Metabolic engineering of non-pathogenic Escherichia coli strains for the controlled production of low molecular weight heparosan and size-specific heparosan oligosaccharides

Microbial polysaccharides biosynthesis and their regulatory strategies

Microbial polysaccharides hold significant potential for various applications, including food, cosmetics, petroleum, and pharmaceuticals. A deeper understanding of their biosynthetic pathways and regulatory strategies is crucial for enhancing production efficiency and reducing associated costs. To summarize synthetic biological modification strategies for microbial polysaccharides from a hierarchical perspective, this review classifies these polymers into three categories based on the depths of carried out research regarding their biosynthetic pathways and regulatory strategies, i.e., (1) microbial polysaccharides with well-elucidated biosynthetic pathways, (2) microbial polysaccharides with well-elucidated precursor sugar biosynthetic pathways but synthase-encoding genes incompletely understood, and (3) those whose biosynthesis depends on a single synthetic enzyme. We systematically summarize the biosynthetic pathways of these three categories and provide insights into yield-improvement strategies. This review aims to serve as a valuable reference for metabolic regulation of microbial polysaccharides and to facilitate future advances in their production.

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.

Quality control, safety assessment and preparation approaches of low molecular weight heparin

Low Molecular Weight Heparins (LMWHs) are well-established for use in the prevention and treatment of thrombotic diseases, and as a substitute for unfractionated heparin (UFH) due to their predictable pharmacokinetics and subcutaneous bioavailability. LMWHs are produced by various depolymerization methods from UFH, resulting in heterogeneous compounds with similar biochemical and pharmacological properties. However, the delicate supply chain of UFH and potential contamination from animal sources require new manufacturing approaches for LMWHs. Various LMWH preparation methods are emerging, such as chemical synthesis, enzymatic or chemical depolymerization and chemoenzymatic synthesis. To establish the sameness of active ingredients in both innovator and generic LMWH products, the Food and Drug Administration has implemented a stringent scientific method of equivalence based on physicochemical properties, heparin source material and depolymerization techniques, disaccharide composition and oligosaccharide mapping, biological and biochemical properties, and in vivo pharmacodynamic profiles. In this review, we discuss currently available LMWHs, potential manufacturing methods, and recent progress for manufacturing quality control of these LMWHs.

Enzymatic construction of a library of even- and odd-numbered heparosan oligosaccharides and their N-sulfonated derivatives

Low-molecular-weight heparins (LMWHs), especially the specific-sized heparin oligosaccharides, are attractive for the therapeutic applications, while their synthesis remains challenging. In the present study, unsaturated even-numbered heparosan oligosaccharides were firstly prepared by cleaving high-molecular-weight heparosan using recombinant heparinase III (HepIII). The conversion rates of the unsaturated disaccharides, tetrasaccharides, hexasaccharides, octasaccharides, and decasaccharides were 33.9 %, 47.9 %, 78.7 %, 71.8 %, and 53.4 %, respectively. After processing the aforementioned heparosan oligosaccharides with the Δ4,5 unsaturated glycuronidase, saturated odd-numbered heparosan trisaccharides, pentasaccharides, heptasaccharides, and nonasaccharides were produced. It was observed that among them, the pentasaccharides were the smallest units of saturated odd-numbered oligosaccharides recognized by HepIII. These oligosaccharides were further catalyzed with bifunctional heparan sulfate N-deacetylase/N-sulfotransferase (NDST) under optimized reaction conditions. It was found that the tetrasaccharide was defined as the smallest recognition unit for NDST, obtaining the N-sulfonated heparosan tetrasaccharides, pentasaccharides, and hexasaccharides with a single sulfonate group, as well as N-sulfonated heparosan heptasaccharides, octasaccharides, and nonasaccharides with multiple sulfonate groups. These results provide an easy pathway for constructing a library of specific-sized N-sulfonated heparosan oligosaccharides that can be used as the substrates for the enzymatic synthesis of LMWHs and heparin oligosaccharides, shedding new light on the substrate preference of NDST.

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.

Bacterial glycobiotechnology: A biosynthetic route for the production of biopharmaceutical glycans

The recent advancement in the human glycome and progress in the development of an inclusive network of glycosylation pathways allow the incorporation of suitable machinery for protein modification in non-natural hosts and explore novel opportunities for constructing next-generation tailored glycans and glycoconjugates. Fortunately, the emerging field of bacterial metabolic engineering has enabled the production of tailored biopolymers by harnessing living microbial factories (prokaryotes) as whole-cell biocatalysts. Microbial catalysts offer sophisticated means to develop a variety of valuable polysaccharides in bulk quantities for practical clinical applications. Glycans production through this technique is highly efficient and cost-effective, as it does not involve expensive initial materials. Metabolic glycoengineering primarily focuses on utilizing small metabolite molecules to alter biosynthetic pathways, optimization of cellular processes for glycan and glycoconjugate production, characteristic to a specific organism to produce interest tailored glycans in microbes, using preferably cheap and simple substrate. However, metabolic engineering faces one of the unique challenges, such as the need for an enzyme to catalyze desired substrate conversion when natural native substrates are already present. So, in metabolic engineering, such challenges are evaluated, and different strategies have been developed to overcome them. The generation of glycans and glycoconjugates via metabolic intermediate pathways can still be supported by glycol modeling achieved through metabolic engineering. It is evident that modern glycans engineering requires adoption of improved strain engineering strategies for creating competent glycoprotein expression platforms in bacterial hosts, in the future. These strategies include logically designing and introducing orthogonal glycosylation pathways, identifying metabolic engineering targets at the genome level, and strategically improving pathway performance (for example, through genetic modification of pathway enzymes). Here, we highlight current strategies, applications, and recent progress in metabolic engineering for producing high-value tailored glycans and their applications in biotherapeutics and diagnostics.

Chromosome evolution of Escherichia coli Nissle 1917 for high-level production of heparosan

Heparosan is a crucial-polysaccharide precursor for the chemoenzymatic synthesis of heparin, a widely used anticoagulant drug. Presently, heparosan is mainly extracted with the potential risk of contamination from Escherichia coli strain K5, a pathogenic bacterium causing urinary tract infection. Here, a nonpathogenic probiotic, E. coli strain Nissle 1917 (EcN), was metabolically engineered to carry multiple copies of the 19-kb kps locus and produce heparosan to 9.1 g/L in fed-batch fermentation. Chromosome evolution driven by antibiotics was employed to amplify the kps locus, which governed the synthesis and export of heparosan from EcN at 21 mg L^-1  OD^-1 . The average copy number of kps locus increased from 1 to 24 copies per cell, which produced up to 104 mg L^-1  OD^-1 of heparosan in the shaking flask cultures of engineered strains. The following in-frame deletion of recA stabilized the recombinant duplicates of chromosomal kps locus and the productivity of heparosan in continuous culture for at least 56 generations. Fed-batch fermentation of the engineered strain EcN8 was carried out to bring the yield of heparosan up to 9.1 g/L. Heparosan from the fermentation culture was further purified at a 75% overall recovery. The structure of purified heparosan was characterized and further modified by N-sulfotransferase with 3'-phosphoadenosine-5'-phosphosulfate as the sulfo-donor. The analysis of element composition showed that heparosan was N-sulfated by over 80%. These results indicated that duplicating large DNA cassettes up to 19-kb, followed by high-cell-density fermentation, was promising in the large-scale preparation of chemicals and could be adapted to engineer other industrial-interest bacteria metabolically.

Microbial synthesis of glycosaminoglycans and their oligosaccharides

Compared with chemical synthesis and tissue extraction methods, microbial synthesis of glycosaminoglycans (GAGs) is attractive because of the advantages of eco-friendly processes, production safety, and sustainable development. However, boosting the efficiency of microbial cell factories, precisely regulating GAG molecular weights, and rationally controlling the sulfation degree of GAGs remain challenging. To address these issues, various strategies, including genetic, enzymatic, metabolic, and fermentation engineering, have been developed. In this review, we summarize the recent progress in the construction of efficient GAG-producing microbial cell factories, regulation of the molecular weight of GAGs, and modification of GAG chains. Moreover, future studies, remaining challenges, and potential solutions in this field are discussed.

Pharmacology of Heparin and Related Drugs: An Update

Heparin has been used extensively as an antithrombotic and anticoagulant for close to 100 years. This anticoagulant activity is attributed mainly to the pentasaccharide sequence, which potentiates the inhibitory action of antithrombin, a major inhibitor of the coagulation cascade. More recently it has been elucidated that heparin exhibits anti-inflammatory effect via interference of the formation of neutrophil extracellular traps and this may also contribute to heparin's antithrombotic activity. This illustrates that heparin interacts with a broad range of biomolecules, exerting both anticoagulant and nonanticoagulant actions. Since our previous review, there has been an increased interest in these nonanticoagulant effects of heparin, with the beneficial role in patients infected with SARS2-coronavirus a highly topical example. This article provides an update on our previous review with more recent developments and observations made for these novel uses of heparin and an overview of the development status of heparin-based drugs. SIGNIFICANCE STATEMENT: This state-of-the-art review covers recent developments in the use of heparin and heparin-like materials as anticoagulant, now including immunothrombosis observations, and as nonanticoagulant including a role in the treatment of SARS-coronavirus and inflammatory conditions.

Heparin mimetics as potential intervention for COVID-19 and their bio-manufacturing

The COVID-19 pandemic has caused severe health problems worldwide and unprecedented decimation of the global economy. Moreover, after more than 2 years, many populations are still under pressure of infection. Thus, a broader perspective in developing antiviral strategies is still of great importance. Inspired by the observed multiple benefits of heparin in the treatment of thrombosis, the potential of low molecular weight heparin (LMWH) for the treatment of COVID-19 have been explored. Clinical applications found that LMWH decreased the level of inflammatory cytokines in COVID-19 patients, accordingly reducing lethality. Furthermore, several in vitro studies have demonstrated the important roles of heparan sulfate in SARS-CoV-2 infection and the inhibitory effects of heparin and heparin mimetics in viral infection. These clinical observations and designed studies argue for the potential to develop heparin mimetics as anti-SARS-CoV-2 drug candidates. In this review, we summarize the properties of heparin as an anticoagulant and the pharmaceutical possibilities for the treatment of virus infection, focusing on the perspectives of developing heparin mimetics via chemical synthesis, chemoenzymatic synthesis, and bioengineered production by microbial cell factories. The ultimate goal is to pave the eminent need for exploring novel compounds to treat coronavirus infection-caused diseases.