THE SERUM ALBUMIN-BINDING REGION OF STREPTOCOCCAL PROTEIN-G - A BACTERIAL FUSION PARTNER WITH CARRIER-RELATED PROPERTIES

In this study, we have explored the use of the serum albumin-binding r egion (BE) from streptococcal protein G (SpG) as a bacterial fusion pa rtner for production of peptide immunogens. The fusion protein BB-M3, containing BE and repeated structures from the Plasmodium falciparum m alaria antigen Pf155/RESA, was efficiently purified from Escherichia c oli culture supernatants by affinity chromatography using BE as an aff inity tag. Rabbits immunized with BB-M3 in Freund's adjuvant produced high levels of antibodies which reacted with both M3 and BE in ELISA a nd stained intact Pf155/RESA in the membrane of infected erythrocytes. These antibody levels were sustained for more than 30 weeks. BB-M3 al so induced antibody responses to M3, BE and intact Pf155/RESA in a num ber of mouse strains, including several strains which are non-responde rs to the malaria sequences. In the latter mice, however, BB-M3 only a ctivated BE-specific T cells, suggesting that BE has ability to provid e carrier-related T cell help for antibody production. Moreover, the m inimal albumin-binding motif of SpG, containing only 46 amino acids, w as immunogenic in both B10.BR, B10.D2 and C57BL/6 mice (H-2(k), H-2(d) and H-2(b), respectively). These results indicate that BE has both af finity tag and carrier-related properties and suggest that fusion prot eins containing BE can be efficient tools for the generation of antibo dy responses to peptides which are weak immunogens.