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#sperm-egg binding

3 public questions tagged with this topic.

Regeneration -ll

Which of these is true for bindin protein?

Bindin represents classic example of rapidly evolving reproductive protein under positive selection driving speciation. It is insoluble acrosomal protein retained on acrosomal process after exocytosis, contacting vitelline envelope receptor EBR1. Sequence analysis reveals lectin domains mediating species-specific adhesion plus amphipathic helical regions destabilizing membranes promoting fusion, qualifying as fusogenic. It is not jelly component dissolving in seawater, not cortical granule enzyme released by egg, nor constituent of hardened fertilization envelope that consists of crosslinked vitelline glycoproteins. Its localization strictly on sperm ensures sperm side contributes adhesive and fusogenic activity essential for membrane merger and reproductive isolation.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Bindin as sperm fusogenic and adhesive protein.

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Sea urchin -l

Which of these is true for bindin protein?

Bindin is not component of egg jelly or fertilization envelope but major cell adhesion protein uniquely sequestered inside intact sperm acrosomal vesicle. Upon Ca2+-triggered acrosome reaction it becomes prominently exposed on surface of extended acrosomal process where it performs dual functions: mediating species-specific attachment to EBR1 receptor complex of vitelline envelope through lectin-like domain, and also possessing hydrophobic fusogenic sequence promoting merger of sperm and egg lipid bilayers after adhesion. Rapid sequence divergence among Strongylocentrotus species establishes potent prezygotic reproductive barrier. Biochemically insoluble collagen-like protein, bindin represents definitive species-specific fusogenic adhesion protein essential for productive gamete recognition and membrane fusion.

Ref: Vacquier & Moy, J Biol Chem 1997, Bindin fusogenic function; Gilbert Chapter 7: Bindin as species-specific fusogen.

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Sea urchin -l

The primary role of the bindin protein in sea urchin sperm is:

Bindin is major insoluble protein sequestered inside acrosomal vesicle and exposed exclusively after Ca2+-dependent acrosomal exocytosis, localized on tip of extended acrosomal process. It possesses lectin-like carbohydrate recognition domain that binds sulfated polysaccharides on vitelline envelope and amphipathic sequences mediating fusion between egg and sperm lipid bilayers. Sequence analyses reveal hypervariable domains determining species-specific recognition, functioning as prezygotic isolation mechanism preventing interspecies hybridization between Strongylocentrotus species. Antibody blocking or recombinant bindin competition inhibits fertilization in species-specific manner. Its dedicated role is selective binding and membrane fusion ensuring accurate gamete union.

Ref: Glabe et al., 1982, Bindin species specificity; Gilbert, Developmental Biology, Chapter 7: Bindin function in fertilization.

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