioinks, thereby enabling the flexible construction of conductive networks according to specific requirements. Furthermore, these bioinks are compatible with a variety of manufacturing technologies such as 3D printing, electrospinning, spin coating, and injection molding, expanding their application range in the biomedical field. Overall, the results suggest that these conducting/insulating bioinks offer improved mechanical, electronic, and biological properties for various emerging biomedical applications.

Biosynthesis of High Toughness Poly(3-Hydroxypropionate)-Based Block Copolymers With Poly(D-2-Hydroxybutyrate) and Poly(D-Lactate) Segments Using Evolved Monomer Sequence-Regulating Polyester Synthase

This study synthesized poly(3-hydroxypropionate) [P(3HP)]-containing polyhydroxyalkanoate (PHA) block copolymers, P(3HP)-b-P[2-hydroxybutyrate (2HB)] and P(3HP)-b-P(D-lactate) (PDLA), using Escherichia coli. The cells expressing an evolved sequence-regulating PHA synthase, PhaCARNDFH, and propionyl-CoA transferase were cultured with the supplementation of the corresponding monomer precursors in the medium. The block structure of P(3HP)-b-PDLA was confirmed by proton nuclear magnetic resonance analysis and solvent fractionation. The molecular weights of the polymers were in the range of 0.8-2.8 × 105. The solvent-cast polymer films were subjected to isothermal treatment to promote phase separation and crystallization and were subsequently melt-quenched to produce an amorphous phase. The melt-quenched P(3HP)-b-P(2HB) film exhibited a high elongation at break (1153%), resulting in a toughness of 181 MJ/m3. The solvent-cast film of P(3HP)-b-65 mol% PDLA exhibited partial elastic deformation, in which the P(3HP) phase functioned as a soft segment. The melt-quenching of the polymer resulted in embrittlement presumably due to the high lactate fraction. Overall, the P(3HP)-based block copolymers exhibited several mechanical properties depending on the higher-order structure of the polymer and the properties of the P(2-hydroxyalkanoate) segments. This study findings show that P(3HP)-b-P(2HB) and P(3HP)-b-PDLA can function excellently if their microstructures are properly controlled.

Self-controlled in silico gene knockdown strategies to enhance the sustainable production of heterologous terpenoid by Saccharomyces cerevisiae

Microbial bioengineering is a growing field for producing plant natural products (PNPs) in recent decades, using heterologous metabolic pathways in host cells. Once heterologous metabolic pathways have been introduced into host cells, traditional metabolic engineering techniques are employed to enhance the productivity and yield of PNP biosynthetic routes, as well as to manage competing pathways. The advent of computational biology has marked the beginning of a novel epoch in strain design through in silico methods. These methods utilize genome-scale metabolic models (GEMs) and flux optimization algorithms to facilitate rational design across the entire cellular metabolic network. However, the implementation of in silico strategies can often result in an uneven distribution of metabolic fluxes due to the rigid knocking out of endogenous genes, which can impede cell growth and ultimately impact the accumulation of target products. In this study, we creatively utilized synthetic biology to refine in silico strain design for efficient PNPs production. OptKnock simulation was performed on the GEM of Saccharomyces cerevisiae OA07, an engineered strain for oleanolic acid (OA) bioproduction that has been reported previously. The simulation predicted that the single deletion of fol1, fol2, fol3, abz1, and abz2, or a combined knockout of hfd1, ald2 and ald3 could improve its OA production. Consequently, strains EK1∼EK7 were constructed and cultivated. EK3 (OA07△fol3), EK5 (OA07△abz1), and EK6 (OA07△abz2) had significantly higher OA titers in a batch cultivation compared to the original strain OA07. However, these increases were less pronounced in the fed-batch mode, indicating that gene deletion did not support sustainable OA production. To address this, we designed a negative feedback circuit regulated by malonyl-CoA, a growth-associated intermediate whose synthesis served as a bypass to OA synthesis, at fol3, abz1, abz2, and at acetyl-CoA carboxylase-encoding gene acc1, to dynamically and autonomously regulate the expression of these genes in OA07. The constructed strains R_3A, R_5A and R_6A had significantly higher OA titers than the initial strain and the responding gene-knockout mutants in either batch or fed-batch culture modes. Among them, strain R_3A stand out with the highest OA titer reported to date. Its OA titer doubled that of the initial strain in the flask-level fed-batch cultivation, and achieved at 1.23 ± 0.04 g L-1 in 96 h in the fermenter-level fed-batch mode. This indicated that the integration of optimization algorithm and synthetic biology approaches was efficiently rational for PNP-producing strain design.

Efficient bioproduction of poly(3-hydroxypropionate) homopolymer using engineered Escherichia coli strains

This study focuses on the development of a scalable method for producing poly(3-hydroxypropionate), a homopolymer with significant physico-mechanical properties, through the use of metabolically-engineered Escherichia coli K12 (MG1655) and externally supplied 3-hydroxypropionate. The polymer synthesis pathway was established and optimized through synthetic biology techniques, including the effects of overexpressing phasin and cell division proteins. The optimized strain achieved unprecedented production titers of 9.5 g/L in flask cultures and 80 g/L in fed-batch bioreactors within 45 h. The analysis of poly(3-hydroxypropionate) polymer properties revealed it possesses excellent elasticity (Young's modulus < 6 MPa) and tensile strength (∼80 MPa), positioning it within the category of elastomers or flexible plastics. These findings suggest a viable path for the sustainable, large-scale production of the poly(3-hydroxypropionate) biopolymer.

PHA is not just a bioplastic!

Polyhydroxyalkanoates (PHA) have evolved into versatile biopolymers, transcending their origins as mere bioplastics. This extensive review delves into the multifaceted landscape of PHA applications, shedding light on the diverse industries that have harnessed their potential. PHA has proven to be an invaluable eco-conscious option for packaging materials, finding use in films foams, paper coatings and even straws. In the textile industry, PHA offers a sustainable alternative, while its application as a carbon source for denitrification in wastewater treatment showcases its versatility in environmental remediation. In addition, PHA has made notable contributions to the medical and consumer sectors, with various roles ranging from 3D printing, tissue engineering implants, and cell growth matrices to drug delivery carriers, and cosmetic products. Through metabolic engineering efforts, PHA can be fine-tuned to align with the specific requirements of each industry, enabling the customization of material properties such as ductility, elasticity, thermal conductivity, and transparency. To unleash PHA's full potential, bridging the gap between research and commercial viability is paramount. Successful PHA production scale-up hinges on establishing direct supply chains to specific application domains, including packaging, food and beverage materials, medical devices, and agriculture. This review underscores that PHA's future rests on ongoing exploration across these industries and more, paving the way for PHA to supplant conventional plastics and foster a circular economy.

Kinetic characterization of the N-terminal domain of Malonyl-CoA reductase

Climate change is driving a search for environmentally safe methods to produce chemicals used in ordinary life. One such molecule is 3-hydroxypropionic acid, which is a platform industrial chemical used as a precursor for a variety of other chemical end products. The biosynthesis of 3-hydroxypropionic acid can be achieved in recombinant microorganisms via malonyl-CoA reductase in two separate reactions. The reduction of malonyl-CoA by NADPH to form malonic semialdehyde is catalyzed in the C-terminal domain of malonyl-CoA reductase, while the subsequent reduction of malonic semialdehyde to 3-hydroxypropionic acid is accomplished in the N-terminal domain of the enzyme. A new assay for the reverse reaction of the N-terminal domain of malonyl-CoA reductase from Chloroflexus aurantiacus activity has been developed. This assay was used to determine the kinetic mechanism and for isotope effect studies. Kinetic characterization using initial velocity patterns revealed random binding of the substrates NADP+ and 3-hydroxypropionic acid. Isotope effects showed substrates react to give products faster than they dissociate and that the products of the reverse reaction, NADPH and malonic semialdehyde, have a low affinity for the enzyme. Multiple isotope effects suggest proton and hydride transfer occur in a concerted fashion. This detailed kinetic characterization of the reaction catalyzed by the N-terminal domain of malonyl-CoA reductase could aid in engineering of the enzyme to make the biosynthesis of 3-hydroxypropionic acid commercially competitive with its production from fossil fuels.

Current status of carbon monoxide dehydrogenases (CODH) and their potential for electrochemical applications

Anthropogenic carbon dioxide (CO2) levels are rising to alarming concentrations in earth's atmosphere, causing adverse effects and global climate changes. In the last century, innovative research on CO2 reduction using chemical, photochemical, electrochemical and enzymatic approaches has been addressed. In particular, natural CO2 conversion serves as a model for many processes and extensive studies on microbes and enzymes regarding redox reactions involving CO2 have already been conducted. In this review we focus on the enzymatic conversion of CO2 to carbon monoxide (CO) as the chemical conversion downstream of CO production render CO particularly attractive as a key intermediate. We briefly discuss the different currently known natural autotrophic CO2 fixation pathways, focusing on the reversible reaction of CO2, two electrons and protons to CO and water, catalyzed by carbon monoxide dehydrogenases (CODHs). We then move on to classify the different type of CODHs, involved catalyzed chemical reactions and coupled metabolisms. Finally, we discuss applications of CODH enzymes in photochemical and electrochemical cells to harness CO2 from the environment transforming it into commodity chemicals.