Molecular cloning, identification, and sequence of the hyaluronan synthase gene from group A Streptococcus pyogenes

Deficiency of hasB accelerated the clearance of Streptococcus equi subsp. Zooepidemicus through gasdermin d-dependent neutrophil extracellular traps

Streptococcus equi subsp. zooepidemicus (S. zooepidemicus, SEZ) is an essential zoonotic bacterial pathogen that can cause various inflammation, such as meningitis, endocarditis, and pneumonia. UDP-glucose dehydrogenase (hasB) is indispensable in synthesizing SEZ virulence factor hyaluronan capsules. Our study investigated the infection of hasB on mice response to SEZ by employing a constructed capsule-deficient mutant strain designated as the ΔhasB strain. This deficiency was associated with a reduced SEZ bacterial load in the mice's blood and peritoneal lavage fluid (PLF) post-infection. Besides, the ΔhasB SEZ strain exhibited a higher propensity for neutrophil infiltration and release of cell-free DNA (cfDNA) in vivo compared to the wild-type (WT) SEZ strain. In vitro experiments further revealed that ΔhasB SEZ more effectively induced the formation of neutrophil extracellular traps (NETs) containing histone 3 (H3), neutrophil elastase (NE), and DNA, than its WT counterpart. Moreover, the release of NETs was determined to be gasdermin D (GSDMD)-dependent during the infection process. Taken together, these findings underscore that the deficiency of the hasB gene in SEZ leads to enhanced GSDMD-dependent NET release from neutrophils, thereby reducing SEZ's capacity to resist NETs-mediated eradication during infection. Our finding paves the way for the development of innovative therapeutic strategies against SEZ.

Hyaluronan synthases; mechanisms, myths, & mysteries of three types of unique bifunctional glycosyltransferases

Hyaluronan (HA), the essential [-3-GlcNAc-1-β-4-GlcA-1-β-]n matrix polysaccharide in vertebrates and molecular camouflage coating in select pathogens, is polymerized by "HA synthase" (HAS) enzymes. The first HAS identified three decades ago opened the window for new insights and biotechnological tools. This review discusses current understanding of HA biosynthesis, its biotechnological utility, and addresses some misconceptions in the literature. HASs are fascinating enzymes that polymerize two different UDP-activated sugars via different glycosidic linkages. Therefore, these catalysts were the first examples to break the "one enzyme/one sugar transferred" dogma. Three distinct types of these bifunctional glycosyltransferases (GTs) with disparate architectures and reaction modes are known. Based on biochemical and structural work, we present an updated classification system. Class I membrane-integrated HASs employ a processive chain elongation mechanism and secrete HA across the plasma membrane. This complex operation is accomplished by functionally integrating a cytosolic catalytic domain with a channel-forming transmembrane region. Class I enzymes, containing a single GT family-2 (GT-2) module that adds both monosaccharide units to the nascent chain, are further subdivided into two groups that construct the polymer with opposite molecular directionalities: Class I-R and I-NR elongate the HA polysaccharide at either the reducing or the non-reducing end, respectively. In contrast, Class II HASs are membrane-associated peripheral synthases with a non-processive, non-reducing end elongation mechanism using two independent GT-2 modules (one for each type of monosaccharide) and require a separate secretion system for HA export. We discuss recent mechanistic insights into HA biosynthesis that promise biotechnological benefits and exciting engineering approaches.

Hyaluronic acid: More than a carrier, having an overpowering extracellular and intracellular impact on cancer

Hyaluronic acid (HA), also named hyaluronan, is an omnipresent component of the tissue microenvironment. It is extensively used to formulate targeted drug delivery systems for cancer. Although HA itself has pivotal influences in various cancers, its calibers are somewhat neglected when using it as delivering platform to treat cancer. In the last decade, multiple studies revealed roles of HA in cancer cell proliferation, invasion, apoptosis, and dormancy through pathways like mitogen-activated protein kinase-extracellular signal-regulated kinase (MAPK/ERK), P³⁸, and nuclear factor kappa-light chain-enhancer of activated B cells (NFκB). A more fascinating fact is that the distinct molecular weight (MW) of HA exerts disparate effects on the same type of cancer. Its overwhelming use in cancer therapy and other therapeutic products make collective research on the sundry impact of it on various types of cancer, an essential aspect to be considered in all of these domains. Even the development of new therapies against cancer needed meticulous studies on HA because of its divergence of activity based on MW. This review will provide painstaking insight into the extracellular and intracellular bioactivity of HA, its modified forms, and its MW in cancers, which may improve the management of cancer.

HYBID in osteoarthritis: Potential target for disease progression

HYBID is a new hyaluronan-degrading enzyme and exists in various cells of the human body. Recently, HYBID was found to over-express in the osteoarthritic chondrocytes and fibroblast-like synoviocytes. According to these researches, high level of HYBID is significantly correlated with cartilage degeneration in joints and hyaluronic acid degradation in synovial fluid. In addition, HYBID can affect inflammatory cytokine secretion, cartilage and synovium fibrosis, synovial hyperplasia via multiple signaling pathways, thereby exacerbating osteoarthritis. Based on the existing research of HYBID in osteoarthritis, HYBID can break the metabolic balance of HA in joints through the degradation ability independent of HYALs/CD44 system and furthermore affect cartilage structure and mechanotransduction of chondrocytes. In particular, in addition to HYBID itself being able to trigger some signaling pathways, we believe that low-molecular-weight hyaluronan produced by excess degradation can also stimulate some disease-promoting signaling pathways by replacing high-molecular-weight hyaluronan in joints. The specific role of HYBID in osteoarthritis is gradually revealed, and the discovery of HYBID raises the new way to treat osteoarthritis. In this review, the expression and basic functions of HYBID in joints were summarized, and reveal potential role of HYBID as a key target in treatment for osteoarthritis.

Evaluation of transmembrane domain deletions on hyaluronic acid polymerization of hyaluronan synthase isolated from Streptococcus equisimilis group G

The membrane enzyme of hyaluronan synthase (HAS) is the key enzyme in hyaluronic acid (HA) biosynthesis by coupling UDP-sugars. Prior studies proposed the C-terminus region of HAS enzyme mediates the production rate and molecular weight of HA. The current study describes the isolation and characterizations of a transmembrane HAS enzyme isolated from Streptococcus equisimilis Group G (GGS-HAS) in vitro. The effect of transmembrane domains (TMDs) on HA productivity was determined and the shortest active variant was also identified by recombinant expression of full-length and five truncated forms of GGS-HAS in Escherichia coli. We found that the GGS-HAS enzyme is longer than that of S. equisimilis group C (GCS-HAS) which includes three more residues (LER) at the C-terminus region (positions 418-420) and also one-point mutation at position 120 (E120D). Amino acid sequence alignment demonstrated 98% and 71% identity of GGS-HAS with that of S. equisimilis Group C and S. pyogenes Group A, respectively. The in vitro productivity of the full-length enzyme was 35.57 µg/nmol, however, extended TMD deletions led to a reduction in the HA productivity. The HAS-123 variant showed the highest activity among the truncated forms, indicating the essential role of first, second, and third TMDs for the full activity. Despite a decline in activity, the intracellular variant can still mediate the binding and polymerization of HA without any need for TMDs. This significant finding suggests that the intracellular domain is the core for HA biosynthesis in the enzyme and other domains are probably involved in other attributes including the enzyme kinetics that affect the size distribution of the polymer. However, more investigations on the recombinant forms are still needed to confirm clearly the role of each transmembrane domain on these properties.

Aggrecan and Hyaluronan: The Infamous Cartilage Polyelectrolytes - Then and Now

Cartilages are unique in the family of connective tissues in that they contain a high concentration of the glycosaminoglycans, chondroitin sulfate and keratan sulfate attached to the core protein of the proteoglycan, aggrecan. Multiple aggrecan molecules are organized in the extracellular matrix via a domain-specific molecular interaction with hyaluronan and a link protein, and these high molecular weight aggregates are immobilized within the collagen and glycoprotein network. The high negative charge density of glycosaminoglycans provides hydrophilicity, high osmotic swelling pressure and conformational flexibility, which together function to absorb fluctuations in biomechanical stresses on cartilage during movement of an articular joint. We have summarized information on the history and current knowledge obtained by biochemical and genetic approaches, on cell-mediated regulation of aggrecan metabolism and its role in skeletal development, growth as well as during the development of joint disease. In addition, we describe the pathways for hyaluronan metabolism, with particular focus on the role as a "metabolic rheostat" during chondrocyte responses in cartilage remodeling in growth and disease.Future advances in effective therapeutic targeting of cartilage loss during osteoarthritic diseases of the joint as an organ as well as in cartilage tissue engineering would benefit from 'big data' approaches and bioinformatics, to uncover novel feed-forward and feed-back mechanisms for regulating transcription and translation of genes and their integration into cell-specific pathways.

The Streptococcus pyogenes hyaluronic acid capsule promotes experimental nasal and skin infection by preventing neutrophil-mediated clearance

Streptococcus pyogenes is a globally prominent human-specific pathogen responsible for an enormous burden of human illnesses, including >600 million pharyngeal and >100 million skin infections each year. Despite intensive efforts that focus on invasive indications, much remains unknown about this bacterium in its natural state during colonization of the nasopharynx and skin. Using acute experimental infection models in HLA-transgenic mice, we evaluated how the hyaluronic acid (HA) capsule contributes to S. pyogenes MGAS8232 infection within these limited biological niches. Herein, we demonstrate that HA capsule expression promotes bacterial burden in murine nasal turbinates and skin lesions by resisting neutrophil-mediated killing. HA capsule production is encoded by the hasABC operon and compared to wildtype S. pyogenes infections, mice infected with a ΔhasA mutant exhibited over a 1000-fold CFU reduction at 48-hours post-nasal challenge, and a 10,000-fold CFU reduction from skin lesions 72-hours post-skin challenge. HA capsule expression contributed substantially to skin lesion size development following subdermal inoculations. In the absence of capsule expression, S. pyogenes revealed drastically impeded growth in whole human blood and increased susceptibility to killing by isolated neutrophils ex vivo, highlighting its important role in resisting phagocytosis. Furthermore, we establish that neutrophil depletion in mice recovered the reduced burden by the ΔhasA mutant in both the nasopharynx and skin. Together, this work confirms that the HA capsule is a key virulence determinant during acute infections by S. pyogenes and demonstrates that its predominant function is to protect S. pyogenes against neutrophil-mediated killing.

Facile Synthesis of Sugar Nucleotides from Common Sugars by the Cascade Conversion Strategy

Sugar nucleotides are essential glycosylation donors in the carbohydrate metabolism. Naturally, most sugar nucleotides are derived from a limited number of common sugar nucleotides by de novo biosynthetic pathways, undergoing single or multiple reactions such as dehydration, epimerization, isomerization, oxidation, reduction, amination, and acetylation reactions. However, it is widely believed that such complex bioconversions are not practical for synthetic use due to the high preparation cost and great difficulties in product isolation. Therefore, most of the discovered sugar nucleotides are not readily available. Here, based on de novo biosynthesis mainly, 13 difficult-to-access sugar nucleotides were successfully prepared from two common sugars D-Man and sucrose in high yields, at a multigram scale, and without the need for tedious purification manipulations. This work demonstrated that de novo biosynthesis, although undergoing complex reactions, is also practical and cost-effective for synthetic use by employing a cascade conversion strategy.

Hyaluronic Acid: Known for Almost a Century, but Still in Vogue

Hyaluronic acid (HA) has a special position among glycosaminoglycans. As a major component of the extracellular matrix (ECM). This simple, unbranched polysaccharide is involved in the regulation of various biological cell processes, whether under physiological conditions or in cases of cell damage. This review summarizes the history of this molecule's study, its distinctive metabolic pathway in the body, its unique properties, and current information regarding its interaction partners. Our main goal, however, is to intensively investigate whether this relatively simple polymer may find applications in protecting against ionizing radiation (IR) or for therapy in cases of radiation-induced damage. After exposure to IR, acute and belated damage develops in each tissue depending upon the dose received and the cellular composition of a given organ. A common feature of all organ damage is a distinct change in composition and structure of the ECM. In particular, the important role of HA was shown in lung tissue and the variability of this flexible molecule in the complex mechanism of radiation-induced lung injuries. Moreover, HA is also involved in intermediating cell behavior during morphogenesis and in tissue repair during inflammation, injury, and would healing. The possibility of using the HA polymer to affect or treat radiation tissue damage may point to the missing gaps in the responsible mechanisms in the onset of this disease. Therefore, in this article, we will also focus on obtaining answers from current knowledge and the results of studies as to whether hyaluronic acid can also find application in radiation science.

Low cost and sustainable hyaluronic acid production in a manufacturing platform based on Bacillus subtilis 3NA strain

Hyaluronic acid (HA) is a high value glycosaminoglycan mostly used in health and cosmetic applications. Commercial HA is produced from animal tissues or in toxigenic bacteria of the genus Streptococcus grown in complex media, which are expensive and raise environmental concerns due to the disposal of large amounts of broth with high organic loads. Other microorganisms were proposed as hosts for the heterologous production of HA, but the methods are still costly. The extraordinary capacity of this biopolymer to bind and retain water attracts interest for large-scale applications where biodegradable materials are needed, but its high cost and safety concerns are barriers for its adoption. Bacillus subtilis 3NA strain is prototrophic, amenable for genetic manipulation, GRAS, and can rapidly reach high cell densities in salt-based media. These phenotypic traits were exploited to create a platform for biomolecule production using HA as a proof of concept. First, the 3NA strain was engineered to produce HA; second, a chemically defined medium was formulated using commodity-priced inorganic salts combined at the stoichiometric ratios needed to build the necessary quantities of biomass and HA; and third, a scalable fermentation process, where HA can be produced at the maximum volumetric productivity (VP), was designed. A comparative economic analysis against other methods indicates that the new process may increase the operating profit of a manufacturing plant by more than 100%. The host, the culture medium, and the rationale employed to develop the fermentation process described here, introduce an IP-free platform that could be adaptable for production of other biomolecules. KEY POINTS: • A biomolecule production platform based on B. subtilis 3NA strain and a synthetic medium was tested for hyaluronic acid biosynthesis • A fermentation process with the maximum volumetric productivity was designed • A techno-economic analysis forecasts a significant reduction in the manufacturing cost compared to the current methods.

Bacterial exopolysaccharides: Chemical structures, gene clusters and genetic engineering

In recent decades, the composition, structure, biosynthesis, and function of bacterial extracellular polysaccharides (EPS) have been extensively studied. EPS are synthesized through different biosynthetic pathways. The genes responsible for EPS synthesis are usually clustered on the genome or large plasmids of bacteria. Generally, different EPS synthesis gene clusters direct the synthesis of EPS with different chemical structures and biological activities. A better understanding of the gene functions involved in EPS biosynthesis is critical for the production of EPS with special biological activities. Genetic engineering methods are usually used to study EPS synthesis related genes. This review organizes the available information on EPS, including their structures, synthesis of related genes, and highlights the research progress of modifying EPS gene clusters through gene-editing methods.

Role of membrane proteins in bacterial synthesis of hyaluronic acid and their potential in industrial production

Hyaluronic acid (HA) is a glycosaminoglycan polymer found in various parts of human body and is required for functions like lubrication, water homeostasis etc. Hyaluronic acid is mostly produced industrially by bacterial fermentation for pharmaceutical and cosmetic applications. This review discusses on the role of membrane proteins involved in synthesis and transport of bacterial HA, since HA is a transmembrane product. The different types of membrane proteins involved, their transcriptional control in wild type bacteria and the expression of those proteins in various recombinant hosts have been discussed. The role of phospholipids and metal ions on membrane proteins activity, HA yield and size of HA have also been discussed. Today with an estimated market of US$ 8.3 billion and which is expected to grow to US$ 15.25 billion in 2026, it is essential to increase the efficiency of the industrial HA production process. So this review also proposes on how those membrane proteins and cellular mechanisms like the transcriptional control can be utilised to develop efficient industrial strains that enhance the yield and size of HA produced.

Tumor Microenvironment-Associated Extracellular Matrix Components Regulate NK Cell Function

The tumor microenvironment (TME) is composed of multiple infiltrating host cells (e.g., endothelial cells, fibroblasts, lymphocytes, and myeloid cells), extracellular matrix, and various secreted or cell membrane-presented molecules. Group 1 innate lymphoid cells (ILCs), which includes natural killer (NK) cells and ILC1, contribute to protecting the host against cancer and infection. Both subsets are able to quickly produce cytokines such as interferon gamma (IFN-γ), chemokines, and other growth factors in response to activating signals. However, the TME provides many molecules that can prevent the potential effector function of these cells, thereby protecting the tumor. For example, TME-derived tumor growth factor (TGF)-β and associated members of the superfamily downregulate NK cell cytotoxicity, cytokine secretion, metabolism, proliferation, and induce effector NK cells to upregulate ILC1-like characteristics. In concert, a family of carbohydrate-binding proteins called galectins, which can be produced by different cells composing the TME, can downregulate NK cell function. Matrix metalloproteinase (MMP) and a disintegrin and metalloproteinase (ADAM) are also enzymes that can remodel the extracellular matrix and shred receptors from the tumor cell surface, impairing the activation of NK cells and leading to less effective effector functions. Gaining a better understanding of the characteristics of the TME and its associated factors, such as infiltrating cells and extracellular matrix, could lead to tailoring of new personalized immunotherapy approaches. This review provides an overview of our current knowledge on the impact of the TME and extracellular matrix-associated components on differentiation, impairment, and function of NK cells.

Self-regenerating giant hyaluronan polymer brushes

Tailoring interfaces with polymer brushes is a commonly used strategy to create functional materials for numerous applications. Existing methods are limited in brush thickness, the ability to generate high-density brushes of biopolymers, and the potential for regeneration. Here we introduce a scheme to synthesize ultra-thick regenerating hyaluronan polymer brushes using hyaluronan synthase. The platform provides a dynamic interface with tunable brush heights that extend up to 20 microns - two orders of magnitude thicker than standard brushes. The brushes are easily sculpted into micropatterned landscapes by photo-deactivation of the enzyme. Further, they provide a continuous source of megadalton hyaluronan or they can be covalently-stabilized to the surface. Stabilized brushes exhibit superb resistance to biofilms, yet are locally digested by fibroblasts. This brush technology provides opportunities in a range of arenas including regenerating tailorable biointerfaces for implants, wound healing or lubrication as well as fundamental studies of the glycocalyx and polymer physics.

The journey of hyaluronan research in the Journal of Biological Chemistry

Hyaluronan has a very simple structure. It is a linear glycosaminoglycan composed of disaccharide units of GlcNAc and d-glucuronic acid with alternating β-1,4 and β-1,3 glycosidic bonds that can be repeated 20,000 or more times, a molecular mass >8 million Da, and a length >20 μm. However, it has a very complex biology. It is a major, ubiquitous component of extracellular matrices involved in everything from fertilization, development, inflammations, to cancer. This JBC Review highlights some of these processes that were initiated through publications in the Journal of Biological Chemistry.

Streptococcus pneumoniae Capsular Polysaccharide

The polysaccharide capsule of Streptococcus pneumoniae is the dominant surface structure of the organism and plays a critical role in virulence, principally by interfering with host opsonophagocytic clearance mechanisms. The capsule is the target of current pneumococcal vaccines, but there are 98 currently recognised polysaccharide serotypes and protection is strictly serotype-specific. Widespread use of these vaccines is driving changes in serotype prevalence in both carriage and disease. This chapter summarises current knowledge on the role of the capsule and its regulation in pathogenesis, the mechanisms of capsule synthesis, the genetic basis for serotype differences, and provides insights into how so many structurally distinct capsular serotypes have evolved. Such knowledge will inform ongoing refinement of pneumococcal vaccination strategies.

Capsular Polysaccharide of Group A Streptococcus

Most clinical isolates of Streptococcus pyogenes elaborate a capsular polysaccharide, which is composed of hyaluronic acid, a high-molecular-mass polymer of alternating residues of N-acetyl glucosamine and glucuronic acid. Certain strains, particularly those of the M18 serotype, produce abundant amounts of capsule, resulting in formation of large, wet-appearing, translucent or "mucoid" colonies on solid media, whereas strains of M-types 4 and 22 produce none. Studies of acapsular mutant strains have provided evidence that the capsule enhances virulence in animal models of infection, an effect attributable, at least in part, to resistance to complement-mediated opsonophagocytic killing by leukocytes. The presence of the hyaluronic acid capsule may mask adhesins on the bacterial cell wall. However, the capsule itself can mediate bacterial attachment to host cells by binding to the hyaluronic-acid binding protein, CD44. Furthermore, binding of the S. pyogenes capsule to CD44 on host epithelial cells can trigger signaling events that disrupt cell-cell junctions and facilitate bacterial invasion into deep tissues. This article summarizes the biochemistry, genetics, regulation, and role in pathogenesis of this important virulence determinant.

Distinct reaction mechanisms for hyaluronan biosynthesis in different kingdoms of life

Hyaluronan (HA) is an acidic high molecular weight cell surface polysaccharide ubiquitously expressed by vertebrates, some pathogenic bacteria and even viruses. HA modulates many essential physiological processes and is implicated in numerous pathological conditions ranging from autoimmune diseases to cancer. In various pathogens, HA functions as a non-immunogenic surface polymer that reduces host immune responses. It is a linear polymer of strictly alternating glucuronic acid and N-acetylglucosamine units synthesized by HA synthase (HAS), a membrane-embedded family-2 glycosyltransferase. The enzyme synthesizes HA and secretes the polymer through a channel formed by its own membrane-integrated domain. To reveal how HAS achieves these tasks, we determined the biologically functional units of bacterial and viral HAS in a lipid bilayer environment by co-immunoprecipitation, single molecule fluorescence photobleaching, and site-specific cross-linking analyses. Our results demonstrate that bacterial HAS functions as an obligate homo-dimer with two functional HAS copies required for catalytic activity. In contrast, the viral enzyme, closely related to vertebrate HAS, functions as a monomer. Using site-specific cross-linking, we identify the dimer interface of bacterial HAS and show that the enzyme uses a reaction mechanism distinct from viral HAS that necessitates a dimeric assembly.

A Trickster in Disguise: Hyaluronan's Ambivalent Roles in the Matrix

Hyaluronan (HA) is a simple but diverse glycosaminoglycan. It plays a major role in aging, cellular senescence, cancer, and tissue homeostasis. In which way HA affects the surrounding tissues greatly depends on the molecular weight of HA. Whereas high molecular weight HA is associated with homeostasis and protective effects, HA fragments tend to be linked to the pathologic state. Furthermore, the interaction of HA with its binding partners, the hyaladherins, such as CD44, is essential for sustaining tissue integrity and is likewise related to cancer. The naked mole rat, a rodent species, possesses a special form of very high molecular weight (vHMW) HA, which is associated with the extraordinary cancer resistance and longevity of those animals. This review addresses HA and its diverse facets: from HA synthesis to degradation, from oligomeric HA to vHMW-HA and from its beneficial properties to the involvement in pathologies. We further discuss the functions of HA in the naked mole rat and compare them to human conditions. Though intensively researched, this simple polymer bears some secrets that may hold the key for a better understanding of cellular processes and the development of diseases, such as cancer.

Absorption of Orally Administered Hyaluronan

Hyaluronan (HA) has been utilized as a supplement. However, the absorption of orally administrated HA remains controversial. The degradation and absorption of HA in the intestine were investigated in this study. HA excretion into the feces, degradation in the intestinal tract, absorption through the large intestine, and translocation to the blood and skin were examined. HA administered orally was not detected in rat feces. HA was degraded by cecal content, but not by artificial gastric juice and intestinal juice. Oligosaccharide HA passed through excised large intestine sacs. Furthermore, disaccharides, tetrasaccharides, and polysaccharides HA were distributed to the skin of rats following oral administration of high molecular weight HA (300 kDa). The results of the study suggest that orally administered HA is degraded to oligosaccharides by intestinal bacteria, and oligosaccharide HA is absorbed in the large intestine and is subsequently distributed throughout the tissues, including the skin.

Hyaluronan synthase control of synthesis rate and hyaluronan product size are independent functions differentially affected by mutations in a conserved tandem B-X7-B motif

Hyaluronan synthases (HAS) normally make large (>MDa) hyaluronan (HA) products. Smaller HA fragments (e.g. 100-400 kDa) produced in vivo are associated with inflammation and cell signaling by HA receptors that bind small, but not large, HA. Although HA fragments can arise from breakdown by hyaluronidases, HAS might also be regulated directly to synthesize small HA. Here we examined the Streptococcus equisimilis HAS (SeHAS) C-terminus, which contains a tandem B-X₇-B motif (K³⁹⁸-X₇-R⁴⁰⁶-X₇-K⁴¹⁴), by testing the effects of 27 site-specific scanning mutations and 7 C-terminal truncations on HA synthesis activity and weight-average mass. Although HAS enzymes cannot be HA-binding proteins, these motifs are highly conserved within the Class I HAS family. Fifteen Arg⁴⁰⁶ mutants made large MDa HA (86-110% wildtype size), with specific activities from 70% to 177% of wildtype. In contrast, 10 of 12 Lys³⁹⁸ mutants made HA that was 8-14% of wildtype size (≤250-480 kDa), with specific activities from 14% to 64% of wildtype. Four nearly inactive (2% wildtype activity) C-terminal truncation mutants made MDa HA (56-71% wildtype). The results confirm earlier findings with Cys-mutants [Weigel PH, Baggenstoss BA. 2012. Hyaluronan synthase polymerizing activity and control of product size are discrete enzyme functions that can be uncoupled by mutagenesis of conserved cysteines. Glycobiology 22:1302-1310] that HAS uses two independent activities to control HA size and HA synthesis rate; these are two separate functions. We conclude that HAS regulatory modifications that alter tandem B-X₇-B motif conformation could mimic these mutagenesis-induced effects, allowing HAS in vivo to make small HA directly. The results also support a model in which the tandem-motif region is part of the intra-HAS pore and interacts directly with HA.

Hyaluronic Acid--an "Old" Molecule with "New" Functions: Biosynthesis and Depolymerization of Hyaluronic Acid in Bacteria and Vertebrate Tissues Including during Carcinogenesis

Hyaluronic acid is an evolutionarily ancient molecule commonly found in vertebrate tissues and capsules of some bacteria. Here we review modern data regarding structure, properties, and biological functions of hyaluronic acid in mammals and Streptococcus spp. bacteria. Various aspects of biogenesis and degradation of hyaluronic acid are discussed, biosynthesis and degradation metabolic pathways for glycosaminoglycan together with involved enzymes are described, and vertebrate and bacterial hyaluronan synthase genes are characterized. Special attention is given to the mechanisms underlying the biological action of hyaluronic acid as well as the interaction between polysaccharide and various proteins. In addition, all known signaling pathways involving hyaluronic acid are outlined. Impaired hyaluronic acid metabolism, changes in biopolymer molecular weight, hyaluronidase activity, and enzyme isoforms often accompany carcinogenesis. The interaction between cells and hyaluronic acid from extracellular matrix that may be important during malignant change is discussed. An expected role for high molecular weight hyaluronic acid in resistance of naked mole rat to oncologic diseases and the protective role of hyaluronic acid in bacteria are discussed.

Genetic basis for hyper production of hyaluronic acid in natural and engineered microorganisms

Hyaluronic acid, or HA, is a rigid and linear biopolymer belonging to the class of the glycosaminoglycans, and composed of repeating units of the monosaccharides glucuronic acid and N-acetylglucosamine. HA has multiple important functions in the human body, due to its properties such as bio-compatibility, lubricity and hydrophilicity, it is widely applied in the biomedical, food, health and cosmetic fields. The growing interest in this molecule has motivated the discovery of new ways of obtaining it. Traditionally, HA has been extracted from rooster comb-like animal tissues. However, due to legislation laws HA is now being produced by bacterial fermentation using Streptococcus zooepidemicus, a natural producer of HA, despite it being a pathogenic microorganism. With the expansion of new genetic engineering technologies, the use of organisms that are non-natural producers of HA has also made it possible to obtain such a polymer. Most of the published reviews have focused on HA formulation and its effects on different body tissues, whereas very few of them describe the microbial basis of HA production. Therefore, for the first time this review has compiled the molecular and genetic bases for natural HA production in microorganisms together with the main strategies employed for heterologous production of HA.

Insights into the structure and function of membrane-integrated processive glycosyltransferases

Complex carbohydrates perform essential functions in life, including energy storage, cell signaling, protein targeting, quality control, as well as supporting cell structure and stability. Extracellular polysaccharides (EPS) represent mainly structural polymers and are found in essentially all kingdoms of life. For example, EPS are important biofilm and capsule components in bacteria, represent major constituents in cell walls of fungi, algae, arthropods and plants, and modulate the extracellular matrix in vertebrates. Different mechanisms evolved by which EPS are synthesized. Here, we review the structures and functions of membrane-integrated processive glycosyltransferases (GTs) implicated in the synthesis and secretion of chitin, alginate, hyaluronan and poly-N-acetylglucosamine (PNAG).

Quantitative proteogenomics of human pathogens using DIA-MS

The increasing number of bacterial genomes in combination with reproducible quantitative proteome measurements provides new opportunities to explore how genetic differences modulate proteome composition and virulence. It is challenging to combine genome and proteome data as the underlying genome influences the proteome. We present a strategy to facilitate the integration of genome data from several genetically similar bacterial strains with data-independent analysis mass spectrometry (DIA-MS) for rapid interrogation of the combined data sets. The strategy relies on the construction of a composite genome combining all genetic data in a compact format, which can accommodate the fusion with quantitative peptide and protein information determined via DIA-MS. We demonstrate the method by combining data sets from whole genome sequencing, shotgun MS and DIA-MS from 34 clinical isolates of Streptococcus pyogenes. The data structure allows for fast exploration of the data showing that undetected proteins are on average more amenable to amino acid substitution than expressed proteins. We identified several significantly differentially expressed proteins between invasive and non-invasive strains. The work underlines how integration of whole genome sequencing with accurately quantified proteomes can further advance the interpretation of the relationship between genomes, proteomes and virulence. This article is part of a Special Issue entitled: Computational Proteomics.

Hyaluronan Synthase: The Mechanism of Initiation at the Reducing End and a Pendulum Model for Polysaccharide Translocation to the Cell Exterior

Hyaluronan (HA) biosynthesis has been studied for over six decades, but our understanding of the biochemical details of how HA synthase (HAS) assembles HA is still incomplete. Class I family members include mammalian and streptococcal HASs, the focus of this review, which add new intracellular sugar-UDPs at the reducing end of growing hyaluronyl-UDP chains. HA-producing cells typically create extracellular HA coats (capsules) and also secrete HA into the surrounding space. Since HAS contains multiple transmembrane domains and is lipid-dependent, we proposed in 1999 that it creates an intraprotein HAS-lipid pore through which a growing HA-UDP chain is translocated continuously across the cell membrane to the exterior. We review here the evidence for a synthase pore-mediated polysaccharide translocation process and describe a possible mechanism (the Pendulum Model) and potential energy sources to drive this ATP-independent process. HA synthases also synthesize chitin oligosaccharides, which are created by cleavage of novel oligo-chitosyl-UDP products. The synthesis of chitin-UDP oligomers by HAS confirms the reducing end mechanism for sugar addition during HA assembly by streptococcal and mammalian Class I enzymes. These new findings indicate the possibility that HA biosynthesis is initiated by the ability of HAS to use chitin-UDP oligomers as self-primers.

Hyaluronan synthase 1: a mysterious enzyme with unexpected functions

Hyaluronan synthase 1 (HAS1) is one of three isoenzymes responsible for cellular hyaluronan synthesis. Interest in HAS1 has been limited because its role in hyaluronan production seems to be insignificant compared to the two other isoenzymes, HAS2 and HAS3, which have higher enzymatic activity. Furthermore, in most cell types studied so far, the expression of its gene is low and the enzyme requires high concentrations of sugar precursors for hyaluronan synthesis, even when overexpressed in cell cultures. Both expression and activity of HAS1 are induced by pro-inflammatory factors like interleukins and cytokines, suggesting its involvement in inflammatory conditions. Has1 is upregulated in states associated with inflammation, like atherosclerosis, osteoarthritis, and infectious lung disease. In addition, both full length and splice variants of HAS1 are expressed in malignancies like bladder and prostate cancers, multiple myeloma, and malignant mesothelioma. Interestingly, immunostainings of tissue sections have demonstrated the role of HAS1 as a poor predictor in breast cancer, and is correlated with high relapse rate and short overall survival. Utilization of fluorescently tagged proteins has revealed the intracellular distribution pattern of HAS1, distinct from other isoenzymes. In all cell types studied so far, a high proportion of HAS1 is accumulated intracellularly, with a faint signal detected on the plasma membrane and its protrusions. Furthermore, the pericellular hyaluronan coat produced by HAS1 is usually thin without induction by inflammatory agents or glycemic stress and depends on CD44–HA interactions. These specific interactions regulate the organization of hyaluronan into a leukocyte recruiting matrix during inflammatory responses. Despite the apparently minor enzymatic activity of HAS1 under normal conditions, it may be an important factor under conditions associated with glycemic stress like metabolic syndrome, inflammation, and cancer.

Biological functions of hyaluronan and cytokine-inducible deubiquitinating enzymes

The modification of proteins through post-translation and degradation by the ubiquitin-proteasome system plays a pivotal role in a broad array of biological processes. Reversal of this process by deubiquitination is a central step in the maintenance and regulation of cellular homeostasis. It now appears that the regulation of ubiquitin pathways by deubiquitinating enzymes (DUBs) could be used as targets for anticancer therapy. Recent success in inducing apoptosis in cancerous cells by USP17, a cytokine-inducible DUB encoding two hyaluronan binding motifs (HABMs) showing direct interaction with hyaluronan (HA), could prove a promising step in the development of DUBs containing HABMs as agents in anticancer therapeutics. In this review, we summarize the importance of hyaluronan (HA) in cancer, the role played by DUBs in apoptosis, and a possible relationship between DUBs and HA in cancerous cells, suggesting new strategies for applying DUB enzymes as potential anticancer therapeutics.

Transcription of the Streptococcus pyogenes hyaluronic acid capsule biosynthesis operon is regulated by previously unknown upstream elements

The important human pathogen Streptococcus pyogenes (group A Streptococcus [GAS]) produces a hyaluronic acid (HA) capsule that plays critical roles in immune evasion. Previous studies showed that the hasABC operon encoding the capsule biosynthesis enzymes is under the control of a single promoter, P1, which is negatively regulated by the two-component regulatory system CovR/S. In this work, we characterize the sequence upstream of P1 and identify a novel regulatory region controlling transcription of the capsule biosynthesis operon in the M1 serotype strain MGAS2221. This region consists of a promoter, P2, which initiates transcription of a novel small RNA, HasS, an intrinsic transcriptional terminator that inefficiently terminates HasS, permitting read-through transcription of hasABC, and a putative promoter which lies upstream of P2. Electrophoretic mobility shift assays, quantitative reverse transcription-PCR, and transcriptional reporter data identified CovR as a negative regulator of P2. We found that the P1 and P2 promoters are completely repressed by CovR, and capsule expression is regulated by the putative promoter upstream of P2. Deletion of hasS or of the terminator eliminates CovR-binding sequences, relieving repression and increasing read-through, hasA transcription, and capsule production. Sequence analysis of 44 GAS genomes revealed a high level of polymorphism in the HasS sequence region. Most of the HasS variations were located in the terminator sequences, suggesting that this region is under strong selective pressure. We discovered that the terminator deletion mutant is highly resistant to neutrophil-mediated killing and is significantly more virulent in a mouse model of GAS invasive disease than the wild-type strain. Together, these results are consistent with the naturally occurring mutations in this region modulating GAS virulence.

Mutual exclusivity of hyaluronan and hyaluronidase in invasive group A Streptococcus

A recent analysis of group A Streptococcus (GAS) invasive infections in Australia has shown a predominance of M4 GAS, a serotype recently reported to lack the antiphagocytic hyaluronic acid (HA) capsule. Here, we use molecular genetics and bioinformatics techniques to characterize 17 clinical M4 isolates associated with invasive disease in children during this recent epidemiology. All M4 isolates lacked HA capsule, and whole genome sequence analysis of two isolates revealed the complete absence of the hasABC capsule biosynthesis operon. Conversely, M4 isolates possess a functional HA-degrading hyaluronate lyase (HylA) enzyme that is rendered nonfunctional in other GAS through a point mutation. Transformation with a plasmid expressing hasABC restored partial encapsulation in wild-type (WT) M4 GAS, and full encapsulation in an isogenic M4 mutant lacking HylA. However, partial encapsulation reduced binding to human complement regulatory protein C4BP, did not enhance survival in whole human blood, and did not increase virulence of WT M4 GAS in a mouse model of systemic infection. Bioinformatics analysis found no hasABC homologs in closely related species, suggesting that this operon was a recent acquisition. These data showcase a mutually exclusive interaction of HA capsule and active HylA among strains of this leading human pathogen.

Masquerading microbial pathogens: capsular polysaccharides mimic host-tissue molecules

The increasing prevalence of antibiotic-resistant bacteria portends an impending postantibiotic age, characterized by diminishing efficacy of common antibiotics and routine application of multifaceted, complementary therapeutic approaches to treat bacterial infections, particularly multidrug-resistant organisms. The first line of defense for most bacterial pathogens consists of a physical and immunologic barrier known as the capsule, commonly composed of a viscous layer of carbohydrates that are covalently bound to the cell wall in Gram-positive bacteria or often to lipids of the outer membrane in many Gram-negative bacteria. Bacterial capsular polysaccharides are a diverse class of high molecular weight polysaccharides contributing to virulence of many human pathogens in the gut, respiratory tree, urinary tract, and other host tissues, by hiding cell surface components that might otherwise elicit host immune response. This review highlights capsular polysaccharides that are structurally identical or similar to polysaccharides found in mammalian tissues, including polysialic acid and glycosaminoglycan capsules hyaluronan, heparosan, and chondroitin. Such nonimmunogenic coatings render pathogens insensitive to certain immune responses, effectively increasing residence time in host tissues and enabling pathologically relevant population densities to be reached. Biosynthetic pathways and capsular involvement in immune system evasion are described, providing a basis for potential therapies aimed at supplementing or replacing antibiotic treatment.

Disease manifestations and pathogenic mechanisms of Group A Streptococcus

Streptococcus pyogenes, also known as group A Streptococcus (GAS), causes mild human infections such as pharyngitis and impetigo and serious infections such as necrotizing fasciitis and streptococcal toxic shock syndrome. Furthermore, repeated GAS infections may trigger autoimmune diseases, including acute poststreptococcal glomerulonephritis, acute rheumatic fever, and rheumatic heart disease. Combined, these diseases account for over half a million deaths per year globally. Genomic and molecular analyses have now characterized a large number of GAS virulence determinants, many of which exhibit overlap and redundancy in the processes of adhesion and colonization, innate immune resistance, and the capacity to facilitate tissue barrier degradation and spread within the human host. This improved understanding of the contribution of individual virulence determinants to the disease process has led to the formulation of models of GAS disease progression, which may lead to better treatment and intervention strategies. While GAS remains sensitive to all penicillins and cephalosporins, rising resistance to other antibiotics used in disease treatment is an increasing worldwide concern. Several GAS vaccine formulations that elicit protective immunity in animal models have shown promise in nonhuman primate and early-stage human trials. The development of a safe and efficacious commercial human vaccine for the prophylaxis of GAS disease remains a high priority.

Molecular cloning of a novel glucuronokinase/putative pyrophosphorylase from zebrafish acting in an UDP-glucuronic acid salvage pathway

In animals, the main precursor for glycosaminoglycan and furthermore proteoglycan biosynthesis, like hyaluronic acid, is UDP-glucuronic acid, which is synthesized via the nucleotide sugar oxidation pathway. Mutations in this pathway cause severe developmental defects (deficiency in the initiation of heart valve formation). In plants, UDP-glucuronic acid is synthesized via two independent pathways. Beside the nucleotide sugar oxidation pathway, a second minor route to UDP-glucuronic acid exist termed the myo-inositol oxygenation pathway. Within this myo-inositol is ring cleaved into glucuronic acid, which is subsequently converted to UDP-glucuronic acid by glucuronokinase and UDP-sugar pyrophosphorylase. Here we report on a similar, but bifunctional enzyme from zebrafish (Danio rerio) which has glucuronokinase/putative pyrophosphorylase activity. The enzyme can convert glucuronic acid into UDP-glucuronic acid, required for completion of the alternative pathway to UDP-glucuronic acid via myo-inositol and thus establishes a so far unknown second route to UDP-glucuronic acid in animals. Glucuronokinase from zebrafish is a member of the GHMP-kinase superfamily having unique substrate specificity for glucuronic acid with a K_m of 31±8 µM and accepting ATP as the only phosphate donor (K_m: 59±9 µM). UDP-glucuronic acid pyrophosphorylase from zebrafish has homology to bacterial nucleotidyltransferases and requires UTP as nucleosid diphosphate donor. Genes for bifunctional glucuronokinase and putative UDP-glucuronic acid pyrophosphorylase are conserved among some groups of lower animals, including fishes, frogs, tunicates, and polychaeta, but are absent from mammals. The existence of a second pathway for UDP-glucuronic acid biosynthesis in zebrafish likely explains some previous contradictory finding in jekyll/ugdh zebrafish developmental mutants, which showed residual glycosaminoglycans and proteoglycans in knockout mutants of UDP-glucose dehydrogenase.

Effect of a cholesterol-rich lipid environment on the enzymatic activity of reconstituted hyaluronan synthase

Hyaluronan synthase (HAS) is a unique membrane-associated glycosyltransferase and its activity is lipid dependent. The dependence however is not well understood, especially in vertebrate systems. Here we investigated the functional association of hyaluronan synthesis in a cholesterol-rich membrane-environment. The culture of human dermal fibroblasts in lipoprotein-depleted medium attenuated the synthesis of hyaluronan. The sequestration of cellular cholesterol by methyl-ß-cyclodextrin also decreased the hyaluronan production of fibroblasts, as well as the HAS activity. To directly evaluate the effects of cholesterol on HAS activity, a recombinant human HAS2 protein with a histidine-tag was expressed as a membrane protein by using a baculovirus system, then successfully solubilized, and isolated by affinity chromatography. When the recombinant HAS2 proteins were reconstituted into liposomes composed of both saturated phosphatidylcholine and cholesterol, this provided a higher enzyme activity as compared with the liposomes formed by phosphatidylcholine alone. Cholesterol regulates HAS2 activity in a biphasic manner, depending on the molar ratio of phosphatidylcholine to cholesterol. Furthermore, the activation profiles of different lipid compositions were determined in the presence or absence of cholesterol. Cholesterol had the opposite effect on the HAS2 activity in liposomes composed of phosphatidylethanolamine or phosphatidylserine. Taken together, the present data suggests a clear functional association between HAS activity and cholesterol-dependent alterations in the physical and chemical properties of cell membranes.

Production of hyaluronic acid by mutant strains of group C Streptococcus

This study addresses the influence of upstream region sequence on the strength of has operon promoter in highly encapsulated S. equi subsp. zooepidemicus (SEZ). For this purpose, seven different strains were constructed. Each strain carries a point mutation in one of the following positions upstream of the has promoter: -43, -44, -49, and -50 bp. To facilitate measuring of the recombinant promoter relative strength, ß-glucuronidase gene was used as a reporter gene. Three mutations located in positions -49 and -50: AT, GT, and AG, positively impacted has promoter strength when compared to the wild type sequence GG. Conversely, two other mutations: TG and TT, exhibited a slight inhibitory effect. Further, three different strains carrying chromosomal mutations in the has promoter region were constructed. In two cases, the has operon is under the control of a stronger promoter and in the third strain the has operon is controlled by a weaker promoter. The laboratory fermenter scale cultivations confirmed the increase of hyaluronan yields for SEZPhasAG and SEZPhas2G, resulting 116 and 105 %, respectively. As expected, the yield of the hyaluronic acid of SEZPhas2B strain fell to 41 %.

Characterization of a trifunctional glucosyltransferase essential for Moraxella catarrhalis lipooligosaccharide assembly

The human respiratory tract pathogen Moraxella catarrhalis expresses lipooligosaccharides (LOS), glycolipid surface moieties that are associated with enhanced colonization and virulence. Recent studies have delineated the major steps required for the biosynthesis and assembly of the M. catarrhalis LOS molecule. We previously demonstrated that the glucosyltransferase enzyme Lgt3 is responsible for the addition of at least one glucose (Glc) molecule, at the β-(1-4) position, to the inner core of the LOS molecule. Our data further suggested a potential multifunctional role for Lgt3 in LOS biosynthesis. The studies reported here demonstrate that the Lgt3 enzyme possesses two glycosyltransferase domains (A1 and A2) similar to that of other bifunctional glycosyltransferase enzymes involved in surface polysaccharide biosynthesis in Escherichia coli, Pasteurella multocida and Streptococcus pyogenes. Each Lgt3 domain contains a conserved DXD motif, shown to be involved in the catalytic activity of other glycosyltransferases. To determine the function of each domain, A1 (N-terminal), A2 (C-terminal) and double A1A2 site-directed DAD to AAA mutants were constructed and the resulting LOS phenotypes of these modified strains were analyzed. Our studies indicate that the Lgt3 N-terminal A1 catalytic domain is responsible for the addition of the first β-(1-3) Glc to the first Glc on the inner core. The C-terminal catalytic domain A2 then adds the β-(1-4) Glc and the β-(1-6) Glc, confirming the bifunctional nature of this domain. The results from these experiments demonstrate that Lgt3 is a novel, multifunctional transferase responsible for the addition of three Glcs with differing linkages onto the inner core of M. catarrhalis LOS.

Production Methods for Hyaluronan

Hyaluronan is a polysaccharide with multiple functions in the human body being involved in creating flexible and protective layers in tissues and in many signalling pathways during embryonic development, wound healing, inflammation, and cancer. Hyaluronan is an important component of active pharmaceutical ingredients for treatment of, for example, arthritis and osteoarthritis, and its commercial value far exceeds that of other microbial extracellular polysaccharides. Traditionally hyaluronan is extracted from animal waste which is a well-established process now. However, biotechnological synthesis of biopolymers provides a wealth of new possibilities. Therefore, genetic/metabolic engineering has been applied in the area of tailor-made hyaluronan synthesis. Another approach is the controlled artificial (in vitro) synthesis of hyaluronan by enzymes. Advantage of using microbial and enzymatic synthesis for hyaluronan production is the simpler downstream processing and a reduced risk of viral contamination. In this paper an overview of the different methods used to produce hyaluronan is presented. Emphasis is on the advancements made in the field of the synthesis of bioengineered hyaluronan.

A conserved UDP-glucose dehydrogenase encoded outside the hasABC operon contributes to capsule biogenesis in group A Streptococcus

Group A Streptococcus (GAS) is a human-specific bacterial pathogen responsible for serious morbidity and mortality worldwide. The hyaluronic acid (HA) capsule of GAS is a major virulence factor, contributing to bloodstream survival through resistance to neutrophil and antimicrobial peptide killing and to in vivo pathogenicity. Capsule biosynthesis has been exclusively attributed to the ubiquitous hasABC hyaluronan synthase operon, which is highly conserved across GAS serotypes. Previous reports indicate that hasA, encoding hyaluronan synthase, and hasB, encoding UDP-glucose 6-dehydrogenase, are essential for capsule production in GAS. Here, we report that precise allelic exchange mutagenesis of hasB in GAS strain 5448, a representative of the globally disseminated M1T1 serotype, did not abolish HA capsule synthesis. In silico whole-genome screening identified a putative HasB paralog, designated HasB2, with 45% amino acid identity to HasB at a distant location in the GAS chromosome. In vitro enzymatic assays demonstrated that recombinant HasB2 is a functional UDP-glucose 6-dehydrogenase enzyme. Mutagenesis of hasB2 alone slightly decreased capsule abundance; however, a ΔhasB ΔhasB2 double mutant became completely acapsular. We conclude that HasB is not essential for M1T1 GAS capsule biogenesis due to the presence of a newly identified HasB paralog, HasB2, which most likely resulted from gene duplication. The identification of redundant UDP-glucose 6-dehydrogenases underscores the importance of HA capsule expression for M1T1 GAS pathogenicity and survival in the human host.

Glycosaminoglycan polysaccharide biosynthesis and production: today and tomorrow

Glycosaminoglycans [GAGs] are essential heteropolysaccharides in vertebrate tissues that are also, in certain cases, employed as virulence factors by microbes. Hyaluronan [HA], heparin, and chondroitin sulfate [CS] are GAGs currently used in various medical applications and together are multi-billion dollar products thus targets for production by animal-free manufacture. By using bacteria as the source of GAGs, the pathogen's sword may be converted into a plowshare to help avoid potential liabilities springing from the use of animal-derived GAGs including adventitious agents (e.g., prions, pathogens), antigenicity, degradation of the environment, and depletion of endangered species. HA from microbes, which have a chemical structure identical to human HA, has already been commercialized and sold at the ton-scale. Substantial progress towards microbial heparin and CS has been made, but these vertebrate polymers are more complicated structurally than the unsulfated bacterial polysaccharide precursors thus require additional processing steps. This review provides an overview of GAG structure, medical applications, microbial biosynthesis, and the state of bacterial GAG production systems. Representatives of all glycosyltransferase enzymes that polymerize the sugar chains of the three main GAGs have been identified and serve as the core technology to harness, but the proteins involved in sugar precursor formation and chain export steps of biosynthesis are also essential to the GAG production process. In addition, this review discusses future directions and potential important issues. Overall, this area is poised to make great headway to produce safer (both increased purity and more secure supply chains) non-animal GAG-based therapeutics.

Hyaluronan synthase mediates dye translocation across liposomal membranes

Background

Hyaluronan (HA) is made at the plasma membrane and secreted into the extracellular medium or matrix by phospolipid-dependent hyaluronan synthase (HAS), which is active as a monomer. Since the mechanism by which HA is translocated across membranes is still unresolved, we assessed the presence of an intraprotein pore within HAS by adding purified Streptococcus equisimilis HAS (SeHAS) to liposomes preloaded with the fluorophore Cascade Blue (CB).

Results

CB translocation (efflux) was not observed with mock-purified material from empty vector control E. coli membranes, but was induced by SeHAS, purified from membranes, in a time- and dose-dependent manner. CB efflux was eliminated or greatly reduced when purified SeHAS was first treated under conditions that inhibit enzyme activity: heating, oxidization or cysteine modification with N-ethylmaleimide. Reduced CB efflux also occurred with SeHAS K48E or K48F mutants, in which alteration of K48 within membrane domain 2 causes decreased activity and HA product size. The above results used liposomes containing bovine cardiolipin (BCL). An earlier study testing many synthetic lipids found that the best activating lipid for SeHAS is tetraoleoyl cardiolipin (TO-CL) and that, in contrast, tetramyristoyl cardiolipin (TM-CL) is an inactivating lipid (Weigel et al, J. Biol. Chem. 281, 36542, 2006). Consistent with the effects of these CL species on SeHAS activity, CB efflux was more than 2-fold greater in liposomes made with TO-CL compared to TM-CL.

Conclusions

The results indicate the presence of an intraprotein pore in HAS and support a model in which HA is translocated to the exterior by HAS itself.

Structure of the has operon promoter and the effect of mutations on the has promoter strength in Streptococcus equi subsp. zooepidemicus

The purpose of this study is to determine the effect of the corresponding nucleotides from Streptococcus pyogenes on the has promoter strength in highly encapsulated strain S. equi subsp. zooepidemicus (SEZ) and detect an empowering mutations in SEZ. Eight different strains of SEZ carrying nucleotide mutations in the -73 to -38 region upstream of the has promoter were constructed. The significant activity decrease to 36-1% was observed after the introduction of mutations in the promoter region from -44 to -38 site. The exception was observed in mutation in -49 site when no significant decrease was observed. When nucleotides TTT were used in positions -73 the promoter became weaker, whereas no significant effect was observed after using nucleotides CCC (96%). Unfortunately, introduction of these mutations into chromosome SEZ has no empowering effect. Six strains, which carried nucleotide sequences of different lengths upstream from the transcription start of hasA promoter, were constructed to determine the minimum upstream region required for the maximum transcription efficiency of the has operon. No change of the activity of the has promoter constructs containing as few as 101 nucleotides upstream from the transcription start point was observed.

Production of glucuronic acid-based polysaccharides by microbial fermentation for biomedical applications

This review provides an overview of the properties, different biosynthetic machineries, and biotechnological production processes of four microbially derived glucuronic acid-based polysaccharides that are of interest for diverse biomedical purposes. In particular, the utilization of hyaluronic acid and heparin sulfate in high-value medical applications is already well established, whereas chondroitin sulfate and alginate show high potential within this ever-growing field. Furthermore, new strategies exploiting genetically engineered microorganisms generated through improving naturally existing pathways or de novo designed ones are described. These new developments result in increased fermentation titers, and thereby, pave the way towards feasible, or at least improved, process economy. Moreover, these strategies also allow for the future possibility of producing tailor-made biopolymers with specified characteristics, even novel molecules.