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 of MRSA. In contemporary MRSA isolates, sensory induction of β-lactam resistance originates at the membrane-associated BlaR1, which, upon detection of β-lactam drugs, triggers a signal transduction cascade that promotes mecA induction. We hereby show that phosphorylation of BlaR1, mediated through the serine-threonine kinase, Stk1, stabilizes its membrane-spanning state and retention, allowing for proper drug sensing and subsequent signal transduction events to occur, culminating in mecA-mediated β-lactam resistance. Our results demonstrate that targeting Stk1 can potentiate synthetic lethality to β-lactams in the majority of naturally isolated strains of MRSA. We additionally present the structural and kinetic basis for a Stk1-inhibitor complex that can enable rational design of Stk1-directed anti-MRSA therapeutics in the future. Our results reveal a novel role of the STK signaling pathway in bacterial protein stabilization in the cytosolic membrane. In this study, the authors demonstrate that targeting Stk1, which activates the resistance regulator BlaR1, could potentiate synthetic lethality to β-lactams in the majority of naturally isolated strains of MRSA, using a combination of biochemical and genetic methods.