Evans J P, Schultz R M, Kopf G S
Center for Research on Reproduction and Women's Health, University of Pennsylvania, Philadelphia 19104, USA.
Dev Biol. 1997 Jul 1;187(1):94-106. doi: 10.1006/dbio.1997.8612.
Fertilin (previously known as PH-30) is a sperm protein that is a candidate molecule for mediating the binding and fusion of the sperm and egg plasma membranes. Fertilin is a heterodimer, with a beta subunit that has a region of homology to the disintegrin family of integrin ligands and an alpha subunit that has a region of homology to viral fusion peptides. It has been hypothesized that fertilin beta and alpha subunits mediate the interactions between sperm and egg plasma membranes, namely, binding and fusion, respectively. To address this hypothesis and to examine specifically the role of fertilin alpha in fertilization, we have expressed the predicted extracellular domain of mouse fertilin alpha as a bacterial fusion protein with maltose-binding protein. This fusion protein (hereafter referred to as recombinant fertilin alpha-EC) binds to the microvillar region of zona pellucida (ZP)-free eggs, the region of the membrane to which sperm bind. This binding is reduced in the absence of divalent cations and is supported by Ca2+, Mg2+, or Mn2+. Eggs that have been treated with chymotrypsin bind less recombinant fertilin alpha-EC than do untreated eggs, suggesting that a chymotrypsin-sensitive binding site for recombinant fertilin alpha-EC is present on egg surfaces. Binding to eggs is also affected by the method used to remove the ZP. Finally, recombinant fertilin alpha-EC inhibits the binding of sperm to eggs during in vitro fertilization of ZP-free eggs. These data are the first evidence to suggest that fertilin alpha can function as a cell adhesion molecule during fertilization, mediating the binding of sperm and egg plasma membranes.
受精素（以前称为PH-30）是一种精子蛋白，是介导精子与卵细胞质膜结合和融合的候选分子。受精素是一种异二聚体，其β亚基有一个与整合素配体的解整合素家族同源的区域，α亚基有一个与病毒融合肽同源的区域。据推测，受精素β亚基和α亚基分别介导精子与卵细胞质膜之间的相互作用，即结合和融合。为了验证这一假设并具体研究受精素α在受精过程中的作用，我们将小鼠受精素α的预测胞外结构域表达为与麦芽糖结合蛋白的细菌融合蛋白。这种融合蛋白（以下简称重组受精素α-EC）与无透明带（ZP）卵的微绒毛区域结合，精子正是与该膜区域结合。在没有二价阳离子的情况下，这种结合会减少，而Ca2+、Mg2+或Mn2+能支持这种结合。用胰凝乳蛋白酶处理过的卵与重组受精素α-EC的结合比未处理的卵少，这表明卵表面存在对重组受精素α-EC敏感的胰凝乳蛋白酶结合位点。与卵的结合也受到去除ZP所用方法的影响。最后，重组受精素α-EC在无ZP卵的体外受精过程中抑制精子与卵的结合。这些数据首次表明，受精素α在受精过程中可作为一种细胞粘附分子，介导精子与卵细胞质膜的结合。
