Abalone lysin: the dissolving and evolving sperm protein

Abalone sperm lysin is a non-enzymatic protein that creates a hole for sperm passage in the envelope surrounding the egg. Lysin exhibits species-specificity in making the hole and it evolves rapidly by positive selection. Our studies have focused on combining structural, biochemical, and evolutionary data to understand the mechanism of action and evolution of this remarkable protein. Currently, more is known about lysin than about any other protein involved in animal fertilization. We present an hypothesis to explain lysin's rapid evolution and the evolution of species-specific fertilization in this order of mollusks. We also propose a two-step model for lysin's action in which a dimer of lysin binds species-specifically to its glycoprotein receptor, and then monomerizes and binds the receptor in a non-species-specific manner. This experimental system yields data relevant to the general problem of molecular recognition between cell surfaces, and is also important to our thinking about how new species arise in the sea. BioEssays 23:95-103, 2001.