RESUMO
Fertilization is a complex and fascinating biological process. The interactions between gametes transform two differentiated cells on a totipotent zygote. A few cell surface proteins in both gametes have been identified as essential for binding and fusion of gametes. At the zona pellucida level the binding is initiated by species-restricted binding of the sperm to the zona pellucida and is facilitated by the protein SED1 and or by the binding of sperm surface beta1/4-galactosyltransferase I (GaIT-I) to glycoside chains of the ZP3. This binding triggers the acrosome reaction. Among the molecules that participate on binding and fusion of gametes are included disintegrins on the sperm (ADAM1 and ADAM2) which interact with integrins (alpha6/beta-1, CD9, GPI-protein) in the egg plasma membrane, while cysteine-rich secretory proteins (CRISP) and the proteins named as Izumo participate in the fusion. The knowledge of the molecules and mechanisms involved in these processes will allow us not only a better understanding of the events underlying mammalian sperm-egg interaction, but also the development of new methods for both fertility regulation and diagnosis and clinic treatment of human and animal infertility.