Activation of streptolysin S in vitro by oligonucleotides

When washed streptococci were incubated in a phosphate buffer containing MgSO4 and maltose (Bernheimer's basal medium) and centrifuged, no hemolytic activity was detected in the supernatant. Although incubation of the spent medium with carrier oligonucleotide did not yield active hemolysin, the mixture turned to be significantly hemolytic, upon ethanol precipitation and dehydration. Oxygen stability, sensitivity to trypan blue, absence in the spent medium from strain C203U, as well as chromatographic properties demonstrated that the hemolytic activity was due to streptolysin S-oligonucleotide complex. The latent streptolysin S was detected in the streptococcal culture supernatant as well. These results indicate that, even in the absence of exogenous carrier, streptolysin S is produced extracellularly by hemolytic streptococci but suffers rapid denaturation, and that the carrier oligonucleotide serves as an effector for the toxin peptide to assume active conformation, through noncovalent interaction. Effects of several protein denaturants were investigated on the toxin activation in vitro.