Creates a 3 um hole in the egg vitelline layer through which the sperm passes (PubMed:2377618). Does not have enzyme activity. 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 (By similarity). Plays a role in ensuring species-specific fertilization (PubMed:2377618, PubMed:9192632). Monomer. Homodimer. Molecules associate into dimers and then rapidly dissociate again (By similarity). Interacts (as a monomer) with the egg vitelline layer protein VERL (via VERL repeats); each VERL chain can bind multiple copies of lysin (PubMed:2377618, PubMed:9192632). Sperm (at protein level).