Identification of porcine sperm plasma membrane proteins that may play a role in sperm-egg fusion.

Sperm plasma membrane (PM) proteins that demonstrate affinity for egg PM preparations have the potential to be biologically important during sperm-egg binding and/or fusion. In this study four such proteins have been identified. To provide quantitative evidence for possible biological function, the large natural variation among different porcine sperm populations with regard to their ability to interact with the egg was compared with the relative binding of egg PM material to individual proteins. An aliquot from each of 24 porcine ejaculates was evaluated by the zona-free hamster ova bioassay and the remainder processed to yield sperm PM vesicles. Aliquots of sperm PM were solubilised, separated by SDS-PAGE, western blotted and probed with partially purified, biotinylated egg PM protein. Bound egg PM proteins were visualised on western blots by an avidin/biotin/horseradish peroxidase system and analysed by scanning laser densitometry. Four sperm PM proteins (62, 39, 27 and 7 kDa estimated molecular mass) were the predominant binders of egg PM. The amount of egg PM bound to the 62 kDa protein was significantly correlated with the ability of sperm from the 24 ejaculates to penetrate zona-free hamster ova (percentage of ova penetrated, p = 0.01, R = 0.65; number of penetrated sperm per ovum, p = 0.02, R = 0.63).