Streptococcal antitumor protein: expression in Escherichia coli cells and properties of the recombinant protein.

Streptococcal antitumor protein (SAGP) was produced by transformed E. coli JM103 carrying the SAGP gene downstream from the tac promoter. The purified recombinant SAGP had the same N-terminal amino acid sequence as that of the native SAGP isolated from Streptococcus pyogenes Su cells. Gel filtration analysis showed that the recombinant SAGP was a dimer, while the native SAGP was a tetramer. When the antitumor activity was tested against sarcoma 180 cells, the IC50 of the recombinant SAGP was 0.3 microgram/ml, about a quarter as active as the native SAGP. These results suggest that the quaternary structure of SAGP is important for the antitumor activity.