Zanich Alan, Pascall John C, Jones Roy
Gamete Signalling Laboratory, The Babraham Institute, Cambridge CB2 4AT, United Kingdom.
Biol Reprod. 2003 Dec;69(6):1831-42. doi: 10.1095/biolreprod.103.018606. Epub 2003 Jul 30.
The plasma membrane of spermatozoa undergoes substantial remodeling during passage through the epididymal duct, principally because of changes in phospholipid composition, exchange of glycoproteins with epididymal fluid, and processing of existing membrane proteins. Here, we describe the interaction of an epididymal glycoprotein recognized by monoclonal antibody 2D6 with the plasma membrane of rat spermatozoa. Our goals have been to understand more about the mechanism of secretion of epididymal glycoproteins, how they interact with the sperm's plasma membrane, and their disposition within it. Reactivity to 2D6 monoclonal antibody was first detectable in principal cells in the distal caput epididymidis and as a soluble high-molecular-weight complex in the secreted fluid. It was not associated with membranous vesicles in the duct lumen. On cauda spermatozoa 2D6 monoclonal antibody recognized a 24-kDa glycoprotein (the subunit of a disulfide cross-linked homodimer of 48 kDa) that was present on the plasma membrane overlying the sperm tail. Binding of 2D6 to immature spermatozoa in vitro was cell-type specific but not species specific, and the antigen could only be extracted from cauda spermatozoa with detergents. Sequencing studies revealed that the 24-kDa glycoprotein was a member of the beta-defensin superfamily of small pore-forming glycopeptides of which several others (ESP13.2, Bin1b, E-2, EP2, HE2) are found in the epididymis. This evidence suggests that some epididymal glycoproteins are secreted into the luminal fluid in a soluble form and bind to specific regions of the sperm's surface via hydrophobic interactions. Given the antimicrobial function of beta-defensins, they have a putative role in protecting spermatozoa and the epididymis from bacterial infections.
精子的质膜在通过附睾管的过程中会经历大量重塑，主要原因是磷脂组成的变化、糖蛋白与附睾液的交换以及现有膜蛋白的加工。在此，我们描述了单克隆抗体2D6识别的一种附睾糖蛋白与大鼠精子质膜的相互作用。我们的目标是更多地了解附睾糖蛋白的分泌机制、它们如何与精子质膜相互作用以及它们在质膜内的分布情况。对2D6单克隆抗体的反应性首先在附睾头远端的主细胞中可检测到，并以可溶性高分子量复合物的形式存在于分泌液中。它与管腔内的膜泡无关。在附睾尾精子上，2D6单克隆抗体识别一种24 kDa的糖蛋白（48 kDa二硫键交联同型二聚体的亚基），该糖蛋白存在于覆盖精子尾部的质膜上。2D6在体外与未成熟精子的结合具有细胞类型特异性，但不具有物种特异性，并且该抗原只能用去污剂从附睾尾精子中提取。测序研究表明，24 kDa的糖蛋白是β-防御素超家族的成员，该超家族是形成小孔的糖肽，附睾中还发现了其他几种（ESP13.2、Bin1b、E-2、EP2、HE2）。这一证据表明，一些附睾糖蛋白以可溶性形式分泌到管腔液中，并通过疏水相互作用与精子表面的特定区域结合。鉴于β-防御素的抗菌功能，它们在保护精子和附睾免受细菌感染方面具有推定作用。
