Production of Glucaric Acid from Hemicellulose Substrate by Rosettasome Enzyme Assemblies

4-O-Methylglucaric Acid Production from Xylan with Uronic Acid Oxidase and Comparison to Glucaric Acid from Glucose

This study describes an enzymatic pathway to produce high purity 4-O-methylglucaric acid from xylan, an underutilized fraction of lignocellulosic biomass. Beechwood xylan was enzymatically hydrolysed using a commercial xylanase and an α-glucuronidase from Amphibacillus xylanus to form 4-O-methylglucuronic acid, which was then purified by anion exchange chromatography and subsequently oxidized to 4-O-methylglucaric acid using a recombinantly produced uronic acid oxidase from Citrus sinensis. Enzymatic oxidation with uronic acid oxidase afforded 95 % yield in 72 hours which is considerably higher than yields previously achieved using a glucooligosaccharide oxidase from Sarocladium strictum. 4-O-methylglucaric acid was isolated by precipitation and purified by recrystallization. Characterization by liquid chromatography mass spectrometry and nuclear magnetic resonance spectroscopy confirmed product identity and high purity (97.8 % w/w). 4-O-methylglucaric acid's performance as a detergent builder was compared to commercial glucaric acid. At 10 : 1 molar ratios of detergent builder to calcium, 4-O-methylglucaric acid provided similar calcium sequestration performance to glucaric acid (less than 5 % difference) at pH 7 and pH 10 in the presence of surfactants, including sodium dodecylbenzene sulfonate. Given their similar calcium sequestration performance, 4-O-methylglucaric acid could effectively substitute for glucaric acid in detergent formulations.

Production of D-glucaric acid with phosphoglucose isomerase-deficient Saccharomyces cerevisiae

D-Glucaric acid is a potential biobased platform chemical. Previously mainly Escherichia coli, but also the yeast Saccharomyces cerevisiae, and Pichia pastoris, have been engineered for conversion of D-glucose to D-glucaric acid via myo-inositol. One reason for low yields from the yeast strains is the strong flux towards glycolysis. Thus, to decrease the flux of D-glucose to biomass, and to increase D-glucaric acid yield, the four step D-glucaric acid pathway was introduced into a phosphoglucose isomerase deficient (Pgi1p-deficient) Saccharomyces cerevisiae strain. High D-glucose concentrations are toxic to the Pgi1p-deficient strains, so various feeding strategies and use of polymeric substrates were studied. Uniformly labelled 13C-glucose confirmed conversion of D-glucose to D-glucaric acid. In batch bioreactor cultures with pulsed D-fructose and ethanol provision 1.3 g D-glucaric acid L-1 was produced. The D-glucaric acid titer (0.71 g D-glucaric acid L-1) was lower in nitrogen limited conditions, but the yield, 0.23 g D-glucaric acid [g D-glucose consumed]-1, was among the highest that has so far been reported from yeast. Accumulation of myo-inositol indicated that myo-inositol oxygenase activity was limiting, and that there would be potential to even higher yield. The Pgi1p-deficiency in S. cerevisiae provides an approach that in combination with other reported modifications and bioprocess strategies would promote the development of high yield D-glucaric acid yeast strains.

Efficient Production of Glucaric Acid by Engineered Saccharomyces cerevisiae

Glucaric acid is a valuable chemical with applications in the detergent, polymer, pharmaceutical and food industries. In this study, two key enzymes for glucaric acid biosynthesis, MIOX4 (myo-inositol oxygenase) and Udh (uronate dehydrogenase), were fused and expressed with different peptide linkers. It was found that a strain harboring the fusion protein MIOX4-Udh linked by the peptide (EA3K)3 produced the highest glucaric acid titer and thereby resulted in glucaric acid production that was 5.7-fold higher than that of the free enzymes. Next, the fusion protein MIOX4-Udh linked by (EA3K)3 was integrated into delta sequence sites of the Saccharomyces cerevisiae opi1 mutant, and a strain, GA16, that produced a glucaric acid titer of 4.9 g/L in a shake flask fermentation was identified by a high-throughput screening method using an Escherichia coli glucaric acid biosensor. Strain improvement by further engineering was performed to regulate the metabolic flux of myo-inositol to increase the supply of glucaric acid precursors. The downregulation of ZWF1 and the overexpression of INM1 and ITR1 increased glucaric acid production significantly, and glucaric acid production was increased to 8.49 g/L in the final strain GA-ZII in a shake flask fermentation. Finally, in a 5-L bioreactor, GA-ZII produced a glucaric acid titer of 15.6 g/L through fed-batch fermentation. IMPORTANCE Glucaric acid is a value-added dicarboxylic acid that was synthesized mainly through the oxidation of glucose chemically. Due to the problems of the low selectivity, by-products, and highly polluting waste of this process, producing glucaric acid biologically has attracted great attention. The activity of key enzymes and the intracellular myo-inositol level were both rate-limiting factors for glucaric acid biosynthesis. To increase glucaric acid production, this work improved the activity of the key enzymes in the glucaric acid biosynthetic pathway through the expression of a fusion of Arabidopsis thaliana MIOX4 and Pseudomonas syringae Udh as well as a delta sequence-based integration. Furthermore, intracellular myo-inositol flux was optimized by a series of metabolic strategies to increase the myo-inositol supply, which improved glucaric acid production to a higher level. This study provided a way for constructing a glucaric acid-producing strain with good synthetic performance, making glucaric acid production biologically in yeast cells much more competitive.

Recent advances in microbial production of diamines, aminocarboxylic acids, and diacids as potential platform chemicals and bio-based polyamides monomers

Recently, bio-based manufacturing processes of value-added platform chemicals and polymers in biorefineries using renewable resources have extensively been developed for sustainable and carbon dioxide (CO₂) neutral-based industry. Among them, bio-based diamines, aminocarboxylic acids, and diacids have been used as monomers for the synthesis of polyamides having different carbon numbers and ubiquitous and versatile industrial polymers and also as precursors for further chemical and biological processes to afford valuable chemicals. Until now, these platform bio-chemicals have successfully been produced by biorefinery processes employing enzymes and/or microbial host strains as main catalysts. In this review, we discuss recent advances in bio-based production of diamines, aminocarboxylic acids, and diacids, which has been developed and improved by systems metabolic engineering strategies of microbial consortia and optimization of microbial conversion processes including whole cell bioconversion and direct fermentative production.

Fusion of Oligopeptide to the C Terminus of α-Glucuronidase from Thermotoga maritima Improves the Catalytic Efficiency for Hemicellulose Biotransformation

Fusion protein combined the oligopeptide (HQAFFHA) with the C terminus of α-glucuronidase from Thermotoga maritima was produced in E. coli and purified for characterization and applications of glucuronic and glucaric acid production. The fusion protein with oligopeptide exhibited a 2.97-fold higher specific activity than individual protein. Their catalytic efficiency k_cat/K_m and k_cat increased from 469.3 ± 2.6 s^-1 (g mL^-1)^-1 and 62.4 ± 0.9 s^-1 to 2209.5 ± 26.3 s^-1 (g mL^-1)^-1 and 293.9 ± 4.9 s^-1, respectively. Fusion protein had similar temperature and pH profiles to those without oligopeptide, but the thermal stability decreases and the pH stability shifts to alkaline. Using beech xylan hydrolysate as a substrate, the glucuronic acid yield of fusion enzyme increased by 9.94% compared with its parent at 65 °C pH 8.5 for 10 h, and can hydrolyze corn cob xylan with xylanase to obtain glucuronic acid, and can be combined with uronate dehydrogenase to obtain high-added value glucaric acid. Homologous modeling analysis revealed the factors contributing to the high catalytic efficiency of fusion enzyme. These results show that the peptide fusion strategy described here may be useful for improving the catalytic efficiency and stability of other industrial enzymes, and has great potential for producing high value-added products from agricultural waste.

Nature Inspired Multienzyme Immobilization: Strategies and Concepts

In a biological system, the spatiotemporal arrangement of enzymes in a dense cellular milieu, subcellular compartments, membrane-associated enzyme complexes on cell surfaces, scaffold-organized proteins, protein clusters, and modular enzymes have presented many paradigms for possible multienzyme immobilization designs that were adapted artificially. In metabolic channeling, the catalytic sites of participating enzymes are close enough to channelize the transient compound, creating a high local concentration of the metabolite and minimizing the interference of a competing pathway for the same precursor. Over the years, these phenomena had motivated researchers to make their immobilization approach naturally realistic by generating multienzyme fusion, cluster formation via affinity domain-ligand binding, cross-linking, conjugation on/in the biomolecular scaffold of the protein and nucleic acids, and self-assembly of amphiphilic molecules. This review begins with the discussion of substrate channeling strategies and recent empirical efforts to build it synthetically. After that, an elaborate discussion covering prevalent concepts related to the enhancement of immobilized enzymes' catalytic performance is presented. Further, the central part of the review summarizes the progress in nature motivated multienzyme assembly over the past decade. In this section, special attention has been rendered by classifying the nature-inspired strategies into three main categories: (i) multienzyme/domain complex mimic (scaffold-free), (ii) immobilization on the biomolecular scaffold, and (iii) compartmentalization. In particular, a detailed overview is correlated to the natural counterpart with advances made in the field. We have then discussed the beneficial account of coassembly of multienzymes and provided a synopsis of the essential parameters in the rational coimmobilization design.

Cell-based and cell-free biocatalysis for the production of D-glucaric acid

D-Glucaric acid (GA) is a value-added chemical produced from biomass, and has potential applications as a versatile platform chemical, food additive, metal sequestering agent, and therapeutic agent. Marketed GA is currently produced chemically, but increasing demand is driving the search for eco-friendlier and more efficient production approaches. Cell-based production of GA represents an alternative strategy for GA production. A series of synthetic pathways for GA have been ported into Escherichia coli, Saccharomyces cerevisiae and Pichia pastoris, respectively, and these engineered cells show the ability to synthesize GA de novo. Optimization of the GA metabolic pathways in host cells has leapt forward, and the titer and yield have increased rapidly. Meanwhile, cell-free multi-enzyme catalysis, in which the desired pathway is constructed in vitro from enzymes and cofactors involved in GA biosynthesis, has also realized efficient GA bioconversion. This review presents an overview of studies of the development of cell-based GA production, followed by a brief discussion of potential applications of biosensors that respond to GA in these biosynthesis routes.

Enzymatic production of 4-O-methyl d-glucaric acid from hardwood xylan

BACKGROUND

Dicarboxylic acids offer several applications in detergent builder and biopolymer fields. One of these acids, 4-O-methyl d-glucaric acid, could potentially be produced from glucuronoxylans, which are a comparatively underused fraction of wood and agricultural biorefineries.

RESULTS

Accordingly, an enzymatic pathway was developed that combines AxyAgu115A, a GH115 α-glucuronidase from Amphibacillus xylanus, and GOOX, an AA7 gluco-oligosaccharide oxidase from Sarocladium strictum, to produce this bio-based chemical from glucuronoxylan. AxyAgu115A was able to release almost all 4-O-methyl d-glucuronic acid from glucuronoxylan while a GOOX variant, GOOX-Y300A, could convert 4-O-methyl d-glucuronic acid to the corresponding glucaric acid at a yield of 62%. Both enzymes worked effectively at alkaline conditions that increase xylan solubility. Given the sensitivity of AxyAgu115A to hydrogen peroxide and optimal performance of GOOX-Y300A at substrate concentrations above 20 mM, the two-step enzyme pathway was demonstrated as a sequential, one-pot reaction. Additionally, the resulting xylan was easily recovered from the one-pot reaction, and it was enzymatically hydrolysable.

CONCLUSIONS

The pathway in this study requires only two enzymes while avoiding a supplementation of costly cofactors. This cell-free approach provides a new strategy to make use of the underutilized hemicellulose stream from wood and agricultural biorefineries.

Broadening the Scope of Biocatalysis in Sustainable Organic Synthesis

This Review is aimed at synthetic organic chemists who may be familiar with organometallic catalysis but have no experience with biocatalysis, and seeks to provide an answer to the perennial question: if it is so attractive, why wasn't it extensively used in the past? The development of biocatalysis in industrial organic synthesis is traced from the middle of the last century. Advances in molecular biology in the last two decades, in particular genome sequencing, gene synthesis and directed evolution of proteins, have enabled remarkable improvements in scope and substantially reduced biocatalyst development times and cost contributions. Additionally, improvements in biocatalyst recovery and reuse have been facilitated by developments in enzyme immobilization technologies. Biocatalysis has become eminently competitive with chemocatalysis and the biocatalytic production of important pharmaceutical intermediates, such as enantiopure alcohols and amines, has become mainstream organic synthesis. The synthetic space of biocatalysis has significantly expanded and is currently being extended even further to include new-to-nature biocatalytic reactions.

Artificial scaffolds for enhanced biocatalysis

Proteins are not designed to be standalone entities and must coordinate their collective action for optimum performance. Nature has developed through evolution the ability to colocalize the functional partners of a cascade enzymatic reaction in order to ensure efficient exchange of intermediates. Inspired by these natural designs, synthetic scaffolds have been created to enhance the overall biological pathway performance. In this chapter, we describe several DNA- and protein-based scaffold approaches to assemble artificial enzyme cascades for a wide range of applications. We highlight the key benefits and drawbacks of these approaches to provide insights on how to choose the appropriate scaffold for different cascade systems.

Saccharification of thermochemically pretreated cellulosic biomass using native and engineered cellulosomal enzyme systems

Tethering hydrolytic enzymes (e.g., cellulases) to protein scaffolds enhances biomass saccharification to sugars.