After an epididymal successful transit, a mature spermatozoid released through masculine reproductive routes, is capable to attach itself to oocyte’ membrane and initiate the process of fertilization. This is an important domain of scientific research: spermatozoids binding with the oocyte and serious revisions to traditional theories have been made in the past years.
Among the first fertilization studies, connected to the mechanisms of sperm-egg recognition, and gametes surfaces were made by Frank Rattray Lillie and Colab between 1914 and 1919, but those studies haven’t brought, until now, significant improvements to identifying the molecules responsible with gametes interaction.
A pellucid zone glycoprotein called ZP3 is the most important constituent in the egg-sperm binding reaction. Other less important egg components are: ZP2 also found in the pellucid zone and a large number of oocyte’ plasmatic membrane polypeptides involved in a secondary reaction necessary to fecundation. It is possible that, in the first ZP3 adhesion reaction, more than one spermatozoid is likely to trigger an acrozomal reaction. For the ZP3 spermatic receptors are three candidates: β-1, 4-Galactosyltransferase, (GalTase, found in the sperm of every mammal), a protein Sp56, (which has a great affinity for ZP3) and a spermatic polypeptide p95- which increases its Phosphotyrosine concentration after ZP3 binding.
GalTase is strongly involved in the gametes-recognition process. If the oocyte is treated with an Acetyl-glucosamine derivate the spermatozoid-oocyte binding is inhibited. This enzyme is automatically released from egg’s cortical granules during the phenomenon of polyspermy which can occur during fertilization. ZP3 binds with GalTase only if the linking O-oligosaccharides are removed. Many studies demonstrate the binding relation receptor-Ligand, GalTase-ZP3.
The protein Sp56 is a homomultimer located on the spermatozoid plasmatic membrane external surface at the spermatozoid head level. Recent experiments have shown that Sp56 and ZP3 interact through a linking O-oligosaccharide.
Finally a spermatic polypeptide, p95, located on the acrozomal region of the spermatozoid serves as a tyrosine kinase activity substrate, which accompanies the acrozomal reaction.
GalTase, Sp56 and p95 aren’t the only sperm surface molecule involved in the process of fertilization, but certainly they are the most important ones. Due to their great importance in the field of fertilization, further research is intended in order to establish how they can be useful in treating infertility.