Stk1 is required for BlaR1-mediated broad-spectrum β-lactam resistance in epidemic-causing strains of Staphylococcus aureus

Sensory induction of mecA expression plays a pivotal role in mediating broad-spectrum β-lactam resistance (BBR) of MRSA. In contemporary MRSA isolates, sensory induction of BBR originates at the membrane-localized BlaR1, which, upon detection of β-lactam drugs, triggers a signal transduction cascade that promotes mecA induction. We hereby showed that phosphorylation of BlaR1, mediated through the serine-threonine kinase, Stk1, stabilizes its membrane spanning state and localization, allowing for proper drug sensing and subsequent signal transduction events to occur, culminating in mecA-mediated BBR. Our results demonstrated that targeting Stk1 could potentiate synthetic lethality to β-lactams in the majority of naturally isolated strains of MRSA. We also presented the structural and kinetic basis for a Stk1-inhibitor complex that could enable rational design of Stk1 directed anti-MRSA therapeutics in the future. Our results reveal a unique and hitherto unknown role of the STK signaling pathway in bacterial protein stabilization in the cytosolic membrane.