Required for virulence (PubMed:18479146). Acts both as a protease, which degrades and/or refolds damaged substrate targets, and as a chaperone (PubMed:18479146, PubMed:20061478). Plays an important role in the stress response network mediated through the two-component regulatory system MprAB and SigE signaling networks (PubMed:20061478). May utilize its PDZ domain to recognize and process misfolded proteins at the cell membrane, leading to activation of the MprAB and SigE signaling pathways and subsequent establishment of a positive feedback loop that facilitates bacterial adaptation (PubMed:20061478). Interacts with and potentially cleaves several proteins, including the 35 kDa antigen PspA (PubMed:21445360). Proteolytic cleavage of PspA may help to maintain cell envelope homeostasis in Mycobacterium and regulate specific stress response pathways during periods of extracytoplasmic stress (PubMed:21445360). In vitro, exhibits proteolytic activity against the artificial substrate beta-casein (PubMed:18479146, PubMed:20061478). Acts on substrates that are at least partially unfolded. The cleavage site P1 residue is normally between a pair of hydrophobic residues, such as Val-|-Val. Probably regulates its own activity by autocleavage, which removes the PDZ domain (PubMed:18479146). Inhibited by the serine protease inhibitor diisopropylfluorophosphate (DFP) (PubMed:20061478). Inhibited by fluoroquinolone such as ciprofloxacin, moxifloxacin and ofloxacin and their analogs (PubMed:23440996). Optimum pH is between 7.0 and 8.5. Optimum temperature is 37 degrees Celsius. Homotrimer (PubMed:18479146). Interacts with numerous proteins, including the 35 kDa antigen PspA (PubMed:21445360). Traffics from the cytoplasm through the cell membrane to the cell wall where it is autoprocessed and eventually secreted into the culture filtrate protein. Transcribed from three distinct promoters, one that is located in the intergenic region between mprB and pepD, one that overlaps with the translational start site for mprA, and one upstream of mprA that resides in a predicted SigE-regulated promoter region. Each subunit is composed of an N-terminal cytoplasmic domain, a transmembrane domain, a catalytic serine protease domain, and a single C-terminal PDZ domain (PubMed:18479146, PubMed:21445360). The protease domains form the central core of the trimer and the PDZ domains extend to the periphery (PubMed:18479146). PDZ domain is required for protease activity (PubMed:20061478). Deletion of the gene triggers a stress response under physiological conditions that results in the up-regulation of a number of gene products, including sigE, and a subset that are regulated by SigE (PubMed:20061478). Deletion mutant shows attenuated virulence in a mouse model of infection (PubMed:18479146). Belongs to the peptidase S1C family.