Defense against own arms: staphylococcal cysteine proteases and their inhibitors.

Staphylococcus aureus is a human pathogen causing a wide range of diseases. Most staphylococcal infections, unlike those caused by other bacteria are not toxigenic and very little is known about their pathogenesis. It has been proposed that a core of secreted proteins common to many infectious strains is responsible for colonization and infection. Among those proteins several proteases are present and over the years many different functions in the infection process have been attributed to them. However, little direct, in vivo data has been presented. Two cysteine proteases, staphopain A (ScpA) and staphopain B (SspB) are important members of this group of enzymes. Recently, two cysteine protease inhibitors, staphostatin A and staphostatin B (ScpB and SspC, respectively) were described in S. aureus shedding new light on the complexity of the processes involving the two proteases. The scope of this review is to summarize current knowledge on the network of staphylococcal cysteine proteases and their inhibitors in view of their possible role as virulence factors.