Mammalian zona pellucida glycoproteins: structure and function during fertilization

Area of Science:

• Reproductive Biology
• Glycobiology
• Cellular Signaling

Background:

• The zona pellucida (ZP) is a vital glycoprotein matrix surrounding mammalian oocytes, essential for fertilization.
• Human ZP comprises ZP1, ZP2, ZP3, and ZP4; mouse ZP lacks ZP4.
• Human ZP proteins ZP1 and ZP4 are paralogs with 47% sequence identity.

Purpose of the Study:

• To investigate the roles of human zona pellucida proteins in sperm binding and acrosome reaction induction.
• To compare the mechanisms of sperm-egg interaction in humans versus mice.
• To elucidate the specific glycoproteins involved in human fertilization.

Main Methods:

• Utilized affinity-purified native and recombinant human zona proteins.
• Assessed binding of ZP proteins to capacitated and acrosome-reacted human spermatozoa.
• Analyzed glycan involvement (N-linked vs. O-linked) and downstream signaling pathways.

Main Results:

• Human ZP1, ZP3, and ZP4 bind capacitated sperm and induce acrosome reaction; ZP2 binds only to acrosome-reacted sperm.
• N-linked glycans on human ZP3 and ZP4 are critical for acrosome reaction induction, unlike O-linked glycans in mice.
• Sialyl-Lewis(x) sequences on human ZP glycans are important for sperm-egg binding.
• ZP3-mediated acrosome reaction involves Gi protein-coupled receptor activation, distinct from ZP1/ZP4 pathways.

Conclusions:

• In humans, multiple zona pellucida proteins (ZP1, ZP3, ZP4) actively participate in sperm binding and acrosome reaction induction.
• Human sperm-zona pellucida interactions are more complex than in mice, involving distinct protein roles and signaling pathways.
• Glycan structures, particularly N-linked glycans and Sialyl-Lewis(x), play a significant role in human fertilization.