Creates a 3 um hole in the egg vitelline layer through which the sperm passes (PubMed:7106382). Does not have enzyme activity (PubMed:7106382). 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 (PubMed:7106382, PubMed:28622512). Plays a role in ensuring species-specific fertilization (PubMed:2377618, PubMed:9192632, PubMed:28622512). Monomer (PubMed:7657696, PubMed:10666624). Homodimer (PubMed:7657696, PubMed:10666624). Molecules associate into dimers and then rapidly dissociate again (PubMed:7657696, PubMed:10666624). Interacts (as a monomer) with the egg vitelline layer protein VERL (via VERL repeats); each VERL chain can bind multiple copies of lysin (PubMed:9192632, PubMed:28622512). Sperm (at protein level).