Cells expressing the DG42 gene from early Xenopus embryos synthesize hyaluronan

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.

Inhibition of hyaluronan secretion by novel coumarin compounds and chitin synthesis inhibitors

Elevated plasma levels of hyaluronic acid (HA) is a disease marker in liver pathology and other inflammatory disorders. Inhibition of HA synthesis with coumarin 4-methylumbelliferone (4MU) has a beneficial effect in animal models of fibrosis, inflammation, cancer and metabolic syndrome. 4MU is an active compound of approved choleretic drug hymecromone with low bioavailability and a broad spectrum of action. New, more specific and efficient inhibitors of hyaluronan synthases (HAS) are required. We have tested several newly synthesized coumarin compounds and commercial chitin synthesis inhibitors to inhibit HA production in cell culture assay. Coumarin derivative compound VII (10'-methyl-6'-phenyl-3'H-spiro[piperidine-4,2'-pyrano[3,2-g]chromene]-4',8'-dione) demonstrated inhibition of HA secretion by NIH3T3 cells with the half-maximal inhibitory concentration (IC50) = 1.69 ± 0.75 μΜ superior to 4MU (IC50 = 8.68 ± 1.6 μΜ). Inhibitors of chitin synthesis, etoxazole, buprofezin, triflumuron, reduced HA deposition with IC50 of 4.21 ± 3.82 μΜ, 1.24 ± 0.87 μΜ and 1.48 ± 1.44 μΜ, respectively. Etoxazole reduced HA production and prevented collagen fibre formation in the CCl4 liver fibrosis model in mice similar to 4MU. Bioinformatics analysis revealed homology between chitin synthases and HAS enzymes, particularly in the pore-forming domain, containing the proposed site for etoxazole binding.

Current advances in the biosynthesis of hyaluronic acid with variable molecular weights

Hyaluronic acid (HA) is a naturally formed acidic mucopolysaccharide, with excellent moisturising properties and used widely in the medicine, cosmetics, and food industries. The industrial production of specific molecular weight HA has become imperative. Different biological activities and physiological functions of HA mainly depend on the degree of polymerisation. This article reviews the research status and development prospects of the green biosynthesis and molecular weight regulation of HA. There is an application-based prerequisite of specific molecular weight of HA that could be regulated either during the fermentation process or via a controlled HA degradation process. This work provides an important theoretical basis for the downstream efficient production of diversified HA, which will further accelerate the research applications of HA and provide a good scientific basis and method reference for the study of the molecular weight regulation of similar biopolymers.

Expression of Chitotriosidase in Macrophages Modulates Atherosclerotic Plaque Formation in Hyperlipidemic Mice

Objective

To determine whether overexpression of the chitin degrading enzyme, chitotriosidase (CHIT1), modulates macrophage function and ameliorates atherosclerosis.

Approach and Results

Using a mouse model that conditionally overexpresses CHIT1 in macrophages (CHIT1-Tg) crossbred with the Ldlr ^-/- mouse provided us with a means to investigate the effects of CHIT1 overexpression in the context of atherosclerosis. In vitro, CHIT1 overexpression by murine macrophages enhanced protein expression of IL-4, IL-8, and G-CSF by BMDM upon stimulation with a combination of lipopolysaccharide (LPS) and interferon-γ (IFN-γ). Phosphorylation of ERK1/2 and Akt was also down regulated when exposed to the same inflammatory stimuli. Hyperlipidemic, Ldlr ^-/--CHIT1-Tg (CHIT1-OE) mice were fed a high-fat diet for 12 weeks in order to study CHIT1 overexpression in atherosclerosis. Although plaque size and lesion area were not affected by CHIT1 overexpression in vivo, the content of hyaluronic acid (HA) and collagen within atherosclerotic plaques of CHIT1-OE mice was significantly greater. Localization of both ECM components was markedly different between groups.

Conclusions

These data demonstrate that CHIT1 alters cytokine expression and signaling pathways of classically activated macrophages. In vivo, CHIT1 modifies ECM distribution and content in atherosclerotic plaques, both of which are important therapeutic targets.

Possible Role of Chitin-Like Proteins in the Etiology of Alzheimer's Disease

Chitin is a β-linked straight chain carbohydrate matrix monopolymer prominent in invertebrates, from fungi to arthropods. Surprisingly, chitin is now documented in vertebrates, including humans, a component of vertebrate physiology that has been neglected until now. Chitin levels are elevated in Alzheimer's disease (AD) patients, not only in the central nervous system but also in the cerebrospinal fluid and plasma. Elevated levels of chitin lectin have been reported in patients with AD. Chitinase activity varies widely in the human population. Chitin levels can increase in individuals with intrinsically low chitinase activity. Elevated amounts of chitin can reflect accumulation of the small chitin fragments that remain wherever rapid hyaluronan synthesis occurs. Another source of chitin may be from remote fungal infections. Chitin can be toxic for neurons, and its accumulation may lead to the development of AD. We present new suggestions for animal models and treatment modalities that could prove useful in future research endeavors. An unexpected connection with Gaucher's disease patients and their heterozygote relatives is also identified. These chitin-related mechanisms are novel approaches to AD whose etiology until now has defied explication.

Chitin, chitinases, and chitin lectins: Emerging roles in human pathophysiology

Chitin is a simple β-linked repeating sugar polymer prominent in the building block structures of a wide variety of organisms, from the yeast cell wall to the exoskeleton and shells of arthropods and other forms of invertebrate life. It had previously been assumed that vertebrates did not contain chitins. However, chitin and chitinases are now documented to occur in vertebrate tissues. Chitin, chitinases and particularly chitinase-like proteins are involved in important human pathologies, though the mechanisms by which these function is unknown. These chitinase-like proteins bind to chitin and function as chitin lectins in that they bind to chitin but have lost the ability to degrade it. Emphasis is placed on one of the chitinase-like proteins, CHI3L1, that has acquired wide clinical importance. The purpose of this review is to place an array of bewildering observations associated with various human disorders into a framework, particularly the pathologies of the human gastro-intestinal tract. A reasonably cohesive story may eventually emerge.

Inhibition of Mammalian Glycoprotein YKL-40: IDENTIFICATION OF THE PHYSIOLOGICAL LIGAND

YKL-40 is a mammalian glycoprotein associated with progression, severity, and prognosis of chronic inflammatory diseases and a multitude of cancers. Despite this well documented association, identification of the lectin's physiological ligand and, accordingly, biological function has proven experimentally difficult. YKL-40 has been shown to bind chito-oligosaccharides; however, the production of chitin by the human body has not yet been documented. Possible alternative ligands include proteoglycans, polysaccharides, and fibers like collagen, all of which makeup the extracellular matrix. It is likely that YKL-40 is interacting with these alternative polysaccharides or proteins within the body, extending its function to cell biological roles such as mediating cellular receptors and cell adhesion and migration. Here, we consider the feasibility of polysaccharides, including cello-oligosaccharides, hyaluronan, heparan sulfate, heparin, and chondroitin sulfate, and collagen-like peptides as physiological ligands for YKL-40. We use molecular dynamics simulations to resolve the molecular level recognition mechanisms and calculate the free energy of binding the hypothesized ligands to YKL-40, addressing thermodynamic preference relative to chito-oligosaccharides. Our results suggest that chitohexaose and hyaluronan preferentially bind to YKL-40 over collagen, and hyaluronan is likely the preferred physiological ligand, because the negatively charged hyaluronan shows enhanced affinity for YKL-40 over neutral chitohexaose. Collagen binds in two locations at the YKL-40 surface, potentially related to a role in fibrillar formation. Finally, heparin non-specifically binds at the YKL-40 surface, as predicted from structural studies. Overall, YKL-40 likely binds many natural ligands in vivo, but its concurrence with physical maladies may be related to associated increases in hyaluronan.

Interleukin-1β induces hyaluronan and CD44-dependent cell protrusions that facilitate fibroblast-monocyte binding

Persistent inflammation is a well-known determinant of progressive tissue fibrosis; however, the mechanisms underlying this process remain unclear. There is growing evidence indicating a role of the cytokine IL-1β in profibrotic responses. We previously demonstrated that fibroblasts stimulated with IL-1β increased their generation of the polysaccharide hyaluronan (HA) and increased their expression of the HA synthase enzyme (HAS-2). The aim of this study was to determine the significance of IL-1β-induced changes in HA and HAS-2 generation. In this study, we found that stimulation of fibroblasts with IL-1β results in the relocalization of HA associated with the cell to the outer cell membrane, where it forms HAS2- and CD44-dependent cell membrane protrusions. CD44 is concentrated within the membrane protrusions, where it co-localizes with the intracellular adhesion molecule 1. Furthermore, we have identified that these cell protrusions enhance IL-1β-dependent fibroblast-monocyte binding through MAPK/ERK signaling. Although previous data have indicated the importance of the HA-binding protein TSG-6 in maintaining the transforming growth factor β1-dependent HA coat, TSG-6 was not essential for the formation of the IL-1β-dependent HA protrusions, thus identifying it as a key difference between IL-1β- and transforming growth factor β1-dependent HA matrices. In summary, these data suggest that IL-1β-dependent HA generation plays a role in fibroblast immune activation, leading to sequestration of monocytes within inflamed tissue and providing a possible mechanism for perpetual inflammation.

Putative chitin synthases from Branchiostoma floridae show extracellular matrix-related domains and mosaic structures

The transition from unicellular to multicellular life forms requires the development of a specialized structural component, the extracellular matrix (ECM). In Metazoans, there are two main supportive systems, which are based on chitin and collagen/hyaluronan, respectively. Chitin is the major constituent of fungal cell walls and arthropod exoskeleton. However, presence of chitin/chitooligosaccharides has been reported in lower chordates and during specific stages of vertebrate development. In this study, the occurrence of chitin synthases (CHSs) was investigated with a bioinformatics approach in the cephalochordate Branchiostoma floridae, in which the presence of chitin was initially reported in the skeletal rods of the pharyngeal gill basket. Twelve genes coding for proteins containing conserved amino acid residues of processive glycosyltransferases from GT2 family were found and 10 of them display mosaic structures with novel domains never reported previously in a chitin synthase. In particular, the presence of a discoidin (DS) and a sterile alpha motif (SAM) domain was found in nine identified proteins. Sequence analyses and homology modelling suggest that these domains might interact with the extracellular matrix and mediate protein–protein interaction. The multi-domain putative chitin synthases from B. floridae constitute an emblematic example of the explosion of domain innovation and shuffling which predate Metazoans.

YKL-40-A Protein in the Field of Translational Medicine: A Role as a Biomarker in Cancer Patients?

YKL-40 is a 40 kDa glycoprotein produced by cancer cells, inflammatory cells and stem cells. It probably has a role in cell proliferation and differentiation, inflammation, protection against apoptosis, stimulation of angiogenesis, and regulation of extracellular tissue remodelling. Plasma levels of YKL-40 are often elevated in patients with localized or advanced cancer compared to age-matched healthy subjects. Several studies have demonstrated that high plasma YKL-40 is an independent prognostic biomarker of short survival in patients with different types of cancer. However, there is not yet sufficient data to support determination of plasma YKL-40 outside research projects as a biomarker for screening of gastrointestinal cancer and determination of treatment response and poor prognosis before or during treatment and follow-up. Plasma YKL-40 is also elevated in patients with other diseases than cancer, e.g., severe infections, cardiovascular disease, diabetes, chronic obstructive lung disease, asthma, liver fibrosis and rheumatoid arthritis. Co-morbidity should therefore always be considered in patients with cancer, since other sources than cancer cells can increase plasma YKL-40 levels. Future focused translational research projects combining basic and clinical research are needed in a joint effort to answer questions of the complex function and regulation of YKL-40 and the question if plasma YKL-40 is a clinical useful biomarker in patients with cancer.

Plasma YKL-40: a potential new cancer biomarker?

YKL-40, a 40-kDa secreted glycoprotein, with its gene located on chromosome 1q32.1, is produced by cancer cells and inflammatory cells and has a role in inflammation, cell proliferation, differentiation, protection against apoptosis, stimulation of angiogenesis and regulation of extracellular tissue remodeling. Plasma levels of YKL-40 are elevated in a subgroup of patients with primary or advanced cancer compared with age-matched healthy subjects, but also in patients with many different diseases characterized by inflammation. Elevated plasma YKL-40 levels are an independent prognostic biomarker of short survival. There is still insufficient evidence to support its value outside of clinical trials as a screening tool, prognosticator of survival, predictor of treatment response and as a monitoring tool in the routine management of individual patients with cancer or diseases characterized by inflammation. Large prospective, longitudinal clinical cancer studies are needed to determine if plasma YKL-40 is a new cancer biomarker, or is mainly a biomarker of inflammation.

The role of novel chitin-like polysaccharides in Alzheimer disease

While controversy over the role of carbohydrates in amyloidosis has existed since the initial recognition of amyloid, current understanding of the role of polysaccharides in the pathogenesis of amyloid deposition of Alzheimer disease and other amyloidoses is limited to studies of glyco-conjugates such as heparin sulfate proteoglycan. We hypothesized that polysaccharides may play a broader role in light of 1) the impaired glucose utilization in Alzheimer disease; 2) the demonstration of amylose in the Alzheimer disease brain; 3) the role of amyloid in Alzheimer disease pathogenesis. Specifically, as with glucose polymers (amyloid), we wanted to explore whether glucosamine polymers such as chitin were being synthesized and deposited as a result of impaired glucose utilization and aberrant hexosamine pathway activation. To this end, using calcofluor histochemistry, we recently demonstrated that amyloid plaques and blood vessels affected by amyloid angiopathy in subjects with sporadic and familial Alzheimer disease elicit chitin-type characteristics. Since chitin is a highly insoluble molecule and a substrate for glycan-protein interactions, chitin-like polysaccharides within the Alzheimer disease brain could provide a scaffolding for amyloid-beta deposition. As such, glucosamine may facilitate the process of amyloidosis, and /or provide neuroprotection in the Alzheimer disease brain.

Hyaluronan synthases: a decade-plus of novel glycosyltransferases

Hyaluronan synthases (HASs) are glycosyltransferases that catalyze polymerization of hyaluronan found in vertebrates and certain microbes. HASs transfer two distinct monosaccharides in different linkages and, in certain cases, participate in polymer transfer out of the cell. In contrast, the vast majority of glycosyltransferases form only one sugar linkage. Although our understanding of HAS biochemistry is still incomplete, very good progress has been made since the first genetic identification of a HAS in 1993. New enzymes have been discovered, and some molecular details have emerged. Important findings are the lipid dependence of Class I HASs, the function of HASs as protein monomers, and the elucidation of mechanisms of synthesis by Class II HAS. We propose three classes of HASs based on differences in protein sequences, predicted membrane topologies, potential architectures, mechanisms, and direction of polymerization.

Putative role of hyaluronan and its related genes, HAS2 and RHAMM, in human early preimplantation embryogenesis and embryonic stem cell characterization

Human embryonic stem cells (hESC) promise tremendous potential as a developmental and cell therapeutic tool. The combined effort of stimulatory and inhibitory signals regulating gene expression, which drives the tissue differentiation and morphogenetic processes during early embryogenesis, is still very poorly understood. With the scarcity of availability of human embryos for research, hESC can be used as an alternative source to study the early human embryogenesis. Hyaluronan (HA), a simple hydrating sugar, is present abundantly in the female reproductive tract during fertilization, embryo growth, and implantation and plays an important role in early development of the mammalian embryo. HA and its binding protein RHAMM regulate various cellular and hydrodynamic processes from cell migration, proliferation, and signaling to regulation of gene expression, cell differentiation, morphogenesis, and metastasis via both extracellular and intracellular pathways. In this study, we show for the first time that HA synthase gene HAS2 and its binding receptor RHAMM are differentially expressed during all stages of preimplantation human embryos and hESC. RHAMM expression is significantly downregulated during differentiation of hESC, in contrast to HAS2, which is significantly upregulated. Most importantly, RHAMM knockdown results in downregulation of several pluripotency markers in hESC, induction of early extraembryonic lineages, loss of cell viability, and changes in hESC cycle. These data therefore highlight an important role for RHAMM in maintenance of hESC pluripotency, viability, and cell cycle control. Interestingly, HAS2 knockdown results in suppression of hESC differentiation without affecting hESC pluripotency. This suggests an intrinsic role for HAS2 in hESC differentiation process. In accordance with this, addition of exogenous HA to the differentiation medium enhances hESC differentiation to mesodermal and cardiac lineages. Disclosure of potential conflicts of interest is found at the end of this article.

Involvement of hyaluronan in regulation of fibroblast phenotype

This study aimed to understand the role of the matrix polysaccharide, hyaluronan (HA), in influencing the scarring process by assessing its impact on regulating fibroblast behavior. Donor-matched human oral and dermal fibroblasts were used as models of nonscarring and scarring fibroblast phenotypes, respectively. Phenotypic differences in these two fibroblast populations were assessed and related to differences in HA synthesis and assembly. The two fibroblast populations showed intrinsic differences in their response to the profibrotic cytokine, transforming growth factor-beta1 (TGFbeta1), in that oral fibroblasts were resistant to TGFbeta1-driven myofibroblastic differentiation. In dermal fibroblasts, differentiation was associated with an induction of HA synthase (HAS1 and HAS2) transcription and assembly of pericellular HA coats. In comparison, resistance to differentiation in oral fibroblasts was associated with failure of induction of HAS1 and HAS2 transcription and failure of pericellular coat assembly. Furthermore, inhibition of HA synthesis in dermal fibroblasts significantly attenuated TGFbeta1-mediated differentiation. Interleukin-1beta stimulation resulted in induction of HAS1 and HAS2 transcription but did not induce phenotypic differentiation or induce HA coat assembly. In addition, neither overexpression nor down-regulation of HAS1 (the isoform uniquely deficient in nonscarring oral fibroblasts) influenced phenotypic differentiation. In conclusion, inhibiting HA synthesis modulates TGFbeta1-dependent responses in these cells preventing fibroblast to myofibroblast differentiation. Moreover, HA pericellular coat assembly, rather than HAS isoform expression, appears to be associated with phenotypic differentiation.

Matrix assisted laser desorption ionization-time of flight mass spectrometry analysis of hyaluronan oligosaccharides

A new method is presented for the identification of oligosaccharides obtained by enzymatic digestion of hyaluronan (HA) with bacterial hyaluronidase (E.C. 4.2.2.1, from Streptomyces hyalurolyticus) using matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOFMS). Mixtures containing HA oligosaccharides of tetrasaccharide (4-mer)-34-mer were analyzed using this method. The carboxyl groups of the glucuronate residues in the prepared HA oligomers, were modified as the acidic form (-COOH), sodium salts (-COONa), organic ammonium salts, or methylesters before MALDI-TOFMS measurement. Among these samples, the methylester form of glucuronate residues in HA oligosaccharides, prepared by methylation using trimethylsilyl diazomethane, afforded high sensitivity for spectra. This simple modification method for carboxyl group methylation of acidic polysaccharides [Hirano et al., Carbohydr. Res., 340, (2005) 2297-2304] provides samples suitable for MALDI-TOF mass spectrometric analysis throughout a significantly enhanced range of masses.

The biology of the Gaucher cell: the cradle of human chitinases

Gaucher disease (GD) is the most common lysosomal storage disorder and is caused by inherited deficiencies of glucocerebrosidase, the enzyme responsible for the lysosomal breakdown of the lipid glucosylceramide. GD is characterized by the accumulation of pathological, lipid laden macrophages, so-called Gaucher cells. Following the development of enzyme replacement therapy for GD, the search for suitable surrogate disease markers resulted in the identification of a thousand-fold increased chitinase activity in plasma from symptomatic Gaucher patients and that decreases upon successful therapeutic intervention. Biochemical investigations identified a single enzyme, named chitotriosidase, to be responsible for this activity. Chitotriosidase was found to be an excellent marker for lipid laden macrophages in Gaucher patients and is now widely used to assist clinical management of patients. In the wake of the identification of chitotriosidase, the presence of other members of the chitinase family in mammals was discovered. Amongst these is AMCase, an enzyme recently implicated in the pathogenesis of asthma. Chitinases are omnipresent throughout nature and are also produced by vertebrates in which they play important roles in defence against chitin-containing pathogens and in food processing.

Is YKL-40 a new therapeutic target in cancer?

YKL-40 is produced by cancer cells and tumour-associated macrophages. YKL-40 may play a role in cancer cell proliferation, differentiation, survival, invasiveness, metastasis, in angiogenesis and the inflammation and remodelling of the extracellular matrix surrounding the tumour. Serum YKL-40 is a biomarker of prognosis, confirmed in 13 different types of cancer including > 2500 patients. Highest serum YKL-40 is found in patients with metastatic cancer with the shortest recurrence-free interval and shortest overall survival. Serum YKL-40 provides independent information compared with clinical characteristics and biomarkers, such as HER2, carcinoembryonic antigen, CA-125, prostate-specific antigen and lactate dehydrogenase. The authors hypothesise that inhibition of YKL-40 by monoclonal antibodies either directly or towards its receptor may be as efficient a cancer therapeutic as the monoclonal antibodies against HER2, HER1, vascular endothelial growth factor and CD20. Drugs inhibiting YKL-40 should be explored as new cancer therapeutics.

The functional molecular mass of the Pasteurella hyaluronan synthase is a monomer

Hyaluronan (HA), a linear polysaccharide composed of beta1,3-GlcNAc-beta1,4-GlcUA repeats, is found in the extracellular matrix of vertebrate tissues as well as the capsule of several pathogenic bacteria. All known HA synthases (HASs) are dual-action glycosyltransferases that catalyze the addition of two different sugars from UDP-linked precursors to the growing HA chain. The bacterial hyaluronan synthase, PmHAS from Gram-negative Pasteurella multocida, is a 972-residue membrane-associated protein. Previously, the Gram-positive Streptococcus pyogenes enzyme, SpHAS (419 residues), and the vertebrate enzyme, XlHAS1 (588 residues), were found to function as monomers of protein, but the PmHAS is not similar at the protein sequence level and has quite different enzymological properties. We have utilized radiation inactivation to measure the target size of recombinant full-length and truncated PmHAS. The target size of HAS activity was confirmed using internal enzyme standards of known molecular weight. We found that the Pasteurella HA synthase protein functions catalytically as a monomer. Functional truncated soluble PmHAS also behaves as a polypeptide monomer as assessed by gel filtration chromatography and light scattering.

Potential role of chitotriosidase gene in nonalcoholic fatty liver disease evolution

BACKGROUND

Nonalcoholic steatohepatitis (NASH) is a liver disease characterized by steatosis and periportal and lobular inflammation. The molecular mechanisms involved in the anomalous behavior of liver cells have only partially been disclosed. Human Chitotriosidase (Chit) is a member of the chitinase family that it is mainly synthesized by activated macrophages. We investigated chitotriosidase gene expression in Kupffer cells to determine the potential implication of this enzyme in the inflammation and in the progression from uncomplicated steatosis to steatohepatitis with progressive fibrosis.

METHODS

Seventy-five liver biopsies from 40 subjects with NASH, 20 with simple steatosis, and 15 controls were used to detect CHIT expression, tumor necrosis factor-alpha (TNF-alpha), alpha-smooth muscle actin (alpha-SMA), and lipid peroxidation.

RESULTS

CHIT was expressed exclusively by Kupffer cells. The levels of CHIT expression were significantly higher in NASH patients than in simple steatosis patients and in the control group. In addition, we found that CHIT over-expression influenced hepatic stellate cells activation, as demonstrated by the significant correlation between CHIT and alpha-SMA expression in NASH patients. A significant correlation was observed also between CHIT, TNF-alpha and lipid peroxidation in both NASH and simple steatosis.

CONCLUSION

These results suggest that CHIT over-produced by Kupffer cells may contribute to the progression of hepatic fibrosis.

Chitotriosidase gene expression in Kupffer cells from patients with non-alcoholic fatty liver disease

BACKGROUND AND AIMS

Non-alcoholic steatohepatitis (NASH) is a clinicopathological condition characterised by a necroinflammatory disorder with fatty infiltration of the hepatocytes. The molecular mechanisms involved in the anomalous behaviour of liver cells have only partially been determined. Human chitotriosidase (Chit) is a chitinolytic enzyme mainly produced by activated macrophages. The aim of this study was to investigate the expression of the chitinase-like gene in Kupffer cells, to determine how chitotriosidase may be implicated in the progression from uncomplicated steatosis to steatohepatitis with progressive fibrosis.

METHODS

75 subjects were studied: 40 with NASH, 20 with simple steatosis, and 15 normal controls. Kupffer cells obtained from liver biopsies were used to detect CHIT expression, superoxide anion (O2-), lipid peroxidation, and tumour necrosis factor alpha (TNFalpha) and ferritin levels.

RESULTS

CHIT expression differed markedly in livers from normal controls and in those from patients with simple steatosis or non-alcoholic steatohepatitis. A significant correlation between mRNA CHIT and O2-, lipid peroxidation, TNFalpha, and ferritin levels was observed in both NASH and simple steatosis.

CONCLUSIONS

Human Kupffer cells in NASH patients overproduce chitotriosidase. At the highest levels of production, this enzyme may play a role in increasing the risk for a poor outcome in steatohepatitis.

Serum YKL-40, a new prognostic biomarker in cancer patients?

YKL-40, a member of the "mammalian chitinase-like proteins," is expressed and secreted by several types of solid tumors. The exact function of YKL-40 in cancer diseases is unknown and is an important objective of future studies. YKL-40 exhibits growth factor activity for cells involved in tissue remodeling processes. YKL-40 may have a role in cancer cell proliferation, survival, and invasiveness, in the inflammatory process around the tumor, angiogenesis, and remodeling of the extracellular matrix. YKL-40 is neither organ- nor tumor-specific. However, the present retrospective clinical studies of patients with eight different types of primary or advanced solid tumors suggest that serum concentration of YKL-40 may be a new biomarker in cancer patients used as a "prognosticator." Elevated serum YKL-40 is found in a subgroup of patients with different types of solid tumors, including several types of adenocarcinomas, small cell lung carcinoma, glioblastoma, and melanoma. The highest serum YKL-40 is detected in patients with advanced cancer and with the poorest prognosis. In many cases, serum YKL-40 provides independent information of survival. Serum YKL-40 cannot be used as a single screening test for cancer. The use of serum YKL-40 has not received Food and Drug Administration approval for use as a biomarker for cancer or any other disease. Large multicenter retrospective and prospective studies of patients with different types of cancer are required to determine: (a) if serum YKL-40 is a useful prognostic cancer biomarker, (b) if serum YKL-40 can be of value in monitoring patients with cancer in order to provide information about metastases before these are detected by routine methods, and (c) if serum YKL-40 can be useful for screening of cancer together with a panel of other cancer biomarkers and imaging techniques.

The mammalian chitinase-like lectin, YKL-40, binds specifically to type I collagen and modulates the rate of type I collagen fibril formation

YKL-40 is expressed in arthritic cartilage and produced in large amounts by cultured chondrocytes, but its exact role is unclear, and the identities of its physiological ligands remain unknown. Purification of YKL-40 from resorbing bovine nasal cartilage and chondrocyte monolayers demonstrated the existence of three isoforms, a major and minor form from resorbing cartilage and a third species from chondrocytes. Affinity chromatography experiments with purified YKL-40 demonstrated specific binding of all three forms to collagen types I, II, and III, thus identifying collagens as potential YKL-40 ligands. Binding to immobilized type I collagen was inhibited by soluble native ligand, but not heat-denatured ligand, confirming a specific interaction. Binding of the chondrocyte-derived species to type I collagen was also demonstrated by surface plasmon resonance analysis, and the dissociation rate constant was calculated (3.42 x 10(-3) to 4.50 x 10(-3) s(-1)). The chondrocyte-derived species was found to prevent collagenolytic cleavage of type I collagen and to stimulate the rate of type I collagen fibril formation in a concentration-dependent manner. By contrast, the cartilage major form had an inhibitory effect on type I collagen fibrillogenesis. Digestion with N-glycosidase F, endoglycosidase H and lectin blotting did not reveal any difference in the carbohydrate component of these two YKL-40 species, indicating that this does not account for the opposing effects on fibril formation rate.

Characterization of the purified hyaluronan synthase from Streptococcus equisimilis

Hyaluronan synthase (HAS) utilizes UDP-GlcUA and UDP-GlcNAc in the presence of Mg(2+) to form the GAG hyaluronan (HA). The purified HAS from Streptococcus equisimilis (seHAS) shows high fidelity in that it only polymerizes the native substrates, UDP-GlcNAc and UDP-GlcUA. However, other uridinyl nucleotides and UDP-sugars inhibited enzyme activity, including UDP-GalNAc, UDP-Glc, UDP-Gal, UDP-GalUA, UMP, UDP, and UTP. Purified seHAS was approximately 40% more active in 25 mM, compared to 50 mM, PO(4) in the presence of either 50 mM NaCl or KCl, and displayed a slight preference for KCl over NaCl. The pH profile was surprisingly broad, with an effective range of pH 6.5-11.5 and the optimum between pH 9 and 10. SeHAS displayed two apparent pK(a) values at pH 6.6 and 11.8. As the pH was increased from approximately 6.5, both K(m) and V(max) increased until pH approximately 10.5, above which the kinetic constants gradually declined. Nonetheless, the overall catalytic constant (120/s) was essentially unchanged from pH 6.5 to 10.5. The enzyme is temperature labile, but more stable in the presence of substrate and cardiolipin. Purified seHAS requires exogenous cardiolipin for activity and is very sensitive to the fatty acyl composition of the phospholipid. The enzyme was inactive or highly activated by synthetic cardiolipins containing, respectively, C14:0 or C18:1(Delta9) fatty acids. The apparent E(act) for HA synthesis is 40 kJ (9.5 kcal/mol) disaccharide. Increasing the viscosity by increasing concentrations of PEG, ethylene glycol, glycerol, or sucrose inhibited seHAS activity. For PEGs, the extent of inhibition was proportional to their molecular mass. PEGs with average masses of 2.7, 11.7, and 20 kg/mol caused 50% inhibition of V(max) at 21, 6.5, and 3.5 mM, respectively. The apparent K(i) values for ethylene glycol, glycerol, and sucrose were, respectively, 4.5, 3.3, and 1.2 mM.

Myofibroblastic differentiation leads to hyaluronan accumulation through reduced hyaluronan turnover

During the initiation and progression of fibrosis there is extensive differentiation of cells to a myofibroblastic phenotype. Because the synthesis of hyaluronan (HA) was recently linked to oncogenic epithelial-mesenchymal transformation, the present study investigated whether increased HA synthesis was also associated with myofibroblastic differentiation. HA synthesis and size were measured by incorporation of [(3)H]glucosamine, ion exchange, and size exclusion chromatography. Hyaluronan synthase (HAS) or hyaluronidase (HYAL) mRNA levels were assessed by reverse transcription-PCR. HYAL was detected by immunoblotting and the degradation of [(3)H]HA. Between 2- and 3-fold more HA appeared in the conditioned medium and became associated with the cells upon myofibroblastic differentiation. Inhibition of HAS and examination of HAS mRNA expression demonstrated that this was not the result of increased synthesis of HA or the induction of HAS 2. After differentiation, however, myofibroblasts metabolized exogenously supplied [(3)H]HA at a slower rate than fibroblasts and expressed lower levels of both HYAL 1 and HYAL 2 mRNA. Immunoblotting revealed more HYAL 1 and 2 in the myofibroblast conditioned medium. After acidification, however, there was no difference in HA degradation. This suggests that much of the released HYAL is inactive and that the observed differences in HA degradation are caused by cell-associated rather than secreted activity. This was confirmed by immunohistochemical staining for HYAL 1 and HYAL 2. This finding indicates the potential importance of the HYAL enzymes in controlling fibrotic progression and contrasts HA synthesis as a mediator of oncogenic transformation with that of HA degradation controlling fibrogenic differentiation.

Molecular cloning, genomic organization and developmental expression of the Xenopus laevis hyaluronan synthase 3

The content of hyaluronan (HA), a polymer of the extracellular matrix involved in a variety of physiological and pathological processes, depends on the activity of synthetic (HAS) and degrading enzymes. Since HA is also involved in embryogenesis, we have used Xenopus as a model organism because information is available for HAS1 and HAS2, but not for HAS3. We report the sequence of xlHAS3 mRNA, its genomic organization and its expression in adult tissues as well as during embryonic development. Interestingly, evidence from in situ hybridization indicates that xlHAS3 expression is restricted to the developing inner ear and cement gland. In addition, we have correlated the expression pattern of the enzymes involved in HA metabolism with the HA content during development.

Crystal structure and carbohydrate-binding properties of the human cartilage glycoprotein-39

The human cartilage glycoprotein-39 (HCgp-39 or YKL40) is expressed by synovial cells and macrophages during inflammation. Its precise physiological role is unknown. However, it has been proposed that HCgp-39 acts as an autoantigen in rheumatoid arthritis, and high expression levels have been associated with cancer development. HCgp-39 shares high sequence homology with family 18 chitinases, and although it binds to chitin it lacks enzymatic activity. The crystal structure of HCgp-39 shows that the protein displays a (beta/alpha)8-barrel fold with an insertion of an alpha + beta domain. A 43-A long carbohydrate-binding cleft is present at the C-terminal side of the beta-strands in the (beta/alpha)8 barrel. Binding of chitin fragments of different lengths identified nine sugar-binding subsites in the groove. Protein-carbohydrate interactions are mainly mediated by stacking of side chains of aromatic amino acid residues. Surprisingly, the specificity of chitin binding to HCgp-39 depends on the length of the oligosaccharide. Although chitin disaccharides tend to occupy the distal subsites, longer chains bind preferably to the central subsites in the groove. Despite the absence of enzymatic activity, long chitin fragments are distorted upon binding, with the GlcNAc at subsite -1 in a boat conformation, similar to what has been observed in chitinases. The presence of chitin in the human body has never been documented so far. However, the binding features observed in the complex structures suggest that either chitin or a closely related oligosaccharide could act as the physiological ligand for HCgp-39.

'Piggy-back' transport of Xenopus hyaluronan synthase (XHAS1) via the secretory pathway to the plasma membrane

Hyaluronan is the sole glycosaminoglycan whose biosynthesis takes place directly at the plasma membrane. The mechanism by which hyaluronan synthase (HAS) becomes inserted there, as well as the question of how the enzyme discriminates between particular membrane species in polarized cells, are largely unknown. In vitro translation of HAS suggested that the nascent protein becomes stabilized in the presence of microsomal membranes, but would not insert spontaneously into membranes after being translated in the absence of those. We therefore monitored the membrane attachment of enzymatically active fusion proteins consisting of Xenopus HAS1 and green fluorescent protein shortly after de novo synthesis in Vero cells. Our data strongly suggest that HAS proteins are directly translated on the ER membrane without exhibiting an N-terminal signal sequence. From there the inactive protein is transferred to the plasma membrane via the secretory pathway. For unknown reasons, HAS inserted into membranes other than the plasma membrane remains inactive.

Hyaluronan is an abundant constituent of the extracellular matrix of Xenopus embryos

The spatiotemporal distribution of hyaluronan (HA), a major constituent of the vertebrate extracellular matrix, was analyzed during early embryonic development of Xenopus laevis. This polysaccharide is abundantly present in ventricular structures such as the blastocoel, the archenteron as well as later on in the hepatic cavity, the brain ventricles and the developing heart. At the blastula stage, HA was detected in the extracellular matrix of the ecto- and mesodermal primordia. Shortly before gastrulation, it becomes enriched at the basal site of the superficial cell layer of the ectoderm. During gastrulation, enhanced synthesis of HA takes place in the involuting marginal zone, shortly before invagination starts, hence, resulting in a torus-like deposition in the deep layer of the equatorial mesodermal primordium. After gastrulation, HA appears to accumulate within the extracellular matrix demarcating the primary germ layers. During tailbud stages, it is found highly enriched in many mesodermal derivatives, e.g., in mesenchyme, the heart, precordal cartilage and the lung primordia. Furthermore, extracellular matrix of the ventral mesodermal cell layer in the trunk region and the immediate proximity of blood vessels contain high amounts of HA.

Functional molecular mass of a vertebrate hyaluronan synthase as determined by radiation inactivation analysis

Hyaluronan (HA), a linear polysaccharide composed of N-acetylglucosamine-glucuronic acid repeats, is found in the extracellular matrix of vertebrate tissues as well as the capsule of several pathogenic bacteria. The HA synthases (HASs) are dual-action glycosyltransferases that catalyze the addition of two different sugars from UDP-linked precursors to the growing HA chain. The prototypical vertebrate hyaluronan synthase, xlHAS1 (or DG42) from Xenopus laevis, is a 588-residue membrane protein. Recently, the streptococcal enzyme was found to function as a monomer of protein with approximately 16 lipid molecules. The vertebrate enzymes are larger than the streptococcal enzymes; based on the vertebrate HAS deduced amino acid sequence, two additional membrane-associated regions at the carboxyl terminus are predicted. We have utilized radiation inactivation to measure the target size of yeast-derived recombinant xlHAS1. The target size of HAS activity was confirmed using two internal standards. First, samples were spiked with glucose-6-phosphate dehydrogenase, an enzyme of known molecular weight. Second, parallel samples of native xlHAS1 and a xlHAS1-green fluorescent protein fusion (833 residues) were compared; substantial confidence was gained by using this novel internal standard. Our test also corroborated the basic tenets of radiation inactivation theory. We found that the vertebrate HAS protein functions catalytically as a monomer.

Regulation of YKL-40 production by human articular chondrocytes

OBJECTIVE

YKL-40 (human cartilage glycoprotein 39) is one of the most abundant proteins secreted by cultured chondrocytes. The objectives of the present study were to identify regulators of YKL-40 production in cartilage and chondrocytes and to map the localization of YKL-40 in chondrocytes.

METHODS

Human articular chondrocytes and cartilage explants (obtained from subjects at autopsy, from a tissue bank, and from osteoarthritis [OA] patients undergoing total joint replacement surgery) were stimulated with cytokines, growth factors, and other agents. YKL-40 expression was analyzed by Northern blot and polymerase chain reaction. YKL-40 secretion into the media was determined by enzyme-linked immunosorbent assay.

RESULTS

YKL-40 production increased to very high levels during the early phase of chondrocyte monolayer culture and in normal cartilage explant cultures as a response to tissue injury. Spontaneous YKL-40 release was higher in OA than in normal cartilage explant cultures. In chondrocyte monolayer cultures, interleukin-1beta (IL-1beta) and transforming growth factor beta (TGFbeta) decreased the levels of secreted YKL-40, and this was associated with a reduction in YKL-40 messenger RNA levels. IL-1beta, but not TGFbeta, reduced YKL-40 production in cartilage explant cultures. Media from explants treated with cycloheximide had no detectable YKL-40, suggesting that the released protein was newly synthesized. Immunofluorescence microscopy showed YKL-40 staining in the Golgi system of the chondrocytes, but YKL-40 could not be detected in the extracellular matrix.

CONCLUSION

The spontaneous increase in the production of YKL-40 in the early phase of culture appears to represent a cellular response to changes in the extracellular matrix environment. This, coupled with the profound suppressive effects of IL-1beta and TGFbeta on YKL-40 production, identifies a novel regulatory pattern for this major chondrocyte-derived protein.

Topological organization of the hyaluronan synthase from Streptococcus pyogenes

Since we first reported (DeAngelis, P. L., Papaconstantinou, J., and Weigel, P. H. (1993) J. Biol. Chem. 268, 19181-19184) the cloning of the hyaluronan (HA) synthase from Streptococcus pyogenes (spHAS), numerous membrane-bound HA synthases have been discovered in both prokaryotes and eukaryotes. The HASs are unique among enzymes studied to date because they mediate 6-7 discrete functions in order to assemble a polysaccharide containing hetero-disaccharide units and simultaneously effect translocation of the growing HA chain through the plasma membrane. To understand how the relatively small spHAS performs these various functions, we investigated the topological organization of the protein utilizing fusion analysis with two reporter enzymes, alkaline phosphatase and beta-galactosidase, as well as several other approaches. From these studies, we conclude that the NH2 terminus and the COOH terminus, as well as the major portion of a large central domain are localized intracellularly. The first two predicted membrane domains were confirmed to be transmembrane domains and give rise to a very small extracellular loop that is inaccessible to proteases. Several regions of the large internal central domain appear to be associated with, but do not traverse, the membrane. Following the central domain, there are two additional transmembrane domains connected by a second small extracellular loop that also is inaccessible to proteases. The COOH-terminal approximately 25% of spHAS also contains a membrane domain that does not traverse the membrane and may contain extensive re-entrant loops or amphipathic helices. Numerous membrane associations of this latter COOH-terminal region and the central domain may be required to create a pore-like structure through which a growing HA chain can be extruded to the cell exterior. Based on the high degree of similarity among Class I HAS family members, these enzymes may have a similar topological organization for their spHAS-related domains.

Preparation and inhibitory activity on hyaluronidase of fully O-sulfated hyaluro-oligosaccharides

Hyaluronan was partially depolymerized on a large-scale quantity using bacterial hyaluronidase (E.C. 4.2.2.1) for preparation of chemically fully O-sulfated oligosaccharides. The hyaluro-oligosaccharide (HAoligo) mixture obtained by partial digestion was repeatedly applied to low pressure gel permeation chromatographic separation to purify the size-unified oligosaccharide ranged from 4- to 20-mer. The purity and size of each HAoligo was confirmed by using proton nuclear magnetic resonance ((1)H NMR) spectroscopy, capillary electrophoresis (CE) on normal polarity mode, and a newly established separation method by normal phase chromatography with Amide-80 column. The purified HAoligos ranged 4- to 20-mer were applied to chemically fully O-sulfation. Characterization of chemically fully O-sulfated HAoligos was performed by both chemical compositional analyses after hydrolysis and (1)H NMR spectroscopy. While the anti-factor IIa activity of 4- to 20-mer O-sulfated HAoligos was less than 3.1 units/mg, the inhibitory action for hyaluronidase (bovine testicular hyaluronidase (E.C.3.2.1.35)) of the oligosaccharides ranged 16- to 20-mer were corresponding to 79% of that shown by fully O-sulfated hyaluronan (MW 100 kDa) through both competitive and noncompetitive effects.

Function of chitin oligosaccharides in plant and animal development

In plant development chitin oligosaccharides have been studied intensively as part of the communication between leguminous plants and Rhizobium bacteria. The Rhizobium bacteria synthesize and secrete lipochitin oligosaccharides (LCOs) to induce the development of a root nodule, in which the bacteria will infiltrate to start a symbiotic relation with the plant. Here we will give an overview of the biosynthetic route used by the bacteria to synthesize these LCOs. Perception by the plant will also be discussed as well as early responses to the LCOs. By working with the genes from the biosynthetic route, other genes were identified that share homology with the chitin synthase genes from Rhizobium. These genes are now isolated from human, mouse, chick, Xenopus and zebrafish and can be divided into three classes. They are mainly expressed during early development at the same stage as chitin oligosaccharide synthase activity can be detected. A controversy has been risen about their biochemical activity and will be further discussed here.

Serum YKL-40 is increased in patients with hepatic fibrosis

BACKGROUND/AIMS

YKL-40, a mammalian member of the chitinase family, is a lectin that binds heparin and chitin. The function of YKL-40 is unknown, but it may function in tissue remodelling. The aims of this study were to assess the level of circulating YKL-40 in patients with various kinds and degree of chronic liver disease and its possible relation to liver fibrosis.

METHODS

Serum YKL-40 levels were determined by radioimmunoassay in 129 patients with suspected liver disease and related to histological findings and immunohistochemical staining of YKL-40 in a liver biopsy taken simultaneously with the blood sample.

RESULTS

The median serum YKL-40 was highest in patients with alcoholic cirrhosis (532 microg/l), in particular in patients with additional alcoholic hepatitis (740 microg/l). Patients with alcoholic cirrhosis, post-hepatitic cirrhosis (425 microg/l) and non-cirrhotic fibrosis (330 microg/l) had significantly higher serum YKL-40 than normal subjects (102 microg/l), patients with fatty liver (195 microg/l) or patients with viral hepatitis without fibrosis (174 microg/l). Serum YKL-40 was significantly (p<0.001) related to the degree of liver fibrosis with the highest levels in patients with moderate (466 microg/l) to severe (676 microg/l) fibrosis. Serum YKL-40 was also increased (p=0.018) in patients with slight fibrosis (270 microg/l) compared to patients without fibrosis. Immunohistochemical analysis demonstrated positive staining for YKL-40 antigen in areas with fibrosis, particularly areas with active fibrogenesis. YKL-40 staining was never found in hepatocytes.

CONCLUSIONS

Our study indicates that the increased serum YKL-40 in patients with liver disease of various degree and aetiology seems to reflect fibrosis and fibrogenesis.

Mechanism of type 3 capsular polysaccharide synthesis in Streptococcus pneumoniae

The glycosidic linkages of the type 3 capsular polysaccharide of Streptococcus pneumoniae ([3)-beta-D-GlcUA-(1-->4)-beta-D-Glc-(1-->](n)) are formed by the membrane-associated type 3 synthase (Cps3S), which is capable of synthesizing polymer from UDP sugar precursors. Using membrane preparations of S. pneumoniae in an in vitro assay, we observed type 3 synthase activity in the presence of either Mn(2+) or Mg(2+) with maximal levels seen with 10-20 mM Mn(2+). High molecular weight polymer synthesized in the assay was composed of Glc and glucuronic acid and could be degraded to a low molecular weight product by a type 3-specific depolymerase from Bacillus circulans. Additionally, the polymer bound specifically to an affinity column made with a type 3 polysaccharide-specific monoclonal antibody. The polysaccharide was rapidly synthesized from smaller chains and remained associated with the enzyme-containing membrane fraction throughout its synthesis, indicating a processive mechanism of synthesis. Release of the polysaccharide was observed, however, when the level of one of the substrates became limiting. Finally, addition of sugars to the growing type 3 polysaccharide was shown to occur at the nonreducing end of the polysaccharide chain.

Synthesis of hyaluronan of distinctly different chain length is regulated by differential expression of Xhas1 and 2 during early development of Xenopus laevis

The localization of hyaluronan has been determined in tailbud stage embryos of Xenopus laevis using a neurocan-alkaline phosphatase fusion protein. This polysaccharide was located between the germ layers and enriched in mesenchyme, the lumen of the neural tube, the embryonic gut, the hepatic cavity and the heart. A full-length cDNA for a hyaluronan synthase, Xhas2 has been cloned. The expression pattern of Xhas1 and 2 is closely similar to the distribution of hyaluronan in the embryo. Xhas1 produces hyaluronan with a molecular mass of around 40-200 kDa, while the product formed by Xhas2 has a molecular mass above 1 million Da.

In vitro synthesis of hyaluronan by a single protein derived from mouse HAS1 gene and characterization of amino acid residues essential for the activity

HAS1 was expressed as a FLAG-tagged HAS1 fusion protein in COS-1 cells. This recombinant protein was extracted with CHAPS (3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid) from the membrane fraction and purified by anti-FLAG affinity chromatography and subsequent SDS-polyacrylamide gel electrophoresis. A protein solubilized from the one single band on the gel was able to synthesize hyaluronan when incubated with UDP-GlcNAc and UDP-GlcA as donor substrates without any further additions. The detergent-solubilized and purified HAS1 protein, however, exhibited quite different kinetic properties from the membrane-bound protein. When assayed under the reconstitutive conditions where the reaction mixture was layered onto the buffer containing high concentration of CHAPS, the activity was enhanced and the kinetic properties became similar to those of the membrane-bound protein. In addition, a HAS1 gene product by an in vitro transcription/translation system also showed HAS1 activity under the reconstitutive conditions. To our surprise, when incubated with UDP-GlcNAc alone, the protein was found to synthesize chito-oligosaccharide. Taking advantage of these enzyme reaction properties, active sites on the protein involved in for hyaluronan and chito-oligosaccharide synthesis were characterized. Site-directed mutagenesis induced in the cytoplasmic central loop domain of the protein revealed that several amino acid residues conserved among those domains of various proteins of a HAS family were essential for both hyaluronan and chito-oligosaccharide syntheses but one of them was not for chito-oligosaccharide synthesis. The substitutions that caused partial or severe loss of the activity gave no significant changes of the K(m) values of the mutated proteins, suggesting that no conformational or other indirect changes were involved in the effect. Taken together, the results suggest that the HAS1 protein alone is able to synthesize hyaluronan and different amino acid residues on the cytoplasmic central loop domain are involved in transferring GlcNAc and GlcA residues, respectively.

Inhibition of hyaluronidase by fully O-sulfonated glycosaminoglycans

We report a new flow injection assay (FIA) method for determining hyaluronidase activity and the inhibitory effects of chemical fully O-sulfonated glycosaminoglycans on this enzyme. The products of enzymatic action on hyaluronidase can be detected by FIA using fluorometric detection with the fluorogenic reagent 2-cyanoacetamide. The major products derived from hyaluronan by the action of mammalian testicular hyaluronidase (a hydrolyase) were confirmed by (1)H NMR spectroscopy and capillary electrophoresis. The FIA method was next applied to the assay of hyman urinary hyaluronidase activity and the screening of hyaluronidase inhibitors. The human urinary hyaluronidase activity measured ranged from 46 to 59 turbidity reducing units/mg protein. Among the glycosaminoglycans only heparin showed hyaluronidase inhibition. Chemically O-sulfonated glycosaminoglycans showed IC(50) values of hyaluronidase inhibition that correlated with the degree of O-sulfonation. Heparin was found to inhibit hyaluronidase activity noncompetitively, while chemically O-sulfonated HA strongly inhibited hyaluronidase through both competitive and noncompetitive effects.

Expression pattern of a novel hyaluronidase during Xenopus embryogenesis

We have isolated a cDNA encoding a novel hyaluronidase, which is expressed during embryogenesis. The encoded protein was expressed as a fusion polypeptide with glutathione S-transferase, and the affinity-purified fusion protein was shown to possess hyaluronidase activity with a pH optimum about pH 4.0. The expression of the XEH1 gene was analysed by in situ hybridization, and was first apparent in scattered cells in a broad ventral region of late gastrula embryos. As development proceeded through to tailbud stages, the domain of expression became progressively more restricted, eventually being located in the developing liver rudiment near the primary hepatic cavity. The results reveal the dynamic regulation of the contrasting activities of hyaluronan synthesis and degradation during early morphogenetic movements.

Chitin oligosaccharide synthesis by rhizobia and zebrafish embryos starts by glycosyl transfer to O4 of the reducing-terminal residue

Lipochitin oligosaccharides are organogenesis-inducing signal molecules produced by rhizobia to establish the formation of nitrogen-fixing root nodules in leguminous plants. Chitin oligosaccharide biosynthesis by the Mesorhizobium loti nodulation protein NodC was studied in vitro using membrane fractions of an Escherichia coli strain expressing the cloned M. loti nodC gene. The results indicate that prenylpyrophosphate-linked intermediates are not involved in the chitin oligosaccharide synthesis pathway. We observed that, in addition to N-acetylglucosamine (GlcNAc) from UDP-GlcNAc, NodC also directly incorporates free GlcNAc into chitin oligosaccharides. Further analysis showed that free GlcNAc is used as a primer that is elongated at the nonreducing terminus. The synthetic glycoside p-nitrophenyl-beta-N-acetylglucosaminide (pNPGlcNAc) has a free hydroxyl group at C4 but not at C1 and could also be used as an acceptor by NodC, confirming that chain elongation by NodC takes place at the nonreducing-terminal residue. The use of artificial glycosyl acceptors such as pNPGlcNAc has not previously been described for a processive glycosyltransferase. Using this method, we show that also the DG42-directed chitin oligosaccharide synthase activity, present in extracts of zebrafish embryos, is able to initiate chitin oligosaccharide synthesis on pNPGlcNAc. Consequently, chain elongation in chitin oligosaccharide synthesis by M. loti NodC and zebrafish DG42 occurs by the transfer of GlcNAc residues from UDP-GlcNAc to O4 of the nonreducing-terminal residue, in contrast to earlier models on the mechanism of processive beta-glycosyltransferase reactions.