Tyrosine phosphorylation activates surface chaperones facilitating sperm-zona recognition

Area of Science:

• Reproductive Biology
• Molecular Cell Biology
• Biochemistry

Background:

• Mammalian sperm capacitation involves molecular changes enabling fertilization.
• Tyrosine phosphorylation of sperm proteins is a key aspect of capacitation, but its direct role in fertilization remains unclear.
• Understanding sperm-zona pellucida interaction is critical for reproductive science.

Purpose of the Study:

• To establish a causal link between tyrosine phosphorylation and sperm-zona pellucida interaction.
• To identify specific proteins phosphorylated during sperm capacitation and their role in fertilization.
• To elucidate the mechanism of mammalian gamete recognition.

Main Methods:

• Analysis of phosphotyrosine expression in live and permeabilized spermatozoa.
• Assessment of sperm-zona pellucida binding.
• Phosphoproteome analysis to identify phosphorylated proteins.
• Immunofluorescence to localize proteins on sperm surface.

Main Results:

• A strong correlation was observed between tyrosine phosphorylation patterns and sperm binding to the zona pellucida.
• Phosphotyrosine expression was detected on the sperm head surface in live cells that bound to the zona pellucida.
• Endoplasmin (erp99) and heat shock protein 60 (hsp60) were identified as novel tyrosine phosphorylation targets on the sperm surface.
• These chaperones were localized to the sperm head region involved in zona recognition.

Conclusions:

• Tyrosine phosphorylation plays a significant role in remodeling the sperm surface during capacitation, facilitating zona pellucida recognition.
• Activated sperm-surface chaperones, through tyrosine phosphorylation, may trigger conformational changes leading to a functional zona pellucida receptor complex.
• This study proposes a novel mechanism for mammalian gamete interaction involving sperm-surface chaperone activation.