Bindin

Bindin is a sperm protein involved in fertilization in sea urchins and related echinoderms. It is stored in the acrosomal vesicle of sperm and becomes exposed to the exterior during the acrosome reaction, enabling the sperm to attach to and fuse with the egg.

Function and mechanism: Bindin mediates adhesion to the egg by interacting with receptors on the egg surface and the surrounding extracellular matrix of the vitelline layer. This interaction supports species-specific recognition, helping ensure that fertilization occurs between compatible gametes.

Genetic and evolutionary significance: The bindin gene and its protein product show rapid evolution and high allelic diversity among sea urchin species. This pattern is cited as an example of how reproductive proteins can drive speciation through prezygotic isolation.

Discovery and study: Bindin was identified through work on sea urchin fertilization in the late 20th century, with foundational contributions from researchers studying gamete recognition. It has become a classic model for investigating molecular evolution of gamete interaction proteins.

Broader context: While bindin is best characterized in sea urchins, related proteins and analogous gamete-recognition systems exist in other echinoderms and in distant taxa, illustrating diverse solutions to species-specific fertilization.