Catalytic component of the signal peptidase complex (SPC) which catalyzes the cleavage of N-terminal signal sequences from nascent proteins as they are translocated into the lumen of the endoplasmic reticulum (PubMed:18054093, PubMed:30127496). Specifically cleaves N-terminal signal peptides that contain a hydrophobic alpha-helix (h-region) shorter than 18-20 amino acids (By similarity). Cleavage of hydrophobic, N-terminal signal or leader sequences from secreted and periplasmic proteins. Phosphorylation increases catalytic activity (PubMed:18054093). Ca(2+) slightly increases catalytic activity in vitro (PubMed:18054093). Component of the signal peptidase complex (SPC) composed of a catalytic subunit SEC11/SPC21 and three accessory subunits SPC25, SPC3/SPC22, SPC1/SPC12 (PubMed:30127496). Within the complex, interacts with SPC25 (PubMed:30127496). The complex induces a local thinning of the ER membrane which is used to measure the length of the signal peptide (SP) h-region of protein substrates (By similarity). This ensures the selectivity of the complex towards h-regions shorter than 18-20 amino acids (By similarity). The complex interacts with the SEC61 channel-forming translocon complex and is involved in the import of classical signal sequence-containing proteins (PubMed:30127496). Partially colocalizes with SPC25 in the endoplasmic reticulum. Expressed during the asexual blood stage, including ring, trophozoite and schizont stages (at protein level). The C-terminal short (CTS) helix is essential for catalytic activity (By similarity). It may be accommodated as a transmembrane helix in the thinned membrane environment of the complex, similarly to the signal peptide in the complex substrates (By similarity). Phosphorylated (PubMed:18054093). Phosphorylation increases catalytic activity (PubMed:18054093). Causes a reduction in parasite growth in the host erythrocyte (PubMed:30127496, PubMed:18054093). Reduces levels of the mature form of SERA5 but not of PEXEL-containing proteins (PubMed:30127496). Belongs to the peptidase S26B family.