Characterization and biological properties of L-HGP, a glycoprotein from the amphibian oviduct with acrosome-stabilizing effects.

Background Information: The role of the jelly coat that surrounds the amphibian oocytes has been widely discussed, but is poorly understood. The presence of the jelly coat is essential for fertilization. However, the structure and function of the molecules that comprise the jelly coat have not been thoroughly documented. L-HGP (low-molecular-mass highly glycosylated protein) is a highly glycosylated protein that is present in the jelly coat of the toad, Bufo arenarum, oocytes and diffuses to the surrounding media. L-HGP, when purified from egg water, protects the sperm acrosome from breakdown induced by hypotonic solutions.

Results: L-HGP is an acidic glycoprotein, formed by two different subunits, linked by disulphide bonds. We raised polyclonal antibodies in rabbits against the deglycosylated protein. We determined that L-HGP is secreted along the oviduct, being hence present in all the jelly layers. The molecular mass of L-HGP is higher in the most cephalic region of the oviduct. The lower-M(r) L-HGP isoform, produced in the caudal regions of the oviduct, presents an acrosome-protecting property. L-HGP is produced by secretory cells in the oviduct and is deposited on the cilia at the oviduct lumen.

Conclusions: Biochemical characterization of L-HGP has been carried out. It is synthesized by secretory cells in the oviduct and, when secreted, is deposited over the ciliated surface of the cells. The lower-M(r) isoform, secreted by the caudal region of the oviduct, protects acrosome integrity. This isoform diffuses into the medium. The role of the higher-M(r) L-HGP isoform in fertilization remains unknown.