Haider Afreen, Allen Stacey M, Jackson Katherine E, Ralph Stuart A, Habib Saman
Division of Molecular and Structural Biology, CSIR-Central Drug Research Institute, Lucknow, India.
Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, Vic., 3010, Australia.
Mol Microbiol. 2015 May;96(4):796-814. doi: 10.1111/mmi.12972. Epub 2015 Mar 16.
The malaria parasite Plasmodium falciparum has two translationally active organelles - the apicoplast and mitochondrion, which import nuclear-encoded translation factors to mediate protein synthesis. Initiation of translation is a complex step wherein initiation factors (IFs) act in a regulated manner to form an initiation complex. We identified putative organellar IFs and investigated the targeting, structure and function of IF1, IF2 and IF3 homologues encoded by the parasite nuclear genome. A single PfIF1 is targeted to the apicoplast. Apart from its critical ribosomal interactions, PfIF1 also exhibited nucleic-acid binding and melting activities and mediated transcription anti-termination. This suggests a prominent ancillary function for PfIF1 in destabilisation of DNA and RNA hairpin loops encountered during transcription and translation of the A+T rich apicoplast genome. Of the three putative IF2 homologues, only one (PfIF2a) was an organellar protein with mitochondrial localisation. We additionally identified an IF3 (PfIF3a) that localised exclusively to the mitochondrion and another protein, PfIF3b, that was apicoplast targeted. PfIF3a exhibited ribosome anti-association activity, and monosome splitting by PfIF3a was enhanced by ribosome recycling factor (PfRRF2) and PfEF-G(Mit). These results fill a gap in our understanding of organellar translation in Plasmodium, which is the site of action of several anti-malarial compounds.
疟原虫恶性疟原虫有两个具有翻译活性的细胞器——顶质体和线粒体，它们导入核编码的翻译因子来介导蛋白质合成。翻译起始是一个复杂的步骤，其中起始因子（IFs）以一种受调控的方式发挥作用以形成起始复合物。我们鉴定了假定的细胞器IFs，并研究了由寄生虫核基因组编码的IF1、IF2和IF3同源物的靶向、结构和功能。单个PfIF1靶向顶质体。除了其关键的核糖体相互作用外，PfIF1还表现出核酸结合和解链活性，并介导转录抗终止。这表明PfIF1在富含A+T的顶质体基因组转录和翻译过程中遇到的DNA和RNA发夹环的去稳定化中具有重要的辅助功能。在三个假定的IF2同源物中，只有一个（PfIF2a）是具有线粒体定位的细胞器蛋白。我们还鉴定了一种仅定位于线粒体的IF3（PfIF3a）和另一种靶向顶质体的蛋白PfIF3b。PfIF3a表现出核糖体抗缔合活性，核糖体循环因子（PfRRF2）和PfEF-G（Mit）增强了PfIF3a介导的单体分裂。这些结果填补了我们对疟原虫细胞器翻译理解上的空白，疟原虫是几种抗疟化合物的作用位点。
