Malaria is one of the major causes of mortality as well as morbidity in many tropical and subtropical countries around the world. Although artemisinin combination therapies (ACTs) are contributing to substantial decline in the worldwide malaria burden, it is becoming vulnerable by the emergence of artemisinin resistance in Plasmodium falciparum leading to clinical failure of ACTs in Southeast Asia. Helicases play important role in nucleic acid metabolic processes and have been also identified as therapeutic drug target for different diseases. Previously, it has been reported that P. falciparum contains a group of DEAD-box family of helicases which are homologous to Has1 family of yeast. Here, we present the characterization of a member of Has1 family (PlasmoDB number PF3D7_1419100) named as PfDDX55. The biochemical characterization of PfDDX55C revealed that it contains both DNA- and RNA-dependent ATPase activity. PfDDX55C unwinds partially duplex DNA in 3′ to 5′ direction and utilizes mainly ATP or dATP for its activity. The immunofluorescence assay and q-RT PCR analysis show that PfDDX55 is a nucleocytoplasmic protein expressed in all the intraerythrocytic development of P. falciparum 3D7 strain with maximum expression level in trophozoite stage. The LC-MS/MS experiment results and STRING analysis show that PfDDX55 interacts with AAA-ATPase which has been shown to be involved in ribosomal biogenesis.

中文翻译：

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恶性疟原虫 DDX55 是一种核质蛋白和 3'-5' 方向特异性 DNA 解旋酶

疟疾是世界上许多热带和亚热带国家死亡和发病的主要原因之一。尽管青蒿素联合疗法 (ACTs) 正在推动全球疟疾负担的大幅下降，但由于恶性疟原虫对青蒿素耐药的出现导致 ACTs 在东南亚的临床失败，它变得脆弱。解旋酶在核酸代谢过程中发挥重要作用，也已被确定为不同疾病的治疗药物靶点。此前，据报道，恶性疟原虫含有一组与酵母 Has1 家族同源的 DEAD-box 解旋酶家族。在这里，我们介绍了名为 PfDDX55 的 Has1 家族成员（PlasmoDB 编号 PF3D7_1419100）的特征。PfDDX55C 的生化特征表明它同时包含依赖于 DNA 和 RNA 的 ATPase 活性。PfDDX55C 在 3' 到 5' 方向解开部分双链 DNA，主要利用 ATP 或 dATP 进行活性。免疫荧光分析和 q-RT PCR 分析表明，PfDDX55 是一种在恶性疟原虫 3D7 菌株红细胞内发育过程中均有表达的核质蛋白，在滋养体阶段表达水平最高。LC-MS/MS 实验结果和 STRING 分析表明 PfDDX55 与 AAA-ATPase 相互作用，AAA-ATPase 已被证明参与核糖体生物发生。免疫荧光分析和 q-RT PCR 分析表明，PfDDX55 是一种在恶性疟原虫 3D7 菌株红细胞内发育过程中均有表达的核质蛋白，在滋养体阶段表达水平最高。LC-MS/MS 实验结果和 STRING 分析表明 PfDDX55 与 AAA-ATPase 相互作用，AAA-ATPase 已被证明参与核糖体生物发生。免疫荧光分析和 q-RT PCR 分析表明，PfDDX55 是一种在恶性疟原虫 3D7 菌株红细胞内发育过程中均有表达的核质蛋白，在滋养体阶段表达水平最高。LC-MS/MS 实验结果和 STRING 分析表明 PfDDX55 与 AAA-ATPase 相互作用，AAA-ATPase 已被证明参与核糖体生物发生。