Nonreducing end structures of chondroitin sulfate chains on aggrecan isolated from Swarm rat chondrosarcoma cultures

Keratan sulfate, an electrosensory neurosentient bioresponsive cell instructive glycosaminoglycan

The roles of keratan sulfate (KS) as a proton detection glycosaminoglycan in neurosensory processes in the central and peripheral nervous systems is reviewed. The functional properties of the KS-proteoglycans aggrecan, phosphacan, podocalyxcin as components of perineuronal nets in neurosensory processes in neuronal plasticity, cognitive learning and memory are also discussed. KS-glycoconjugate neurosensory gels used in electrolocation in elasmobranch fish species and KS substituted mucin like conjugates in some tissue contexts in mammals need to be considered in sensory signalling. Parallels are drawn between KS's roles in elasmobranch fish neurosensory processes and its roles in mammalian electro mechanical transduction of acoustic liquid displacement signals in the cochlea by the tectorial membrane and stereocilia of sensory inner and outer hair cells into neural signals for sound interpretation. The sophisticated structural and functional proteins which maintain the unique high precision physical properties of stereocilia in the detection, transmittance and interpretation of acoustic signals in the hearing process are important. The maintenance of the material properties of stereocilia are essential in sound transmission processes. Specific, emerging roles for low sulfation KS in sensory bioregulation are contrasted with the properties of high charge density KS isoforms. Some speculations are made on how the molecular and electrical properties of KS may be of potential application in futuristic nanoelectronic, memristor technology in advanced ultrafast computing devices with low energy requirements in nanomachines, nanobots or molecular switches which could be potentially useful in artificial synapse development. Application of KS in such innovative areas in bioregulation are eagerly awaited.

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

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

Functions of chondroitin/dermatan sulfate containing GalNAc4,6-disulfate

Chondroitin sulfate (CS) and dermatan sulfate (DS) containing GalNAc4,6-disulfate (GalNAc4S6S) were initially discovered in marine animals. Following the discovery, these glycosaminoglycans have been found in various animals including human. In the biosynthesis of CS/DS containing GalNAc4S6S, three groups of sulfotransferases are involved; chondroitin 4-sulfotransferases (C4STs), dermatan 4-sulfotransferase-1 (D4ST-1) and GalNAc 4-sulfate 6-O-sulfotransferase (GalNAc4S-6ST). GalNAc4S-6ST and its products have been shown to play important roles in the abnormal pathological conditions such as central nervous system injury, cancer development, abnormal tissue fibrosis, development of osteoporosis, and infection with viruses or nematodes. CS/DS containing GalNAc4S6S has been shown to increase with the functional differentiation of mast cells, macrophages and neutrophils. Genetic approaches using knockout or knockdown of GalNAc4S-6ST, blocking of the epitopes containing GalNAc4S6S by specific antibodies and chemical technology that enabled the synthesis of oligosaccharides with defined sulfation patterns have been applied successfully to these investigations. These studies contributed significantly to the basic understanding of the functional roles of CS/DS containing GalNAc4S6S in various abnormal conditions, and appear to provide promising clues to the development of possible measures to treat them.

Pentosan Polysulphate (PPS), a Semi-Synthetic Heparinoid DMOAD With Roles in Intervertebral Disc Repair Biology emulating The Stem Cell Instructive and Tissue Reparative Properties of Heparan Sulphate

This review highlights the attributes of pentosan polysulphate (PPS) in the promotion of intervertebral disc (IVD) repair processes. PPS has been classified as a disease modifying osteoarthritic drug (DMOAD) and many studies have demonstrated its positive attributes in the countering of degenerative changes occurring in cartilaginous tissues during the development of osteoarthritis (OA). Degenerative changes in the IVD also involve inflammatory cytokines, degradative proteases and cell signalling pathways similar to those operative in the development of OA in articular cartilage. PPS acts as a heparan sulphate (HS) mimetic to effect its beneficial effects in cartilage. The IVD contains small cell membrane HS-proteoglycans (HSPGs) such as syndecan, and glypican and a large multifunctional HS/chondroitin sulphate (CS) hybrid proteoglycan (HSPG2/perlecan) that have important matrix stabilising properties and sequester, control and present growth factors from the FGF, VEGF, PDGF and BMP families to cellular receptors to promote cell proliferation, differentiation and matrix synthesis. HSPG2 also has chondrogenic properties and stimulates the synthesis of extracellular matrix (ECM) components, expansion of cartilaginous rudiments and has roles in matrix stabilisation and repair. Perlecan is a perinuclear and nuclear proteoglycan in IVD cells with roles in chromatin organisation and control of transcription factor activity, immunolocalises to stem cell niches in cartilage, promotes escape of stem cells from quiescent recycling, differentiation and attainment of pluripotency and migratory properties. These participate in tissue development and morphogenesis, ECM remodelling and repair. PPS also localises in the nucleus of stromal stem cells, promotes development of chondroprogenitor cell lineages, ECM synthesis and repair and discal repair by resident disc cells. The availability of recombinant perlecan and PPS offer new opportunities in repair biology. These multifunctional agents offer welcome new developments in repair strategies for the IVD.

Aggrecan, the Primary Weight-Bearing Cartilage Proteoglycan, Has Context-Dependent, Cell-Directive Properties in Embryonic Development and Neurogenesis: Aggrecan Glycan Side Chain Modifications Convey Interactive Biodiversity

This review examines aggrecan's roles in developmental embryonic tissues, in tissues undergoing morphogenetic transition and in mature weight-bearing tissues. Aggrecan is a remarkably versatile and capable proteoglycan (PG) with diverse tissue context-dependent functional attributes beyond its established role as a weight-bearing PG. The aggrecan core protein provides a template which can be variably decorated with a number of glycosaminoglycan (GAG) side chains including keratan sulphate (KS), human natural killer trisaccharide (HNK-1) and chondroitin sulphate (CS). These convey unique tissue-specific functional properties in water imbibition, space-filling, matrix stabilisation or embryonic cellular regulation. Aggrecan also interacts with morphogens and growth factors directing tissue morphogenesis, remodelling and metaplasia. HNK-1 aggrecan glycoforms direct neural crest cell migration in embryonic development and is neuroprotective in perineuronal nets in the brain. The ability of the aggrecan core protein to assemble CS and KS chains at high density equips cartilage aggrecan with its well-known water-imbibing and weight-bearing properties. The importance of specific arrangements of GAG chains on aggrecan in all its forms is also a primary morphogenetic functional determinant providing aggrecan with unique tissue context dependent regulatory properties. The versatility displayed by aggrecan in biodiverse contexts is a function of its GAG side chains.

Emerging tools to study proteoglycan function during skeletal development

In the past 20years, appreciation for the varied roles of proteoglycans (PGs), which are specific types of sugar-coated proteins, has increased dramatically. PGs in the extracellular matrix were long known to impart structural functions to many tissues, especially articular cartilage, which cushions bones and allows mobility at skeletal joints. Indeed, osteoarthritis is a debilitating disease associated with loss of PGs in articular cartilage. Today, however, PGs have a demonstrated role in cell biological processes, such as growth factor signalling, prompting new perspectives on the etiology of PG-associated diseases. Here, we review diseases associated with defects in PG synthesis and sulfation, also highlighting current understanding of the underlying genetics, biochemistry, and cell biology. Since most research has analyzed a class of PGs called heparan sulfate PGs, more attention is paid here to studies of chondroitin sulfate PGs (CSPGs), which are abundant in cartilage. Interestingly, CSPG synthesis is tightly linked to the cell biological processes of secretion and lysosomal degradation, suggesting that these systems may be linked genetically. Animal models of loss of CSPG function have revealed CSPGs to impact skeletal development. Specifically, our work from a mutagenesis screen in zebrafish led to the hypothesis that cartilage PGs normally delay the timing of endochondral ossification. Finally, we outline emerging approaches in zebrafish that may revolutionize the study of cartilage PG function, including transgenic methods and novel imaging techniques. Our recent work with X-ray fluorescent imaging, for example, enables direct correlation of PG function with PG-dependent biological processes.

LC-MS and LC-MS/MS studies of incorporation of 34SO3 into glycosaminoglycan chains by sulfotransferases

The specificities of glycosaminoglycan (GAG) modification enzymes, particularly sulfotransferases, and the locations and concentrations of these enzymes in the Golgi apparatus give rise to the mature GAG polysaccharides that bind protein ligands. We studied the substrate specificities of sulfotransferases with a stable isotopically labeled donor substrate, 3'-phosphoadenosine-5'-phosphosulfate. The sulfate incorporated by in vitro sulfation using recombinant sulfotransferases was easily distinguished from those previously present on the GAG chains using mass spectrometry. The enrichment of the [M + 2] isotopic peak caused by (34)S incorporation, and the [M + 2]/[M + 1] ratio, provided reliable and sensitive measures of the degree of in vitro sulfation. It was found that both CHST3 and CHST15 have higher activities at the non-reducing end (NRE) units of chondroitin sulfate, particularly those terminating with a GalNAc monosaccharide. In contrast, both NDST1 and HS6ST1 showed lower activities at the NRE of heparan sulfate (HS) chains than at the interior of the chain. Contrary to the traditional view of HS biosynthesis processes, NDST1 also showed activity on O-sulfated GlcNAc residues.

Adult bone marrow stromal cell-based tissue-engineered aggrecan exhibits ultrastructure and nanomechanical properties superior to native cartilage

OBJECTIVE

To quantify the structural characteristics and nanomechanical properties of aggrecan produced by adult bone marrow stromal cells (BMSCs) in peptide hydrogel scaffolds and compare to aggrecan from adult articular cartilage.

DESIGN

Adult equine BMSCs were encapsulated in 3D-peptide hydrogels and cultured for 21 days with TGF-β1 to induce chondrogenic differentiation. BMSC-aggrecan was extracted and compared with aggrecan from age-matched adult equine articular cartilage. Single molecules of aggrecan were visualized by atomic force microscopy-based imaging and aggrecan nanomechanical stiffness was quantified by high resolution force microscopy. Population-averaged measures of aggrecan hydrodynamic size, core protein structures and CS sulfation compositions were determined by size-exclusion chromatography, Western analysis, and fluorescence-assisted carbohydrate electrophoresis (FACE).

RESULTS

BMSC-aggrecan was primarily full-length while cartilage-aggrecan had many fragments. Single molecule measurements showed that core protein and GAG chains of BMSC-aggrecan were markedly longer than those of cartilage-aggrecan. Comparing full-length aggrecan of both species, BMSC-aggrecan had longer GAG chains, while the core protein trace lengths were similar. FACE analysis detected a ∼ 1:1 ratio of chondroitin-4-sulfate to chondroitin-6-sulfate in BMSC-GAG, a phenotype consistent with aggrecan from skeletally-immature cartilage. The nanomechanical stiffness of BMSC-aggrecan was demonstrably greater than that of cartilage-aggrecan at the same total sGAG (fixed charge) density.

CONCLUSIONS

The higher proportion of full-length monomers, longer GAG chains and greater stiffness of the BMSC-aggrecan makes it biomechanically superior to adult cartilage-aggrecan. Aggrecan stiffness was not solely dependent on fixed charge density, but also on GAG molecular ultrastructure. These results support the use of adult BMSCs for cell-based cartilage repair.

High-performance liquid chromatography-mass spectrometry for mapping and sequencing glycosaminoglycan-derived oligosaccharides

Glycosaminoglycans (GAGs) have proven to be very difficult to analyze and characterize because of their high negative charge density, polydispersity and sequence heterogeneity. As the specificity of the interactions between GAGs and proteins results from the structure of these polysaccharides, an understanding of GAG structure is essential for developing a structure-activity relationship. Electrospray ionization (ESI) mass spectrometry (MS) is particularly promising for the analysis of oligosaccharides chemically or enzymatically generated by GAGs because of its relatively soft ionization capacity. Furthermore, on-line high-performance liquid chromatography (HPLC)-MS greatly enhances the characterization of complex mixtures of GAG-derived oligosaccharides, providing important structural information and affording their disaccharide composition. A detailed protocol for producing oligosaccharides from various GAGs, using controlled, specific enzymatic or chemical depolymerization, is presented, together with their HPLC separation, using volatile reversed-phase ion-pairing reagents and on-line ESI-MS structural identification. This analysis provides an oligosaccharide map together with sequence information from a reading frame beginning at the nonreducing end of the GAG chains. The preparation of oligosaccharides can be carried out in 10 h, with subsequent HPLC analysis in 1-2 h and HPLC-MS analysis taking another 2 h.

Extended N-sulfated domains reside at the nonreducing end of heparan sulfate chains

Heparan sulfate (HS) serves as a cell-surface co-receptor for growth factors, morphogens, and chemokines. These HS and protein binding events depend on the fine structure and distribution of domains along an HS chain. A given domain can vary in terms of uronic acid epimer, N- and O-sulfate, and N-acetate content. The most highly sulfated regions of HS chains, N-sulfated (NS) domains, play prominent roles in HS and protein binding. We have analyzed HS oligosaccharides from various mammalian sources and provide evidence that NS domains residing at the nonreducing end (NRE) are, on average, longer than those residing in the internal regions of the chain. Additionally, they are more highly sulfated than their internal counterparts. These features are independent of the sulfation pattern of the bulk HS chains. From disaccharide analysis, it is clear that NS domains do not always occupy HS NREs. However, when they do, they tend to terminate in a subset of N-sulfated disaccharides. Our observations are consistent with a significant role of NRE NS domains in HS-growth factor interactions.

High-performance liquid chromatography and on-line mass spectrometry detection for the analysis of chondroitin sulfates/hyaluronan disaccharides derivatized with 2-aminoacridone

In this study, we developed an on-line reverse-phase high-performance liquid chromatography-electrospray ionization-mass spectrometry (RP-HPLC-ESI-MS) separation and structural characterization of hyaluronan (HA)/chondroitin sulfate (CS)/dermatan sulfate (DS) disaccharides released by enzymatic treatment and derivatized with 2-aminoacridone (AMAC), providing a high-resolution system also applicable by using a further fluorimetric detector (Fp) before ESI-MS spectral acquisition. Isomeric nonsulfated HA and CS/DS disaccharides, isomeric monosulfated and isomeric disulfated CS/DS disaccharides, and the trisulfated species were distinctly separated and unambiguously identified by their retention times and mass spectra in negative ionization mode. In general, no multiply charged ions were detected even for highly charged disaccharides, but the presence of desulfonated products for highly sulfated species due to the relative instability of sulfo groups was observed. RP-HPLC-ESI-MS of each AMAC disaccharide was found to be linear from 3 to 500 ng with very high coefficient of correlation values due to the high efficiency of separation and the sharp outline of the peaks. Various CS/DS samples were characterized for disaccharide composition, and minor oligomer species identified as GalNAcSO(4) at the nonreducing end of chains was observed as a common component of these macromolecules. Furthermore, purified endogenous normal human plasma CS disaccharides were also evaluated by means of RP-HPLC-(Fp)-ESI-MS.

Intermittent mechanical loading of articular cartilage explants modulates chondroitin sulfate fine structure

OBJECTIVE

Alterations in the sulfation pattern of chondroitin sulfate (CS) chains of proteoglycans have been associated with aging and degeneration of articular cartilage. The purpose of the present study was to investigate systematically the effect of load amplitudes, frequencies and load durations of intermittently applied mechanical pressure on the sulfation of CS chains of cultured bovine articular cartilage explants.

METHODS

Using a sinusoidal waveform of 0.5 Hz frequency, cyclic compressive pressure of 0.1-1.0 MPa was applied for 10s followed by a period of unloading lasting 10-1000 s. These intermittent loading protocols were repeated for a total duration of 1-6 days. Newly synthesized as well as endogenous CS chains were isolated, depolymerized and subsequently quantitated after fractionation by high-performance anion-exchange chromatography.

RESULTS

Increasing the mechanical demands on cartilage explants by elevating either the duration or the frequency of loading can significantly alter the fine structure of newly synthesized CS in that less chains terminate on galNAc4,6S and, in that simultaneously the ratio of the internal disaccharides DeltaDi6S to DeltaDi4S is increased. Similar results were obtained with explants being slightly mechanically challenged by low magnitudes of loads.

CONCLUSION

Our data show for the first time that intermittent loading of articular cartilage explants can significantly alter the sulfation pattern of the terminal CS residues as well as of the internal disaccharides. Furthermore, our results indicate that explants possess a physiological window of stress in which they are able to produce also a normal extracellular matrix.

Recognition of Sulfation Pattern of Chondroitin Sulfate by Uronosyl 2-O-Sulfotransferase

We have shown previously that a highly sulfated sequence, GalNAc(4,6-SO(4))-GlcA(2SO(4))-GalNAc(6SO(4)), is present at the nonreducing terminal of chondroitin sulfate (CS), and this structure was synthesized from a unique sequence, GalNAc(4SO(4))-GlcA(2SO(4))-GalNAc(6SO(4)), by sulfation with N-acetylgalactosamine 4-sulfate 6-O-sulfotransferase. Uronosyl 2-O-sulfotrasferase (2OST), which transfers sulfate from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to position 2 of the GlcA residue of CS, is expected to be involved in synthesis of these structures; however, the specificity of 2OST concerning recognition of the sulfation pattern of the acceptor has largely remained unclear. In the present study, we examined the specificity of 2OST in terms of recognition of the sulfation pattern around the targeting GlcA residue. The recombinant 2OST could sulfate CS-A, CS-C, and desulfated dermatan sulfate. When [(35)S]glycosaminoglycans formed from CS-A after the reaction with the recombinant 2OST and [(35)S]PAPS were subjected to limited digestion with chondroitinase ACII, a radioactive tetrasaccharide (Tetra A) was obtained as a sole intermediate product. The sequence of Tetra A was found to be DeltaHexA-GalNAc(4SO(4))-GlcA(2SO(4))-GalNAc(6SO(4)) by enzymatic and chemical reactions. These observations indicate that 2OST transfers sulfate preferentially to the GlcA residue located in a unique sequence, -GalNAc(4SO(4))-GlcA-GalNAc(6SO(4))-. When oligosaccharides with different sulfation patterns were used as the acceptor, GalNAc(4SO(4))-GlcA-GalNAc(6SO(4)) and GlcA-GalNAc(4SO(4))-GlcA-GalNAc(6SO(4)) were the best acceptors for 2OST among trisaccharides and tetrasaccharides, respectively. These results suggest that 2OST may be involved in the synthesis of the highly sulfated structure found in CS-A.

Synthesis of sulfated phenyl 2-acetamido-2-deoxy-D-galactopyranosides. 4-O-Sulfated phenyl 2-acetamido-2-deoxy-β-D-galactopyranoside is a competitive acceptor that decreases sulfation of chondroitin sulfate by N-acetylgalactosamine 4-sulfate 6-O-sulfotransferase

We have previously cloned N-acetylgalactosamine 4-sulfate 6-O-sulfotransferase (GalNAc4S-6ST), which transfers sulfate from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to the C-6 hydroxyl group of the GalNAc 4-sulfate residue of chondroitin sulfate A and forms chondroitin sulfate E containing GlcA-GalNAc(4,6-SO(4)) repeating units. To investigate the function of chondroitin sulfate E, the development of specific inhibitors of GalNAc4S-6ST is important. Because GalNAc4S-6ST requires a sulfate group attached to the C-4 hydroxyl group of the GalNAc residue as the acceptor, the sulfated GalNAc residue is expected to interact with GalNAc4S-6ST and affect its activity. In this study, we synthesized phenyl alpha- or -beta-2-acetamido-2-deoxy-beta-D-galactopyranosides containing a sulfate group at the C-3, C-4, or C-6 hydroxyl groups and examined their inhibitory activity against recombinant GalNAc4S-6ST. We found that phenyl beta-GalNAc(4SO(4)) inhibits GalNAc4S-6ST competitively and also serves as an acceptor. The sulfated product derived from phenyl beta-GalNAc(4SO(4)) was identical to phenyl beta-GalNAc(4,6-SO(4)). These observations indicate that derivatives of beta-D-GalNAc(4SO(4)) are possible specific inhibitors of GalNAc4S-6ST.

Application of fluorophore-assisted carbohydrate electrophoresis to analysis of disaccharides and oligosaccharides derived from glycosaminoglycans

Various combinations of fluorescent dyes, polyacrylamide gels, and electrophoresis buffers were tested by fluorophore-assisted carbohydrate electrophoresis (FACE) for the purpose of analyzing sulfated and nonsulfated glycosaminoglycan (GAG) oligosaccharides in which disaccharides and low-molecular weight oligosaccharides were included. A nonionic fluorescent dye was found to be suitable for analyzing sulfated disaccharides derived from sulfated GAGs (e.g., chondroitin sulfate, dermatan sulfate) because sulfated disaccharides themselves had enough anionic potential for electrophoresis. The migration rates of chondroitin sulfate (CS) disaccharides in polyacrylamide gels were affected by the number of sulfate residues and the conformation of each disaccharide. When an anionic fluorescent dye, 8-aminonaphthalene-1,3,6-trisulfonic acid disodium salt (ANTS), was coupled with sulfated GAG oligosaccharides, nearly all of the conjugates migrated at the electrophoretic front due to the added anionic potential. Nonsulfated hyaluronan (HA) oligosaccharides (2-16 saccharides) were subjected to electrophoresis by coupling with a nonionic fluorescent dye, 2-aminoacridone (AMAC), but did not migrate in the order of their molecular size. Especially di-, tetra-, hexa-, and octasaccharides of HA migrated in the reverse order of their molecular size. HA/CS oligosaccharides were able to migrate in the order of their chain lengths by coupling with an anionic fluorescent dye in a nonborate condition.

Liquid Chromatography/Mass Spectrometry Sequencing Approach for Highly Sulfated Heparin-derived Oligosaccharides

Liquid chromatography/mass spectrometry (LC/MS) is applied to the analysis of complex mixtures of oligosaccharides obtained through the controlled, heparinase-catalyzed depolymerization of heparin. Reversed-phase ion-pairing chromatography, utilizing a volatile mobile phase, results in the high resolution separation of highly sulfated, heparin-derived oligosaccharides. Simultaneous detection by UV absorbance and electrospray ionization-mass spectrometry (ESI-MS) provides important structural information on the oligosaccharide components of this mixture. Highly sensitive and easily interpretable spectra were obtained through post-column addition of tributylamine in acetonitrile. High resolution mass spectrometry afforded elemental composition of many known and previously unknown heparin-derived oligosaccharides. UV in combination with MS detection led to the identification of oligosaccharides arising from the original non-reducing end (NRE) of the heparin chain. The structural identification of these oligosaccharides provided sequence from a reading frame that begins at the non-reducing terminus of the heparin chain. Interestingly, 16 NRE oligosaccharides are observed, having both an even and an odd number of saccharide residues, most of which are not predicted based on biosynthesis or known pathways of heparin catabolism. Quantification of these NRE oligosaccharides afforded a number-averaged molecular weight consistent with that expected for the pharmaceutical heparin used in this analysis. Molecular ions could be assigned for oligosaccharides as large as a tetradecasaccharide, having a mass of 4625 Da and a net charge of -32. Furthermore, MS detection was demonstrated for oligosaccharides with up to 30 saccharide units having a mass of >10000 Da and a net charge of -60.

A unique nonreducing terminal modification of chondroitin sulfate by N-acetylgalactosamine 4-sulfate 6-o-sulfotransferase

N-Acetylgalactosamine 4-sulfate 6-O-sulfotransferase (GalNAc4S-6ST) transfers sulfate from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to position 6 of N-acetylgalactosamine 4-sulfate (GalNAc(4SO4)). We previously identified human GalNAc4S-6ST cDNA and showed that the recombinant GalNAc4S-6ST could transfer sulfate efficiently to the nonreducing terminal GalNAc(4SO4) residues. We here present evidence that GalNAc4S-6ST should be involved in a unique nonreducing terminal modification of chondroitin sulfate A (CSA). From the nonreducing terminal of CS-A, a GlcA-containing oligosaccharide (Oligo I) that could serve as an acceptor for GalNAc4S-6ST was obtained after chondroitinase ACII digestion. Oligo I was found to be GalNAc(4SO4)-GlcA(2SO4)-GalNAc(6SO4) because GalNAc(4SO4) and deltaHexA(2SO4)-GalNAc(6SO4) were formed after chondroitinase ABC digestion. When Oligo I was used as the acceptor for GalNAc4S-6ST, sulfate was transferred to position 6 of GalNAc(4SO4) located at the nonreducing end of Oligo I. Oligo I was much better acceptor for GalNAc4S-6ST than GalNAc(4SO4)-GlcAGalNAc(6SO4). An oligosaccharide (Oligo II) whose structure is identical to that of the sulfated Oligo I was obtained from CS-A after chondroitinase ACII digestion, indicating that the terminal modification occurs under the physiological conditions. When CS-A was incubated with [35S]PAPS and GalNAc4S-6ST and the 35S-labeled product was digested with chondroitinase ACII, a 35S-labeled trisaccharide (Oligo III) containing [35S]GalNAc(4,6-SO4) residue at the nonreducing end was obtained. Oligo III behaved identically with the sulfated Oligos I and II. These results suggest that GalNAc4S-6ST may be involved in the terminal modification of CS-A, through which a highly sulfated nonreducing terminal sequence is generated.

The sulfation pattern of chondroitin sulfate from articular cartilage explants in response to mechanical loading

Chondrocytes within articular cartilage experience complete unloading between loading cycles thereby utilizing mechanical signals to regulate their own anabolic and catabolic activities. Structural alterations of proteoglycans (PGs) during aging and the development of osteoarthritis (OA) have been reported; whether these can be attributed to altered load or compression is largely unknown. We report here on experiments in which the effect of intermittent loading on the fine structure of newly synthesized chondroitin sulfate (CS) in bovine articular cartilage explants was examined. Tissues were subjected for 6 days to cyclic compressive pressure using a sinusoidal waveform of 0.1, 0.5 or 1.0 Hz frequency with a peak stress of 0.5 MPa for a period of 5, 10 or 20 s, followed by an unloading period lasting 10, 100 or 1000 s. During the final 18 h of the culture, cartilage explants were radiolabeled with 50 microCi/ml D-6-[3H]glucosamine, and newly synthesized as well as endogenous CS chains were isolated after proteinase solubilization of the tissue. CS chains were depolymerized with chondroitinase ABC and ACII, and the 3H-digestion products were quantified after fractionation by high-performance anion-exchange chromatography using a CarboPac PA1 column. Intermittently applied cyclic mechanical loading did not affect the proportion of 4- and 6-sulfated disaccharide repeats, but caused a significant decrease in the abundance of the 4,6-disulfated nonreducing terminal galNAc residues. In addition, loading induced elongation of CS chains. Taken together, these data provide evidence for the first time that long-term in vitro loading results in marked and reproducible changes in the fine structure of newly synthesized CS, and that accumulation of such chains may in turn modify the physicochemical and biological response of articular cartilage. Moreover, data presented here suggest that in vitro dynamic compression of cartilage tissue can induce some of the same alterations in CS sulfation that have previously been shown to occur during the development of degenerative joint diseases such as OA.

Increased incidence of unsulphated and 4-sulphated residues in the chondroitin sulphate linkage region observed by high-pH anion-exchange chromatography

We report the isolation, characterization and quantification of five octasaccharides, four hexasaccharides and two tetrasaccharides, derived from the chondroitin sulphate (CS) linkage region of 6-8-year-old bovine articular cartilage aggrecan, following digestion with chondroitin ABC endolyase. Using a novel high-pH anion-exchange chromatography (HPAEC) method, in conjunction with one- and two-dimensional (1)H-NMR spectroscopy, we have identified the following basic structure for the CS linkage region of aggrecan: DeltaUA(beta1-3)GalNAc[0S/4S/6S](beta1-4)GlcA(beta1-3)GalNAc[0S/4S/6S](beta1-4)GlcA(beta1-3)Gal[0S/6S](beta1-3)Gal(beta1-4)Xyl, where DeltaUA represents 4,5-unsaturated hexuronic acid, and 4S and 6S represent an O-ester sulphate group on C-4 and C-6 respectively. The octa-, hexa- and tetra-saccharide linkage region fragments were used to develop a HPAEC fingerprinting method, with detection at A(232 nm), and a linear response to approx. 0.1 nmol of substance. The sulphation patterns of CS linkage regions, of up to octasaccharide in size, from articular and tracheal cartilage aggrecan were examined. The results show that in articular cartilage, for the majority (53%) of octasaccharides the 2-deoxy-2-N-acetyl amino-D-galactose (GalNAc) residues closest to the linkage region are both 6-sulphated; however, in a significant portion (34%), one or more of these GalNAc residues are unsulphated, and in 8% both are unsulphated. Approximately 10-18% of the chains have a 4-sulphated GalNAc in the first disaccharide, and 12% have a sulphated linkage region Gal residue. No evidence was found for uronic acid sulphation. These data show that there is a significant increase in the incidence of unsulphated and 4-sulphated GalNAc residues adjacent to the linkage region compared with the rest of the chain. Bovine tracheal cartilage linkage regions displayed very similar sulphation profiles to those from articular cartilage, despite the presence of a higher level of GalNAc 4-sulphation within the repeat region of the main CS chain.

Adaptation of FACE methodology for microanalysis of total hyaluronan and chondroitin sulfate composition from cartilage

Protocols for analyzing the fine structure of hyaluronan and chondroitin sulfate using fluorophore-assisted carbohydrate electrophoresis of 2-aminoacridone-derivatized hyaluronidase/chondroitinase digestion products were adapted for direct analysis of previously characterized cartilage-derived samples. The chondroitin sulfate disaccharide compositions for fetal and 68 year human aggrecan from FACE analyses were DeltaDi4S (50%), DeltaDi6S (43%), and DeltaDi0S (7%); and DeltaDi4S (3%), DeltaDi6S (96%), and DeltaDi0S (1%), respectively. The nonreducing terminal structures included predominantly 4S-galNAc with minor amounts of 6S-galNAc and Di6S for the fetal aggrecan sample and, in addition, included 4,6S-galNAc in the 68 year aggrecan sample. FACE analysis of a proteinase K digest of rat chondrosarcoma tissue gave an internal disaccharide composition for its chondroitin sulfate chains of DeltaDi0S (7%) and DeltaDi4S (93%) with no DeltaDi6S and DeltaDi4, 6S detected, while DeltaDiHA from hyaluronan was 5% of the total. Analysis of nonreducing terminal structures indicated the presence of 4S-galNAc (51%), galNAc (27%), and Di4S (22%) with no 4,6S-galNAc or Di6S detected. Unexpectedly, FACE analysis detected putative linkage oligosaccharide structures from the chondroitin sulfate chains including both unsulfated (85%) and 4-sulfated (15%) linkage oligosaccharides. Finally, the number averaged chain length estimated from the ratio of the molar fluorescence of the Deltadisaccharides to that of the nonreducing termini or the linkage oligosaccharide structures was calculated as approximately 16 kDa. A tissue glucose concentration of 0.72 g/l was also measured. These results for both samples as determined by FACE analysis were similar to results previously reported, using more labor and time intensive procedures, validating the FACE protocols.

Microanalysis of enzyme digests of hyaluronan and chondroitin/dermatan sulfate by fluorophore-assisted carbohydrate electrophoresis (FACE)

Hyaluronan and chondroitin/dermatan sulfate are glycosaminoglycans that play major roles in the biomechanical properties of a wide variety of tissues, including cartilage. A chondroitin/dermatan sulfate chain can be divided into three regions: (1) a single linkage region oligosaccharide, through which the chain is attached to its proteoglycan core protein, (2) numerous internal repeat disaccharides, which comprise the bulk of the chain, and (3) a single nonreducing terminal saccharide structure. Each of these regions of a chondroitin/dermatan sulfate chain has its own level of microheterogeneity of structure, which varies with proteoglycan class, tissue source, species, and pathology. We have developed rapid, simple, and sensitive protocols for detection, characterization and quantitation of the saccharide structures from the internal disaccharide and nonreducing terminal regions of hyaluronan and chondroitin/dermatan sulfate chains. These protocols rely on the generation of saccharide structures with free reducing groups by specific enzymatic treatments (hyaluronidase/chondroitinase) which are then quantitatively tagged though their free reducing groups with the fluorescent reporter, 2-aminoacridone. These saccharide structures are further characterized by modification through additional enzymatic (sulfatase) or chemical (mercuric ion) treatments. After separation by fluorophore-assisted carbohydrate electrophoresis, the relative fluorescence in each band is quantitated with a cooled, charge-coupled device camera for analysis. Specifically, the digestion products identified are (1) unsaturated internal Deltadisaccharides including DeltaDiHA, DeltaDi0S, DeltaDi2S, DeltaDi4S, DeltaDi6S, DeltaDi2,4S, DeltaDi2,6S, DeltaDi4,6S, and DeltaDi2,4,6S; (2) saturated nonreducing terminal disaccharides including DiHA, Di0S, Di4S and Di6S; and (3) nonreducing terminal hexosamines including glcNAc, galNAc, 4S-galNAc, 6S-galNAc, and 4, 6S-galNAc.

Human skin dermatan sulfate with sulfated and unsulfated non-reducing ends

The non-reducing ends of the preponderant dermatan sulfates of adult human skin (DS18 and DS28) can have D-GalNAc, D-GlcA and L-1doA. D-GlcA of DS18 and D-GalNAc of both DS18 and DS28 are sulfated.

Interaction between collagens and glycosaminoglycans investigated using a surface plasmon resonance biosensor

The interactions of glycosaminoglycans with collagens and other glycoproteins in extracellular matrix play important roles in cell adhesion and extracellular matrix assembly. In order to clarify the chemical bases for these interactions, glycosaminoglycan solutions were injected onto sensor surfaces on which collagens, fibronectin, laminin, and vitronectin were immobilized. Heparin bound to type V collagen, type IX collagen, fibronectin, laminin, and vitronectin; and chondroitin sulfate E bound to type II, type V, and type VII collagen. Heparin showed a higher affinity for type IX collagen than for type V collagen. On the other hand, chondroitin sulfate E showed the highest affinity for type V collagen. The binding of chondroitin sulfate E to type V collagen showed higher affinity than that of heparin to type V collagen. These data suggest that a novel characteristic sequence included in chondroitin sulfate E is involved in binding to type V collagen.

Microanalysis of glycosaminoglycan-derived oligosaccharides labeled with a fluorophore 2-aminobenzamide by high-performance liquid chromatography: application to disaccharide composition analysis and exosequencing of oligosaccharides

A series of disaccharides derived from chondroitin sulfate and heparin/heparan sulfate were derivatized at their reducing ends with a fluorophore 2-aminobenzamide to develop a sensitive microanalytical method for glycosaminoglycans. The resulting labeled compounds derived from chondroitin sulfate or heparin/heparan sulfate were well-separated and quantified by HPLC equipped with a fluorescence detector. The detection limit was a low picomole level. This method was applied to the analysis of the disaccharide composition of tetra- and hexasaccharides derived from chondroitin sulfate and heparin/heparan sulfate as well as these glycosaminoglycan polysaccharides. The method was also successfully applied to the exosequencing of chondrohexasaccharides, where the fluorophore-labeled oligosaccharides were degraded exolytically from the nonreducing ends using bacterial eliminases. The resultant labeled fragments were identified by HPLC.

Purification and characterization of chondroitin 4-sulfotransferase from the culture medium of a rat chondrosarcoma cell line

Chondroitin 4-sulfotransferase, which transfers sulfate from 3'-phosphoadenosine 5'-phosphosulfate to position 4 of N-acetylgalactosamine in chondroitin, was purified 1900-fold to apparent homogeneity with 6.1% yield from the serum-free culture medium of rat chondrosarcoma cells by affinity chromatography on heparin-Sepharose CL-6B, Matrex gel red A-agarose, 3',5'-ADP-agarose, and the second heparin-Sepharose CL-6B. SDS-polyacrylamide gel electrophoresis of the purified enzyme showed two protein bands. Molecular masses of these protein were 60 and 64 kDa under reducing conditions and 50 and 54 kDa under nonreducing conditions. Both the protein bands coeluted with chondroitin 4-sulfotransferase activity from Toyopearl HW-55 around the position of 50 kDa, indicating that the active form of chondroitin 4-sulfotransferase is a monomer. Dithiothreitol activated the purified chondroitin 4-sulfotransferase. The purified enzyme transferred sulfate to chondroitin and desulfated dermatan sulfate. Chondroitin sulfate A and chondroitin sulfate C were poor acceptors. Chondroitin sulfate E from squid cartilage, dermatan sulfate, heparan sulfate, and completely desulfated N-resulfated heparin hardly served as acceptors of the sulfotransferase. The transfer of sulfate to the desulfated dermatan sulfate occurred preferentially at position 4 of the N-acetylgalactosamine residues flanked with glucuronic acid residues on both reducing and nonreducing sides.

Up-regulation of inducible nitric oxide synthase and production of nitric oxide by the Swarm rat and human chondrosarcoma

Production of nitric oxide by solid tumors may have important ramifications regarding tumor growth and potential metastasis. This study demonstrated that the chondrosarcoma of the Swarm rat has upregulated mRNA for inducible nitric oxide synthase and produces nitric oxide. These results were confirmed by (a) the presence of a 4.4-kb band of mRNA detected by Northern blot using a probe for inducible nitric oxide synthase, (b) a 133-kDa band of protein that was detected with either a polyclonal or monoclonal antibody to the inducible nitric oxide synthase of the murine macrophage, and (c) the detection of nitrites from the culture medium of freshly cultured, isolated chondrosarcoma cells. This study showed that the expression of inducible nitric oxide synthase and the production of nitric oxide by the tumor can be increased by stimulation with endotoxin lipopolysaccharide and can be inhibited by inducible nitric oxide synthase inhibitors (L-N(g)-monomethyl arginine and aminoguanidine). Immunostaining confirmed the presence of inducible nitric oxide synthase within the tumor cells and appeared to localize the enzyme to the cytoplasm of the cells. A human chondrosarcoma was also shown to have an upregulated inducible nitric oxide synthase by both the detection of mRNA for inducible nitric oxide synthase and the presence of nitrites from the culture medium of the tumor in organ culture. Because the chondrosarcoma of the Swarm rat is a well differentiated solid tumor that rarely metastasizes, nitric oxide may be produced by the tumor to promote local growth by effects on vascular supply.

Glycosaminoglycan sulfation in human osteoarthritis. Disease-related alterations at the non-reducing termini of chondroitin and dermatan sulfate

Chondroitin lyase products of aggrecan and small proteoglycans from normal and osteoarthritic cartilages were analyzed for chain internal Deltadisaccharides and terminal mono- or disaccharides. Chondroitin and dermatan sulfate chains from arthritic cartilages were of essentially normal size and internal sulfation but had significantly altered sulfation of the terminal residues. Whereas in normal cartilage, approximately 60% of terminal GalNAc4S was 4, 6-disulfated, it was reduced to approximately 30% in osteoarthritic cartilage. This is most likely due to a lower terminal GalNAc4, 6S-disulfotransferase activity and reveals that metabolic changes in osteoarthritis can affect this distinct sulfation step during chondroitin and dermatan sulfate synthesis. GlcAbeta1,3GalNAc6S-, the mimotope for antibody 3B3(-), was present on approximately 8 and approximately 10% of chains from normal and osteoarthritic cartilages, respectively. 3B3(-) assayed by immunodot blot was within the normal range for most osteoarthritic samples, with only 5 of 24 displaying elevated reactivity. This resulted not from a higher content of mimotope, but possibly from other structural changes in the proteoglycan that increase mimotope reactivity. In summary, chemical determination of sulfation isomers at the non-reducing termini of chondroitin and dermatan sulfate provides a reliable assay for monitoring proteoglycan metabolism not only during normal growth of cartilage but also during remodeling of cartilage in osteoarthritis.

Chondrocytes in culture produce a mechanically functional tissue

A mechanically testable tissue was grown in vitro from rabbit chondrocytes that were initially plated at high density (approximately 80,000 cells/cm2). The DNA, collagen, and proteoglycan content, as well as the tissue thickness, tensile stiffness, and synthesis rates, were measured at 4, 6, and 8 weeks. The biochemical properties were similar to those for immature cartilage, with predominantly type-II collagen produced; this indicated that the cells retained their chondrocytic phenotype. The tissue formed a coherent mechanical layer with testable tensile stiffness as early as 4 weeks. The tensile elastic modulus reached 1.3 MPa at 8 weeks, which is in the range of values for native cartilage from the midzone. Collagen density was approximately 24 mg/ml at 8 weeks, which is about one-half the value for native cartilage, and the collagen fibril diameters were smaller. Chondrocytes in culture responded to culture conditions and were stimulated by cytokine interleukin-1beta. When culture conditions were varied to RPMI nutrient medium with lower fetal bovine serum and higher ascorbic acid concentrations, the thickness decreased and the modulus increased significantly. Interleukin-1beta, added to the 8-week culture for 2 weeks, caused a decrease of 60% in thickness, a decrease of 81% in proteoglycan content, and a decrease of 31% in collagen content; this is similar to the response of cartilage explants to interleukin-1beta. This cartilage analog may be useful as a model system to study structure-function relationships in cartilage or as cartilage-replacement tissue.

Differential effects of Staphylococcus aureus alpha-hemolysin on the synthesis of hyaluronan and chondroitin sulfate by rat chondrosarcoma chondrocytes

The plasma membranes of rat chondrosarcoma chondrocytes were permeabilized by treatment with alpha-hemolysin, the major toxin produced by Staphylococcus aureus, which forms small, stable, heptameric, transmembrane pores (1-2 nm in diameter) permitting influx/efflux of low-molecular-mass molecules (< or = 2000 Da). Treated chondrocytes were permeable to entry of trypan blue and exit of ATP. We describe the effects of alpha-hemolysin on the synthesis of hyaluronan (HA) and chondroitin sulfate (CS) by chondrocytes using the simple sugar [3H]glucosamine as a metabolic precursor. Chondrocytes permeabilized with alpha-hemolysin in serum-free media decreased intracellular ATP and synthesis of CS to approximately 5% of control within 2-4 h, but synthesized HA (80% of control for 8 h; approximately 65% of control at 24 h). Adding fresh medium (with or without serum) to permeabilized cells increased ATP significantly and increased HA synthesis to near initial control values. Under the same conditions, the recovery of CS synthesis approached initial levels in control but not permeabilized cells. Our model demonstrates that the biosynthesis of HA by these cells in vitro is remarkably stable to cellular perturbations which drastically inhibit synthesis of CS on proteoglycans.

Synthetic approach towards sulfated chondroitin di-, tri- and tetrasaccharides corresponding to the repeating unit

Chondroitin di-, tri- and tetrasaccharides, as well as their 4-, 6-mono- and 4,6-disulfates as their 4-methoxyphenyl glycosides, were systematically synthesized. Target disaccharides having beta GalNAc-(1-->4)-beta GlcA sequences were obtained starting from the corresponding pivotal chondroitin disaccharide precursor. A trisaccharide intermediate, which was synthesized by coupling of glucuronate imidate with a known disaccharide acceptor, was transformed into the sulfated and non-sulfated chondroitin trisaccharides. Chondroitin tetrasaccharide and the corresponding 4-disulfate, 6-disulfate as well as 4,6-tetrasulfate were also obtained based on the strategy developed above starting from the reported tetrasaccharide having [beta GalN3-(1-->4)-beta GlcA2] sequence.

Specificity of the hyaluronate lyase of group-B streptococcus toward unsulphated regions of chondroitin sulphate

The purification and properties of a hyaluronate lyase secreted by Streptococcus agalactiae, which is believed to facilitate the invasion of host tissues by the organism, have been described previously [Pritchard, Lin, Willingham and Baker (1994) Arch. Biochem. Biophys. 315, 431-436]. The specificity of the limited cleavage of chondroitin sulphate by the enzyme is the subject of this report. To simplify the task, a chondroitin sulphate from the Swarm rat chondrosarcoma, which contains only 4-sulphated and unsulphated disaccharide repeats, was used in this study. Tetrasaccharides from an ovine testicular hyaluronidase digest of the chondroitin sulphate were isolated, identified and tested as substrates of the streptococcal hyaluronate lyase. Only tetrasaccharides with an unsulphated disaccharide at the reducing end were cleaved (by elimination at the N-acetylgalactosaminidic bond). Thus chondroitin sulphate chains are cleaved by the action of this lyase at every unsulphated disaccharide repeat, but release of unsaturated unsulphated disaccharides only occurs from sites where two or more sequential unsulphated disaccharide repeats are present. Analysis of the chondrosarcoma chondroitin sulphate showed that of approximately five unsulphated disaccharide repeats per chain, two are clustered. The ability of group-B streptococcal hyaluronate lyase to cleave chondroitin sulphate may allow the organisms to invade tissues more efficiently. The demonstrated specific and highly limited cleavage of chondroitin sulphate by this bacterial lyase promises to be a useful tool in the determination of chondroitin sulphate structure and variability.

Chemical and immunological assay of the nonreducing terminal residues of chondroitin sulfate from human aggrecan

Samples of aggrecan chondroitin sulfate, isolated from normal human knee cartilages of individuals from fetal to 72 years of age, were digested with chondroitin lyases. The products were analyzed by fluorescence-based anion exchange high performance liquid chromatography to separate and quantitate nonreducing terminal structures, in addition to internal unsaturated disaccharide products. The predominant terminal structures were the monosaccharides, GalNAc4S and GalNAc4,6S as they were present on 85-90% of all chains. The remaining chains terminated with the disaccharides GlcAbeta1,3GalNAc4S and GlcAbeta1,3GalNAc6S. Marked changes in the relative abundance of these terminals were identified in the transition from growth cartilage to adult articular cartilage. First, terminal GalNAc residues were almost exclusively 4-sulfated in aggrecan from fetal through 15 years of age, but were approximately 50% 4,6-disulfated in aggrecans from adults (22-72 years of age). Second, the terminal disaccharide GlcAbeta1,3GalNAc4S was on approximately 7% of chains on aggrecan from fetal through 15 years of age, but on only approximately 3% of chains on adult aggrecan. In contrast, the proportion of chains terminating in GlcAbeta1,3GalNAc6S, approximately 9%, was unchanged from fetal to 72 years of age. This terminal disaccharide is proposed to be recognized by the widely used monoclonal antibody 3B3. However, chemical quantitation of the structure together with solid phase 3B3(-) immunoassay of fetal and adult aggrecans showed that the content of the terminal disaccharide does not necessarily correlate with immunoreactivity of the proteoglycan, as chain density and presentation on the solid phase are critical factors for recognition of chain terminals by 3B3. The quantitative results obtained from chemical analyses of all nonreducing termini of aggrecan chondroitin sulfate chains revealed important changes in chain termination that occur when cellular activities are altered as adult articular cartilage is formed after removal of growth cartilage. These findings are discussed in relation to specific enzymatic steps that generate the nonreducing termini of chains in the biosynthesis pathway of chondroitin sulfate proteoglycans and their modulation in tissue development and pathology.

Novel tetrasaccharides isolated from squid cartilage chondroitin sulfate E contain unusual sulfated disaccharide units GlcA(3-O-sulfate)beta1-3GalNAc(6-O-sulfate) or GlcA(3-O-sulfate)beta1-3GalNAc

We previously isolated novel tetrasaccharides containing 3-O-sulfated glucuronic acid from king crab cartilage chondroitin sulfate K and demonstrated that the disaccharide units containing 3-O-sulfated glucuronic acid were decomposed by chondroitinase ABC digestion (Sugahara, K., Tanaka, Y., Yamada, S., Seno, N., Kitagawa, H., Haslam, S. M., Morris, H. R., and Dell, A. (1996) J. Biol. Chem. 271, 26745-26754). The findings indicated the necessity to re-evaluate the disaccharide compositions of chondroitin sulfate preparations purified from other biological sources and analyzed using the above enzyme. In this study, to evaluate squid cartilage chondroitin sulfate E a series of even-numbered oligosaccharides were isolated after exhaustive digestion with sheep testicular hyaluronidase and subsequent fractionation by gel chromatography. The tetrasaccharide fraction was subfractionated by high performance liquid chromatography on an amine-bound silica column. Systematic structural analysis of five major fractions, h, l, m, n, and q, by fast atom bombardment mass spectrometry, enzymatic digestions in conjunction with capillary electrophoresis, and 500-MHz 1H NMR spectroscopy revealed one disulfated, three trisulfated, and one tetrasulfated tetrasaccharide structure: fraction h, GlcAbeta1-3GalNAc(4S)beta1-4GlcAbeta1-3GalNAc(4S); fraction l, GlcA(3S)beta1-3GalNAc(6S)beta1-4GlcAbeta1-3GalNAc(4S); fraction m, GlcA(3S)beta1-3GalNAc(4S)beta1-4GlcAbeta1-3GalNAc(4S); fraction n, GlcAbeta1-3GalNAc(4S,6S)beta1-4GlcAbeta1-3GalNAc(4S); and fraction q, GlcA(3S)beta1-3GalNAc(4S,6S)beta1-4GlcAbeta1-3GalNAc(4S), where 3S, 4S, and 6S represent 3-O-, 4-O- and 6-O-sulfate, respectively. The structures found in fractions h and m as well as the unsaturated counterpart of that found in fraction n have been reported, whereas those in fractions l and q are novel in that they contained unusual disulfated and trisulfated disaccharide units where GlcA(3S) is directly linked to GalNAc(6S) and GalNAc(4S,6S), respectively. These novel tetrasaccharide sequences are distinct from those found in other chondroitin sulfate isoforms and may play key roles in the biological functions and activities of chondroitin sulfate E not only from squid cartilage but also from mammalian cells and tissues.

Two distinct chondroitin sulfate ABC lyases. An endoeliminase yielding tetrasaccharides and an exoeliminase preferentially acting on oligosaccharides

Crude enzyme obtained from chondroitin sulfate-induced Proteus vulgaris NCTC 4636 has been fractionated into 1) an endoeliminase capable of depolymerizing chondroitin sulfate and related polysaccharides to produce, as end products, a mixture of Delta4-unsaturated tetra- and disaccharides and 2) an exoeliminase preferentially acting on chondroitin sulfate tetra- and hexasaccharides to yield the respective disaccharides. Isolation of the two enzymes was achieved by a simple two-step procedure: extracting the enzymes from intact P. vulgaris cells with a buffer solution of nonionic surfactant and then treating the extract by cation-exchange chromatography. Each of the enzymes thus prepared was apparently homogeneous as assessed by SDS-polyacrylamide gel electrophoresis and readily crystallized from polyethylene glycol solutions. Both enzymes acted on various substrates such as chondroitin sulfate, chondroitin sulfate proteoglycan, and dermatan sulfate at high, but significantly different, initial rates. They also attacked hyaluronan but at far lower rates and were inactive to keratan sulfate, heparan sulfate, and heparin. Our results show that the known ability of the conventional enzyme called "chondroitinase ABC" to catalyze the complete depolymerization of chondroitin sulfates to unsaturated disaccharides may actually result from the combination reactions by endoeliminase (chondroitin sulfate ABC endolyase) and exoeliminase (chondroitin sulfate ABC exolyase).

Rapid size-exclusion chromatography of proteoglycans

The separation of intact proteoglycans using high-performance liquid chromatography is not trivial because the high molarity denaturing buffers required to maintain proteoglycans in the disaggregated state create back-pressures higher than the limits of many HPLC systems. Until recently, low back-pressure requirements of HPLC size-exclusion columns precluded their use for the separation of intact proteoglycans. In this study we show that rapid size-exclusion chromatography is possible in 8 M urea buffers using a Dionex BioLC system equipped with a Bio-Rad BioSil Sec-400 column. This technique reduced the time required for size-exclusion chromatography of intact proteoglycans from approximately 18 h (Sepharose CL4B) to 25 min and in some cases improved resolution of the sample.

Organization of glycosaminoglycan sulfation in the biosynthesis of proteochondroitin sulfate and proteodermatan sulfate

Although the intermediates for sulfation of proteochondroitin and proteodermatan have been known for several decades, organizational aspects of this formation have not been clearly defined. Work in several laboratories, including our own, have indicated a pattern which strongly suggests that sulfation ordinarily takes place together with glycosaminoglycan polymerization in the same Golgi sites, and with close relationship to aspects of polymer elongation, polymer modification and polymer termination. The organization of sulfation together with polymerization may be a major factor controlling the location, type, and degree of sulfation, which in turn may direct specific functions of these proteoglycans.

Immunology of chondroitin/dermatan sulfate

Variable substitutions and locations of the sulfate esters along the backbone of chondroitin/dermatan sulfate chains, combined with their carbohydrate structures, present topographies to immune systems which can be recognized as antigenic. This has led to the development of a number of monoclonal antibodies which recognize distinct epitopes in the native structures of these glycosaminoglycan chains. In some studies, the original chondroitin/dermatan sulfate proteoglycan was digested with chondroitinase enzymes before being used as an immunogen. in this case, the linkage oligosaccharides remaining bound to the core protein contain a modified (4,5-unsaturated) hexuronic acid derivative at their non-reducing ends as a result of the eliminase mechanism of the enzyme. This 'haptenic' structure is highly antigenic and has led to the development of a number of monoclonal antibodies which recognize this structure as part of their epitopes. Examples of the use of some of these monoclonal antibodies for localization of proteoglycan structures in tissue sections and on transblots are described. The precise structures are known for only a few of the native epitopes recognized by these monoclonal antibodies. Recent analytical methods have been developed for determining structures of chondroitin sulfate oligosaccharides. An example of the use of these methods to analyze the structures of the non-reducing termini of chondroitin/dermatan sulfate chains is discussed. The results show their potential value for quantifying the native epitope recognized by a monoclonal antibody, designated 3B3, which recognizes chains terminated by glucuronic acid-N-acetylgalactosamine-6-sulfate. Such methods should be useful for determining the epitope structures for other monoclonal antibodies in this class.