Stk1-mediated phosphorylation stimulates the DNA-binding properties of the Staphylococcus aureus SpoVG transcriptional factor

The stage V sporulation protein G (SpoVG) homolog of Staphylococcus aureus is a modulator of virulence factor synthesis and antibiotic resistance in this clinically important gram-positive pathogen. Here we demonstrate that SpoVG can be phosphorylated by the staphylococcal Ser/Thr protein kinase Stk1 and that phosphorylation positively affects its DNA-binding properties. Mass spectrometric analyses and site directed mutagenesis identified Thr4, Thr13, Thr24 and Ser41 as phospho-acceptors. Stk1-mediated phosphorylation markedly enhanced the DNA binding activity of SpoVG towards the promoter regions of target genes such as capA, lip, and nuc1. Similarly, trans-complementation of the S. aureus ΔyabJ-spoVG mutant SM148 with a SpoVG derivative that mimics constitutive phosphorylation, SpoVG_Asp, exhibited capA, lip, and nuc1 transcript levels that were comparable to the levels seen with the wild-type, whereas trans-complementation with a phosphoablative variant of SpoVG (SpoVG_Ala) produced transcript levels similar to the ones seen in SM148. Our data suggest that the expression/activity of this transcription factor is tightly controlled in S. aureus by transcriptional, post-transcriptional and post-translational mechanisms.