The founding member of this family of membrane-spanning serine proteases, which is restricted to Actinobacteria, is the acid resistance periplasmic serine protease MarP of Mycobacterium tuberculosis. Recent work shows that MarP is required to cleave and activate the peptidoglycan hydrolase RipA, and loss of RipA activity creates a defect in progeny separation during cell division. Therefore, the requirement for MarP in order to survive acidic conditions may be a consequence of peptidoglycan hydrolysis requirements, explaining why MarP family members are distributed more broadly in the Actinobacteria than the subset of species capable of surviving intracellularly as pathogens.
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