Probable serine protease which plays a role in ookinete traversal of the mosquito host midgut epithelium. Hydrolysis of proteins with broad specificity for peptide bonds, and a preference for a large uncharged residue in P1. Hydrolyzes peptide amides. It is not clear how the protein localizes at the cell membrane. There is a predicted transmembrane domain encompassing the end of the catalytic domain which appears to be intracellular suggesting a single-pass type II membrane topology. Expression is restricted to mosquito host midgut stages (at protein level) (PubMed:28559405). Specifically, expression begins after gametocyte activation and peaks in mature ookinetes (at protein level) (PubMed:28559405). Not expressed in the oocyst (PubMed:28559405). Ookinetes fail to traverse the midgut epithelium resulting in a reduced number of oocysts in the gut epithelium of the mosquito host, A.gambiae or A.stephensi (PubMed:28559405, PubMed:29873127). Gametogenesis, and ookinete development and motility are normal (PubMed:28559405). The capacity to infect the mouse host by the few sporozoites made in the mosquito host is not affected (PubMed:28559405). Belongs to the peptidase S8 family. The three residues, Asp, His and Ser forming the catalytic triad are conserved (PubMed:28559405). However, the conserved motifs HGT and GTS, which encompass His and Ser residues of subtilases, respectively, are not present in PIMMS2, suggesting that the catalytic triad may be non-functional (PubMed:28559405).