Shur B D, Hall N G
J Cell Biol. 1982 Nov;95(2 Pt 1):567-73. doi: 10.1083/jcb.95.2.567.
Studies using genetic and biochemical probes have suggested that mouse sperm surface galactosyltransferases may participate during fertilization by binding N- acetylglucosamine (GlcNAc) residues in the egg zona pellucida. In light of these results, we examined sperm surface galactosyltransferase activity during in vitro capacitation to determine whether changes in enzymatic activity correlated with fertilizing ability. Results show that surface galactosyltransferases on uncapacitated sperm was preferentially loaded with poly N-acetyllactosamine substrates. As a consequence of capacitation in Ca(++)-containing medium, these polylactosaminyl substrates are spontaneously released from the sperm surface, thereby exposing the sperm galactosyltransferase for binding to the zona pellucida. Sperm capacitation can be mimicked, in the absence of Ca(++), either by washing sperm in Ca(++)-free medium, or by pretreating sperm with antiserum that reacts with the galactosyltransferase substrate. In both instances, sperm galgactosylation of endogenous polylactosaminyl substrates is reduced, coincident with increased galactosylation of exogenous GlcNAc, and increased binding to the zona pellucida. Binding of capacitated sperm to the egg can be inhibited by pronase-digested high molecular weight polyactosaminyl glycoside extracted from epidymal fluids or from undifferentiated F9 embryonal carninoma cells. Thus, these glycosides function as "decapacitation factors" when added back to in vitro fertilization assays. These glycoside "decapacitation factors" inhibit sperm-egg binding by competeing for the sperm surface galactosyltransferase, since (a) they are galactosylated by sperm in the presence of UDP[(3)H]galactose, and (b) enzymatic removal of terminal GlcNAc residues reduces "decapacitation factio" competition. On the other hand "conventional" low molecular weight glycosides, isolated from either epididymal fluid or differentiated F9 cells, fail to inhibit capacitated sperm binding to the zona pellucida. These results define a molecular mechanism for one aspect of sperm capacitation, and help explain why removal of "decapacitation factos" is a necessary prerequisite for sperm binding to the zona pellucida.
利用基因和生化探针进行的研究表明，小鼠精子表面的半乳糖基转移酶可能在受精过程中通过结合卵透明带中的N - 乙酰葡糖胺（GlcNAc）残基发挥作用。鉴于这些结果，我们检测了体外获能过程中精子表面半乳糖基转移酶的活性，以确定酶活性的变化是否与受精能力相关。结果显示，未获能精子表面的半乳糖基转移酶优先负载多聚N - 乙酰乳糖胺底物。在含Ca(++)的培养基中获能后，这些多聚乳糖胺基底物会自发地从精子表面释放，从而使精子半乳糖基转移酶暴露出来以便与透明带结合。在无Ca(++)的情况下，精子获能可以通过在无Ca(++)的培养基中洗涤精子，或者用与半乳糖基转移酶底物反应的抗血清预处理精子来模拟。在这两种情况下，内源性多聚乳糖胺基底物的精子半乳糖基化都会减少，同时外源性GlcNAc的半乳糖基化增加，并且与透明带的结合也增加。获能精子与卵子的结合可以被从附睾液或未分化的F9胚胎癌细胞中提取的经链霉蛋白酶消化的高分子量多聚乳糖胺基糖苷所抑制。因此，当将这些糖苷添加回体外受精试验中时，它们起到“去获能因子”的作用。这些糖苷“去获能因子”通过竞争精子表面的半乳糖基转移酶来抑制精子与卵子的结合，因为（a）它们在UDP[(3)H]半乳糖存在的情况下会被精子半乳糖基化，并且（b）末端GlcNAc残基的酶促去除会降低“去获能因子”的竞争。另一方面从附睾液或分化的F9细胞中分离出的“传统”低分子量糖苷不能抑制获能精子与透明带的结合。这些结果确定了精子获能一个方面的分子机制，并有助于解释为什么去除“去获能因子”是精子与透明带结合的必要前提条件。
