Identification of polymerized-albumin receptor domain in the pre-S2 region of hepatitis B virus surface antigen M protein.

The pre-S2-coding region in the hepatitis B virus surface antigen M (P31; pre-S2 + S) protein gene was modified to identify a polymerized-albumin receptor (PAR) domain by deleting restriction fragments or performing site-directed mutagenesis. The modified M protein genes (M-P31x; x = d, e, f, h and i) were cloned into the yeast generalized-expression vector pGLD 906-1 and expressed in Saccharomyces cerevisiae under the control of yeast glyceraldehyde-3-phosphate dehydrogenase gene promoter. The PAR activities of these gene products suggested that the PAR domain is located in the hydrophilic and highly conserved domain in the pre-S2 region (around Leu12 approximately Tyr21). Antibodies specific for a pre-S2 peptide (Phe8 approximately Pro34, subtype adr), which covers the PAR domain, were purified from sera of rabbits immunized with yeast-derived M protein particles having a natural PAR domain. Immune electron microscopy showed that the purified antibodies could aggregate HBV particles. Therefore, it was speculated that the PAR domain overlapped with the dominant virus-neutralizing and virus-protecting epitopes.