#bindin receptors

Regeneration -ll

Which enzyme cleaves bindin receptors during slow block?

Permanent block to polyspermy requires irreversible removal of sperm attachment sites. Cortical granule serine protease, trypsin-like enzyme activated at neutral pH upon exocytosis, cleaves extracellular domain of Egg Bindin Receptor EBR1 within vitelline envelope, releasing peptide fragments and destroying lectin-binding interface. This ensures even if fertilization envelope incompletely hardens, supernumerary sperm cannot remain bound. Acrosomal protease digests egg jelly to allow sperm penetration, ovoperoxidase crosslinks envelope proteins for hardening, phospholipase C generates IP3 and DAG for signaling but does not cleave receptors. Specific serine protease inhibitors prevent receptor loss while envelope still elevates.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Cortical granule serine protease clipping bindin receptor EBR1.

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Regeneration -ll

Bindin receptors in sea urchins are located on the:

Species-specific sperm binding occurs on vitelline envelope where Egg Bindin Receptor glycoprotein complex is concentrated. Biochemical isolation shows EBR1 is 350 kDa transmembrane protein with large extracellular domain containing sulfated oligosaccharides recognized by bindin lectin domain. Immunofluorescence localizes EBR1 to vitelline envelope before fertilization, not soluble jelly, internal cortical granules, or deep plasma membrane domains. After cortical granule serine protease cleaves EBR1 extracellular domain, binding sites are lost, contributing to permanent block. Egg plasma membrane contains fusogenic lipids and integrins mediating final membrane merger after initial vitelline anchoring, but primary bindin receptor resides in envelope.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Localization of bindin receptor EBR1 on vitelline envelope.

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Sea urchin -l

Which enzyme cleaves bindin receptors during slow block?

Permanent elimination of sperm binding capacity during slow block involves enzymatic destruction of specific recognition molecules. Cortical granules discharge large trypsin-like serine protease that cleaves peptide linkages anchoring EBR1 bindin receptor complex to vitelline envelope glycoprotein scaffold and degrades residual fertilizing sperm proteins adhering to envelope. This proteolytic destruction ensures no new bindin-receptor interactions can reform even before envelope hardening physically completes. Acrosomal protease facilitates sperm entry through jelly, ovoperoxidase catalyzes dityrosine crosslinks hardening envelope, phospholipase C generates IP3 for calcium release but does not degrade receptors. Thus enzyme responsible for cleaving bindin receptors is cortical granule serine protease.

Ref: NCBI Bookshelf, Developmental Biology, Chapter 7: Cortical granule protease cleaves bindin receptor.

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Sea urchin -l

Bindin receptors in sea urchins are located on the:

Molecular cloning of bindin receptor revealed EBR1 glycoprotein complex not localized on plasma membrane but embedded within vitelline envelope surrounding egg. Receptor evolved as extracellular matrix component providing docking platform for acrosomal process containing bindin after penetrating jelly. Upon bindin-EBR1 adhesion, sperm becomes tethered, allowing subsequent lipid bilayer fusion lateral to bound site rather than directly at receptor cluster. Only after secure binding does sperm plasma membrane merge with egg membrane. Cortical granules, jelly and cortical cytoplasm lack primary bindin receptor; vitelline envelope serves exclusive scaffold for species-specific gamete adhesion.

Ref: Kamei & Glabe, PNAS 2003, Bindin receptor localization; Gilbert Chapter 7: Vitelline envelope EBR1 receptor.

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