Molecular characterization of covRS mutations in M1_UK Streptococcus pyogenes

Increasingly invasive Streptococcus pyogenes disease has been linked to the emergence of the M1_UK lineage. Here, we used a murine infection model to investigate the ability of M1_UK to accumulate mutations in the covRS operon which regulates up to 15% of the genome, including multiple virulence factors. Assessing an M1_UK isolate carrying an Ala111Val nonsynonymous mutation showed that in vitro, M1_UK CovR^Ala111Val was characterized by decreased SpeB expression, increased streptolysin O and hyaluronic acid capsule expression, and resistance to neutrophil killing. While Ala111Val represents a minor biochemical change, we show that CovR^Ala111Val prevents phosphorylation-dependent dimerization. Specifically, molecular dynamics simulations suggest CovR^Ala111Val destabilizes the interface between CovR monomers that facilitate dimerization, likely inhibiting CovR dimer-mediated transcriptional repression and promoting altered virulence factor expression. Ultimately, this work underscores the need for ongoing epidemiological surveillance to monitor the emergence of such mutations within the already hypervirulent M1_UK lineage.