Inactive metacaspase which plays a role in parasite bloodstream form growth and in parasite virulence within the mammalian host. Secreted by the parasite bloodstream form (PubMed:21949125). Membrane localization is required for MCA4 processing but is dispensable for MCA4 secretion, and parasite growth and virulence in the mammalian host (PubMed:21949125). Specifically expressed in the bloodstream form (at protein level). Palmitoylated. Proteolytic cleavage by MCA3 occurs prior or during secretion and requires MCA4 membrane localization (PubMed:21949125). Cleavage is dispensable for secretion and parasite growth and virulence in the mammalian host (PubMed:21949125). In vitro, can be cleaved by MCA2 but specifically cleaved by MCA3 in vivo (PubMed:21949125). Knockouts in the bloodstream form have an initial slower growth rate in vitro which reaches wild-type levels after several weeks of culture (PubMed:21949125). Knockouts in the bloodstream form have a reduced growth rate and virulence in infected mice (PubMed:21949125). RNAi-mediated knockdown at the bloodstream stage results in a more severe phenotype characterized by a growth arrest due to a failure to undergo cytokinesis (PubMed:21949125). Belongs to the peptidase C14B family. In contrast to other metacaspases (MCA) of the peptidase C14B family, contains a serine residue at the position of the canonical catalytic cysteine and has been shown to lack protease activity.