SDS-PAGE analysis of purified protein. Shown are the CaroS2K (A) and CaroS2I (B). Samples were subjected to electrophoresis in 10% polyacrylamide gels, which were stained with Coomassie blue. Lane M, molecular weight standards (kDa); lane 1, cell lysate of E. coli BL21/pET32a; lane 4, cell lysate of BL21/pET30b; lanes 2 and 5, IPTG-induced cell lysates of BL21/pES2kI and BL21/pES2I, respectively; lanes 3 and 6, purified protein obtained after elution. The arrowheads indicate the killing protein of carocin S2K (A) and the immunity protein of carocin S2I (B).