The enzyme activity of sortase A is regulated by phosphorylation in .

In many Gram-positive bacteria, the transpeptidase enzyme sortase A (SrtA) anchors surface proteins to cell wall and plays a critical role in the bacterial pathogenesis. Here, we show that in , an important human pathogen, the SrtA is phosphorylated by serine/threonine protein kinase Stk1. SrtA can also be phosphorylated by small-molecule phosphodonor acetyl phosphate (AcP) . We determined that various amino acid residues of SrtA are subject to phosphorylation, primarily on its catalytic site residue cysteine-184 in the context of a bacterial cell lysate. Both Stk1 and AcP-mediated phosphorylation inhibited the enzyme activity of SrtA . Consequently, deletion of gene (i.e. ) encoding serine/threonine phosphatase Stp1, the corresponding phosphatase of Stk1, caused an increase in the phosphorylation level of SrtA. The deletion mutant mimicked the phenotypic traits of deletion mutant (i.e. attenuated growth where either haemoglobin or haem as a sole iron source and reduced liver infections in a mouse model of systemic infection). Importantly, the phenotypic defects of the deletion mutant can be alleviated by overexpressing . Taken together, our finding suggests that phosphorylation plays an important role in modulating the activity of SrtA in