Mediation of sperm-egg fusion: evidence that mouse egg α6β1 integrin is the receptor for sperm fertilinβ Original Research Article

A key step leading to fertilization is the binding of sperm to the egg plasma membrane. When a mammalian sperm reaches the egg plasma membrane, fertilinβ, an extracellular sperm membrane protein, is believed to bind to an egg plasma membrane receptor triggering fusion. We set out to identify the fertilinβ binding partner on the egg plasma membrane. Results We synthesized an 125I-labeled peptide with the consensus Asp-Glu-Cys-Asp (DECD) sequence of fertilinβʹs disintegrin domain. This peptide contains a benzophenone photoaffinity probe and inhibits sperm-egg fusion. Upon photoactivation in the presence of whole mouse eggs, a sing e polypeptide was covalently labeled. This polypeptide has been identified by immunoprecipitation as an α6 integrin complexed with β1 integrin. Conclusions Our experiments establish that small peptides containing the consensus DECD sequence of sperm fertilinβ bind specifically to an α6β1 integrin receptor on the egg membrane. We conclude that fertilinβ binds directly to the α6β1 integrin on the egg surface and this partnership mediates sperm-egg fusion.