Creates a 3 um hole in the egg vitelline layer through which the sperm passes. Does not have enzyme activity (By similarity). Species-specific interaction between the sperm protein lysin and the egg protein VERL exposes a basic surface on lysin that may dissociate the egg vitelline layer via electrostatic repulsion. Plays a role in ensuring species-specific fertilization (PubMed:10698629). Monomer (By similarity). Homodimer (PubMed:10698629). Molecules associate into dimers and then rapidly dissociate again. Interacts (as a monomer) with the egg vitelline layer protein VERL (via VERL repeats); each VERL chain can bind multiple copies of lysin (By similarity). Sperm.