| Summary: | The intracellular human pathogen Salmonella enterica serovar Typhi (S. typhi) causes the systemic disease known as typhoid fever. This disease afflicts approximately 17,000,000 people every year, of which over 600,000 cases are fatal. === Sequencing of the S. typhi genome has allowed a better understanding of the pathogenesis caused by this bacterium. In silico research on the genome sequence identified three open reading frames, termed prpZ gene cluster, present in the Ty2 and multi-drug resistant CT18 strains of S. typhi but absent in all other sequenced serovars of S. enterica. Further analysis of this gene cluster revealed that the three genes are transcribed as an operon that encodes two eukaryotic-like Ser/Thr kinases (PrkX and PrkY) and a protein phosphatase 2C (PP2C) (PrpZ). === A previous study has shown that the recombinant His-PrpZ protein has all the hallmarks of a PP2C. Typically, PP2Cs hydrolyze phosphoserine and phosphothreonine residues. In addition, His-PrpZ was found to hydrolyze phosphotyrosine residues, making it a dual specificity phosphatase. A subsequent investigation implicates the prpZ gene cluster in S. typhi virulence as the survival of a prpZ operon deletion mutant is compromised after 48 hours of macrophage infection when compared to wild type bacteria. === It is clear from these results that the prpZ operon plays a role in the pathogenesis of S. typhi. To determine the role of these three genes in virulence, an in vitro characterization of PrkY was carried out as well as an examination of the possible physiological roles of PrpZ. === We have demonstrated that PrkY is an active protein kinase capable of phosphorylating artificial substrates in the presence of Mg2+ and/or Mn2+. Optimal phosphorylation of substrates is achieved in the presence of 5mM Mg2+ at pH 8.0. In addition, we have identified a putative interaction between PrkY and PrpZ, leading to an inhibition of the kinase activity of PrkY. While exploring the possible physiological functions of PrpZ, we have found that this protein is secreted by Ty2 S. typhi in both LB and in the low pH, low phosphate and low Mg 2+ LPM medium. === These findings suggest that PrkY and PrpZ may have antagonistic effects in a S. typhi specific virulence pathway involved in the modulation of host cell signaling by secreted bacterial virulence factors.
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