Characterization of human zona pellucida glycoproteins.
The human egg may only be fertilized by one spermatozoon to prevent polyploidy. In most mammals, the primary block to polyspermy occurs at the zona pellucida (ZP). Little is known of the human ZP and the changes occurring following fertilization to prevent polyploidy. Using antibodies directed against synthetic peptides predicted from the human ZP2 and ZP3 cDNA, we identified ZP3 as a 53-60 kDa glycoprotein and ZP2 as a 90-110 kDa glycoprotein in prophase-I oocytes. Characterization of the ZP from metaphase II arrested eggs (inseminated-unfertilized and fertilized-uncleaved), shows no visible modification of ZP3, but demonstrates that ZP2 undergoes limited proteolysis in the amino terminal domain, to a 60-73 kDa species, denoted ZP2p, which remains linked to the proteolysed fragments by intramolecular disulphide bonds. A lack of ZP2 proteolytic activity in acrosomal supernatants is consistent with an oocyte origin for the protease. The ZP2-specific protease may be released during cortical granule exocytosis which occurs during meiotic maturation and following sperm-egg fusion as part of the block to polyspermy. Since mouse ZP2 acts as a secondary sperm receptor, it is possible that intact ZP2 binds a secondary egg binding protein, whereas cleaved ZP2 does not, suggesting a possible mechanism for the block to polyspermy.
Bauskin
A R
AR
Experimental Biology Unit, Medical Research Council, Tygerberg, Cape Town, 7505, South Africa.
Franken
D R
DR
Eberspaecher
U
U
Donner
P
P
D020101:Acrosome Reaction; D000595:Amino Acid Sequence; D004527:Egg Proteins / Q000276:immunology / Q000378:metabolism*; D005089:Exocytosis; D005260:Female; D005307:Fertilization in Vitro; D006031:Glycosylation; D006801:Humans; D008297:Male; D008562:Membrane Glycoproteins / Q000276:immunology / Q000378:metabolism*; D008677:Metaphase; D008969:Molecular Sequence Data; D009865:Oocytes / Q000502:physiology*; D011418:Prophase; D011956:Receptors, Cell Surface; D013084:Sperm-Ovum Interactions; D015044:Zona Pellucida / Q000378:metabolism*; D000072216:Zona Pellucida Glycoproteins
D004527:Egg Proteins; D008562:Membrane Glycoproteins; D011956:Receptors, Cell Surface; C000606515:ZP2 protein, human; C000606517:ZP3 protein, human; D000072216:Zona Pellucida Glycoproteins; C000606520:Zp2 protein, mouse; C000606521:Zp3 protein, mouse