Greve J M, Salzmann G S, Roller R J, Wassarman P M
Cell. 1982 Dec;31(3 Pt 2):749-59. doi: 10.1016/0092-8674(82)90329-4.
An antiserum directed specifically against ZP2, the major glycoprotein of the mouse egg's extracellular coat (zona pellucida), has been used to immunoprecipitate intracellular precursors of ZP2 that were synthesized by growing mouse oocytes cultured in vitro. Pulse-chase experiments revealed that the immediate precursor of mature, 120 kilodalton (kd) ZP2 is a 91 kd species that unlike mature ZP2, is sensitive to digestion by endo-beta-N-acetylglucosaminidase H (Endo H) and is converted by the endoglycosidase into an 81 kd species. An 81 kd species is only found intracellularly when growing oocytes are cultured in the presence of tunicamycin. These results suggest that ZP2 is synthesized as an 81 kd polypeptide chain that is first "core"-glycosylated at asparagine residues with high-mannose-type oligosaccharides, giving rise to a 91 kd intermediate (Endo-H-sensitive), and then processed to complex-type oligosaccharides prior to secretion as mature, 120 kd ZP2 (Endo H-insensitive). Furthermore, electrophoretic analyses of mature ZP2, ZP2 precursor (91 kd) and Endo H-treated ZP2 precursor (81 kd) suggest that there are six N-linked oligosaccharides per molecule and that the extreme heterogeneity of mature ZP2 is a consequence of the oligosaccharides and not the polypeptide chain itself.
一种特异性针对小鼠卵子细胞外被（透明带）的主要糖蛋白ZP2的抗血清，已被用于免疫沉淀由体外培养的生长中的小鼠卵母细胞合成的ZP2细胞内前体。脉冲追踪实验表明，成熟的120千道尔顿（kd）ZP2的直接前体是一种91 kd的分子，与成熟ZP2不同，它对内切β-N-乙酰氨基葡糖苷酶H（Endo H）的消化敏感，并被该糖苷酶转化为81 kd的分子。只有当生长中的卵母细胞在衣霉素存在的情况下培养时，才在细胞内发现81 kd的分子。这些结果表明，ZP2是以81 kd的多肽链形式合成的，该多肽链首先在天冬酰胺残基处被高甘露糖型寡糖进行“核心”糖基化，产生一种91 kd的中间体（对Endo-H敏感），然后在分泌为成熟的120 kd ZP2（对Endo H不敏感）之前被加工成复合型寡糖。此外，对成熟ZP2、ZP2前体（91 kd）和Endo H处理的ZP2前体（81 kd）的电泳分析表明，每个分子有六个N-连接的寡糖，并且成熟ZP2的极端异质性是寡糖的结果，而不是多肽链本身的结果。
