Following the fertilization of an egg by a single sperm, the egg coat or zona pellucida (ZP) hardens and polyspermy is irreversibly blocked. These events are associated with the cleavage of the N-terminal region (NTR) of glycoprotein ZP2, a major subunit of ZP filaments. ZP2 processing is thought to inactivate sperm binding to the ZP, but its molecular consequences and connection with ZP hardening are unknown. Biochemical and structural studies show that cleavage of ZP2 triggers its oligomerization. Moreover, the structure of a native vertebrate egg coat filament, combined with AlphaFold predictions of human ZP polymers, reveals that two protofilaments consisting of type I (ZP3) and type II (ZP1/ZP2/ZP4) components interlock into a left-handed double helix from which the NTRs of type II subunits protrude. Together, these data suggest that oligomerization of cleaved ZP2 NTRs extensively cross-links ZP filaments, rigidifying the egg coat and making it physically impenetrable to sperm.

中文翻译：

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ZP2 裂解通过调节卵衣的结构来阻止多精受精

单个精子使卵子受精后，卵子外壳或透明带 (ZP) 变硬，多精受精被不可逆地阻止。这些事件与糖蛋白 ZP2（ZP 丝的主要亚基）的 N 末端区域 (NTR) 的裂解有关。 ZP2 处理被认为会使精子与 ZP 结合失活，但其分子后果以及与 ZP 硬化的关系尚不清楚。生化和结构研究表明，ZP2 的裂解会引发其寡聚化。此外，天然脊椎动物蛋皮丝的结构与人类 ZP 聚合物的 AlphaFold 预测相结合，揭示了由 I 型 (ZP3) 和 II 型 (ZP1/ZP2/ZP4) 成分组成的两条原丝互锁成左手双丝。 II 型亚基的 NTR 从中突出的螺旋。总之，这些数据表明，裂解的 ZP2 NTR 的寡聚作用广泛地交联 ZP 丝，使卵壳变硬，使其对精子来说难以穿透。