Spermatozoa are highly specialized cells whose fertilizing and motility functions highly depend on intracellular Ca²⁺‐mediated events and protein posttranslational modifications like phosphorylation. Our group previously identified PPEF1, the Ser/Thr phosphatase with EF‐hand domain 1, among calmodulin‐affinity pulled down sperm proteins. As the mammalian ortholog of the Drosophila phosphatase rdgC that dephosphorylates rhodopsin, PPEF1 has been studied mostly in the retina. The presence and importance of this Ca²⁺/calmodulin‐binding protein phosphatase has not been studied in sperm or testicular functions despite its high expression level. In this study, we show that PPEF1 is present in testicular germ cells, and in mouse, human and bull spermatozoa where it is localized predominantly in the neck and acrosome areas. Different transcript variants encoding four predicted isoforms were detected by reverse transcription polymerase chain reaction in bull testis, spermatocytes and spermatids. Phosphatase activity of immunoprecipitated sperm PPEF1 was detected using the substrate pNPP and analysis of the coimmunoprecipitated proteins reveal an enrichment in the biological processes of sperm capacitation, binding to the zona pellucida and motility. Although this is the first demonstration of the presence of PPEF1 in sperm and testicular germ cells, its involvement in sperm fertilizing ability and motility, and the mechanisms regulating its activity remain to be further investigated.

中文翻译：

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具有 EF 手结构域 1 的蛋白磷酸酶是一种钙调素结合蛋白，可与参与精子获能、与透明带结合和运动的蛋白质相互作用

精子是高度特化的细胞，其受精和运动功能高度依赖于细胞内 Ca ²⁺介导的事件和蛋白质翻译后修饰，如磷酸化。我们小组之前在钙调蛋白亲和性下拉精子蛋白中鉴定了 PPEF1，即具有 EF 手结构域 1 的 Ser/Thr 磷酸酶。作为使视紫质去磷酸化的果蝇磷酸酶 rdgC的哺乳动物直向同源物，PPEF1 主要在视网膜中进行研究。这种 Ca ²⁺的存在和重要性钙调蛋白结合蛋白磷酸酶尽管表达水平很高，但尚未在精子或睾丸功能中进行研究。在这项研究中，我们表明 PPEF1 存在于睾丸生殖细胞以及小鼠、人类和公牛精子中，主要位于颈部和顶体区域。通过逆转录聚合酶链反应在公牛睾丸、精母细胞和精子细胞中检测到编码四种预测同种型的不同转录变体。使用底物 pNPP 检测免疫沉淀精子 PPEF1 的磷酸酶活性，对共免疫沉淀蛋白的分析揭示了精子获能、与透明带结合和运动的生物过程的富集。虽然这是第一次证明精子和睾丸生殖细胞中存在 PPEF1，