Hepatitis B Surface Antigen preS1 Hepatitis B virus (HBV) is a human pathogen, causing serious liver disease. The HBV surface protein antigens (HBsAg) are comprised of three carboxyl co terminal HBs proteins termed large (LHBs), middle (MHBs) and small (SHBs, also called major) protein. LHBs and MHBs also share the highly hydrophobic, repetitive, membrane spanning S domain. In addition, LHBs has a 119 amino acid region called preS1.