Editors' ChoiceMicrobiology

Virulence Through Cysteine Phosphorylation

Science Signaling  25 Sep 2012:
Vol. 5, Issue 243, pp. ec251
DOI: 10.1126/scisignal.2003635

In proteins, cysteine residues participate in various types of biochemical reactions, such as the formation of disulfide bonds, metal binding, enzymatic catalysis, alkylation, nitrosylation, and acylation. Despite its reactivity and compared with histidine, aspartate, tyrosine, threonine, and serine, examples of cysteine phosphorylation are rare. With an in vitro phosphorylation assay, Sun et al. found that proteins of the SarA and MgrA family of transcriptional regulators in Staphylococcus aureus were phosphorylated by cell extracts from wild-type bacteria. Phosphorylation depended on a conserved cysteine residue and was increased in reactions with lysates from bacteria lacking the phosphatase Stp1 or overexpressing the kinase Stk1. Mass spectrometry confirmed the phosphorylation of the cysteine residues in SarA and MgrA. Phosphorylation was reduced by adding H2O2 to oxidize the Cys residue or by the presence of chemical alkylating agents. Electrophoresis mobility shift assay using the Hla promoter and nonphosphorylated or phosphorylated SarA showed that the phosphorylated form had reduced DNA binding. Hla encodes α-hemolysin, and bacteria lacking Stp1 or SarA exhibited reduced hemolysis activity, consistent with a reduction in Hla expression and, for the Stp1-deficient bacterian, with the phosphorylated form of SarA having less DNA binding activity. Strains lacking either SarA or Stp1, or both, exhibited resistance to the antibiotic vancomycin. In vitro phosphorylation of SarA and MgrA in extracts from bacteria lacking Stp1 was reduced in the presence of vancomycin or ceftriaxone. Additionally, Ser/Thr autophosphorylation activity of Stk1 was inhibited in the presence of vancomycin or ceftriaxone. Consistent with a role for phosphorylation in virulence, mice injected with an Stp1-deficient strain of S. aureus were much less effective in causing infection in the liver and kidneys. Thus, reversible cysteine phosphorylation appears to contribute to bacterial regulation of gene expression, is important for virulence, and is a target for antibiotic therapy.

F. Sun, Y. Ding, Q. Ji, Z. Liang, X. Deng, C. C. L. Wong, C. Yi, L. Zhang, S. Xie, S. Alvarez, L. M. Hicks. C. Luo, H. Jiang, L. Lan, C. He, Protein cysteine phosphorylation of SarA/MgrA family transcriptional regulators mediates bacterial virulence and antibiotic resistance. Proc. Natl. Acad. Sci. U.S.A. 109, 15461–15466 (2012). [Abstract] [Full Text]