Nature and mechanism of action of the CAMP protein of group B streptococci

Abstract

The extracellular product of group B streptococci responsible for the CAMP reaction was purified to near homogeneity. It is a relatively thermostable protein having a molecular weight of 23,500 and an isoelectric pH of 8.3. It was found that the CAMP reaction could be simulated by substituting [14C]glucose-containing liposomes prepared from sphingomyelin, cholesterol, and dicetyl phosphate for sheep erythrocytes. In the belief that the liposome system is a valid model, the mechanism of the CAMP reaction was further investigated by using liposomes in which N-acylsphingosine (ceramide) was substituted for sphingomyelin. In this system disruption of liposomes, as measured by release of trapped [14C]glucose, was effected by CAMP protein alone. As judged from thin-layer chromatography, CAMP protein caused no reduction in the amount of ceramide present in ceramide-containing liposomes, nor were split products demonstrable. However, binding of CAMP protein to ceramide-containing liposomes could be shown. It is inferred that in sheep erythrocytes CAMP protein reacts nonenzymatically with membrane ceramide formed by the prior action of staphylococcal sphingomyelinase and that binding of CAMP protein to ceramide disorganizes the lipid bilayer to an extent that results in cell lysis.