The oligomerization domain of C4-binding protein (C4bp) acts as an adjuvant, and the fusion protein comprised of the 19-kilodalton merozoite surface protein 1 fused with the murine C4bp domain protects mice against malaria.

Highly purified protein antigens are usually poor immunogens; in practice, adjuvants are needed to obtain satisfactory immune responses. Plasmodium yoelii 19-kDa merozoite surface protein 1 (MSP1(19)) is a weak antigen, but mice vaccinated with this antigen in strong adjuvants can survive an otherwise lethal parasite challenge. Fusion proteins comprising this antigen fused to the oligomerization domain of the murine complement inhibitor C4-binding protein (C4bp) and a series of homologues have been produced. These C4bp domains acted as adjuvants for the fused antigen; the MSP1(19)-murine C4bp fusion protein induced protective immunity in BALB/c mice. Because this fusion protein also induced antibodies against circulating murine C4bp, distantly related C4bp oligomerization domains fused to the same antigen were tested. These homologous domains did not induce antibodies against murine C4bp and, surprisingly, induced higher antibody titers against the antigen than the murine C4bp domain induced. These results demonstrate a new adjuvantlike effect of C4bp oligomerization domains.

The toxicity of recombinant proteins in Escherichia coli: a comparison of overexpression in BL21(DE3), C41(DE3), and C43(DE3).

Two mutant strains of Escherichia coli BL21(DE3), called C41(DE3) and C43(DE3) and originally described by Miroux and Walker, are frequently used to overcome the toxicity associated with overexpressing recombinant proteins using the bacteriophage T7 RNA polymerase expression system. Even when the toxicity of the plasmids is so high that it prevents transformation in the strain BL21(DE3), the toxic proteins can often be expressed successfully in C41(DE3) and/or C43(DE3). In this work, using a range of plasmids coding for several types of proteins, we investigated in BL21(DE3), C41(DE3), and C43(DE3) their ability to undergo transformation and to express. While transformation was always possible in C41(DE3) and C43(DE3), we could not obtain transformants in BL21(DE3) for 62% of the expression vectors tested. Moreover, after induction, the expression of heterologous proteins in both mutant strains is generally better than in BL21(DE3). In this study, we also enhanced the stability of plasmids in culture during the expression of proteins by adding the par locus from the plasmid pSC101 to the vector backbone. The stability of a subset of the plasmids (measured 3 h after induction) was determined in C41(DE3) and C43(DE3) and varies from 62 to 92% for C43(DE3) and from 10 to 90% for C41(DE3). This study demonstrates the usefulness of these strains C41(DE3) and C43(DE3) in solving the problem of plasmid instability during the expression of toxic recombinant proteins.