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.