Hepatitis B virus infection initiates with a large surface protein-dependent binding to heparan sulfate proteoglycans

Contrary to many other viruses, the initial steps of the hepatitis B virus (HBV) infection, including attachment to hepatocytes, specific receptor interactions, and membrane fusion, are unsolved. Using HepaRG cells as an in vitro cell culture system, we here report that HBV entry into hepatocytes depends on the interaction with the glycosaminoglycan (GAG) side chains of cell-surface-associated heparan sulfate proteoglycans. Binding to GAGs requires the integrity of the pre-S domain as a part of the large (L-) viral envelope protein. HBV infection was abrogated by incubation of virions with heparin, but not the structurally related GAGs chondroitin sulfate A, B, and C. Infection was also abolished by suramin, a known inhibitor of duck hepatitis B virus infection or highly sulfated dextran sulfate. Polycationic substances such as poly-L-lysine, polybrene, and protamine also prevented infection, however, by addressing cellular components. Enzymatic removal of defined acidic carbohydrate structures from the cell surface using heparinase I/III or the obstruction of GAG synthesis by sodium chlorate inhibited HBV infection of HepaRG cells and, moreover, led to a reduction of HBV cell surface binding sites. The biochemical analysis showed selective binding of L-protein-enriched viral particles (virions or filaments) to heparin. GAG-dependent binding of HBV was improved by polyethylene glycol, a substance that specifically enhances HBV infection.

HBV infection requires the initial attachment to the carbohydrate side chains of hepatocyte-associated heparan sulfate proteoglycans as attachment receptors. This interaction initializes the multistep entry process of HBV and cannot be bypassed by alternative routes.