1.G.6 The Hepadnaviral S Fusion Protein (HBV-S Protein)
White et al. (2008) noted that the S protein of hepatitis B virus (HBV) (226 aas and 4-5 TMSs) may mediate viral envelope-cell membrane fusion. Proteolytic processing within the S protein during virus entry may be required (Glebe and Urban 2007). The pre-S region of the viral large envelope protein is required for binding to the duck cell surface gp180 glycoprotein (Kuroki et al. 1994). Maenz et al. (2007) observed that HBV, which exhibits narrow host range specificity mediates this specificity by a means of a domain of the large surface protein, designated L. For duck hepatitis B virus, it has been shown that the pre-S domain of L binds to carboxypeptidase D, a cellular receptor present in many species on a wide variety of cell types. Nonetheless, only hepatocytes become infected. A putative fusogenic region within the amino-terminal end of the small surface protein may participate in viral entry and constitute one of the determinants of the host range of the virus (Maenz et al. 2007).