Probable serine protease, which plays a crucial role in the fertility of male mice including sperm migration and sperm-egg interaction. Mainly found in the membrane part of the cells and only in small amounts in the cytosol. Present primarily in the cytosol and only in minor amounts in the membrane fraction. Additional isoforms seem to exist. Only detected in testis. Expressed in spermatogonia, spermatocytes, spermatids, Leydig and Sertoli cells. Expressed in prostate cancer and ovarian cancer (at protein level). Belongs to the peptidase S1 family. Controversial data exist concerning the topology of PRSS55. One study in mouse shows that PRS55 is a GPI-anchored protein (By similarity). An other study does not confirm the GPI-anchor status of PRSS55 (PubMed:18844450). However as a GPI-anchor motif is detected, the possibility of a GPI-anchor instead of a single-pass type I membrane protein is probable.