Regulation of Bacterial Two-Component Systems by Cardiolipin
The composition of phospholipid membranes is critical to regulating the activity of membrane proteins for cellular functions. Cardiolipin is a unique phospholipid present within the bacterial membrane and mitochondria of eukaryotes and plays a role in maintaining the function and stabilization of membrane proteins. Here, we report that, in the human pathogen Staphylococcus aureus, cardiolipin is required for full activity of the SaeRS two-component system (TCS). Deletion of the cardiolipin synthase genes, cls1, and cls2, reduces the basal activity of SaeRS and other TCSs. Cardiolipin is an indispensable requisite for Sae activation mediated by human neutrophil peptides (HNPs) in the stationary growth phase but not mandatory for Sae induction in the exponential growth phase. Ectopic expression with cls2, but not with cls1, in the cls1 cls2 double mutant fully restores Sae activity. Elimination of cardiolipin from the membranes results in decreased kinase activity of the sensor protein SaeS. Purified SaeS protein directly binds to cardiolipin as well as phosphatidylglycerol. A strain lacking cls2 or cls1cls2 renders S. aureus less cytotoxic to human neutrophils and less virulent in a mouse model of infection. Our findings suggest that cardiolipin enables a pathogen to confer virulence by modulating the kinase activity of SaeS and other sensor kinases upon infection.