The REJ domain is an extracellular module of ~700 amino acids, which is found associated with others domains, such as EGF (see <PDOC00021>), the GPS proteolytic cleavage site (see <PDOC50221>), C-type lectin (see <PDOC00537>), SUEL-type lectin (see <PDOC50228>), LRR, LDL-A, PLAT (see <PDOC50095>) or PKD (see <PDOC50093>) [1,2]. Although its function is unknown, the REJ domain has been shown to be required for cleavage to occur at the GPS [3]. It has been proposed that the REJ domain might function in ion transport homeostasis [1].

Some proteins known to contain a REJ domain are listed below:

• Sea urchin sperm receptor for egg jelly 1 (suREJ1). It binds to the fucose sulfate polymer of egg jelly to induce the sperm acrosome reaction [4].
• Sea urchin sperm receptor for egg jelly 2 (suREJ2). It is present over the entire sperm plasma membrane, but is concentrated over the sperm mitochondrion [4].
• Sea urchin sperm receptor for egg jelly 3 (suREJ3). It localizes over the acrosomal vesicle [4].
• Human autosomal dominant polycystic kidney disease protein polycystin-1. It is thought to be part of a plasma membrane signaling/ion channel complex involved in maintaining the terminally differentiated state of renal tubular epithelial cells.
• Mammalian polycystic kidney disease and receptor for egg jelly related protein (PKDREJ), a testis-specific protein whose function is unknown [5].
• Mammalian polycystic kidney disease 1-like 1 protein (PKD1L1),

The profile we developed covers the entire REJ domain.