Engineering an Mn(II)-oxidizing Pseudomonas whole-cell catalyst chassis to efficiently biosynthesize 2,5-furandicarboxylic acid from hydroxymethylfurfural

2,5-Furandicarboxylic acid (FDCA) is a high-value chemical extensively used in the production of bio-based polymers, but bioconversion of furan derivatives like 5-hydroxymethylfurfural (HMF) into FDCA remains challenging owing to substrate cytotoxicity. Here, we engineered an Mn(II)-oxidizing Pseudomonas sp. MB04B for efficient FDCA biosynthesis from HMF. We deleted 4.6 % of the MB04B genome to generate the engineered MB04C-6 chassis, then introduced two exogenous gene cassettes, PMP00-hmfH and PJ23119-hmfH'. Using the resulting MB04C-6/pHMF as a whole-cell catalyst, optimizing the reaction system, and incorporating CaCO3 increased the FDCA yield by approximately 63.4-fold compared to MB04C-6. We also enhanced the CRISPR-associated transposases system for single-step chromosomal integration of exogenous genes. The optimal chassis strain MB04S-HMF8, rapidly produced 97 mmol/L FDCA from 100 mmol/L HMF in 12 h, with an FDCA production rate of 1.26 g L-1h-1, showcasing its potential as a robust, cost-effective, and environmentally sustainable whole-cell biocatalyst for industrial-scale FDCA production.

Efficient bio-oxidation of biomass-derived furan-2,5-dicarbaldehyde to 5-formyl-2-furoic acid and 2,5-furandicarboxylic acid via whole-cell biocatalysis

The production of bio-based fine chemicals is increasingly important to address fossil energy shortages, climate change, and other environmental issues. Using abundant and renewable bioresource as starting material to manufacture bio-based fine chemicals will achieve a green circular economy. 5-Formyl-2-furoic acid (FFCA) and 2,5-furandicarboxylic acid (FDCA) has broad application prospects in fuels, chemical intermediates, polymers and pharmaceuticals. In this research, a green and effectual biotransformation process was built to manufacture FFCA and FDCA from biomass-derived furan-2,5-dicarbaldehyde (DFF) in DMSO-H2O using recombinant Escherichia coli cells carrying AAOase (aryl-alcohol oxidase) as biocatalyst. Under mild performance conditions, FFCA could be produced from 75 mM DFF in a high yield (92.3 %) within 24 h. 25 mM DFF was fully oxidized to FDCA within 24 h. The research established an effectual biocatalytic system for transforming HMF-derived DFF with AAOase biocatalysts into valuable biomass-derived products. This study holds great promising for sustainably synthesizing FFCA and FDCA.

Polymerization potential of a bacterial CotA-laccase for β-naphthol: enzyme structure and comprehensive polymer characterization

Introduction

Laccases are blue-multicopper containing enzymes that are known to play a role in the bioconversion of recalcitrant compounds. Their role in free radical polymerization of aromatic compounds for their valorization remains underexplored. In this study, we used a pBAD plasmid containing a previously characterized CotA laccase gene (abbreviated as Bli-Lacc) from Bacillus licheniformis strain ATCC 9945a to express this enzyme and explore its biotransformation/polymerization potential on β-naphthol.

Methods

The protein was expressed from TOP10 cells of Escherichia coli after successful transformation of the plasmid. Immobilized metal affinity chromatography (IMAC) was used to generate pure protein. The biocatalytic polymerization reaction was optimized based on temperature, pH and starting enzyme concentration. 1H and 13C solution nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), and solid-state NMR (ssNMR) were used to characterize the formed polymer. A one-gram conversion reaction was done to explore applicability of the reaction in a pilot-scale.

Results

The polymerization reaction generated a brown precipitate, and its chemical structure was confirmed using 1H and 13C NMR and FTIR. SsNMR revealed the presence of two different orientational hydroxyl functional groups in the polymer in addition to the presence of a very small amount of ether linkages (< 2%). This analysis elucidated that polymerization occurred mainly on the carbons of the aromatic rings, rather than on the carbons attached to the hydroxyl groups, resulting in a condensed ring or polynuclear aromatic structure. The reaction was optimized, and the highest yield was attained under conditions of 37°C, pH 10 and a starting enzyme concentration of 440 nM in 50 mM phosphate buffer. A one-gram conversion yielded 216 mg of polymer as dry mass. The crystal structure of the enzyme was solved at 2.7 Å resolution using X-ray crystallography and presented with a hexagonal space group. The final structure was deposited in the Protein Databank (PDB) with an ID-9BD5.

Discussion

This article provides a green/enzymatic pathway for the remediation of phenolics and their valorization into potential useful polymeric materials. The comprehensive analysis of the formed polymer provides insight into its structure and functional moieties present. Based on the yield of the one-gram conversion, this synthetic method proves useful for a pilot-scale production level and opens opportunities to invest in using this polymer for industrial/environmental applications.

Noncanonical Amino Acids: Bringing New-to-Nature Functionalities to Biocatalysis

Biocatalysis has become an important component of modern organic chemistry, presenting an efficient and environmentally friendly approach to synthetic transformations. Advances in molecular biology, computational modeling, and protein engineering have unlocked the full potential of enzymes in various industrial applications. However, the inherent limitations of the natural building blocks have sparked a revolutionary shift. In vivo genetic incorporation of noncanonical amino acids exceeds the conventional 20 amino acids, opening new avenues for innovation. This review provides a comprehensive overview of applications of noncanonical amino acids in biocatalysis. We aim to examine the field from multiple perspectives, ranging from their impact on enzymatic reactions to the creation of novel active sites, and subsequent catalysis of new-to-nature reactions. Finally, we discuss the challenges, limitations, and promising opportunities within this dynamic research domain.

Manganese-catalyzed oxidation of furfuryl alcohols and furfurals to efficient synthesis of furoic acids

Herein, the direct oxidation of furfuryl alcohols and furfurals to the corresponding furoic acids is performed highly efficiently with potassium hydroxide as the base in the presence of a catalytic amount of PNP pincer manganese catalyst in dioxane. The manganese catalytic system can not only achieve the dehydrogenation conversion of furfuryl alcohols to prepare furoic acids but can also achieve the synthesis of furoic acids from furfurals under more moderate conditions and with less reaction time. In addition, the bifunctional furfuryl alcohols or furfurals can also be efficiently converted into dicarboxylic acid products under optimal reaction conditions.

Bimetallic nanozymes synergize to regulate the behavior of oxygen intermediates and substrate HMF adsorption

We have constructed a bimetallic (CoNiP) nanozyme, leveraging the synergistic effect of cobalt and nickel, which efficiently catalyzes the oxidation of TMB from colorless to ox-TMB (blue). Density functional theory (DFT) calculations further highlight the pivotal role of this synergistic effect in improving the adsorption energy of oxygen intermediates, accelerating the catalytic process.

Harnessing biocatalysis to achieve selective functional group interconversion of monomers

Polymeric materials are ubiquitous to modern life. However, reliance of petroleum for polymeric building blocks is not sustainable. The synthesis of macromolecules from recalcitrant polymer waste feedstocks, such as plastic waste and lignocellulosic biomass, presents an opportunity to bypass the use of petroleum-based feedstocks. However, the deconstruction and transformation of these alternative feedstocks remained limited until recently. Herein, we highlight examples of monomers liberated from the deconstruction of recalcitrant polymers, and more extensively, we showcase the state-of-the-art in biocatalytic technologies that are enabling synthesis of diverse upcycled monomeric starting materials for a wide variety of macromolecules. Overall, this review emphasizes the importance of functional group interconversion as a promising strategy by which biocatalysis can aid the diversification and upcycling of monomers.

Identification of redox activators for continuous reactivation of glyoxal oxidase from Trametes versicolor in a two-enzyme reaction cascade

Glyoxal oxidases, belonging to the group of copper radical oxidases (CROs), oxidize aldehydes to carboxylic acids, while reducing O2 to H2O2. Their activity on furan derivatives like 5-hydroxymethylfurfural (HMF) makes these enzymes promising biocatalysts for the environmentally friendly synthesis of the bioplastics precursor 2,5-furandicarboxylic acid (FDCA). However, glyoxal oxidases suffer from inactivation, which requires the identification of suitable redox activators for efficient substrate conversion. Furthermore, only a few glyoxal oxidases have been expressed and characterized so far. Here, we report on a new glyoxal oxidase from Trametes versicolor (TvGLOX) that was expressed at high levels in Pichia pastoris (reclassified as Komagataella phaffii). TvGLOX was found to catalyze the oxidation of aldehyde groups in glyoxylic acid, methyl glyoxal, HMF, 2,5-diformylfuran (DFF) and 5-formyl-2-furancarboxylic acid (FFCA), but barely accepted alcohol groups as in 5-hydroxymethyl-2-furancarboxylic acid (HMFCA), preventing formation of FDCA from HMF. Various redox activators were tested for TvGLOX reactivation during catalyzed reactions. Among them, a combination of horseradish peroxidase and its substrate 2,2'-azino-di-(3-ethylbenzthiazoline sulfonic acid) (ABTS) most efficiently reactivated TvGLOX. Through continuous reactivation of TvGLOX in a two-enzyme system employing a recombinant Moesziomyces antarcticus aryl-alcohol oxidase (MaAAO) almost complete conversion of 8 mM HMF to FDCA was achieved within 24 h.

Control of selectivity in the oxidation of 5-hydroxymethylfurfural to 5- formyl-2-furancarboxylic acid catalyzed by laccase in a multiphasic gas-liquid microbioreactor

The selectivity of 5-formyl-2-furancarboxylic acid (FFCA) was studied in a batch bioreactor and microbioreactors with different internal diameters (ID). Using microbioreactors, the effect of the flow rate of the liquid and gas phase on the yield, space time yield (STYFFCA), and gas-liquid mixture velocity (UM) of the reaction was evaluated. The biooxidation in flow microbioreactors, a selectivity of 100 % for FFCA was achieved, while with the batch bioreactor at the same substrate concentration a selectivity of 6.7 % was obtained. The highest yield (30 %) with 15 mM of 5-hydroxymethylfurfural (HMF) was reached at a gas-liquid flow rate of 0.5 µL/min and the highest STYFFCA (0.07 mol m-3 min-1) was achieved at a gas-liquid flow rate of 1.5 µL/min with the microbioreactor with an ID of 0.5 mm. The UM values (0.5 to 1.6 cm min1) indicated that the reaction takes place under a kinetic regime without mass transfer limitations.

A CRISPR/Cas9-based multicopy integration system for protein production in Aspergillus niger

The filamentous fungus Aspergillus niger is well known for its high protein secretion capacity and a preferred host for homologous and heterologous protein production. To improve the protein production capacity of A. niger even further, a set of dedicated protein production strains was made containing up to 10 glucoamylase landing sites (GLSs) at predetermined sites in the genome. These GLSs replace genes encoding enzymes abundantly present or encoding unwanted functions. Each GLS contains the promotor and terminator region of the glucoamylase gene (glaA), one of the highest expressed genes in A. niger. Integrating multiple gene copies, often realized by random integration, is known to boost protein production yields. In our approach the GLSs allow for rapid targeted gene replacement using CRISPR/Cas9-mediated genome editing. By introducing the same or different unique DNA sequences (dubbed KORE sequences) in each GLS and designing Cas9-compatible single guide RNAs, one is able to select at which GLS integration of a target gene occurs. In this way a set of identical strains with different copy numbers of the gene of interest can be easily and rapidly made to compare protein production levels. As an illustration of its potential, we successfully used the expression platform to generate multicopy A. niger strains producing the Penicillium expansum PatE::6xHis protein catalysing the final step in patulin biosynthesis. The A. niger strain expressing 10 copies of the patE::6xHis expression cassette produced about 70 μg·mL-1 PatE protein in the culture medium with a purity just under 90%.

Application of Rhodococcus jostii RHA1 glycolate oxidase as an efficient accessory enzyme for lignin conversion by bacterial Dyp peroxidase enzymes

Lignin oxidation by bacterial dye-decolorizing peroxidase enzymes requires hydrogen peroxide as a co-substrate, an unstable and corrosive oxidant. We have identified a glycolate oxidase enzyme from Rhodococcus jostii RHA1 that can couple effectively at pH 6.5 with DyP peroxidase enzymes from Agrobacterium sp. or Comamonas testosteroni to oxidise lignin substrates without addition of hydrogen peroxide. Rhodococcus jostii RHA1 glycolate oxidase (RjGlOx) has activity for oxidation of a range of α-ketoaldehyde and α-hydroxyacid substrates, and is also active for oxidation of hydroxymethylfurfural (HMF) to furandicarboxylic acid. The combination of RjGlOx with Agrobacterium sp. DyP or C. testosteroni DyP generated new and enhanced amounts of low molecular weight aromatic products from organosolv lignin substrates, and was able to generate high-value products from treatment of lignin residue from cellulosic biofuel production, and from a polymeric humin substrate.

Enlightening the Path to Protein Engineering: Chemoselective Turn-On Probes for High-Throughput Screening of Enzymatic Activity

Many successful stories in enzyme engineering are based on the creation of randomized diversity in large mutant libraries, containing millions to billions of enzyme variants. Methods that enabled their evaluation with high throughput are dominated by spectroscopic techniques due to their high speed and sensitivity. A large proportion of studies relies on fluorogenic substrates that mimic the chemical properties of the target or coupled enzymatic assays with an optical read-out that assesses the desired catalytic efficiency indirectly. The most reliable hits, however, are achieved by screening for conversions of the starting material to the desired product. For this purpose, functional group assays offer a general approach to achieve a fast, optical read-out. They use the chemoselectivity, differences in electronic and steric properties of various functional groups, to reduce the number of false-positive results and the analytical noise stemming from enzymatic background activities. This review summarizes the developments and use of functional group probes for chemoselective derivatizations, with a clear focus on screening for enzymatic activity in protein engineering.

In Vivo Biocatalytic Cascades Featuring an Artificial-Enzyme-Catalysed New-to-Nature Reaction

Artificial enzymes utilizing the genetically encoded non-proteinogenic amino acid p-aminophenylalanine (pAF) as a catalytic residue are able to react with carbonyl compounds through an iminium ion mechanism to promote reactions that have no equivalent in nature. Herein, we report an in vivo biocatalytic cascade that is augmented with such an artificial enzyme-catalysed new-to-nature reaction. The artificial enzyme in this study is a pAF-containing evolved variant of the lactococcal multidrug-resistance regulator, designated LmrR_V15pAF_RMH, which efficiently converts benzaldehyde derivatives produced in vivo into the corresponding hydrazone products inside E. coli cells. These in vivo biocatalytic cascades comprising an artificial-enzyme-catalysed reaction are an important step towards achieving a hybrid metabolism.

Oxidation of 5-hydroxymethylfurfural with a novel aryl alcohol oxidase from Mycobacterium sp. MS1601

Bio-based 5-hydroxymethylfurfural (HMF) serves as an important platform for several chemicals, among which 2,5-furan dicarboxylic acid (FDCA) has attracted considerable interest as a monomer for the production of polyethylene furanoate (PEF), a potential alternative for fossil-based polyethylene terephthalate (PET). This study is based on the HMF oxidizing activity shown by Mycobacterium sp. MS 1601 cells and investigation of the enzyme catalysing the oxidation. The Mycobacterium whole cells oxidized the HMF to FDCA (60% yield) and hydroxymethyl furan carboxylic acid (HMFCA). A gene encoding a novel bacterial aryl alcohol oxidase, hereinafter MycspAAO, was identified in the genome and was cloned and expressed in Escherichia coli Bl21 (DE3). The purified MycspAAO displayed activity against several alcohols and aldehydes; 3,5 dimethoxy benzyl alcohol (veratryl alcohol) was the best substrate among those tested followed by HMF. 5-Hydroxymethylfurfural was converted to 5-formyl-2-furoic acid (FFCA) via diformyl furan (DFF) with optimal activity at pH 8 and 30-40°C. FDCA formation was observed during long reaction time with low HMF concentration. Mutagenesis of several amino acids shaping the active site and evaluation of the variants showed Y444F to have around 3-fold higher kcat /Km and ~1.7-fold lower Km with HMF.

Research Progress of Highly Efficient Noble Metal Catalysts for the Oxidation of 5-Hydroxymethylfurfural

5-hydroxymethylfurfural (HMF) is considered to be one of the most pivotal multifunctional biomass platform chemicals. This Review discusses recent advances in catalytic oxidation of HMF towards high-value products. The reaction mechanism of different noble metals and the path of HMF oxidation to high-value products have been deeply investigated in the noble metal catalytic system. The reaction mechanisms of different noble metals and HMF conversion paths were compared in detail. Moreover, the factors affecting the performance of different noble metal catalysts were summarized. Finally, effective strategies were put forward to improve the catalytic performance of noble metal catalysts. The purpose is to provide a valuable reference for the academic research on the preparation of oxidation products from biomass-based HMF and the industrial application of noble metal catalysts.

Metal vs. Metal-Free Catalysts for Oxidation of 5-Hydroxymethylfurfural and Levoglucosenone to Biosourced Chemicals

Lignocellulosic feedstocks, such as forestry biomass and agricultural crop residues, can be utilized to generate biofuels and biochemicals. Converting these organic waste materials into biochemicals is widely regarded as a remedial approach to develop a sustainable, clean, and green energy source. Nevertheless, are these methods sustainable and clean? Prior studies have shown that most such conversions use metals - including heavy metals or noble metals - as catalysts. In addition to the fact that many metals (e. g., aluminum, cobalt, titanium, platinum) have been listed as critical minerals, these methods suffer from high cost, deactivation, and leakage problems and the release of toxic wastes. This Review summarizes catalytic methods using metal and metal-free catalysts for the oxidation of the platform molecules 5-hydroxymethylfurfural and levoglucosenone and demonstrates the potential and effectiveness of metal-free catalysts.

Enzymatic Cascade for the Synthesis of 2,5-Furandicarboxylic Acid in Biphasic and Microaqueous Conditions: 'Media-Agnostic' Biocatalysts for Biorefineries

5-hydroxymethylfurfural (HMF) is produced upon dehydration of C6 sugars in biorefineries. As the product, it remains either in aqueous solutions, or is in situ extracted to an organic medium (biphasic system). For the subsequent oxidation of HMF to 2,5-furandicarboxylic acid (FDCA), 'media-agnostic' catalysts that can be efficiently used in different conditions, from aqueous to biphasic, and to organic (microaqueous) media, are of interest. Here, the concept of a one-pot biocatalytic cascade for production of FDCA from HMF was reported, using galactose oxidase (GalOx) for the formation of 2,5-diformylfuran (DFF), followed by the lipase-mediated peracid oxidation of DFF to FDCA. GalOx maintained its catalytic activity upon exposure to a range of organic solvents with only 1 % (v/v) of water. The oxidation of HMF to 2,5-diformylfuran (DFF) was successfully established in ethyl acetate-based biphasic or microaqueous systems. To validate the concept, the reaction was conducted at 5 % (v/v) water, and integrated in a cascade where DFF was subsequently oxidized to FDCA in a reaction catalyzed by Candida antarctica lipase B.

One-Pot Synthesis of 2,5-Furandicarboxylic Acid from 2-Furoic Acid by a Pd-catalyzed Bromination-Hydroxycarbonylation Tandem Reaction in Acetate Buffer

The one-pot synthesis of 2,5-furandicarboxylic acid from 2-furoic acid with a yield of 57 % was achieved for the first time using a Pd-catalyzed bromination-hydroxycarbonylation tandem reaction in HOAc-NaOAc buffer. This synthetic protocol shows major improvements compared to previously reported methods, such as using biomass-based 2-furoic acid as low-cost raw material, one-pot synthesis without isolation of intermediate products, and no need for an acidification procedure. Experiments indicate that the involved Xantphos-modified Pd-catalyst and the buffer solution play significant promoting roles for each individual reaction whereas Br2 (as the brominating reagent) had a negative effect on the second hydroxycarbonylation step, while CO was deleterious for the first bromination step. Hence, in this practical one-pot synthesis, Br2 should be consumed in the first bromination step as fully as possible, and CO is introduced after the first bromination step has been completed.

Selective Electrosynthesis of 2,5-Diformylfuran in a Continuous-Flow System

The gram-scale selective oxidation of biomass-based chemicals, in particular 5-hydroxymethylfurfural (HMF), into value-added 2,5-diformylfuran (DFF) has a high application potential but suffers from high cost, low selectivity, and harsh reaction conditions. Besides, the electrooxidation strategy requires the usage of expensive electrodes and struggles with low selectivity and efficiency, which restricts its further scaled-up application. In this regard, a continuous-flow system was developed through redox mediator I^- /I₂ for the efficient synthesis of DFF, which could accelerate the mass transfer of I^- (I₂ ) to aqueous (organic) phase and avoid over-oxidation to achieve high selectivity. After the solvent system, iodine concentration, and reaction time were optimized, highly efficient DFF synthesis (selectivity >99 %) could be achieved in the electrochemical flow system using inexpensive graphite felt (GF) as electrode. Moreover, selective HMF oxidation was paired with the hydrogen evolution reaction with increased efficiency after using in-situ-loaded GF-CoS₂ /CoS and GF-Pt electrodes. As a result, the required energy to achieve the gram-scale synthesis of DFF was significantly reduced, demonstrating outstanding potential for large-scale production of the target product.

Catalytic Furfural/5-Hydroxymethyl Furfural Oxidation to Furoic Acid/Furan-2,5-dicarboxylic Acid with H2 Production Using Alkaline Water as the Formal Oxidant

Furfural and 5-hydroxymethyl furfural (HMF) are abundantly available biomass-derived renewable chemical feedstocks, and their oxidation to furoic acid and furan-2,5-dicarboxylic acid (FDCA), respectively, is a research area with huge prospective applications in food, cosmetics, optics, and renewable polymer industries. Water-based oxidation of furfural/HMF is a lucrative approach for simultaneous generation of H2 and furoic acid/FDCA. However, this process is currently limited to (photo)electrochemical methods that can be challenging to control, improve, and scale up. Herein, we report well-defined ruthenium pincer catalysts for direct homogeneous oxidation of furfural/HMF to furoic acid/FDCA, using alkaline water as the formal oxidant while producing pure H2 as the reaction byproduct. Mechanistic studies indicate that the ruthenium complex not only catalyzes the aqueous oxidation but also actively suppresses background decomposition by facilitating initial Tishchenko coupling of substrates, which is crucial for reaction selectivity. With further improvement, this process can be used in scaled-up facilities for a simultaneous renewable building block and fuel production.

CoP nanorods anchored on Ni2P-NiCoP nanosheets with abundant heterogeneous interfaces boosting the electrocatalytic oxidation of 5-hydroxymethyl-furfural

CoP nanorods anchored on Ni2P-NiCoP nanosheets have been fabricated. The heterogeneous interfaces can regulate the d-band centers of Co and Ni to approach the Fermi level, thus boosting the electrocatalytic oxidation of HMF.

Cobalt Boride/g-C3N4 Nanosheets-Assisted Electrocatalytic Oxidation of 5-Hydroxymethylfurfural into 2,5-Furandicarboxylic Acid

The electrochemical production of 2,5-furandicarboxylic acid (FDCA) from 5-(hydroxymethyl)furfural (HMF) is receiving growing attention. The FDCA-based polyethylene 2,5-furan dicarboxylate (PEF) polymer is a green candidate for substituting polyethylene terephthalate. This work demonstrated a highly efficient CoB/g-C3N4 nanosheet on the surface of the nickel foam as an electrode for the HMF electrooxidation reaction. Electrolysis at a constant potential combined with liquid chromatography showed the formation of FDCA with a yield of 97% with an excellent faradaic efficiency of near 95%. CoB/g-C3N4 achieved a current density of 20 mA cm−2 for HMF oxidation in 1.0 M KOH with 10 mM HMF at 1.37 V vs. RHE before the competing oxygen evolution reaction. The electrocatalyst was effectively reused up to three times without compromising efficiency. This work demonstrates a cheap and active electrocatalyst material for the electrochemical formation of FDCA from HMF and gives perception into the reaction mechanism.

Recent Advances in Catalytic Conversion of Biomass to 2,5-Furandicarboxylic Acid

Converting biomass into high value-added compounds has attracted great attention for solving fossil fuel consumption and global warming. 5-Hydroxymethylfurfural (HMF) has been considered as a versatile biomass-derived building block that can be used to synthesize a variety of sustainable fuels and chemicals. Among these derivatives, 2,5-furandicarboxylic acid (FDCA) is a desirable alternative to petroleum-derived terephthalic acid for the synthesis of biodegradable polyesters. Herein, to fully understand the current development of the catalytic conversion of biomass to FDCA, a comprehensive review of the catalytic conversion of cellulose biomass to HMF and the oxidation of HMF to FDCA is presented. Moreover, future research directions and general trends of using biomass for FDCA production are also proposed.

Optimizing operational parameters for the enzymatic production of furandicarboxylic acid building block

BACKGROUND

2,5-Furandicarboxylic acid (FDCA) is a precursor for green plastics due to its structural similarity to terephthalic acid, a common precursor of oil-derived polymers, and its potential production from sugars obtained from plant biomass. Hydroxymethylfurfural oxidase (HMFO) has been reported as a promising biocatalyst for FDCA production since it can convert bio-based 5-hydroxymethylfurfural (HMF) into FDCA building block. This three-step oxidation reaction occurs through the diformylfuran and 2,5-formylfurancarboxylic acid (FFCA) intermediates. Several efforts have been made for the development of HMFO variants that increase FDCA yields by improving their activities over the reaction intermediates. However, there is still limited insight into how operational conditions can influence these enzymatic reactions. The setup of optimal reaction conditions would enable to understand potential problems hampering the effective industrial production of this bioplastic precursor using HMFO as biocatalyst.

RESULTS

In this work, several parameters affecting the performance of Methylovorus sp HMFO oxidizing HMF have been analyzed for the wild-type enzyme, and its V367R and W466F single variants, V367R/W466F double variant, and I73V/H74Y/G356H/V367R/T414K/A419Y/A435E/W466F (8BxHMFO) octuple variant. Our results show how the oxidation of HMF by HMFO enzymes is highly influenced by pH, with different optimal pH values for the different improved variants. Moreover, the enzymes are not stable at high hydrogen peroxide concentrations and their activity is inhibited by the FFCA intermediate in a pH-dependent way. These limitations can be efficiently overcome with the addition of catalase to the reaction medium, which removes the hydrogen peroxide formed during the oxidations, and the controlled dosage of the substrate to limit the amount of FFCA accumulated in the reaction. The different behavior of wild-type HMFO and its variants against pH, hydrogen peroxide and FFCA highlights the importance of considering each variant as an individual enzyme with its own operational conditions for an eventual industrial FDCA production.

CONCLUSIONS

This work provides information of those parameters that condition a high production of FDCA by HMFO. Unraveling these factors allowed to increase the FDCA yields by using the most stable enzymes at their optimal pH for HMF oxidation, removing the peroxide with catalase, and avoiding FFCA accumulation by controlling substrate and/or enzyme concentration. These above findings will be useful when planning a future scale-up of these conversions and will provide new viewpoints for the design of HMFO variants that render a more effective performance during HMF conversion into FDCA.

Coupling a recombinant oxidase to catalase through specific noncovalent interaction to improve the oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid

5-Hydroxymethylfurfural oxidase (HMFO) can catalyze both hydroxyl and aldehyde oxidations. It catalyzes 5-hydroxymethylfurfural into 2,5-furandicarboxylic acid. However, the application of HMFO encountered two problems: the expressed HMFO in Escherichia coli. is largely in the form of inclusion bodies, and the by-product of H₂O₂ has a negative effect on HMFO stability. To solve these problems, recombinant HMFO was generated by fusing the C-terminus to an elastin-like polypeptide (ELP). ELP-HMFO can be expressed with significantly reduced inclusion bodies. ELP-HMFO exhibited improved stability and tolerance toward H₂O₂. Further recombination is carried out by fusing the N-terminus of HMFO to a glutamic acid-rich leucine zipper motif (Z_E). Similarly, recombinant catalase (CAT) is generated by fusing the N-terminus to ELP and fusing the C-terminus to an arginine-rich leucine zipper motif (Z_R). ELP-HMFO-Z_E can interact specifically with Z_R-CAT-ELP, ascribing to the coiled-coil association of Z_E and Z_R. ELP-HMFO-Z_E#Z_R-CAT-ELP coordinates the respective catalytic activities of the two enzymes. ELP-HMFO-Z_E catalyzes the oxidation of HMF, and the generated hydrogen peroxide is decomposed by Z_R-CAT-ELP into H₂O and oxygen. During the oxidation of HMF, the cofactor FAD of HMFO is reduced, and molecular oxygen is needed to reoxidize the reduced FAD. The evolved oxygen from the decomposing of H₂O₂ can just meet the requirement, which can be diffused efficiently from Z_R-CAT-ELP to ELP-HMFO-Z_E due to the short distance between the two enzymes.

Sulfidation of nickel foam with enhanced electrocatalytic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid

Electrochemical oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is an intriguing way of biomass conversion. Herein, a sulfidation of nickel foam (Ni₂S₃/NF) was attempted via a hydrothermal method, achieving high selectivity and efficiency for HMF oxidation. The optimized Ni₂S₃/NF electrode exhibits a nearly 100% conversion of HMF, 98% yield of FDCA, and 94% high faradaic efficiency. This material is stable and retains activity after 6 consecutive measurements. This work provides a facile route to design and prepare electrocatalysts for biomass upgrading.

Toward scalable biocatalytic conversion of 5-hydroxymethylfurfural by galactose oxidase using coordinated reaction and enzyme engineering

5-Hydroxymethylfurfural (HMF) has emerged as a crucial bio-based chemical building block in the drive towards developing materials from renewable resources, due to its direct preparation from sugars and its readily diversifiable scaffold. A key obstacle in transitioning to bio-based plastic production lies in meeting the necessary industrial production efficiency, particularly in the cost-effective conversion of HMF to valuable intermediates. Toward addressing the challenge of developing scalable technology for oxidizing crude HMF to more valuable chemicals, here we report coordinated reaction and enzyme engineering to provide a galactose oxidase (GOase) variant with remarkably high activity toward HMF, improved O₂ binding and excellent productivity (>1,000,000 TTN). The biocatalyst and reaction conditions presented here for GOase catalysed selective oxidation of HMF to 2,5-diformylfuran offers a productive blueprint for further development, giving hope for the creation of a biocatalytic route to scalable production of furan-based chemical building blocks from sustainable feedstocks.

5-Hydroxymethylfurfural (HMF) can be transformed to a range of industrially useful derivatives, such as 2,5-diformylfuran (DFF), but the reactions needed for efficient industrial production are hindered by several issues. Here, the authors perform reaction and enzyme engineering resulting in a galactose oxidase variant with high activity towards HMF, improved oxygen binding and high productivity.

Synthetic approaches to 2,5-bis(hydroxymethyl)furan (BHMF): a stable bio-based diol

Biorefinery is defined as a sustainable process where biomass is converted in a spectrum of marketable products and fuels. In this view, C6 furan-based compounds, usually referred as furanics, have been extensively investigated as aromatic promising building blocks from renewables. 5-Hydroxymethylfurfural (HMF) and 2,5-furan dicarboxylic acid (FDCA) are well known examples of furanics whose syntheses and applications have been extensively reviewed in the literature. Herein for the first time it is reported a comprehensive overview on the synthetic procedures to another bio-derived furan compounds, i.e. 2,5-bis(hydroxymethyl)furan (BHMF), a stable bio-based diol with numerous applications as monomer for bio-materials and fuels. Advantages and limitations of the different synthetic approaches are addressed, as well as possible future developments to render this compound part of the biorefinery market.

Enantioselective oxidation of secondary alcohols by the flavoprotein alcohol oxidase from Phanerochaete chrysosporium

The enantioselective oxidation of secondary alcohols represents a valuable approach for the synthesis of optically pure compounds. Flavoprotein oxidases can catalyse such selective transformations by merely using oxygen as electron acceptor. While many flavoprotein oxidases preferably act on primary alcohols, the FAD-containing alcohol oxidase from Phanerochaete chrysosporium was found to be able to perform kinetic resolutions of several secondary alcohols. By selective oxidation of the (S)-alcohols, the (R)-alcohols were obtained in high enantiopurity. In silico docking studies were carried out in order to substantiate the observed (S)-selectivity. Several hydrophobic and aromatic residues in the substrate binding site create a cavity in which the substrates can comfortably undergo van der Waals and pi-stacking interactions. Consequently, oxidation of the secondary alcohols is restricted to one of the two enantiomers. This study has uncovered the ability of an FAD-containing alcohol oxidase, that is known for oxidizing small primary alcohols, to perform enantioselective oxidations of various secondary alcohols.

Biotechnological production and high potential of furan-based renewable monomers and polymers

Of the 25 million tons of plastic waste produced every year in Europe, 40% of these are not reused or recycled, thus contributing to environmental pollution, one of the major challenges of the 21st century. Most of these plastics are made of petrochemical-derived polymers which are very difficult to degrade and as a result, a lot of research efforts have been made on more environmentally friendly alternatives. Bio-based monomers, derived from renewable raw materials, constitute a possible solution for the replacement of oil-derived monomers, with furan derivatives that emerged as platform molecules having a great potential for the synthesis of biobased polyesters, polyamides and their copolymers. This review article summarizes the latest developments in biotechnological production of furan compounds that can be used in polymer chemistry as well as in their conversion into polymers. Moreover, the biodegradability of the resulting materials is discussed.

Biocatalysis: Enzymatic Synthesis for Industrial Applications

Biocatalysis has found numerous applications in various fields as an alternative to chemical catalysis. The use of enzymes in organic synthesis, especially to make chiral compounds for pharmaceuticals as well for the flavors and fragrance industry, are the most prominent examples. In addition, biocatalysts are used on a large scale to make specialty and even bulk chemicals. This review intends to give illustrative examples in this field with a special focus on scalable chemical production using enzymes. It also discusses the opportunities and limitations of enzymatic syntheses using distinct examples and provides an outlook on emerging enzyme classes.

Direct photoelectrochemical oxidation of hydroxymethylfurfural on tungsten trioxide photoanodes

An important target reaction for solar-powered biomass valorization is the conversion of 2,5-hydroxymethylfurfural (HMF) into key monomers for polyester production. Herein, photoanodes of WO3 are demonstrated to directly photo-oxidize HMF in aqueous electrolyte (pH 4) under simulated solar illumination. The addition of 5 mM HMF increases the saturation photocurrent by 26% and suppresses the water oxidation reaction, as determined by rotating ring-disk electrode experiments. Prolonged photoelectrochemical oxidation (64 h) illustrates system robustness and confirms the production of furandicarboxaldehyde (DFF), furandicarboxylic acid (FDCA), and related intermediates. Quantification of the reaction rate constants via a kinetic model gives insight into the modest DFF and FDCA yields (up to 4% and 1%, respectively)-which is due to the formation of by-products-and suggests routes for improvement.

Bioengineering advancements, innovations and challenges on green synthesis of 2, 5-furan dicarboxylic acid

The major drawback of chemical transformations for the production of 2, 5-furan dicarboxylic acid (FDCA) implies the usage of hazardous chemicals, high temperature and high pressure from nonrenewable resources. Alternate to chemical methods, biological methods are promising. Microbial FDCA production is improved through engineering approaches of media conditions, homologous and heterologous expression of genes, genetic and metabolic engineering, etc. The highest FDCA production of 41.29 g/L is observed by an engineered Raultella ornitholytica BF 60 from 35 g/L HMF in sodium phosphate buffer with a 95.14% yield in 72 h. Also, an enzyme cascade system of recombinant and wild enzymes like periplasmic aldehyde oxidase ABC, galactose oxidase M3-5, HRP and catalase have transformed 6.3 g/L HMF to 7.81 g/L FDCA in phosphate buffer with 100% yield in 6 h. Still, these processes are emerging for fulfilling the industrial needs due to the challenges in 'green FDCA production'.

The Increasing Value of Biomass: Moving From C6 Carbohydrates to Multifunctionalized Building Blocks via 5-(hydroxymethyl)furfural

Recent decades have been marked by enormous progress in the field of synthesis and chemistry of 5-(hydroxymethyl)furfural (HMF), an important platform chemical widely recognized as the "sleeping giant" of sustainable chemistry. This multifunctional furanic compound is viewed as a strong link for the transition from the current fossil-based industry to a sustainable one. However, the low chemical stability of HMF significantly undermines its synthetic potential. A possible solution to this problem is synthetic diversification of HMF by modifying it into more stable multifunctional building blocks for further synthetic purposes.

Efficient Synthesis of Phenylacetate and 2-Phenylethanol by Modular Cascade Biocatalysis

The green and sustainable synthesis of chemicals from renewable feedstocks by a biotransformation approach has gained increasing attention in recent years. In this work, we developed enzymatic cascades to efficiently convert l-phenylalanine into 2-phenylethanol (2-PE) and phenylacetic acid (PAA), l-tyrosine into tyrosol (p-hydroxyphenylethanol, p-HPE) and p-hydroxyphenylacetic acid (p-HPAA). The enzymatic cascade was cast into an aromatic aldehyde formation module, followed by an aldehyde reduction module, or aldehyde oxidation module, to achieve one-pot biotransformation by using recombinant Escherichia coli. Biotransformation of 50 mM l-Phe produced 6.76 g/L PAA with more than 99 % conversion and 5.95 g/L of 2-PE with 97 % conversion. The bioconversion efficiencies of p-HPAA and p-HPE from l-Tyr reached to 88 and 94 %, respectively. In addition, m-fluoro-phenylalanine was further employed as an unnatural aromatic amino acid substrate to obtain m-fluoro-phenylacetic acid; >96 % conversion was achieved. Our results thus demonstrated high-yielding and potential industrial synthesis of above aromatic compounds by one-pot cascade biocatalysis.