Serine protease which plays an essential role in merozoite invasion of and egress from host erythrocytes by processing and activating various merozoite surface and parasitophorous vacuole proteins. Mediates the proteolytic maturation of serine proteases SERA4, SERA5 and SERA6 just prior to merozoite egress. Prior to merozoite egress, cleaves merozoite surface proteins MSP1, MSP6 and MSP7, which form the MSP1/6/7 complex, and thereby may prime the parasite cell surface for invasion of fresh erythrocytes. Prior to merozoite egress, cleaves MSRP2 converting it to MSRP2 p25 form, and RAP1 converting it to RAP1 p67 form. Hydrolysis of proteins with broad specificity for peptide bonds, and a preference for a large uncharged residue in P1. Hydrolyzes peptide amides. Binds 3 Ca(2+) ions per subunit. p54 and probably p47 forms are inhibited by the non-covalent interaction with the cleaved propeptide (By similarity). Inhibited by subtilisin propeptide-like protein SUB1-ProM (By similarity). Heterodimer between p54 form and propeptide p31; the interaction inhibits p54 catalytic activity. At the schizont stage, in merozoites, localizes to dense secretory granules called exonemes (PubMed:29074774). Just prior to egress secreted into the parasitophorous vacuole (By similarity). Expressed during the parasite blood stage, specifically in schizonts (at protein level). The propeptide (p31) is cleaved, probably by autocatalysis, during the transport to or in the Golgi apparatus, and remains non-covalently associated with the p54 form as an inhibitor. p54 is further cleaved into the p45 form (By similarity). This cleavage is likely occurring in the exoneme prior to egress and is mediated by PMX/plasmepsin X (PubMed:29074774). The disulfide bond between Cys-521 and Cys-534 acts as a redox-sensitive disulfide switch. The oxidized form is required for catalytic activity. The relevance of N-glycosylation is not clear. In an insect expression system, SUB1 glycosylation appears to affect its processing into the active mature form suggesting that SUB1 may not be N-glycosylated in parasites. Belongs to the peptidase S8 family.