Proteolytic cleavage of the cell surface protein p160 is required for detachment of the fertilization envelope in the sea urchin.
Sea urchin eggs secrete a serine protease activity, CGSP1, at fertilization that is essential for the block to polyspermy. Several targets of this proteolytic activity on the plasma membrane were identified here using a cell surface biotinylation approach. Amino acid microsequencing of one of these proteins led to the identification of a 4.75-kb cDNA clone from a Strongylocentrotus purpuratus ovary cDNA library that encodes a 160-kDa protein called p160. This protein contains five CUB domains and a putative transmembrane domain suggesting that p160 is an integral membrane protein with protein-protein interaction motifs facing the extracellular matrix of the egg. Whole-mount immunolocalization studies demonstrate that p160 is on the surface of the egg, enriched at the tips of microvilli. The protein is removed at fertilization in a protease-dependent manner, and functional assays suggest that p160 serves to link the plasma membrane to the vitelline layer until fertilization. Thus, p160 is a key candidate for a vitelline-layer linker protein, the selective proteolysis of which functions in the block to polyspermy in the sea urchin egg.
Haley
Sheila A
SA
Department of Molecular and Cellular Biology and Biochemistry, Brown University, Providence, RI 02912, USA.
Wessel
Gary M
GM
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002462:Cell Membrane / Q000378:metabolism; D004625:Embryo, Nonmammalian; D010450:Endopeptidases / Q000378:metabolism; D005260:Female; D005306:Fertilization / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010063:Ovum / Q000378:metabolism*; D012617:Sea Urchins / Q000196:embryology / Q000502:physiology*; D012697:Serine Endopeptidases / Q000378:metabolism; D013084:Sperm-Ovum Interactions; D014817:Vitelline Membrane / Q000378:metabolism*
D008565:Membrane Proteins; D010450:Endopeptidases; D012697:Serine Endopeptidases