Hepatitis B virus envelope protein (HBsAg)

The *hepatitis B virus envelope protein* (HBsAg) comprises three forms—large (LHBs), middle (MHBs), and small (SHBs)—all derived from the same gene and expressed on the surface of the virus and subviral particles[1][2][6]. These envelope proteins are essential for viral attachment and entry by binding to the sodium taurocholate co-transporting polypeptide (NTCP) receptor on hepatocytes, as well as being the major antigenic target for neutralizing antibodies in both natural immunity and vaccination[1][2][8]. The “a” determinant region is critical for antibody binding, while the preS1 domain mediates receptor binding. Induction of neutralizing antibodies against these proteins—through vaccination or passive immunization—blocks the entry of HBV into liver cells and forms the basis of current hepatitis B vaccines and some antiviral antibody therapies[1][8].

Other names

Hepatitis B surface antigenLHBsMHBsSHBslarge envelope proteinmiddle envelope proteinsmall envelope protein

**Neutralizing antibodies:** Bind to the “a” determinant or preS1/preS2 domains, prevent viral attachment and entry into hepatocytes **Entry inhibitors:** Compete with HBV for binding to the hepatocyte receptor NTCP by targeting preS1 domain