Heparan Sulfate 3-O-Sulfotransferase Isoform 5 Generates Both an Antithrombin-binding Site and an Entry Receptor for Herpes Simplex Virus, Type 1

Abstract

Heparan sulfates (HSs) 1 are highly sulfated polysaccharides, present on the surface of mammalian cells and in the extracellular matrix in large quantities. HSs play critical roles in a variety of important biological processes, including assisting viral infection, regulating blood coagulation and embryonic development, suppressing tumor growth, and controlling the eating behavior of mice by interacting with specific regulatory proteins (1-5). HS polysaccharides carry negative charges under physiological pH, and the disaccharide repeating units consist of 134-linked sulfated glucosamine and uronic acid. The unique sequences determine to which specific proteins HSs bind, thereby regulating biological processes.The biosynthesis of HS occurs in the Golgi apparatus. It is initially synthesized as a copolymer of glucuronic acid and N-acetylated glucosamine by D-glucuronyl and N-acetyl-D-glucosaminyltransferase, followed by various modifications (6). These modifications include N-deacetylation and N-sulfation of glucosamine, C 5 epimerization of glucuronic acid to form iduronic acid residues, 2-O-sulfation of iduronic and glucuronic acid, as well as 6-O-sulfation and 3-O-sulfation of glucosamine. Several enzymes that are responsible for the biosynthesis of HS have been cloned and characterized (see review by Esko and Lindahl (7). These enzymes have become essential tools for investigating the relationship between the structures and functions of HS.What is still unknown is the detailed mechanism for regulating the biosynthesis of HS with a defined saccharide sequence. A recent report (8) suggests that the expression levels of various HS biosynthetic enzyme isoforms contribute to the synthesis of specific saccharide sequences in specific tissues. HS N-deacetylase/N-sulfotransferase, 3-O-sulfotransferase, and 6-O-sulfotransferase are present in multiple isoforms. Each isoform is believed to recognize a saccharide sequence around the modification site in order to generate a specific sulfated saccharide sequence (8 -10). For instance, HS D-glucosaminyl 3-O-sulfotransferase (3-OST) isoforms generate 3-Osulfated glucosamine residues that are linked to different sulfated uronic acid residues. 3-OST-1 transfers sulfate to the 3-OH position of an N-sulfated glucosamine residue that is linked to a glucuronic acid residue at the nonreducing end

Chemoenzymatic Design of Heparan Sulfate Oligosaccharides*

“…Unlike HS, 11 and 12 do not contain the IdoUA2S-GlcNS motif. It is known that 3-OST-1 acts on GlcUA (or IdoUA)-GlcNS6S sequences, but not on IdoUA2S-GlcNS sequences (15,24,25). It is possible that the presence of IdoUA2S plays a role in down-regulating the level of 3-O-sulfation.…”

Anticoagulant heparan sulfate: structural specificity and biosynthesis

“…NDST is present in four different isoforms, 6-OST is present in three different isoforms and 3-OST in seven. The isoforms have slightly different substrate specificities and unique tissue specific expression patterns (34)(35)(36)(37). It has been hypothesized that cells regulate expression levels of different isoforms of the biosynthetic enzyme in order to synthesize HS with defined saccharide sequences to achieve unique biological functions (38).…”

“…HS 3-OST is present in seven isoforms, including 3-OST-1, -2, -3A, 3B, -4, -5, and 6 (33,34,43). These enzymes catalyze the transfer of a sulfo group from the sulfo donor, 3′-phosphoadenosine-5′-phosphosulfate (PAPS), to the 3-OH position of a glucosamine unit.…”

Heparin and Heparan Sulfate Biosynthesis

“…The enzyme was purified to homogeneity from L-cell conditioned medium (90) followed by cloning of the cDNA (91). The enzyme was designated HS3ST-1 since recent studies have revealed that HS3ST is present in at least six isoforms, HS3ST-1, -2, -3A -3B, -4, and -5 (Table 1) (92,93). The HS3STs, except for HS3ST-1, are type-II transmembrane proteins.…”

“…HS3ST-1 transfers sulfate to C3-position of N -sulfoglucosamine and N -sulfoglucosamine -1 (93, 94). The HS3ST isoforms have distinct expression levels in various human tissues (Table 1) (92,93).…”