Heparan sulfate, a highly sulfated polysaccharide, is present on the surface of mammalian cells and in the extracellular matrix in large quantities. The sulfated monosaccharide sequences within heparan sulfate determine the protein binding specificity and regulate biological functions. Numerous viruses and parasites utilize cell surface heparan sulfate as receptors to infect target cells. Due to the structural complexity of heparan sulfate, it was considered a nonspecific cell surface receptor by interacting with the positive motifs of viral proteins. However, recent studies reveal that heparan sulfate plays multiple roles in assisting viral infection, and the activities in promoting viral infections require unique monosaccharide sequences, suggesting that heparan sulfate could serve as a specific receptor for viral infection. The currently available techniques for the structural analysis of heparan sulfate provide essential information about the specific roles of heparan sulfate in assisting viral infections. The knowledge accumulated in this fast growing field will permit us to have a better understanding of the mechanism of viral infection and will lead to the development of new antiviral agents.

Herpes simplex virus type 1 utilizes cell surface heparan sulfate as receptors to infect target cells. The unique heparan sulfate saccharide sequence offers the binding site for viral envelope proteins and plays critical roles in assisting viral infections. A specific 3-O-sulfated heparan sulfate is known to facilitate the entry of herpes simplex virus 1 into cells. The 3-O-sulfated heparan sulfate is generated by the heparan sulfate D-glucosaminyl-3-O-sulfotransferase isoform 3 (3-OST-3), and it provides binding sites for viral glycoprotein D (gD). Here, we report the purification and structural characterization of an oligosaccharide that binds to gD. The isolated gDbinding site is an octasaccharide, and has a binding affinity to gD around 18 M, as determined by affinity coelectrophoresis. The octasaccharide was prepared and purified from a heparan sulfate oligosaccharide library that was modified by purified 3-OST-3 enzyme. The molecular mass of the isolated octasaccharide was determined using both nanoelectrospray ionization mass spectrometry and matrix-assisted laser desorption/ionization mass spectrometry. The results from the sequence analysis suggest that the structure of the octasaccharide is a heptasulfated octasaccharide. The proposed structure of the octasaccharide is ⌬UA-GlcNSIdoUA2S-GlcNAc-UA2S-GlcNS-IdoUA2S-GlcNH 2 3S6S. Given that the binding of 3-O-sulfated heparan sulfate to gD can mediate viral entry, our results provide structural information about heparan sulfate-assisted viral entry.Heparan sulfates (HS), 1 highly sulfated polysaccharides, are present on the surface of mammalian cells and in the extracellular matrix in large quantities. HS play critical roles in a variety of biological interactions, 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 is initially synthesized as a copolymer of glucuronic acid and N-acetylated glucosamine by D-glucuronyl and N-acetyl-D-glucosaminyl transferase, followed by various modifications (6). These modifications include C 5 -epimerization of glucuronic acid to form iduronic acid residues, 2-O-sulfation of iduronic and glucuronic acid, N-deacetylation and N-sulfation of glucosamine, as well as 6-O-sulfation and 3-O-sulfation of glucosamine. Numerous HS biosynthetic enzymes have been cloned and characterized (for review, see Esko and Lindahl (7)).The specific sulfated saccharide sequences play critical roles in determining the functions of HS. A recent report suggests that the expression levels of various isoforms of each class of HS biosynthetic enzyme contribute to the synthesis of specific saccharide sequences in specific tissues (8). HS N-deacetylase/ N-sulfotransferase, 3-O-sulfotransferase, and 6-O-sulfotransferase are present in multiple isoforms, and each isoform is believed to recognize the saccharide sequence around the modification site to generate a specific sulfated saccharid...

A highly sensitive method to identify and quantify heparan sulfate (HS) oligosaccharides by using nano-electrospray ionization mass spectrometry (nESI-MS) is described. The new approach allows us to detect approximately 50 nM of a chemically synthesized pentasaccharide with a structure of GlcNS6S-GlcA-GlcNS6S-IdoA2S-GlcNS6SOMe (3-OH pentasaccharide). Typically, solutions were infused for a total of 5 min, at an average flow rate of 30 nl/min, and the remaining sample was recovered from the nanovial. The spectra shown were obtained by summing scans for 1--3 min. Hence, our data indicated that as little as 3 x 10(-15) mole of the pentasaccharide was consumed to obtain a reasonable spectrum at the concentration as low as 50 nM. In addition, we found a linear relationship between the relative response of the molecular ion and the concentration of the analyzed 3-OH pentasaccharide, demonstrating that this approach can be used to determine the amount of HS oligosaccharides. To this end, a 3-O-sulfated pentasaccharide was prepared by incubating the 3-OH pentasaccharide with purified HS 3-O-sulfotransferase-1 and 3'-phosphoadenosine-5'-phospho[(35)S]sulfate. The resulting 3-O-sulfated pentasaccharide was purified and analyzed by nESI-MS. Based on the standard curve constructed with the 3-OH pentasaccharide, we calculated the concentration of the 3-O-sulfated pentasaccharide by the relative response. The result indicates that this value is very close to the value measured by [(35)S]sulfate radioactivity. In conclusion, nESI-MS provides both high sensitivity and the capacity to quantify HSs. This approach is likely to become a very important tool for structural analysis and sequencing of HS and heparin oligosaccharides.

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