HBV core particles allow the insertion and surface exposure of the entire potentially protective region of Puumala hantavirus nucleocapsid protein

Core particles of the hepatitis B virus (HBV) potentiate the immune respons e against foreign epitopes presented on their surface. Potential insertion sites in the monomeric subunit of the HBV core protein were previously iden tified at the N- and C-terminus and in the immunodominant c/e1 region, In a C-terminally truncated core protein these sites were used to introduce the entire 120 amino acid (aa)-long potentially immuno-protective region of th e hantavirus (serotype Puumala) nucleocapsid protein, The N- and C-terminal fusion products were unable to form core-like particles in detectable amou nts. However, a suppressable stop codon located between the HBV core and th e C-terminally fused hantavirus sequence restored the ability to form parti cles ('mosaic particles'); in contrast to the C-terminal fusion product the mosaic construct allowed the formation of particles built up by the core p rotein itself and the HBV core-Puumala nucleocapsid-readthrough protein. Th e mosaic particles exposed the 120 aa region of the PUU nucleocapsid protei n on their surface as demonstrated by ELISA and immune electron microscopy applying different monoclonal antibodies, Insertion of the hantaviral seque nce into the c/e1 region not only allowed the formation of chimeric particl es, but again the surface accessibility of the sequence. HBV core antigenic ity itself was, however, reduced in the particles carrying insertions in th e c/e1 region, probably due to a masking effect of the 120 aa long insert.