This domain is the bound prodomain fragment ProdP9 of the SUB1 protein present in Plasmodium falciparum. SUB1 is a serine protease that processes a subset of parasite proteins that play indispensable roles in egress and invasion. The C-terminal stalk of ProdP9 binds in the active site groove in a substrate-like manner and is truncated at the N terminus as a result of the chymotrypsin digestion step used during purification. ProdP9 is structural similar to MIC5 from Toxoplasma gondii, despite low sequence identity [1].

1: The malaria parasite egress protease SUB1 is a calcium-dependent redox switch subtilisin. Withers-Martinez C, Strath M, Hackett F, Haire LF, Howell SA, Walker PA, Christodoulou E, Dodson GG, Blackman MJ; Nat Commun. 2014;5:3726. PMID:24785947