Identification of structural motifs and amino acids within the structure of human heparan sulfate 3-O-sulfotransferase that mediate enzymatic function

Theoretical Study on Storage and Release of Firefly Luciferin

Among numerous bioluminescent organisms, firefly is the most studied one. Recent experiment proposed that sulfoluciferin (SLH₂ ) may serve as a storage form of luciferin (LH₂ ). In the present article, we employed density functional theory calculation to uncover the mechanism and detailed process of the storage and release reactions. Due to lack of available crystallographic structure of the related enzyme, the calculation was performed on a model system. For the storage reaction, possible amino acid residues were used for imitating the protein environment. For the release reaction, the dielectric constant of 3.0 was employed to simulate the polarity of the protein cavity. The computational results indicated that the reactions from LH₂ to SLH₂ and from SLH₂ to LH₂ are both exergonic, which favor the storage and release processes and coincide with the experimental observation. Basing on experimental and current theoretical study, we supplemented the stages of LH₂ storage and release in the entire bioluminescent cycle of firefly. The current theoretical calculation could inspire the study on LH₂ storage and release of other bioluminescent organisms.

Affinity, kinetic, and structural study of the interaction of 3-O-sulfotransferase isoform 1 with heparan sulfate

The 3-O-sulfonation of glucosamine residues in heparan sulfate (HS) by 3-O-sulfotransferase (3-OST) is a key substitution that is present in HS sequences of biological importance, in particular HS anticoagulant activity. Six different isoforms of 3-OST have been identified that exhibit different substrate specificity. In this paper the affinity and kinetics of the interaction between 3-O-sulfotransferase isoform 1 (3-OST-1) and HS have been examined using surface plasmon resonance (SPR). 3-OST-1 binds with micomolar affinity to HS (K(D) = 2.79 microM), and this interaction is apparently independent of the presence of the coenzyme, 3'-phosphoadenosine 5'-phosphosulfate (PAPS). A conformational change in the complex has also been detected, supporting data from previous studies. Selected 3-OST-1 mutants have provided valuable information of amino acid residues that participate in 3-OST-1 interaction with HS substrate and its catalytic activity. The results from this study contribute to understanding the substrate specificity among the 3-OST isoforms and in the mechanism of 3-OST-1-catalyzed biosynthesis of anticoagulant HS.

Oligosaccharide library-based assessment of heparan sulfate 6-O-sulfotransferase substrate specificity

Heparan sulfate mediates numerous complex biological processes. Its action critically depends on the amount and the positions of O-sulfate groups (iduronyl 2-O-sulfates, glucosaminyl 6-O- and 3-O-sulfates) that form binding sites for proteins. The structures and distribution of these protein-binding domains are influenced by the expression and substrate specificity of heparan sulfate biosynthetic enzymes. We describe a general approach to assess substrate specificities of enzymes involved in glycosaminoglycan metabolism, here applied to 6-O-sulfotransferases involved in heparan sulfate biosynthesis. To understand how 2-O-sulfation affects subsequent 6-O-sulfation reactions, the substrate specificity of 6-O-sulfotransferase 3 was probed using substrates from a heparin-based octasaccharide library. Purified 3H-labeled N-sulfated octasaccharides from a library designed to sample 2-O-sulfated motifs were used as sulfate acceptors, 3'-phosphoadenosine 5'-phosphosulfate as sulfate donor, and cell extract from 6-O-sulfotransferase 3-overexpressing 293 cells as enzyme source in the 6-O-sulfotransferase-catalyzed reactions. The first 6-O-sulfate group was preferentially incorporated at the internal glucosamine unit of the octasaccharide substrate. As the reaction proceeded, the octasaccharides acquired three 6-O-sulfate groups. The specificities toward competing octasaccharide substrates, for 6-O-sulfotransferase 2 and 6-O-sulfotransferase 3, were determined using overexpressing 293 cell extracts and purified octasaccharides. Both 6-O-sulfotransferases showed a preference for 2-O-sulfated substrates. The specificity toward substrates with two to three 2-O-sulfate groups was three to five times higher as compared with octasaccharides with no or one 2-O-sulfate group.

Sulfotransferases and sulfated oligosaccharides

Structural diversity of the sugar chains attached to proteins and lipids that arises from the variety of combinations of different monosaccharides, different types of linkages, branch formation and secondary modifications, such as sulfation, possesses a large amount of biological information. A number of proteoglycans, glycoproteins, and glycolipids contain sulfated carbohydrates. Their sulfate groups provide a negative charge and play a role in a specific molecular recognition process. The sulfation of oligosaccharides is catalyzed by the Golgi-associated sulfotransferases. Recent success in molecular cloning of these sulfotransferases has brought a breakthrough in the understanding of biological function of sulfated oligosaccharides in a variety of contexts. Investigations on the relationship of sulfated oligosaccharides to human diseases including hereditary deficiency, cancer, inflammation, and infection may provide hints for curing disastrous diseases.

Expression in Escherichia coli, purification and kinetic characterization of human heparan sulfate 3-O-sulfotransferase-1

Heparan sulfate (HS) glycosaminoglycans are a structurally diverse class of complex biomolecules that modulate many important events at the cell surface and within the extracellular matrix and whose structural heterogeneity derives largely from the sequence-specific N- and O-sulfations catalyzed by an extensive repertoire of sulfating enzymes. We have expressed the human heparan sulfate 3-OST-1 isoform in Escherichia coli and subsequently purified a soluble, active enzyme. To assess its functionality, we determined the kinetic parameters for the recombinant 3-O-sulfotransferase-1 using a radiochemical assay that directly measures the 3-O-sulfation of unlabeled bovine kidney heparan sulfate in vitro using [(35)S]PAPS as the sulfate donor. The apparent K(m) values measured were in the low micromolar range (K(HS)(m) = 4.3 microM; K(PAPS)(m) = 38.6 microM); V(max) values of 18 and 21 pmol sulfate/min/pmol of enzyme for HS and PAPS, respectively. These values were compared with kinetic parameters likewise measured for recombinant 3-OST-1 purified from baculovirus-infected sf9 cells. The two enzymes appear to modify heparan sulfate in vitro to roughly the same extent and with comparable specificities. The expression of 3-OST-1 in E. coli represents an important step in subsequent structure-function studies.