Assays for determining heparan sulfate and heparin O-sulfotransferase activity and specificity

Biosynthesis of animal-free recombinant chondroitin sulfate E using a functional chondroitin sulfotransferase in E. coli

Chondroitin sulfate E (CS-E) is a vital sulfated glycosaminoglycan with diverse biological functions and therapeutic potential. This study marks a significant milestone by achieving the first successful microbial production of chondroitin 4-sulfate 6-O-sulfotransferase (GalNAc4S-6ST) in Escherichia coli, enabling recombinant CS-E biosynthesis. Initially, we identified sulfotransferases capable of converting chondroitin sulfate A (CS-A) to CS-E, but these enzymes were non-functional when expressed in E. coli. Moreover, there is no experimentally derived three-dimensional structure available for this specific sulfotransferase in the protein databases. To overcome this challenge, we developed a 3D model of GalNAc4S-6ST using AlphaFold2 and employed PROSS stability design to identify mutations that enhance enzyme solubility and stability with different N-terminal truncations. Experimental validation of these mutations led to the identification of several functional enzymes. Among various E. coli strains tested for enzyme expression, Origami B (DE3) emerged as the most effective host. This facilitated the enzymatic conversion of CS-A to CS-E, achieving a conversion rate of over 50%, and marking the first successful biosynthesis of animal-free CS-E. These findings represent a significant advancement towards the large-scale synthesis of CS-E using cost-effective carbon sources, offering a sustainable alternative to traditional sourcing from endangered animals like sharks. KEY POINTS: • Functional expression of GalNAc4S-6ST in a simple prokaryote was accomplished. • First-time biosynthesis of animal-free chondroitin sulfate E was accomplished.

Interacting polymer-modification enzymes in heparan sulfate biosynthesis

Glucuronyl 5-epimerase (Hsepi) converts D-glucuronic acid (GlcA) into L-iduronic acid (IdoA) units, through a mechanism involving reversible abstraction of a proton at C5 of hexuronic acid residues. Incubations of a [4GlcAβ1-4GlcNSO₃α1-]_n precursor substrate with recombinant enzymes in a D₂O/H₂O medium enabled an isotope exchange approach to the assessment of functional interactions of Hsepi with hexuronyl 2-O-sulfotransferase (Hs2st) and glucosaminyl 6-O-sulfotransferase (Hs6st), both involved in the final polymer-modification steps. Enzyme complexes were supported by computational modeling and homogeneous time resolved fluorescence. GlcA and IdoA D/H ratios related to product composition revealed kinetic isotope effects that were interpreted in terms of efficiency of the coupled epimerase and sulfotransferase reactions. Evidence for a functional Hsepi/Hs6st complex was provided by selective incorporation of D atoms into GlcA units adjacent to 6-O-sulfated glucosamine residues. The inability to achieve simultaneous 2-O- and 6-O-sulfation in vitro supported topologically separated reactions in the cell. These findings provide novel insight into the roles of enzyme interactions in heparan sulfate biosynthesis.

From Steroid and Drug Metabolism to Glycobiology, Using Sulfotransferase Structures to Understand and Tailor Function

Sulfotransferases are ubiquitous enzymes that transfer a sulfo group from the universal cofactor donor 3'-phosphoadenosine 5'-phosphosulfate to a broad range of acceptor substrates. In humans, the cytosolic sulfotransferases are involved in the sulfation of endogenous compounds such as steroids, neurotransmitters, hormones, and bile acids as well as xenobiotics including drugs, toxins, and environmental chemicals. The Golgi associated membrane-bound sulfotransferases are involved in post-translational modification of macromolecules from glycosaminoglycans to proteins. The sulfation of small molecules can have profound biologic effects on the functionality of the acceptor, including activation, deactivation, or enhanced metabolism and elimination. Sulfation of macromolecules has been shown to regulate a number of physiologic and pathophysiological pathways by enhancing binding affinity to regulatory proteins or binding partners. Over the last 25 years, crystal structures of these enzymes have provided a wealth of information on the mechanisms of this process and the specificity of these enzymes. This review will focus on the general commonalities of the sulfotransferases, from enzyme structure to catalytic mechanism as well as providing examples into how structural information is being used to either design drugs that inhibit sulfotransferases or to modify the enzymes to improve drug synthesis. SIGNIFICANCE STATEMENT: This manuscript honors Dr. Masahiko Negishi's contribution to the understanding of sulfotransferase mechanism, specificity, and roles in biology by analyzing the crystal structures that have been solved over the last 25 years.

Complete biosynthesis of a sulfated chondroitin in Escherichia coli

Sulfated glycosaminoglycans (GAGs) are a class of important biologics that are currently manufactured by extraction from animal tissues. Although such methods are unsustainable and prone to contamination, animal-free production methods have not emerged as competitive alternatives due to complexities in scale-up, requirement for multiple stages and cost of co-factors and purification. Here, we demonstrate the development of single microbial cell factories capable of complete, one-step biosynthesis of chondroitin sulfate (CS), a type of GAG. We engineer E. coli to produce all three required components for CS production–chondroitin, sulfate donor and sulfotransferase. In this way, we achieve intracellular CS production of ~27 μg/g dry-cell-weight with about 96% of the disaccharides sulfated. We further explore four different factors that can affect the sulfation levels of this microbial product. Overall, this is a demonstration of simple, one-step microbial production of a sulfated GAG and marks an important step in the animal-free production of these molecules.

Chondroitin sulfate (CS) is a type of sulfated glycosaminoglycan that is manufactured by extraction from animal tissues for the treatment of osteoarthritis and in drug delivery applications. Here, the authors report the development of single microbial cell factories capable of compete, one-step biosynthesis of animal-free CS production in E. coli.

Elucidating the unusual reaction kinetics of D-glucuronyl C5-epimerase

The chemoenzymatic synthesis of heparin, through a multienzyme process, represents a critical challenge in providing a safe and effective substitute for this animal-sourced anticoagulant drug. D-glucuronyl C5-epimerase (C5-epi) is an enzyme acting on a heparin precursor, N-sulfoheparosan, catalyzing the reversible epimerization of D-glucuronic acid (GlcA) to L-iduronic acid (IdoA). The absence of reliable assays for C5-epi has limited elucidation of the enzymatic reaction and kinetic mechanisms. Real time and offline assays are described that rely on 1D 1H NMR to study the activity of C5-epi. Apparent steady-state kinetic parameters for both the forward and the pseudo-reverse reactions of C5-epi are determined for the first time using polysaccharide substrates directly relevant to the chemoenzymatic synthesis and biosynthesis of heparin. The forward reaction shows unusual sigmoidal kinetic behavior, and the pseudo-reverse reaction displays nonsaturating kinetic behavior. The atypical sigmoidal behavior of the forward reaction was probed using a range of buffer additives. Surprisingly, the addition of 25 mM each of CaCl2 and MgCl2 resulted in a forward reaction exhibiting more conventional Michaelis-Menten kinetics. The addition of 2-O-sulfotransferase, the next enzyme involved in heparin synthesis, in the absence of 3'-phosphoadenosine 5'-phosphosulfate, also resulted in C5-epi exhibiting a more conventional Michaelis-Menten kinetic behavior in the forward reaction accompanied by a significant increase in apparent Vmax. This study provides critical information for understanding the reaction kinetics of C5-epi, which may result in improved methods for the chemoenzymatic synthesis of bioengineered heparin.

Advances in the preparation and synthesis of heparin and related products

Heparin is a naturally occurring glycosaminoglycan from livestock, principally porcine intestine, and is clinically used as an anticoagulant drug. A limitation to heparin production is that it depends on a single animal species and potential problems have been associated with animal-derived heparin. The contamination crisis in 2008 led to a search for new animal sources and the investigation of non-animal sources of heparin. Over the past 5 years, new animal sources, chemical, and chemoenzymatic methods have been introduced to prepare heparin-based drugs. In this review, we describe advances in the preparation and synthesis of heparin and related products.

Heavy Heparin: A Stable Isotope-Enriched, Chemoenzymatically-Synthesized, Poly-Component Drug

Heparin is a highly sulfated, complex polysaccharide and widely used anticoagulant pharmaceutical. In this work, we chemoenzymatically synthesized perdeuteroheparin from biosynthetically enriched heparosan precursor obtained from microbial culture in deuterated medium. Chemical de-N-acetylation, chemical N-sulfation, enzymatic epimerization, and enzymatic sulfation with recombinant heparin biosynthetic enzymes afforded perdeuteroheparin comparable to pharmaceutical heparin. A series of applications for heavy heparin and its heavy biosynthetic intermediates are demonstrated, including generation of stable isotope labeled disaccharide standards, development of a non-radioactive NMR assay for glucuronosyl-C5-epimerase, and background-free quantification of in vivo half-life following administration to rabbits. We anticipate that this approach can be extended to produce other isotope-enriched glycosaminoglycans.

A robust protocol for directed aryl sulfotransferase evolution toward the carbohydrate building block GlcNAc

Bacterial aryl sulfotransferases (AST) utilize p-nitrophenylsulfate (pNPS) as a phenolic donor to sulfurylate typically a phenolic acceptor. Interest in aryl sulfotransferases is growing because of their broad variety of acceptors and cost-effective sulfuryl-donors. For instance, aryl sulfotransferase A (ASTA) from Desulfitobacterium hafniense was recently reported to sulfurylate d-glucose. In this study, a directed evolution protocol was developed and validated for aryl sulfotransferase B (ASTB). Thereby the well-known pNPS quantification system was advanced to operate efficiently as a continuous screening system in 96-well MTP format with a true coefficient of variation of 14.3%. A random mutagenesis library (SeSaM library) of ASTB was screened (1,760 clones) to improve sulfurylation of the carbohydrate building block N-acetylglucosamine (GlcNAc). The beneficial variant ASTB-V1 (Val579Asp) showed an up to 3.4-fold increased specific activity toward GlcNAc when compared to ASTB-WT. HPLC- and MS-analysis confirmed ASTB-V1's increased GlcNAc monosulfurylation (2.4-fold increased product formation) representing the validation of the first successful directed evolution round of an AST for a saccharide substrate.

Engineered heparins as new anticoagulant drugs

Heparin is an anionic polysaccharide that is widely used as a clinical anticoagulant. This glycosaminoglycan is prepared from animal tissues in metric ton quantities. Animal-sourced heparin is also widely used in the preparation of low molecular weight heparins that are gaining in popularity as a result of their improved pharmacological properties. The recent contamination of pharmaceutical heparin together with concerns about increasing demand for this life saving drug and the fragility of the heparin supply chain has led the scientific community to consider other potential sources for heparin. This review examines progress toward the preparation of engineered heparins through chemical synthesis, chemoenzymatic synthesis, and metabolic engineering.

Bioengineered heparins and heparan sulfates

Heparin and heparan sulfates are closely related linear anionic polysaccharides, called glycosaminoglycans, which exhibit a number of important biological and pharmacological activities. These polysaccharides, having complex structures and polydispersity, are biosynthesized in the Golgi of animal cells. While heparan sulfate is a widely distributed membrane and extracellular glycosaminoglycan, heparin is found primarily intracellularly in the granules of mast cells. While heparin has historically received most of the scientific attention for its anticoagulant activity, interest has steadily grown in the multi-faceted role heparan sulfate plays in normal and pathophysiology. The chemical synthesis of these glycosaminoglycans is largely precluded by their structural complexity. Today, we depend on livestock animal tissues for the isolation and the annual commercial production of hundred ton quantities of heparin used in the manufacture of anticoagulant drugs and medical device coatings. The variability of animal-sourced heparin and heparan sulfates, their inherent impurities, the limited availability of source tissues, the poor control of these source materials and their manufacturing processes, suggest a need for new approaches for their production. Over the past decade there have been major efforts in the biotechnological production of these glycosaminoglycans, driven by both therapeutic applications and as probes to study their natural functions. This review focuses on the complex biology of these glycosaminoglycans in human health and disease, and the use of recombinant technology in the chemoenzymatic synthesis and metabolic engineering of heparin and heparan sulfates.

Heparin and related polysaccharides: synthesis using recombinant enzymes and metabolic engineering

Glycosaminoglycans are linear anionic polysaccharides that exhibit a number of important biological and pharmacological activities. The two most prominent members of this class of polysaccharides are heparin/heparan sulfate and the chondroitin sulfates (including dermatan sulfate). These polysaccharides, having complex structures and polydispersity, are biosynthesized in the Golgi of most animal cells. The chemical synthesis of these glycosaminoglycans is precluded by their structural complexity. Today, we depend on food animal tissues for their isolation and commercial production. Ton quantities of these glycosaminoglycans are used annually as pharmaceuticals and nutraceuticals. The variability of animal-sourced glycosaminoglycans, their inherent impurities, the limited availability of source tissues, the poor control of these source materials, and their manufacturing processes suggest a need for new approaches for their production. Over the past decade, there have been major efforts in the biotechnological production of these glycosaminoglycans. This mini-review focuses on the use of recombinant enzymes and metabolic engineering for the production of heparin and chondroitin sulfates.

High cell density cultivation of recombinant Escherichia coli strains expressing 2-O-sulfotransferase and C5-epimerase for the production of bioengineered heparin

Bioengineered heparin is being investigated as a potential substitute for the animal-sourced anticoagulant drug. One step in the current process to prepare bioengineered heparin involves the conversion of N-sulfo heparosan, rich in → 4)GlcNS(1 → 4) GlcA(1 → sequences (where S is sulfo, GlcN is α-D-glucosamine, and GlcA is β-D-glucuronic acid), to a critical intermediate, rich in → 4)GlcNS(1 → 4) IdoA2S(1 → sequences (where S is sulfo and IdoA is α-L-iduronic acid), using 2-O-sulfotransferase (2-OST) and C5 epimerase (C5-epi). Until now, these heparan sulfate biosynthetic enzymes have been expressed in Escherichia coli grown in shake flask culture as fusion proteins. The current study is focused on the high cell density fed-batch cultivation of recombinant E. coli strains expressing both enzymes. We report the high productivity expression of active 2-OST and C5-epi enzymes of 6.0 and 2.2 mg/g dry cell weight, respectively.

Combinatorial one-pot chemoenzymatic synthesis of heparin

Contamination in heparin batches during early 2008 has resulted in a significant effort to develop a safer bioengineered heparin using bacterial capsular polysaccharide heparosan and recombinant enzymes derived from the heparin/heparan sulfate biosynthetic pathway. This requires controlled chemical N-deacetylation/N-sulfonation of heparosan followed by epimerization of most of its glucuronic acid residues to iduronic acid and O-sulfation of the C2 position of iduronic acid and the C3 and C6 positions of the glucosamine residues. A combinatorial study of multi-enzyme, one-pot, in vitro biocatalytic synthesis, carried out in tandem with sensitive analytical techniques, reveals controlled structural changes leading to heparin products similar to animal-derived heparin active pharmaceutical ingredients. Liquid chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy analysis confirms an abundance of heparin's characteristic trisulfated disaccharide, as well as 3-O-sulfo containing residues critical for heparin binding to antithrombin III and its anticoagulant activity. The bioengineered heparins prepared using this simplified one-pot chemoenzymatic synthesis also show in vitro anticoagulant activity.