The cortical granule serine protease CGSP1 of the sea urchin, Strongylocentrotus purpuratus, is autocatalytic and contains a low-density lipoprotein receptor-like domain

Trypsin-like activity is secreted from eggs of many species at fertilizatio n, and this activity is believed to be critical for the block to polyspermy . Here we show that a cortical granule serine protease of sea urchins is th e major and perhaps only protease family member important for fertilization . Zymography assays suggest that the cortical granules contain a single ser ine protease that can undergo autocatalysis and is secreted upon egg activa tion. We used this finding to identify a cDNA clone from a Strongylocentrot us purpuratus ovary cDNA library that encodes a 581-amino-acid-residue prot ein that we refer to as cortical granule serine protease 1 (CGSP1). The cat alytic domain of the protein contains the essential residues of the catalyt ic triad characteristic of a member of the trypsin-like family of serine pr oteases and the N-terminus of CGSP1 resembles the ligand-binding domain of the low-density lipoprotein (LDL) receptor. Antibodies raised separately to both the protease and LDL receptor-like domains each localize to the corti cal granules of unfertilized eggs. Furthermore, the full-length form of CGS P1, as well as intermediate and active forms of the protease, is detected i n cortical granules by immunoblot analysis. Our evidence suggests that CGSP 1 is activated at fertilization and is responsible for the protease-mediate d reactions that follow cortical granule exocytosis and contribute to the b lock to polyspermy. (C) 1999 Academic Press.