Zona pellucida
The zona pellucida is a glycoprotein matrix surrounding the plasma membrane of a mammalian oocyte. This structure binds spermatozoa, and is required to initiate the acrosome reaction. The zona glycoprotein, ZP3, is responsible for sperm binding, adhering to proteins on the sperm plasma membrane. There is evidence that ZP3 is then involved in the induction of the acrosome reaction, whereby a spermatozoon releases the contents of the acrosomal vesicle.
Reference
- Oehninger S. 2003. Biochemical and functional characterization of the human zona pellucida. Reprod Biomed Online 7:641-8.