Macek M B, Lopez L C, Shur B D
Department of Biochemistry and Molecular Biology, University of Texas, M.D. Anderson Cancer Center, Houston 77030.
Dev Biol. 1991 Oct;147(2):440-4. doi: 10.1016/0012-1606(91)90301-i.
beta-1,4-Galactosyltransferase (GalTase) is present on the surface of mouse sperm, where it functions during fertilization by binding to oligosaccharide residues in the egg zona pellucida. The specific oligosaccharide substrates for sperm GalTase reside on the glycoprotein ZP3, which possesses both sperm-binding and acrosome reaction-inducing activity. A variety of reagents that perturb sperm GalTase activity inhibit sperm binding to the zona pellucida, including UDP-galactose, N-acetylglucosamine, alpha-lactalbumin, and anti-GalTase Fab fragments. However, none of these reagents are able to cross-link GalTase within the membrane nor are they able to induce the acrosome reaction. On the other hand, intact anti-GalTase IgG blocks sperm-zona binding as well as induces the acrosome reaction. Anti-GalTase IgG induces the acrosome reaction by aggregating GalTase on the sperm plasma membrane, as shown by the inability of anti-Gal-Tase Fab fragments to induce the acrosome reaction unless cross-linked with goat anti-rabbit IgG. These data suggest that zona pellucida oligosaccharides induce the acrosome reaction by clustering GalTase on the sperm surface.
β-1,4-半乳糖基转移酶（GalTase）存在于小鼠精子表面，在受精过程中，它通过与卵子透明带中的寡糖残基结合发挥作用。精子GalTase的特定寡糖底物存在于糖蛋白ZP3上，ZP3同时具有精子结合和诱导顶体反应的活性。多种干扰精子GalTase活性的试剂会抑制精子与透明带的结合，包括UDP-半乳糖、N-乙酰葡糖胺、α-乳白蛋白和抗GalTase Fab片段。然而，这些试剂都无法在膜内交联GalTase，也不能诱导顶体反应。另一方面，完整的抗GalTase IgG既能阻断精子与透明带的结合，又能诱导顶体反应。抗GalTase IgG通过使精子质膜上的GalTase聚集来诱导顶体反应，这一点可通过抗Gal-Tase Fab片段无法诱导顶体反应得到证明，除非其与山羊抗兔IgG交联。这些数据表明，透明带寡糖通过使精子表面的GalTase聚集来诱导顶体反应。
