Key Factors for A One-Pot Enzyme Cascade Synthesis of High Molecular Weight Hyaluronic Acid

Bioengineered heparin: Advances in production technology

Heparin, a highly sulfated glycosaminoglycan, is considered an indispensable anticoagulant with diverse therapeutic applications and has been a mainstay in medical practice for nearly a century. Its potential extends beyond anticoagulation, showing promise in treating inflammation, cancer, and infectious diseases such as COVID-19. However, its current sourcing from animal tissues poses challenges due to variable structures and adulterations, impacting treatment efficacy and safety. Recent advancements in metabolic engineering and synthetic biology offer alternatives through bioengineered heparin production, albeit with challenges such as controlling molecular weight and sulfonation patterns. This review offers comprehensive insight into recent advancements, encompassing: (i) the metabolic engineering strategies in prokaryotic systems for heparin production; (ii) strides made in the development of bioengineered heparin; and (iii) groundbreaking approaches driving production enhancements in eukaryotic systems. Additionally, it explores the potential of recombinant Chinese hamster ovary cells in heparin synthesis, discussing recent progress, challenges, and future prospects, thereby opening up new avenues in biomedical research.

Advanced enzymatic multigram-scale production of nucleotide sugars in a continuous fed-batch membrane reactor

Enzymatic production of nucleotide sugars on a multigram scale presents a challenge, as only a few processes have been reported for large-scale nucleotide sugar production. They rely primarily on batch synthesis and employ exceptional amounts of enzymes. This study introduces a novel approach for the multigram-scale production of nucleotide sugars with a continuous fed-batch membrane reactor. We successfully synthesized five main nucleotide sugars: UDP-Gal, UDP-GalNAc, UDP-GlcA, GDP-Man, and CMP-Neu5Ac on a multigram scale. Efficient biocatalyst utilization results in high performance, including space-time yield (STY, g*L-1h-1), total turnover number (TTN, g product per g enzyme), and an efficient product formation rate (g/h) suitable for industrially relevant bioprocesses. The established continuous-fed batch reactor system produced up to 8.2 g CMP-Neu5Ac in three consecutive productions in less than 15 h with satisfying TTNs of 91 gProduct/gEnzyme. Continuous production of UDP-GlcA over 28 h resulted in a final product amount of 14.8 g and TTN of 493 gP/gE. This process enables the production of nucleotide sugars with stable product formation, requiring minimal technical equipment for multigram quantities of nucleotide sugars at the laboratory scale. Notably, the system exhibited robustness and flexibility, allowing its application to various enzymatic nucleotide sugar synthesis cascades.

Process Development for the Enzymatic Gram-Scale Production of the Unnatural Nucleotide Sugar UDP-6-Azido-GalNAc

Azido sugars hold great promise as substrates in numerous click-chemistry applications. However, the synthesis of activated azido sugars is limited by cost and complexity. Conventional chemical activation methods are intricate and time-consuming. In response, we have developed a process for the large-scale production of UDP-6-azido-GalNAc through enzymatic nucleotide sugar synthesis on a gram scale. Our optimization strategies encompassed refining the process parameters of an enzyme cascade featuring NahK from Bifidobacterium longum and AGX1 from Homo sapiens. Using the repetitive-batch-mode technology, we synthesized up to 2.1 g of UDP-6-azido-GalNAc, achieving yields up to 97 % in five consecutive batch cycles using a single enzyme batch. The synthesis process demonstrated to have total turnover numbers (TTNs) between 4.4-4.8 g of product per gram of enzyme (gP/gE) and STYs ranging from 1.7-2.4 g per liter per hour (g*L-1*h-1). By purification of a product solution pool containing 2.6 g (4.1 mmol) UDP-6-azido-GalNAc, 2.1 g (2,122.1 mg) UDP-6-azido-GalNAc (sodium salt) with a purity of 99.96 % (HPLC) were obtained. The overall recovery after purification was 81 % (3.32 mmol). Our work establishes a robust production platform for the gram-scale synthesis of unnatural nucleotide sugars, opening new avenues for applications in glycan engineering.

Chemoenzymatic synthesis with the Pasteurella hyaluronan synthase; production of a multitude of defined authentic, derivatized, and analog polymers

Hyaluronan (HA; [-3-GlcNAc-1-beta-4-GlcA-1-beta] n ), an essential matrix polysaccharide of vertebrates and the molecular camouflage coating in certain pathogens, is polymerized by "HA synthase" (HAS) enzymes. Three HAS classes have been identified with biotechnological utility, but only the Class II PmHAS from Pasteurella multocida Type A has been useful for preparation of very defined HA polymers in vitro. Two general chemoenzymatic strategies with different size products are possible: (1) repetitive step-wise extension reactions by sequential addition of a single monosaccharide from a donor UDP-sugar onto an acceptor (or "primer") comprised of a short glycosaminoglycan chain (e.g., HA di-, tri- or tetrasaccharide) or an artificial glucuronide yielding homogeneous oligosaccharides in the range of 2 to ~20 monosaccharide units (n = 1 to ~10), or (2) "one-pot" polymerization reactions employing acceptor-mediated synchronization with stoichiometric size control yielding quasi-monodisperse (i.e., polydispersity approaching 1; very narrow size distributions) polysaccharides in the range of ~7 kDa to ~2 MDa (n = ~17 to 5000). In either strategy, acceptors containing non-carbohydrate functionalities (e.g., biotin, fluorophores, amines) can add useful moieties to the reducing termini of HA chains at 100% efficiency. As a further structural diversification, PmHAS can utilize a variety of unnatural UDP-sugar analogs thus adding novel groups (e.g., trifluoroacetyl, alkyne, azide, sulfhydryl) along the HA backbone and/or at its nonreducing terminus. This review discusses the current understanding and recent advances in HA chemoenzymatic synthesis methods using PmHAS. This powerful toolbox has potential for creation of a multitude of HA-based probes, therapeutics, drug conjugates, coatings, and biomaterials.

Utility of Authentic 13C-Labeled Disaccharide to Calibrate Hyaluronan Content Measurements by LC-MS

Hyaluronan (hyaluronic acid, HA), a key glycosaminoglycan in the extracellular matrix, plays crucial roles in various physiological and pathological processes, including development, tissue hydration, inflammation, and tumor progression. Traditional methods for HA quantification, such as ELISA-like assays, often have limitations in sensitivity and specificity, particularly for lower molecular weight HA. In this work, we introduce a coupled liquid chromatographic-tandem mass spectrometric (LC-MS/MS) method that employs a chemoenzymatically synthesized 13C-labeled lyase-derived authentic HA disaccharide calibrant for quantification of HA at the nanogram level. The method was validated against three HA polysaccharides with the sizes of ~33, 210, and 540 kDa. We applied this quantification technique to mouse tissues and plasma from both healthy and acetaminophen-induced acute liver injury mice. Our data revealed a ~75-fold increase in HA concentration in the liver of acetaminophen-injured mice with a concomitant depletion from plasma. Overall, our method offers a robust, universal, and highly sensitive tool for HA analysis in diverse biological samples that will advance the investigation of the roles of this polysaccharide in human disease conditions.

Nitrilotriacetic Acid Functionalized Microgels for Efficient Immobilization of Hyaluronan Synthase

Enzymes play a vital role in synthesizing complex biological molecules like hyaluronic acid (HA). Immobilizing enzymes on support materials is essential for their efficient use and reuse in multiple cycles. Microgels, composed of cross-linked, highly swollen polymer networks, are ideal for enzyme uptake owing to their high porosity. This study demonstrates the immobilization of His6-tagged hyaluronan synthase from Pasteurella multocida (PmHAS) onto nitrilotriacetic acid functionalized microgels using different bivalent ions (Ni2+, Co2+, Mn2+, Mg2+, and Fe2+) via metal affinity binding. The results indicate that using Ni2+ yields the microgels with the highest enzyme uptake and HA formation. The immobilized PmHAS enables repetitive enzymatic production, producing high molecular weight HAs with decreasing dispersities in each step. Furthermore, the highest reported yield of HA with high molecular weight for immobilized PmHAS is achieved. This system establishes a foundation for continuous HA formation, with future works potentially enhancing PmHAS stability through protein engineering.

Production of different molecular weight glycosaminoglycans with microbial cell factories

Glycosaminoglycans (GAGs) are naturally occurring acidic polysaccharides with wide applications in pharmaceuticals, cosmetics, and health foods. The diverse biological activities and physiological functions of GAGs are closely associated with their molecular weights and sulfation patterns. Except for the non-sulfated hyaluronan which can be synthesized naturally by group A Streptococcus, all the other GAGs such as heparin and chondroitin sulfate are mainly acquired from animal tissues. Microbial cell factories provide a more effective platform for the production of structurally homogeneous GAGs. Enhancing the production efficiency of polysaccharides, accurately regulating the GAGs molecular weight, and effectively controlling the sulfation degree of GAGs represent the major challenges of developing GAGs microbial cell factories. Several enzymatic, metabolic engineering, and synthetic biology strategies have been developed to tackle these obstacles and push forward the industrialization of biotechnologically produced GAGs. This review summarizes the recent advances in the construction of GAGs synthesis cell factories, regulation of GAG molecular weight, and modification of GAGs chains. Furthermore, the challenges and prospects for future research in this field are also discussed.

Strategies for Automated Enzymatic Glycan Synthesis (AEGS)

Glycans are the most abundant biopolymers on earth and are constituents of glycoproteins, glycolipids, and proteoglycans with multiple biological functions. The availability of different complex glycan structures is of major interest in biotechnology and basic research of biological systems. High complexity, establishment of general and ubiquitous synthesis techniques, as well as sophisticated analytics, are major challenges in the development of glycan synthesis strategies. Enzymatic glycan synthesis with Leloir-glycosyltransferases is an attractive alternative to chemical synthesis as it can achieve quantitative regio- and stereoselective glycosylation in a single step. Various strategies for synthesis of a wide variety of different glycan structures has already be established and will exemplarily be discussed in the scope of this review. However, the application of enzymatic glycan synthesis in an automated system has high demands on the equipment, techniques, and methods. Different automation approaches have already been shown. However, while these techniques have been applied for several glycans, only a few strategies are able to conserve the full potential of enzymatic glycan synthesis during the process - economical and enzyme technological recycling of enzymes is still rare. In this review, we show the major challenges towards Automated Enzymatic Glycan Synthesis (AEGS). First, we discuss examples for immobilization of glycans or glycosyltransferases as an important prerequisite for the embedment and implementation in an enzyme reactor. Next, improvement of bioreactors towards automation will be described. Finally, analysis and monitoring of the synthesis process are discussed. Furthermore, automation processes and cycle design are highlighted. Accordingly, the transition of recent approaches towards a universal automated glycan synthesis platform will be projected. To this end, this review aims to describe essential key features for AEGS, evaluate the current state-of-the-art and give thought- encouraging impulses towards future full automated enzymatic glycan synthesis.

Spatially Segregated MOF Bioreactor Enables Versatile Modular Glycoenzyme Assembly for Hierarchical Glycan Library Construction

The multienzyme cascade has received growing attention to obtain structurally defined glycans in vitro. However, due to poor enzyme stability and low compatibility between glycoenzymes, artificially designed multienzyme pathways to access glycans are often inefficient. Herein, based on the strategy "Modular-Enzymes Assembly by Spatial Segregation" (MASS), we developed a universal immobilization platform to assemble multiple glycoenzymes in compartmentalized MOF particles, inside and outside, significantly reducing the undesired interference and cross-inhibitions. By changing the enzyme modules, a series of glycosyl donor, disaccharides, oligosaccharides, and polysaccharides bearing cofactor regeneration were efficiently prepared. This bioreactor was further successfully applied to the reaction system with high substrate concentration to demonstrate its industrial potential. This robust multienzyme immobilization platform should serve to promote the enzymatic synthesis of more complex glycans.

Biocatalytic Approaches to Building Blocks for Enzymatic and Chemical Glycan Synthesis

While the field of biocatalysis has bloomed over the past 20-30 years, advances in the understanding and improvement of carbohydrate-active enzymes, in particular, the sugar nucleotides involved in glycan building block biosynthesis, have progressed relatively more slowly. This perspective highlights the need for further insight into substrate promiscuity and the use of biocatalysis fundamentals (rational design, directed evolution, immobilization) to expand substrate scopes toward such carbohydrate building block syntheses and/or to improve enzyme stability, kinetics, or turnover. Further, it explores the growing premise of using biocatalysis to provide simple, cost-effective access to stereochemically defined carbohydrate materials, which can undergo late-stage chemical functionalization or automated glycan synthesis/polymerization.

Enzyme cascades for the synthesis of nucleotide sugars: Updates to recent production strategies

Nucleotide sugars play an elementary role in nature as building blocks of glycans, polysaccharides, and glycoconjugates used in the pharmaceutical, cosmetics, and food industries. As substrates of Leloir-glycosyltransferases, nucleotide sugars are essential for chemoenzymatic in vitro syntheses. However, high costs and the limited availability of nucleotide sugars prevent applications of biocatalytic cascades on a large industrial scale. Therefore, the focus is increasingly on nucleotide sugar synthesis strategies to make significant application processes feasible. The chemical synthesis of nucleotide sugars and their derivatives is well established, but the yields of these processes are usually low. Enzyme catalysis offers a suitable alternative here, and in the last 30 years, many synthesis routes for nucleotide sugars have been discovered and used for production. However, many of the published procedures shy away from assessing the practicability of their processes. With this review, we give an insight into the development of the (chemo)enzymatic nucleotide sugar synthesis pathways of the last years and present an assessment of critical process parameters such as total turnover number (TTN), space-time yield (STY), and enzyme loading.

Repetitive Synthesis of High-Molecular-Weight Hyaluronic Acid with Immobilized Enzyme Cascades

Industrial hyaluronic acid (HA) production comprises either fermentation with Streptococcus strains or extraction from rooster combs. The hard-to-control product quality is an obstacle to these processes. Enzymatic syntheses of HA were developed to produce high-molecular-weight HA with low dispersity. To facilitate enzyme recovery and biocatalyst re-use, here the immobilization of cascade enzymes onto magnetic beads was used for the synthesis of uridine-5'-diphosphate-α-d-N-acetyl-glucosamine (UDP-GlcNAc), UDP-glucuronic acid (UDP-GlcA), and HA. The combination of six enzymes in the UDP-sugar cascades with integrated adenosine-5'-triphosphate-regeneration reached yields between 60 and 100 % for 5 repetitive batches, proving the productivity. Immobilized HA synthase from Pasteurella multocida produced HA in repetitive batches for three days. Combining all seven immobilized enzymes in a one-pot synthesis, HA production was demonstrated for three days with a HA concentration of up to 0.37 g L-1 , an average MW of 2.7-3.6 MDa, and a dispersity of 1.02-1.03.

The beauty of biocatalysis: sustainable synthesis of ingredients in cosmetics

Covering: 2015 up to July 2021The market for cosmetics is consumer driven and the desire for green, sustainable and natural ingredients is increasing. The use of isolated enzymes and whole-cell organisms to synthesise these products is congruent with these values, especially when combined with the use of renewable, recyclable or waste feedstocks. The literature of biocatalysis for the synthesis of ingredients in cosmetics in the past five years is herein reviewed.

Recent progress in synthesis of carbohydrates with sugar nucleotide-dependent glycosyltransferases

Sugar nucleotide-dependent glycosyltransferases (GTs) are key enzymes that catalyze the formation of glycosidic bonds in nature. They have been increasingly applied in the synthesis of complex carbohydrates and glycoconjugates with or without in situ generation of sugar nucleotides. Human GTs are becoming more accessible and new bacterial GTs have been identified and characterized. An increasing number of crystal structures elucidated for GTs from mammalian and bacterial sources facilitate structure-based design of mutants as improved catalysts for synthesis. Automated platforms have also been developed for chemoenzymatic synthesis of carbohydrates. Recent progress in applying sugar nucleotide-dependent GTs in enzymatic and chemoenzymatic synthesis of mammalian glycans and glycoconjugates, bacterial surface glycans, and glycosylated natural products from bacteria and plants are reviewed.

Recent progress in synthesis of carbohydrates with sugar nucleotide-dependent glycosyltransferases

Sugar nucleotide-dependent glycosyltransferases (GTs) are key enzymes that catalyze the formation of glycosidic bonds in nature. They have been increasingly applied in the synthesis of complex carbohydrates and glycoconjugates with or without in situ generation of sugar nucleotides. Human GTs are becoming more accessible and new bacterial GTs have been identified and characterized. An increasing number of crystal structures elucidated for GTs from mammalian and bacterial sources facilitate structure-based design of mutants as improved catalysts for synthesis. Automated platforms have also been developed for chemoenzymatic synthesis of carbohydrates. Recent progress in applying sugar nucleotide-dependent GTs in enzymatic and chemoenzymatic synthesis of mammalian glycans and glycoconjugates, bacterial surface glycans, and glycosylated natural products from bacteria and plants are reviewed.

Current state on the enzymatic synthesis of glycosaminoglycans

Glycosaminoglycans (GAGs) are linear anionic polysaccharides, and most of them show a specific sulfation pattern. GAGs have been studied for decades, and still, new biological functions are discovered. Hyaluronic acid and heparin are sold for medical or cosmetic applications. With increased market and applications, the production of GAGs stays in the focus of research groups and the industry. Common industrial GAG production relies on the extraction of animal tissue. Contamination, high dispersity, and uncontrolled sulfation pattern are still obstacles to this process. Tailored production strategies for the chemoenzymatic synthesis have been developed to address these obstacles. In recent years, enzyme cascades, including uridine-5'-diphosphate sugar syntheses, were established to obtain defined polymer size and dispersity, as well as defined sulfation patterns. Nevertheless, the complex synthesis of GAGs is still a challenging research field.

Enzymatic Synthesis of Glycans and Glycoconjugates

Glycoconjugates have great potential to improve human health in a multitude of different ways and fields. Prominent examples are human milk oligosaccharides and glycosaminoglycans. The typical choice for the production of homogeneous glycoconjugates is enzymatic synthesis. Through the availability of expression and purification protocols, recombinant Leloir glycosyltransferases are widely applied as catalysts for the synthesis of a wide range of glycoconjugates. Extensive utilization of these enzymes also depends on the availability of activated sugars as building blocks. Multi-enzyme cascades have proven a versatile technique to synthesize and in situ regenerate nucleotide sugar.In this chapter, the functions and mechanisms of Leloir glycosyltransferases are revisited, and the advantage of prokaryotic sources and production systems is discussed. Moreover, in vivo and in vitro pathways for the synthesis of nucleotide sugar are reviewed. In the second part, recent and prominent examples of the application of Leloir glycosyltransferase are given, i.e., the synthesis of glycosaminoglycans, glycoconjugate vaccines, and human milk oligosaccharides as well as the re-glycosylation of biopharmaceuticals, and the status of automated glycan assembly is revisited.

Chemical, enzymatic and biological synthesis of hyaluronic acids

Hyaluronic acid (HA) is a major glycosaminoglycan, a family of structurally complex, linear, anionic hetero-co-polysaccharides. HA is important in various anatomical structures including the eyes, joints, heart and myriad intricate tissues, and is currently widely used in the therapeutics and cosmetics areas. The synthesis of HA of well-defined and uniform chain lengths is of major interest for the development of safer and more reliable drugs and to gain a better understanding of its structure-activity relationships. However, HA has received less attention from the synthetic carbohydrate community compared with other members of the glycosaminoglycan family. In this review, we examine the remarkable progress that has been made in the chemical and chemoenzymatic synthesis of HA, providing a broad spectrum of options to access HA of well controlled chain lengths.