Flori Federica, Ermini Leonardo, La Sala Giovanni Battista, Nicoli Alessia, Capone Antonietta, Focarelli Riccardo, Rosati Floriana, Giovampaola Cinzia Della
Department of Evolutionary Biology, University of Siena, Siena, Italy.
Mol Reprod Dev. 2008 Feb;75(2):326-35. doi: 10.1002/mrd.20738.
CD52 is a human glycosylphosphatidylinositol (GPI)-anchored antigen exclusively expressed in leukocytes and epididymal cells. It is also present in sperm, being inserted in their plasma membrane as they pass through the epididymis. In a previous paper we identified a new CD52 form without GPI anchor by fast performance liquid chromatography (FPLC) fractionation of semen components. The form has a lower negative charge than the GPI-anchored form and occurs as the only CD52 form in prostasome-free seminal plasma. It was also found associated with the ejaculated sperm, but in contrast to the GPI-anchored one, it is lost during the capacitation process. In this paper we indicate that (1) the GPI-anchored CD52 of the sperm surface serves as receptor for semenogelin I during clot formation, (2) liquefaction involves cleavage of the GPI anchor from certain CD52 molecules, releasing sperm from the clot and the soluble antigen bound to semenogelin fragments into the seminal plasma and (3) the clot is a sponge-like structure housing sperm. Soluble CD52 was immunopurified from the soluble CD52-containing FPLC fraction using CAMPATH-1G and was found to be complexed with a semenogelin-derived peptide of the carboxyl terminal portion of semenogelin I, having the sequence SQTEKLVAGKQI and starting from amino acid 376. Immunoprecipitation and immunoblot analyses using CAMPATH-1G and anti-semenogelin as immunoprecipitating antibodies and anti-gp20 and anti-semenogelin as immunoblot detectors of the corresponding antigens, confirmed that the soluble CD52 formed a complex with semenogelin. The semenogelin-CD52 soluble form was found to be a direct consequence of the liquefaction process since only the GPI-anchored CD52 was recovered in uniquefied semen after recovering sperm and seminal plasma by urea solubilization of the clot.
CD52是一种人类糖基磷脂酰肌醇（GPI）锚定抗原，仅在白细胞和附睾细胞中表达。它也存在于精子中，当精子通过附睾时插入其质膜。在之前的一篇论文中，我们通过精液成分的快速液相色谱（FPLC）分离鉴定出一种没有GPI锚定的新CD52形式。这种形式的负电荷比GPI锚定形式低，并且是无前列腺小体精浆中唯一的CD52形式。还发现它与射出的精子相关，但与GPI锚定的形式不同，它在获能过程中会丢失。在本文中我们指出：（1）精子表面的GPI锚定CD52在凝块形成过程中作为精液凝素I的受体；（2）液化涉及从某些CD52分子上切割GPI锚定，将精子从凝块中释放出来，并将与精液凝素片段结合的可溶性抗原释放到精浆中；（3）凝块是容纳精子的海绵状结构。使用CAMPATH-1G从含有可溶性CD52的FPLC馏分中免疫纯化可溶性CD52，发现它与精液凝素I羧基末端部分的精液凝素衍生肽复合，该肽序列为SQTEKLVAGKQI，从氨基酸376开始。使用CAMPATH-1G和抗精液凝素作为免疫沉淀抗体，以及抗gp20和抗精液凝素作为相应抗原的免疫印迹检测器进行免疫沉淀和免疫印迹分析，证实可溶性CD52与精液凝素形成复合物。发现精液凝素-CD52可溶性形式是液化过程的直接结果，因为通过尿素溶解凝块回收精子和精浆后，在未液化的精液中仅回收了GPI锚定的CD52。
