Whole proteome and Secretome analysis of Staphylococcus aureus ClpXP mutant strains

Staphylococcus aureus represents an opportunistic pathogen which utilizes elaborate quorum sensing mechanisms to precisely control the expression and secretion of virulence factors. Previous studies indicated a role of the ClpXP proteolytic system in controlling pathogenesis. While detailed transcriptome data for ClpP and ClpX is available, corresponding studies on the proteome, secretome and metabolome level are largely lacking. In order to decipher the functional roles of ClpP and ClpX more globally we utilized S. aureus deletion mutants of the corresponding genes for in-depth proteomic LC-MS/MS analysis. These studies were complemented by a ClpP active site mutant strain to monitor changes solely depending on the presence and not the activity of the protein. A comparison of these strains with wild type revealed e.g. downregulation of virulence, purine/pyrimidine biosynthesis, iron uptake and stress response. Correspondingly, a reduction of a subset of purine and pyrimidine metabolite levels independently confirmed these results. Interestingly, comparison between the ClpP knockout and ClpP active site mutant strains revealed characteristic differences in UMP biosynthesis and the staphyloferrin B pathway, suggesting that the presence of the protein, although inactive, is important for maintaining these processes. These results are not only of fundamental importance to understand the cellular role of ClpXP but also have implications for the development of novel virulence inhibitor classes.