IMMUNOCHEMICAL STRUCTURE OF THE CARBOXY-TERMINAL PART OF HEPATITIS-B E-ANTIGEN - IDENTIFICATION OF INTERNAL AND SURFACE-EXPOSED SEQUENCES

The C-terminal region of hepatitis B virus (HBV) e antigen (HBeAg), am ino acids (aa) 121 to 147, was characterized for reactivity with 15 mo noclonal antibodies (MAbs) and sera from 16 chronic carriers on the HB surface antigen with anti-HBe. Recombinant proteins exposing fragment s of the HBc/e polypeptide (aa 29 to 176, 60 to 176, 101 to 176, 121 t o 176, 134 to 176, 138 to 176, 139 to 176, 140 to 176, 146 to 176 and 156 to 176) fused to the N terminus of the coat protein of RNA phage f r were constructed, as were two sets of synthetic peptides covering re sidues 121 to 136 and 130 to 147, where each residue was sequentially substituted by alanine. The MAbs were found to recognize overlapping e pitopes in the fusion proteins within residues 121 to 176; however, no ne of the MAbs reacted with proteins covering residues 146 to 176 and 156 to 176. Using the synthetic peptides it was found that the MAbs re cognized epitopes at residues 128-TPPAYR-133, 133-RPPNAP-138, 135-PNAP IL-140, 138-PILSTLPE-145 and 143-LPET-146. Only MAbs recognizing the e pitope 128-TPPAYR-133 were found to react with both native HBeAg and d enatured HBcAG, whereas MAbs recognizing epitopes located closer to th e C terminus of HBeAg were reactive only with denatured HBcAg. The rec ognition sites for the human IgG1 overlapped with the epitopes of the MAbs recognizing native HBeAg. Our interpretation of these findings is that the region 124 to 133 is on the surface of native HBeAg and dena tured HBcAg, and that the adjacent region 135 to 147 is not accessible on the surface of native HBeAg, but becomes exposed on denatured HBcA g.