No abstract

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.

Sec12 is a guanine nucleotide-exchange factor (GEF) of the GTPbinding protein Sar1. Its GEF activity on Sar1 makes it a key element in vesicle budding from the endoplasmic reticulum to the Golgi apparatus in yeast. Sec12 is an integral membrane glycoprotein of 70 kDa. A 38.5 kDa N-cytoplasmic domain (Sec12Áp) has been expressed in Saccharomyces cerevisiae and in Escherichia coli, puri®ed to homogeneity and crystallized. Two crystal forms were obtained. Crystal form I belongs to space group P6 2 /P6 4 , with unitcell parameters a = b = 191.7, c = 53.3 A Ê , = 120 , and diffracts to 2.6 A Ê resolution. Crystal form II belongs to space group P1, with unitcell parameters a = 52.6, b = 53.0, c = 116.8 A Ê , = 98.0, = 97.4, = 93.4 , and diffracts to 2.0 A Ê resolution.