Immunochemical characteristics of hepatitis B e antigen subspecificities, HBeAg/1 and HBeAg/2

The molecular interrelation between hepatitis B e Ag 1 (HBeAg/1) and HBeAg/2 was examined immunochemically. Major polypeptides with m.w. around 17,000 (P17) and one minor polypeptide with m.w. 18,000 (P18) that had HBeAg activity were consistently detected in 12 different serum samples by immunoblotting analysis. To examine the polypeptide composition of HBeAg/1 and HBeAg/2, precipitin lines of HBeAg/1-anti-HBeAg/1 and HBeAg/2-anti-HBeAg/2 were separately cut from the agarose gel and analyzed by immunoblotting. HBeAg/1 and HBeAg/2 showed similar P17 and P18 compositions. Monomeric forms of P17 and P18 in a solution of 0.1% SDS showed HBeAg/1 activity, whereas polymeric forms of these polypeptides showed HBeAg/2 activity. The stability of HBeAg subspecificities to SDS and 2-ME was examined. When HBeAg was incubated in a buffer containing 0.1% SDS and 0.1% 2-ME, only the HBeAg/2 precipitin line disappeared in agarose gel concurrently with the conversion of HBeAg molecules to a monomeric from a polymeric form. In contrast, neither monomerization nor the disappearance of HBeAg/2 was seen when SDS or 2-ME was used by itself. These results indicate that hydrophobic forces and disulfide bonds may be involved in the association of P17 and P18 in serum and that HBeAg/2 activity depends upon association of HBeAg-polypeptides but that HBeAg/1 activity does not. The possibility that the epitopes of HBeAg/2 are specific for the conformation of polymerized molecules is discussed.