The effect of precursor structures on the action of glucosaminyl 3-O-sulfotransferase-1 and the biosynthesis of anticoagulant heparan sulfate

Light-induced 3-O-sulfotransferase expression alters pineal heparan sulfate fine structure. A surprising link to circadian rhythm

Proteoglycans are dominant glycoconjugates located on the cell surface and in extracellular spaces and consist of a core protein with one or more glycosaminoglycan side chains linked covalently. Heparan sulfate (HS) belongs to the family of glycosaminoglycans. HS has been assigned a variety of physiological and pathological functions, such as cell-cell adhesion, cell-matrix adhesion, cell proliferation, motility and differentiation, lipoprotein metabolism, blood coagulation, inflammation, tissue regeneration, tumor progression and invasion, pathogenic infection by bacteria, protozoa, and viruses, through specific interaction with a wide array of proteins, ligands, receptors, and pathogens (Bernfield, M., Gotte, M., Park, P. W., Reizes, O., Fitzgerald, M. L., Lincecum, J., and Zako, M. (1999) Annu. Rev. Biochem. 68, 729-777). We have shown here for the first time that light induces changes in pineal HS fine structure and that occurrence of the rare 3-O sulfation catalyzed by HS 3-O-sulfotransferase (3-OST2) is predominantly restricted to daytime pineal glands.

Biosynthesis of 3-O-sulfated heparan sulfate: unique substrate specificity of heparan sulfate 3-O-sulfotransferase isoform 5

Heparan sulfate 3-O-sulfotransferase transfers sulfate to the 3-OH position of a glucosamine to generate 3-O-sulfated heparan sulfate (HS), which is a rare component in HS from natural sources. We previously reported that 3-O- sulfotransferase isoform 5 (3-OST-5) generates both an antithrombin-binding site to exhibit anticoagulant activity and a binding site for herpes simplex virus 1 glycoprotein D to serve as an entry receptor for herpes simplex virus. In this study, we characterize the substrate specificity of 3-OST-5 using the purified enzyme. The enzyme was expressed in insect cells using the baculovirus expression approach and was purified by using heparin-Sepharose and 3',5'-ADP- agarose chromatographies. As expected, the purified enzyme generates both an antithrombin binding site and a glycoprotein D binding site. We isolated IdoUA-AnMan3S and IdoUA-AnMan3S6S from nitrous acid-degraded 3-OST-5-modified HS (pH 1.5), suggesting that 3-OST-5 enzyme sulfates the glucosamine residue that is linked to an iduronic acid residue at the nonreducing end. We also isolated a disaccharide with a structure of DeltaUA2S-GlcNS3S and a tetrasaccharide with a structure of DeltaUA2S-GlcNS-IdoUA2S-GlcNH23S6S from heparin lyases-digested 3-OST-5-modified HS. Our results suggest that 3-OST-5 enzyme sulfates both N-sulfated glucosamine and N-unsubstituted glucosamine residues. Taken together, the results indicate that 3-OST-5 has broader substrate specificity than those of 3-OST-1 and 3-OST-3. The unique substrate specificity of 3-OST-5 serves as an additional tool to study the mechanism for the biosynthesis of biologically active HS.

Chemoenzymatic synthesis of classical and non-classical anticoagulant heparan sulfate polysaccharides

Heparan sulfate (HS) polysaccharides interact with numerous proteins at the cell surface and orchestrate many different biological functions. Though many functions of HS are well established, only a few specific structures can be attributed to HS functions. The extreme diversity of HS makes chemical synthesis of specific bioactive HS structures a cumbersome and tedious undertaking that requires laborious and careful functional group manipulations. Now that many of the enzymes involved in HS biosynthesis are characterized, we show in this study how one can rapidly and easily assemble bioactive HS structures with a set of cloned enzymes. We have demonstrated the feasibility of this new approach to rapidly assemble antithrombin III-binding classical and non-classical anticoagulant polysaccharide structures for the first time.

The involvement of heparan sulfate (HS) in FGF1/HS/FGFR1 signaling complex

Fibroblast growth factor (FGF) signaling begins with the formation of a ternary complex of FGF, FGF receptor (FGFR), and heparan sulfate (HS). Multiple models have been proposed for the ternary complex. However, major discrepancies exist among those models, and none of these models have evaluated the functional importance of the interacting regions on the HS chains. To resolve the discrepancies, we measured the size and molar ratio of HS in the complex and showed that both FGF1 and FGFR1 simultaneously interact with HS; therefore, a model of 2:2:2 FGF1.HS.FGFR1 was shown to fit the data. Using genetic and biochemical methods, we generated HSs that were defective in FGF1 and/or FGFR1 binding but could form the signaling ternary complex. Both genetically and chemically modified HSs were subsequently assessed in a BaF3 cell mitogenic activity assay. The ability of HS to support the ternary complex formation was found to be required for FGF1-stimulated cell proliferation. Our data also proved that specific critical groups and sites on HS support complex formation. Furthermore, the molar ratio of HS, FGF1, and FGFR1 in the ternary complex was found to be independent of the size of HS, which indicates that the selected model can take place on the cell surface proteoglycans. Finally, a mechanism for the FGF.FGFR signaling complex formation on cell membrane was proposed, where FGF and FGFR have their own binding sites on HS and a distinct ternary complex formation site is directly responsible for mitogenic activity.

Normal levels of anticoagulant heparan sulfate are not essential for normal hemostasis

Endothelial cell production of anticoagulant heparan sulfate (HS(act)) is controlled by the Hs3st1 gene, which encodes the rate-limiting enzyme heparan sulfate 3-O-sulfotransferase-1 (3-OST-1). In vitro, HS(act) dramatically enhances the neutralization of coagulation proteases by antithrombin. The in vivo role of HS(act) was evaluated by generating Hs3st1(-/-) knockout mice. Hs3st1(-/-) animals were devoid of 3-OST-1 enzyme activity in plasma and tissue extracts. Nulls showed dramatic reductions in tissue levels of HS(act) but maintained wild-type levels of tissue fibrin accumulation under both normoxic and hypoxic conditions. Given that vascular HS(act) predominantly occurs in the subendothelial matrix, mice were subjected to a carotid artery injury assay in which ferric chloride administration induces de-endothelialization and occlusive thrombosis. Hs3st1(-/-) and Hs3st1(+/+) mice yielded indistinguishable occlusion times and comparable levels of thrombin.antithrombin complexes. Thus, Hs3st1(-/-) mice did not show an obvious procoagulant phenotype. Instead, Hs3st1(-/-) mice exhibited genetic background-specific lethality and intrauterine growth retardation, without evidence of a gross coagulopathy. Our results demonstrate that the 3-OST-1 enzyme produces the majority of tissue HS(act). Surprisingly, this bulk of HS(act) is not essential for normal hemostasis in mice. Instead, 3-OST-1-deficient mice exhibited unanticipated phenotypes suggesting that HS(act) or additional 3-OST-1-derived structures may serve alternate biologic roles.

Order out of chaos: assembly of ligand binding sites in heparan sulfate

Virtually every cell type in metazoan organisms produces heparan sulfate. These complex polysaccharides provide docking sites for numerous protein ligands and receptors involved in diverse biological processes, including growth control, signal transduction, cell adhesion, hemostasis, and lipid metabolism. The binding sites consist of relatively small tracts of variably sulfated glucosamine and uronic acid residues in specific arrangements. Their formation occurs in a tissue-specific fashion, generated by the action of a large family of enzymes involved in nucleotide sugar metabolism, polymer formation (glycosyltransferases), and chain processing (sulfotransferases and an epimerase). New insights into the specificity and organization of the biosynthetic apparatus have emerged from genetic studies of cultured cells, nematodes, fruit flies, zebrafish, rodents, and humans. This review covers recent developments in the field and provides a resource for investigators interested in the incredible diversity and specificity of this process.

A new strategy for defining critical functional groups on heparan sulfate

Heparan sulfate (HS) is a sulfated polysaccharide present on cell surfaces and in the extracellular matrix. Accumulating evidence shows that HS plays key roles in many biological systems by interacting with various proteins in a structural-specific manner. Due to technical difficulties, however, the understanding of critical functional groups on HS for protein interaction is vague. We report a rapid, convenient, sensitive, and inexpensive strategy using in vitro modification with pure enzymes and gel mobility shift assay to study the subject. We demonstrated the requirements of 3-O, 6-O sulfates and the minimal length of oligosaccharide for antithrombin III (AT-III) binding. We regenerated the binding sites for AT-III on completely desulfated N-resulfated heparin and revealed the critical modification enzymes. This new strategy could be used to identify critical functional groups on HS and to generate HS library and biologically active HS, providing information applicable to the design of HS drugs, such as anticoagulant reagents and viral infection blockers. The binding assay with fibroblast growth factors and receptors confirmed the general usefulness of this approach.

6-O-sulfotransferase-1 represents a critical enzyme in the anticoagulant heparan sulfate biosynthetic pathway

Using recombinant retroviral transduction, we have introduced the heparin/heparan sulfate (HS) 3-O-sulfotransferase 1 (3-OST-1) gene into Chinese hamster ovary (CHO) cells. Expression of 3-OST-1 confers upon CHO cells the ability to produce anticoagulantly active HS (HS(act)). To understand how 6-OST and other proteins regulate HS(act) biosynthesis, a CHO cell clone with three copies of 3-OST-1 was chemically mutagenized. Resulting mutants that make HS but are defective in generating HS(act) were single-cell-cloned. One cell mutant makes fewer 6-O-sulfated residues. Modification of HS chains from the mutant with pure 6-OST-1 and 3'-phosphoadenosine 5'-phosphosulfate increased HS(act) from 7% to 51%. Transfection of this mutant with 6-OST-1 created a CHO cell line that makes HS, 50% of which is HS(act). We discovered in this study that (i) 6-OST-1 is a limiting enzyme in the HS(act) biosynthetic pathway in vivo when the limiting nature of 3-OST-1 is removed; (ii) HS chains from the mutant cells serve as an excellent substrate for demonstrating that 6-OST-1 is the limiting factor for HS(act) generation in vitro; (iii) in contradiction to the literature, 6-OST-1 can add 6-O-sulfate to GlcNAc residues, especially the critical 6-O-sulfate in the antithrombin binding motif; (iv) both 3-O- and 6-O-sulfation can be the final step in HS(act) biosynthesis in contrast to prior publications that concluded 3-O-sulfation is the final step in HS(act) biosynthesis; (v), in the presence of HS interacting protein peptide, 3-O-sulfate-containing sugars can be degraded into disaccharides by heparitinase digestion as demonstrated by capillary high performance liquid chromatography coupled with mass spectrometry.