Structural determination of novel tetra- and hexasaccharide sequences isolated from chondroitin sulfate H (oversulfated dermatan sulfate) of hagfish notochord

Heterologous production of chondroitin

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Chondroitin sulfate (CS) is a glycosaminoglycan with a growing variety of applications.

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CS can be produced from microbial fermentation of native or engineered strains.

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Synthetic biology tools are being used to improve CS yields in different hosts.

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Integrated polymerization and sulfation can generate cost-effective CS.

Chondroitin sulfate (CS) is a glycosaminoglycan with a broad range of applications being a popular dietary supplement for osteoarthritis. Usually, CS is extracted from animal sources. However, the known risks of animal products use have been driving the search for alternative methods and sources to obtain this compound. Several pathogenic bacteria naturally produce chondroitin-like polysaccharides through well-known pathways and, therefore, have been the basis for numerous studies that aim to produce chondroitin using non-pathogenic hosts. However, the yields obtained are not enough to meet the high demand for this glycosaminoglycan. Metabolic engineering strategies have been used to construct improved heterologous hosts. The identification of metabolic bottlenecks and regulation points, and the screening for efficient enzymes are key points for constructing microbial cell factories with improved chondroitin yields to achieve industrial CS production. The recent advances on enzymatic and microbial strategies to produce non-animal chondroitin are herein reviewed. Challenges and prospects for future research are also discussed.

Glycosaminoglycans from fresh water fish processing discard - Isolation, structural characterization, and osteogenic activity

Glycosaminoglycans (GAGs) play an important role in various biological activities. A lot of them are present in fish processing discards from abattoirs and fish processing industries which can serve as a valuable source of GAGs. We have, in this paper, isolated and characterized GAGs from fish processing discard (head) generated from the processing of Labeo rohita (L. rohita) and Piaractus brachypomus (P. brachypomus) and have determined their ability to promote osteogenic activity. Isolated GAGs showed higher amounts of chondroitin sulfate/dermatan sulfate (CS/DS) than heparan sulfate (HS). CS/DS from both the fish have a distinct disaccharide composition indicating differences in their structure. Biological activity, in terms of promoting osteogenesis, evaluated in MC3T3-E1 cells and primary cells of the calvaria showed that early mineralization, characterized by alkaline phosphatase staining and activity, and late mineralization, was supported by both the GAGs.

Recent advances in the structural study of functional chondroitin sulfate and dermatan sulfate in health and disease

Chondroitin sulfate (CS) dermatan sulfate (DS), and CS/DS hybrid chains are biologically active like heparan sulfate, and structurally the most complex species of the glycosaminoglycan family along with heparan sulfate. They exist at the cell surface and extracellular matrix in the form of proteoglycans. They function as regulators of functional proteins such as growth factors, cytokines, chemokines, adhesion molecules, and lipoproteins through interactions with the ligands of these proteins via specific saccharide domains. Structural alterations have been often implicated in pathological conditions, such as cancer and atherosclerosis. Recent microsequencing of CS/DS oligosaccharides that bind growth factors, such as pleiotrophin, and various monoclonal antibodies against CS/DS, have revealed a considerable number of unique oligosaccharide sequences. This review focuses on recent advances in the study of the structure-function relation of CS, DS and their hybrid chains in physiological and pathological conditions.

Antibody GD3G7 selected against embryonic glycosaminoglycans defines chondroitin sulfate-E domains highly up-regulated in ovarian cancer and involved in vascular endothelial growth factor binding

Chondroitin sulfate (CS) is abundantly present in the tumor stroma, and tumor-specific CS modifications might be potential targets to influence tumor development. We applied the phage display technology to select antibodies that identify these tumor-specific CS modifications. Antibody GD3G7 was selected against embryonic glycosaminoglycans, and it reacted strongly with CS-E (rich in GlcA-GalNAc4S6S units). In ovarian adenocarcinomas, strong expression of this CS-E epitope was found in the extracellular matrix, and occasionally on tumor cells. No expression was found in normal ovary and cystadenomas. Differential expression was found in ovarian carcinoma cell lines, which correlated with the gene expression of the GalNAc4S-6st enzyme, involved in biosynthesis of CS-E. Vascular endothelial growth factor (VEGF)-sensitive fenestrated (in normal tissues) and tumor blood vessels were both identified by antibody GD3G7, which might implicate a role for CS-E in VEGF biology. VEGF bound to CS-E and antibody GD3G7 could compete for binding of VEGF to CS-E. In conclusion, antibody GD3G7 identified rare CS-E-like structures that were strongly expressed in ovarian adenocarcinomas. This antibody might therefore be instrumental for identifying tumor-related CS alterations.

Functions of Chondroitin Sulfate/Dermatan Sulfate Chains in Brain Development

Chondroitin sulfate (CS) and dermatan sulfate (DS) have been implicated in the processes of neural development in the brain. In this study, we characterized developmentally regulated brain CS/DS chains using a single chain antibody, GD3G7, produced by the phage display technique. Evaluation of the specificity of GD3G7 toward various glycosaminoglycan preparations showed that this antibody specifically reacted with squid CS-E (rich in the GlcUAbeta1-3GalNAc(4,6-O-sulfate) disaccharide unit E), hagfish CS-H (rich in the IdoUAalpha1-3GalNAc(4,6-O-sulfate) unit iE), and shark skin DS (rich in both E and iE units). In situ hybridization for the expression of N-acetylgalac-tosamine-4-sulfate 6-O-sulfotransferase in the postnatal mouse brain, which is involved in the biosynthesis of CS/DS-E, showed a widespread expression of the transcript in the developing brain except at postnatal day 7, where strong expression was observed in the external granule cell layer in the cerebellum. The expression switched from the external to internal granule cell layer with development. Immunohistochemical localization of GD3G7 in the mouse brain showed that the epitope was relatively abundant in the cerebellum, hippocampus, and olfactory bulb. GD3G7 suppressed the growth of neurites in embryonic hippocampal neurons mediated by CS-E, suggesting that the epitope is embedded in the neurite outgrowth-promoting motif of CS-E. In addition, a CS-E decasaccharide fraction was found to be the critical minimal structure needed for recognition by GD3G7. Four discrete decasaccharide epitopic sequences were identified. The antibody GD3G7 has broad applications in investigations of CS/DS chains during the central nervous system's development and under various pathological conditions.

Novel sulfated octa- and decasaccharides from squid cartilage chondroitin sulfate E: sequencing and application for determination of the epitope structure of the monoclonal antibody MO-225

A mixture of octa- and decasaccharides obtained by the digestion with the hyaluronidase of chondroitin sulfate E derived from squid cartilage was subfractionated into 20 and 23 different components, respectively, by anion-exchange HPLC. MALDI-TOF/MS was used to assign the sugar and sulfate composition of the putative octa- and decasaccharides, and a disaccharide composition analysis revealed the building blocks to be A- [GlcUAbeta1-3GalNAc(4S)], C- [GlcUAbeta1-3GalNAc(6S)], and E- [GlcUAbeta1-3GalNAc(4S,6S)] units, where 4S and 6S represent 4-O- and 6-O-sulfate, respectively. The sequences of these octa- and decasaccharides were determined at low picomole amounts by a combination of enzymatic digestions with chondroitinases in conjunction with anion-exchange HPLC. Sequencing revealed that each fraction is a mixture of a major component together with one to three minor components, reflecting the heterogeneity of the parent polysaccharide. Among the 11 different octasaccharide sequences reported here, 8 are novel, while all of the 6 decasaccharide sequences are novel, and this is the first report of the sequencing of CS oligosaccharides longer than octasaccharides. The reactivity of the monoclonal antibody MO-225 with octa- and decasaccharides tested with an oligosaccharide microarray revealed that a CS-E decasaccharide is the minimal requirement for antibody recognition. Among the 6 decasaccharides, only E-E-E-E-C was recognized by MO-225, suggesting the requirement of a C-unit at the reducing end and also the importance of chain length, which in turn may indicate the importance of the conformation acquired by this specific sequence for antibody recognition.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update covering the period 1999-2000

This review describes the use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the analysis of carbohydrates and glycoconjugates and continues coverage of the field from the previous review published in 1999 (D. J. Harvey, Matrix-assisted laser desorption/ionization mass spectrometry of carbohydrates, 1999, Mass Spectrom Rev, 18:349-451) for the period 1999-2000. As MALDI mass spectrometry is acquiring the status of a mature technique in this field, there has been a greater emphasis on applications rather than to method development as opposed to the previous review. The present review covers applications to plant-derived carbohydrates, N- and O-linked glycans from glycoproteins, glycated proteins, mucins, glycosaminoglycans, bacterial glycolipids, glycosphingolipids, glycoglycerolipids and related compounds, and glycosides. Applications of MALDI mass spectrometry to the study of enzymes acting on carbohydrates (glycosyltransferases and glycosidases) and to the synthesis of carbohydrates, are also covered.

Glycoform quantification of chondroitin/dermatan sulfate using a liquid chromatography-tandem mass spectrometry platform

Chondroitin sulfate (CS) is a glycosaminoglycan consisting of repeating uronic acid, N-acetylgalactosamine disaccharide units {[HexAbeta/alpha(1-3)GalNAcbeta(1-4)](n)()}. CS chains are polydisperse with respect to chain length, sulfate content, and glucuronic acid epimerization content, resulting in a distribution of glycoforms for a chain bound to any given serine residue. Usually, CS glycoforms exist, differing in sulfation position and uronic acid epimerization. This work introduces a novel LC-MS/MS platform for the quantification of mixtures of CS oligosaccharides. The CS polysaccharides were partially depolymerized and labeled with either the light (d(0)) or heavy (d(4)) form of 2-anthranilic acid (2-AA). Excess reagent was removed, and mixtures of the CS standard (d(0)) and unknown (d(4)) were made. The CS mixture was subjected to size exclusion chromatography (SEC) with on-line electrospray ionization mass spectrometric detection in the negative ion mode. Tandem mass spectra were acquired, and quantification of unknown samples within the mixture was made using relative ion abundances of specific diagnostic ions. The high accuracy and precision of the glycomics platform were demonstrated using glycoform mixtures made from standard CS preparations. The CS glycoform analysis method was then applied to cartilage extract, versican, and several dermatan sulfate preparations. This work presents the first application of a glycomics platform for the quantification of CS oligosaccharide mixtures for obtaining specific information about the positions of GalNAc sulfation and uronic acid epimerization.

Metabolism and biochemical/physiological roles of chondroitin sulfates: analysis of endogenous and supplemental chondroitin sulfates in blood circulation

Chondroitin sulfate (CS) is a linear heteropolysaccharide consisting of repeating disaccharide units of glucuronic acid and galactosamine, which is commonly sulfated at C-4 and/or C-6 of galactosamine. The administration of CS as a supplement or a drug for the treatment of osteoarthrosis, the prevention of subsequent coronary events, treatment of psoriasis and ophthalmic diseases has been suggested. Much debate on the metabolism of CS and therefore the effectiveness of these treatments, especially after oral administration, has arisen due to the macromolecular nature of CS. Difficulties in analysing CS in blood due to the low endogenous concentrations and the covalent and anionic complexes with proteins have hampered the resolution of these issues. In this review, the information on the pharmacokinetics of CS obtained from studies in experimental animals and in humans is presented. Emphasis has been given to the analytical methods used for the determination of glycosaminoglycans, intact CS and CS-derived disaccharides in blood serum and plasma.

Demonstration of the Pleiotrophin-binding Oligosaccharide Sequences Isolated from Chondroitin Sulfate/Dermatan Sulfate Hybrid Chains of Embryonic Pig Brains

Mammalian brains contain significant amounts of chondroitin sulfate (CS), dermatan sulfate (DS), and CS/DS hybrid chains. CS/DS chains isolated from embryonic pig brains (E-CS/DS) promote the outgrowth of neurites in embryonic mouse hippocampal neurons in culture by interacting with pleiotrophin (PTN), a heparin-binding growth factor. Here, we analyzed oligosaccharides isolated from E-CS/DS, which showed that octasaccharides were the minimal size capable of interacting with PTN at a physiological salt concentration. Five and eight sequences were purified from fluorescently labeled PTN-bound and -unbound octasaccharide fractions, respectively, by enzymatic digestion followed by PTN-affinity chromatography. Their sequences were determined by enzymatic digestion in conjunction with high performance liquid chromatography, revealing a critical role for oversulfated D and/or iD disaccharides in the low yet significant affinity for PTN, which is required for neuritogenesis. The critical D and iD units are GlcUA(2-O-sulfate)beta1-3GalNAc(6-O-sulfate) and IdoUA(2-O-sulfate)alpha1-3GalNAc(6-O-sulfate), respectively, where IdoUA represents L-iduronic acid. In contrast, high affinity interactions with PTN required decasaccharides with E units (GlcUAbeta1-3GalNAc(4, 6-O-disulfate)), B units (GlcUA(2-O-sulfate)beta1-3GalNAc(4-O-sulfate)), and/or their IdoUA-containing counterparts (iE and iB) in addition to D/iD units, although the biological significance of such strong interactions remains to be investigated. Thus, chain size and composition are crucial to the interaction with PTN, and PTN binds to multiple sequences in E-CS/DS chains with distinct affinity. Notably, not only heparan sulfate but also CS/DS hybrid chain structures of mammalian brains contain a high degree of microheterogeneity with a cluster of oversulfated disaccharides and appear to play roles in regulating the functions of PTN.

Chondroitin 4-sulphotransferase-1 and chondroitin 6-sulphotransferase-1 are affected differently by uronic acid residues neighbouring the acceptor GalNAc residues

C4ST-1 (chondroitin 4-sulphotransferase-1) and C6ST-1 (chondroitin 6-sulphotransferase-1) transfer sulphate from PAPS (adenosine 3'-phosphate 5'-phosphosulphate) to positions 4 and 6 respectively of the GalNAc residues of chondroitin. We showed previously that C4ST-1 purified from rat chondrosarcoma and recombinant C4ST-1 both transfer sulphate efficiently to position 4 of the GalNAc residues of DSDS (desulphated dermatan sulphate). We report here the specificity of C4ST-1 and C6ST-1 in terms of uronic acid residue recognition around the GalNAc residue to which sulphate is transferred. When [35S]glycosaminoglycans formed from DSDS after incubation with [35S]PAPS and C4ST-1 were digested with chondroitinase ACII, a major part of the radioactivity was recovered in disaccharide fractions and the remainder distributed to tetrasaccharides and larger fractions, indicating that C4ST-1 mainly transferred sulphate to position 4 of the GalNAc residue located at the GlcA-GalNAc-GlcA sequence. Structural analysis of tetrasaccharide and larger oligosaccharide fractions indicated that C4ST-1 mainly transferred sulphate to the GalNAc residue adjacent to the reducing side of the GlcA residue. On the other hand, when [35S]glycosaminoglycans formed from DSDS after incubation with [35S]PAPS and C6ST-1 were digested with chondroitinase ACII, a major part of the radioactivity was recovered in fractions larger than hexasaccharides, indicating that C6ST-1 transferred sulphate to the GalNAc residues located in the L-iduronic acid-rich region. Structural analysis of the tetrasaccharide and larger oligosaccharide fractions indicated that C6ST-1 showed very little preference for the GalNAc residue neighbouring the GlcA residue. These results indicate that C4ST-1 and C6ST-1 differ from each other in the recognition of uronic acid residues adjacent to the targeted GalNAc residue.

Structural and Functional Characterization of Oversulfated Chondroitin Sulfate/Dermatan Sulfate Hybrid Chains from the Notochord of Hagfish

Oversulfated chondroitin sulfate (CS)/dermatan sulfate (DS) hybrid chains were purified from the notochord of hagfish. The chains (previously named CS-H for hagfish) have an average molecular mass of 18 kDa. Composition analysis using various chondroitinases demonstrated a variety of D-glucuronic acid (GlcUA)- and L-iduronic acid (IdoUA)-containing disaccharides variably sulfated with a higher proportion of GlcUA/IdoUA-GalNAc 4,6-O-disulfate, revealing complex CS/DS hybrid features. The hybrid chains showed neurite outgrowth-promoting activity of an axonic nature, which resembled the activity of squid cartilage CS-E and which was abolished fully by chondroitinase ABC digestion and partially by chondroitinase AC-I or B digestion, suggesting the involvement of both GlcUA and IdoUA in neuritogenic activity. Purified CS-H exhibited interactions in a BIAcore system with various heparin-binding proteins and neurotrophic factors (viz. fibroblast growth factor-2, -10, -16, and -18; midkine; pleiotrophin; heparin-binding epidermal growth factor-like growth factor; vascular endothelial growth factor; brain-derived neurotrophic factor; and glial cell line-derived neurotrophic factor), most of which are expressed in the brain, although fibroblast growth factor-1 and ciliary neurotrophic factor showed no binding. Kinetic analysis revealed high affinity binding of these growth factors and, for the first time, of the neurotrophic factors. Competitive inhibition revealed the involvement of both IdoUA and GlcUA in the binding of these growth factors, suggesting the importance of the hybrid nature of CS-H for the efficient binding of these growth factors. These findings, together with those from the recent analysis of brain CS/DS chains from neonatal mouse and embryonic pig (Bao, X., Nishimura, S., Mikami, T., Yamada, S., Itoh, N., and Sugahara, K. (2004) J. Biol. Chem. 279, 9765-9776), suggest physiological roles of the hybrid chains in the development of the brain.

Novel 70-kDa chondroitin sulfate/dermatan sulfate hybrid chains with a unique heterogeneous sulfation pattern from shark skin, which exhibit neuritogenic activity and binding activities for growth factors and neurotrophic factors

Chondroitin sulfate (CS) and dermatan sulfate (DS) hybrid chains of proteoglycans are critical in growth factor binding, neuritogenesis, and brain development. Here we isolated CS/DS hybrid chains from shark skin aiming to develop therapeutic agents. Digestion with various chondroitinases showed that both GlcUA- and IdoUA-containing disaccharides are scattered along the polysaccharide chains with an unusually large average molecular mass of 70 kDa. The CS/DS chains were separated into major (80%) and minor (20%) fractions by anion-exchange chromatography. Both fractions had relatively low degrees of sulfation (sulfate/disaccharide molar ratio=1.17 versus 0.87), showing a unique feature compared with the marine CS and DS isolated to date, most of which are oversulfated. They were highly heterogeneous and characterized by multiple disaccharides including GlcUA-GalNAc, GlcUA-GalNAc(6S), GlcUA-GalNAc(4S), IdoUA-GalNAc(4S), GlcUA-GalNAc(4S,6S), IdoUA-GalNAc(4S,6S), GlcUA(2S)-GalNAc(6S), and/or IdoUA(2S)-GalNAc(6S), IdoUA(2S)-GalNAc(4S) and novel GlcUA(2S)-GalNAc(4S), where 2S, 4S, and 6S represent 2-O-, 4-O- and 6-O-sulfate, respectively. The CS/DS chains bound two neurotrophic factors and various growth factors expressed in the brain with high affinity as evaluated for the major fraction by kinetic analysis using a surface plasmon resonance detector, and also promoted the outgrowth of neurites of both an axonic and a dendritic nature. The neuritogenic activity was abolished completely by digestion with chondroitinase ABC, AC-I, or B, suggesting the importance of both GlcUA- and IdoUA-containing moieties. It also showed anti-heparin cofactor II activity comparable to that exhibited by DS from porcine skin. Thus, by virtue of its unique structure and biological activities, DS will find a potential use in therapeutics.

Oversulfated dermatan sulfate exhibits neurite outgrowth-promoting activity toward embryonic mouse hippocampal neurons: implications of dermatan sulfate in neuritogenesis in the brain

Brain-specific chondroitin sulfate (CS) proteoglycan (PG) DSD-1-PG/6B4-PG/phosphacan isolated from neonatal mouse brains exhibits neurite outgrowth-promoting activity toward embryonic rat and mouse hippocampal neurons in vitro through the so-called DSD-1 epitope embedded in its glycosaminoglycan side chains. Oversulfated CS variants, CS-D from shark cartilage and CS-E from squid cartilage, also possess similar activities. We have proposed that the neuritogenic property of the DSD-1 epitope may be attributable to a distinct CS structure characterized by the disulfated D disaccharide unit [GlcUA(2S)-GalNAc(6S)]. In this study, we assessed neuritogenic potencies of various oversulfated dermatan sulfate (DS) preparations purified from hagfish notochord, the bodies of two kinds of ascidians and embryonic sea urchin, which are characterized by the predominant disulfated disaccharide units of [IdoUA-GalNAc(4S,6S)] (68%), [IdoUA(2S)-GalNAc(4S)] (66%) plus [IdoUA(2S)-GalNAc(6S)] (5%), [IdoUA(2S)-GalNAc (6S)] (>90%), and [IdoUA-GalNAc(4S,6S)] (74%), respectively. They exerted marked neurite outgrowth-promoting activities, resulting in distinct morphological features depending on the individual structural features. Such activities were not observed for a less sulfated DS preparation derived from porcine skin, which has a monosulfated disaccharide unit [IdoUA-Gal-NAc(4S)] as a predominant unit. The neurite outgrowth-promoting activities of these oversulfated DS preparations and DSD-1-PG were eliminated by the specific enzymatic cleavage of GalNAc-IdoUA linkages characteristic of DS using chondroitinase B. In addition, chemical analysis of the glycosaminoglycan side chains of DSD-1-PG revealed the DS-type structures. These observations suggest potential novel neurobiological functions of oversulfated DS structures and may reflect the physiological neuritogenesis during brain development by mammalian oversulfated DS structures exemplified by the DSD-1 epitope.

Advances in analysis of glycosaminoglycans: its application for the assessment of physiological and pathological states of connective tissues

Glycosaminoglycans are a class of biological macromolecules found mainly in connective tissues as constituents of proteoglycans, covalently linked to their core protein. Hyaluronan is the only glycosaminoglycan present under its single form and possesses the ability to aggregate with the class of proteoglycans termed hyalectans. Proteoglycans are localised both at the extracellular and cellular (cell-surface and intracellular) levels and, via either their glycosaminoglycan chains or their core proteins participate in and regulate several cellular events and (patho)physiological processes. Advances in analytical separational techniques, including high-performance liquid chromatography, capillary electrophoresis and fluorophore assisted carbohydrate electrophoresis, make possible to examine alterations of glycosaminoglycans with respect to their amounts and fine structural features in various pathological conditions, thus becoming applicable for diagnosis. In this review we present the chromatographic and electromigration procedures developed to analyse and characterise glycosaminoglycans. Moreover, a critical evaluation of the biological relevance of the results obtained by the developed methodology is discussed.

Appican, the proteoglycan form of the amyloid precursor protein, contains chondroitin sulfate E in the repeating disaccharide region and 4-O-sulfated galactose in the linkage region

Chondroitin sulfate (CS)-D and CS-E, which are characterized by oversulfated disaccharide units, have been shown to regulate neuronal adhesion, cell migration, and neurite outgrowth. CS proteoglycans (CSPGs) consist of a core protein to which one or more CS chains are attached via a serine residue. Although several brain CSPGs, including mouse DSD-1-PG/phosphacan, have been found to contain the oversulfated D disaccharide motif, no brain CSPG has been reported to contain the oversulfated E motif. Here we analyzed the CS chain of appican, the CSPG form of the Alzheimer's amyloid precursor protein. Appican is expressed almost exclusively by astrocytes and has been reported to have brain- and astrocyte-specific functions including stimulation of both neural cell adhesion and neurite outgrowth. The present findings show that the CS chain of appican has a molecular mass of 25-50 kDa. This chain contains a significant fraction (14.3%) of the oversulfated E motif GlcUA beta 1-3GalNAc(4,6-O-disulfate). The rest of the chain consists of GlcUA beta 1-3GalNAc(4-O-sulfate) (81.2%) and minor fractions of GlcUA beta 1-3GalNAc and GlcUA beta 1-3GalNAc(6-O-sulfate). We also show that the CS chain of appican contains in its linkage region the 4-O-sulfated Gal structure. Thus, appican is the first example of a specific brain CSPG that contains the E disaccharide unit in its sugar backbone and the 4-O-sulfated Gal residue in its linkage region. The presence of the E unit is consistent with and may explain the neurotrophic activities of appican.

Hexuronyl C5-epimerases in alginate and glycosaminoglycan biosynthesis

The sugar residues in most polysaccharides are incorporated as their corresponding monomers during polymerization. Here we summarize the three known exceptions to this rule, involving the biosynthesis of alginate, and the glycosaminoglycans, heparin/heparan sulfate and dermatan sulfate. Alginate is synthesized by brown seaweeds and certain bacteria, while glycosaminoglycans are produced by most animal species. In all cases one of the incorporated sugar monomers are being C5-epimerized at the polymer level, from D-mannuronic acid to L-guluronic acid in alginate, and from D-glucuronic acid to L-iduronic acid in glycosaminoglycans. Alginate epimerization modulates the mechanical properties of seaweed tissues, whereas in bacteria it seems to serve a wide range of purposes. The conformational flexibility of iduronic acid units in glycosaminoglycans promotes apposition to, and thus functional interactions with a variety of proteins at cell surfaces and in the extracellular matrix. In the bacterium Azotobacter vinelandii the alginates are being epimerized at the cell surface or in the extracellular environment by a family of evolutionary strongly related modular type and Ca(2+)-dependent epimerases (AlgE1-7). Each of these enzymes introduces a specific distribution pattern of guluronic acid residues along the polymer chains, explaining the wide structural variability observed in alginates isolated from nature. Glycosaminoglycans are synthesized in the Golgi system, through a series of reactions that include the C5-epimerization reaction along with extensive sulfation of the polymers. The single, Ca(2+)-independent, epimerase in heparin/heparan sulfate biosynthesis and the Ca(2+)-dependent dermatan sulfate epimerase(s) also generate variable epimerization patterns, depending on other polymer-modification reactions. The alginate and heparin epimerases appear unrelated at the amino acid sequence level, and have probably evolved through independent evolutionary pathways; however, hydrophobic cluster analysis indicates limited similarity. Seaweed alginates are widely used in industry, while heparin is well established in the clinic as an anticoagulant.

Evidence of block and randomly sequenced chondroitin polysaccharides: sequential enzymatic digestion and quantification using ion trap tandem mass spectrometry

A method for determining the sequence type of the disaccharide repeat region of cartilage samples is introduced. The samples are sequentially subjected to selective and nonselective enzymatic digestion, and the isomeric products from each step are quantified using tandem mass spectrometry. The two-step digestion/quantification protocol identifies whether the global makeup of the polymer is "alternating", "random", or "blocked" with respect to the two main components of the cartilage, 4- and 6-sulfated disaccharides. Using this procedure, the sequence type of two biologically isolated chondroitin polysaccharides was identified. The results for chondroitin sulfate A, isolated from bovine trachea, are consistent with the 4- and 6-sulfated disaccharides randomly distributed throughout the repeat region of the polysaccharide. For chondroitin sulfate C, shark cartilage, the 6-sulfated disaccharides are adjacent to each other to a larger extent than one would expect for a randomly distributed polymer, indicating that "blocks" of repeating disaccharides with the same sulfation site are present.

Identification of oligomeric domains within dermatan sulfate chains using differential enzymic treatments, derivatization with 2-aminoacridone and capillary electrophoresis

Galactosaminoglycans, i.e. dermatan sulfate (DS) and chondroitin sulfate, are linear heteropolysaccharides consisting of repeating disaccharide units of L-iduronic acid (L-IdoA) or D-glucuronic acid (D-GlcA) residues linked to N-acetyl-galactosamine. High-performance capillary electrophoresis (HPCE or CE) has been successfully used for determining the disaccharide composition of glycosaminoglycans. However, only limited information is available on how to identify oligomeric domains rich in D-GlcA or L-IdoA. The aim of this study was therefore to develop a rapid and accurate CE procedure by which such oligosaccharides can be determined together with the variously sulfated disaccharides. Isolated dermatan sulfates of human origin were separately digested with chondroitinases ABC, AC and B and the enzymic products were derivatized with 2-aminoacridone. CE analysis of these products was performed using a phosphate buffer, pH 3.0, and reversed polarity at 30 kV. The derivatization enabled their detection with laser-induced fluorescence (LIF) and UV at 260 nm at much higher sensitivity than the detection of nonderivatized delta-saccharides at 232 nm and therefore components undetectable at 232 nm were nicely detected after derivatization. Except for delta-disaccharides, altogether five distinct oligosaccharides with differences in charge density were identified. Depending on the lyase that produced these oligomers, information on the presence of L-IdoA- or D-GlcA-containing domains within the DS chain and the sulfation pattern of these oligomeric domains was obtained. This CE method could also be useful in studying the functional oligomeric domains in galactosaminoglycan chains.

Requirement of chondroitin sulfate/dermatan sulfate recognition in midkine-dependent migration of macrophages

Midkine (MK) is a heparin-binding growth factor that promotes cell migration, cell growth and cell survival. The promotion of migration of inflammatory cells, especially macrophages, by MK is involved in formation of a vascular abnormality, i.e. neointima formation. MK-induced migration of peritoneal exudate macrophages was inhibited by heparin, chondroitin sulfate E and dermatan sulfate, but not by chondroitin sulfate D or chondroitin 6-sulfate. Digestion of macrophages with chondroitinase ABC as well as chondroitinase B decreased the migratory activity. However, heparitinase digestion showed only slight effects. These results indicated that a chondroitin sulfate, i.e. an E-type oversulfated structure with dermatan sulfate domain, is involved in MK-induced migration of macrophages. Although a chondroitin sulfate proteoglycan, receptor-type protein tyrosine phosphatase zeta (PTP zeta), participates in MK-induced migration of neurons and osteoblasts, PTP zeta was not detected in macrophages. The MK-induced migration was inhibited by PP1, wortomanin, PD 98059 and vanadate, indicating that the downstream signaling system, which includes Src, PI3 kinase and ERK as important components, is shared with other MK signaling systems in which PTP zeta is involved.

Neuronal cell adhesion, mediated by the heparin-binding neuroregulatory factor midkine, is specifically inhibited by chondroitin sulfate E. Structural ans functional implications of the over-sulfated chondroitin sulfate

The heparin-binding neurotrophic factor midkine (MK) has been proposed to mediate neuronal cell adhesion and neurite outgrowth promotion by interacting with cell-surface heparan sulfate. We have observed that over-sulfated chondroitin sulfate (CS) D and CS-E show neurite outgrowth-promoting activity in embryonic day (E) 18 rat hippocampal neurons (Nadanaka, S., Clement, A., Masayama, K., Faissner, A., and Sugahara, K. (1998) J. Biol. Chem. 273, 3296-3307). In the present study, various CS isoforms were examined for their ability to inhibit the MK-mediated cell adhesion of cortical neuronal cells in comparison with heparin from porcine intestine and heparan sulfate from bovine kidney. E17-18 rat cortical neuronal cells were cultured on plates coated with recombinant MK in a grid pattern. The cells attached to and extended their neurites along the MK substratum. Cell adhesion was inhibited by squid cartilage over-sulfated CS-E as well as by heparin, but not by heparan sulfate or other CS isoforms. Direct interactions of MK with various glycosaminoglycans were then evaluated using surface plasmon resonance, showing that CS-E bound MK as strongly as heparin, followed by other over-sulfated CS isoforms, CS-H and CS-K. Furthermore, E18 rat brain extracts showed an E disaccharide unit, GlcUAbeta1-3GalNAc(4,6-O-disulfate). These findings indicate that CS chains containing the E unit as well as heparin-like glycosaminoglycans may be involved in the expression and/or modulation of the multiple neuroregulatory functions of MK such as neuronal adhesion and migration and promotion of neurite outgrowth.