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#bindin protein

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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Regeneration -ll

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

Bindin is a thirty-five kilodalton insoluble protein sequestered within sperm acrosomal vesicle and exposed at tip of acrosomal process after calcium-dependent exocytosis. It contains lectin-like domains recognizing sulfated polysaccharides on Egg Bindin Receptor EBR1 glycoprotein embedded in vitelline envelope. Interaction confers species-specific binding, constituting major barrier to heterospecific fertilization and reproductive isolation. Beyond adhesion, bindin exhibits amphipathic fusogenic activity promoting mixing of sperm and egg lipid bilayers facilitating membrane fusion. It does not power dynein-driven motility, regulate intracellular alkalization, or mediate chromatin condensation occurring during spermiogenesis.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Bindin - species-specific adhesion and membrane fusion in sea urchin.

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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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