Translation of most cellular mRNAs in eukaryotes proceeds through a cap-dependent pathway, whereby the cap-binding complex, eIF4F, anchors the preinitiation complex at the 5' end of mRNAs and regulates translation initiation. The requirement of Leishmania to survive in changing environments can explain why they encode multiple eIF4E (LeishIF4Es) and eIF4G (LeishIF4Gs) paralogs, as each could be assigned a discrete role during their life cycle. Here we show that the expression and activity of different LeishIF4Es change during the growth of cultured promastigotes, urging a search for regulatory proteins. We describe a novel LeishIF4E-interacting protein, Leish4E-IP2, which contains a conserved Y(X)4LΦ IF4E-binding-motif. Despite its capacity to bind several LeishIF4Es, Leish4E-IP2 was not detected in m7GTP-eluted cap-binding complexes, suggesting that it could inhibit the cap-binding activity of LeishIF4Es. Using a functional assay, we show that a recombinant form of Leish4E-IP2 inhibits the cap-binding activity of LeishIF4E-1 and LeishIF4E-3. Furthermore, we show that transgenic parasites expressing a tagged version of Leish4E-IP2 also display reduced cap-binding activities of tested LeishIF4Es, and decreased global translation. Given its ability to bind more than a single LeishIF4E, we suggest that Leish4E-IP2 could serve as a broad-range repressor of Leishmania protein synthesis.

中文翻译：

---

新鉴定的与利什曼原虫IF4E相互作用的蛋白Leish4E-IP2调节帽结合蛋白旁系同源物的活性。

真核生物中大多数细胞mRNA的翻译都是通过帽依赖性途径进行的，由此帽结合复合物eIF4F将预启动复合物锚定在mRNA的5'端并调节翻译起始。利什曼原虫在不断变化的环境中生存的要求可以解释为什么它们编码多个eIF4E（LeishIF4E）和eIF4G（LeishIF4Gs）旁系同源物，因为它们各自在其生命周期中可能被分配为独立角色。在这里，我们显示了不同的LeishIF4Es的表达和活性在培养的前鞭毛体的生长过程中发生了变化，这促使人们寻找调节蛋白。我们描述了一种新型的LeishIF4E相互作用蛋白Leish4E-IP2，其中包含一个保守的Y（X）4LΦIF4E结合基序。尽管具有结合多种LeishIF4E的能力，但在m7GTP洗脱的帽结合复合物中未检测到Leish4E-IP2，提示它可能抑制LeishIF4E的帽结合活性。使用功能测定，我们显示Leish4E-IP2的重组形式抑制LeishIF4E-1和LeishIF4E-3的帽结合活性。此外，我们表明表达标记版本的Leish4E-IP2的转基因寄生虫还显示减少了测试的LeishIF4Es的帽结合活性，并减少了整体翻译。考虑到其结合多个LeishIF4E的能力，我们建议Leish4E-IP2可以作为利什曼原虫蛋白合成的广泛阻遏物。我们显示表达Leish4E-IP2标记版本的转基因寄生虫还显示出经过测试的LeishIF4E的帽结合活性降低，并且全球翻译降低。考虑到其结合多个LeishIF4E的能力，我们建议Leish4E-IP2可以作为利什曼原虫蛋白合成的广泛阻遏物。我们显示表达Leish4E-IP2标记版本的转基因寄生虫还显示出经过测试的LeishIF4E的帽结合活性降低，并且全球翻译降低。鉴于其结合多个LeishIF4E的能力，我们建议Leish4E-IP2可以作为利什曼原虫蛋白合成的广泛阻遏物。