DISCOVERY OF LIGNIN SULFATE AS A POTENT INHIBITOR OF HSV ENTRY INTO CELLS

The herpes virus family consists of more than hundred members that infect organisms, of which eight, differing markedly in the biology are known to infect humans. HSV- I is the most common one, causing oral lesions and sporadic encephalitis. These infections are highly prevalent affecting at least one in three individuals in the United States.The entry of the herpes virus into the cell is a two-step process. The initial step involves the cell surface heparan sulfate and glycoproteins in the viral envelope which enables the virus to penetrate into the cell. The second step is the fusion step. Depending on the nature of interaction and size of HS chain, a single chain may bind multiple viral ligands on a virion. There is substantial evidence showing that HS plays an important role in viral binding.HS is a heterogeneous, linear sulfated oligosaccharide composed of alternating glucosamine and uronic acid residues, which could specify distinct receptor for various viral ligands. HS, present on most exposed cell surfaces, make an ideal snare for the capture of most herpes viruses and may facilitate subsequent interactions with other co-receptors required for entry. Number of viruses, including HSV- I, HSV- II, HIV- I and dengue virus use sites of HS as receptors for binding to cells. Recently 2000 Liu et.al have characterized a HS based octasaccharide that binds to HSV-I gD. The distinguished feature in the composition of the octasaccharide is the presence of 3-O-sulfate glucosamine residue, which is an uncommon structural modification in HS. Its presence in the HSV-I gD binding sequence may confer specificity of interaction and assist HSV-I entry into the cell.Numerous sulfated molecules have been explored as mimics of HS in the inhibition of HSV-1 entry into cells. To date, most of the sulfated molecules screened for anti-viral activity have been carbohydrates. So, we reasoned that it should be possible to mimic critical interactions of HS with one or more viral glycoprotein using synthetic, non-polysaccharide, sulfated compounds. Further, it may be possible to mimic specific sequence(s) in HS, which play a role in HSV infection, with small synthetic, sulfated, non-carbohydrate molecules. In a search for synthetic mimics of HS as inhibitors of HSV-I infection, we screened a small, synthetic, sulfated flavonoids to discover a potent inhibitory activity arising from sulfation of a macromolecule present as an impurity in a crude natural product.The active principle was identified through an array of biophysical and chemical analyses as lignin sulfate, a heterogeneous; polydisperse network polymer composed of substituted phenylpropanoid monomers. Further, LC-MS with APCI in negative ionization mode, which have been reported in here for the first time for analysis of lignin, has been successfully used to deduce oligomeric structures present in the precursor of the active macromolecule based on the spectrum of the depolymerized lignin. This corroborates well with the structural information obtained using other analytical techniques. We hypothesize that the structural heterogeneity and polydispersity of lignin coupled with optimal combination of sulfate charge and hydrophobicity result in high potency. Given that the native lignin is inactive, lignin sulfate discovered here provides a variety of organic scaffolds that with the critical sulfate groups in space can mimic the HSV-I gD binding sequence