Host cytoplasmic targets of the Staphylococcus aureus cysteine protease Staphopain A involved in host cell death

Staphylococcus aureus constitutes a major opportunistic pathogen of humans. S. aureus is readily internalized by non-professional phagocytes such as epithelial cells where it can escape from the phagosomal membrane and replicate within the host cytoplasm. Eventually, the host cells are killed whereby the bacteria exit into the extracellular environment. Previously, we had identified the staphylococcal cysteine protease staphopain A (ScpA) to be involved in this intracellular cytotoxicity in infected epithelial cells.

Targeted release of wild-typic ScpA or its active site mutant ScpA(C238A) to host cytoplasm by the otherwise non-cytotoxic laboratory strain S. aureus RN4220 demonstrated that the protease activity in host cytoplasm was required for accelerated cell death. Thus the S. aureus cysteine protease staphopain A must possess intracellular host targets. These targets, however, are currently unknown.

To identify these targets, we ectopically expressed ScpA or its proteolytically inactive variant ScpA(C238), harvested the samples at the first sign of host cell death in wild-type infected cells and compared the proteomes of infected cell cultures to each other.

We here present data on the identified target candidates as well as potential modes of action of the protease during intracellular S. aureus virulence.