The Staphylococcus aureus Ser/Thr kinase Stk1 specifically phosphorylates GraR, a transcription factor involved in global signal transduction

Staphylococcus aureus coordinates gene expression at appropriate times throughout its life cycle. The work herein demonstrates S. aureus serine-threonine kinase (Stk1) can phosphorylate the response regulator GraR in vitro. Phosphorylation was confirmed by mass spectrometry and specifically occurs at the DNA-binding domain at three threonine positions: Thr128, 130 and 149. Stk1 could not phosphorylate BceR, a GraR homolog with 56% sequence similarity. We have also discovered, through in vivo work, novel phenotypes of an S. aureus [delta]graR knockout. It is shown that GraR plays a role in proper cell growth, division and wall teichoic acid maintenance. [delta]graR mutant complemented with ectopically expressed GraR-WT reverts phenotypes to normal, whereas GraR-D51N does not. Collectively our data suggest a novel, more global, regulatory role for the GraSR system. Understanding signaling and post-translational modification networks and their downstream effects is essential in order to rationally develop new strategies to treat S. aureus infections.