The Plasmodium PHIST and RESA-Like Protein Families of Human and Rodent Malaria Parasites

The phist gene family has members identified across the Plasmodium genus, defined by the presence of a domain of roughly 150 amino acids having conserved aromatic residues and an all alpha-helical structure. The family is highly amplified in P. falciparum, with 65 predicted genes in the genome of the 3D7 isolate. In contrast, in the rodent malaria parasite P. berghei 3 genes are identified, one of which is an apparent pseudogene. Transcripts of the P. berghei phist genes are predominant in schizonts, whereas in P. falciparum transcript profiles span different asexual blood stages and gametocytes. We pursued targeted disruption of P. berghei phist genes in order to characterize a simplistic model for the expanded phist gene repertoire in P. falciparum. Unsuccessful attempts to disrupt P. berghei PBANKA_114540 suggest that this phist gene is essential, while knockout of phist PBANKA_122900 shows an apparent normal progression and non-essential function throughout the life cycle. Epitope-tagging of P. falciparum and P. berghei phist genes confirmed protein export to the erythrocyte cytoplasm and localization with a punctate pattern. Three P. berghei PEXEL/HT-positive exported proteins exhibit at least partial co-localization, in support of a common vesicular compartment in the cytoplasm of erythrocytes infected with rodent malaria parasites.

phist基因家族（phist gene family）在疟原虫属（Plasmodium）各物种中均有鉴定出的同源成员，其定义特征为包含一段约150个氨基酸的结构域，该结构域带有保守的芳香族氨基酸残基且整体呈全α螺旋折叠结构。该家族在恶性疟原虫（Plasmodium falciparum）基因组中发生了显著扩增，其3D7分离株的基因组中预测存在65个该家族基因。与之形成对比的是，在啮齿类疟原虫伯氏疟原虫（Plasmodium berghei）中仅鉴定出3个基因，其中一个为疑似假基因。伯氏疟原虫phist基因的转录本主要在裂殖体阶段高表达，而恶性疟原虫的转录谱则覆盖不同的无性血液阶段以及配子体阶段。为了解析恶性疟原虫中扩增的phist基因家族的简化研究模型，我们对伯氏疟原虫的phist基因开展了靶向敲除实验。针对伯氏疟原虫PBANKA_114540的敲除尝试均告失败，提示该phist基因是必需基因；而敲除phist基因PBANKA_122900则未观察到明显表型异常，其在整个生命周期中均发挥非必需功能。对恶性疟原虫和伯氏疟原虫的phist基因进行表位标签标记后证实，其编码的蛋白可被分泌至红细胞胞质，且呈现点状定位模式。3个伯氏疟原虫的PEXEL/HT阳性分泌蛋白至少存在部分共定位，这为啮齿类疟原虫感染的红细胞胞质中存在共同的囊泡区室提供了实验佐证。