Uy Juliette N, Lou Qing, Zhou Z Hong, Bradley Peter J
bioRxiv. 2025 Jun 4:2025.06.03.657516. doi: 10.1101/2025.06.03.657516.
and related apicomplexan parasites utilize a unique membrane and cytoskeletal organelle called the inner membrane complex (IMC) for maintaining cell shape, motility, host cell invasion, and replication. The cytoskeleton portion of the organelle is a network of filaments composed of proteins called alveolins, whose precise functions and organization are poorly understood. Here we describe the function of the founding member of the alveolins, IMC1, which we show is expressed and loaded onto forming daughter buds with IMC4, but later than the other key alveolins IMC3, IMC6, and IMC10. Disruption of IMC1 results in severe morphological defects that impact the integrity of the parasite's cytoskeleton and disrupt invasion, replication, and egress. Loss of IMC1 in a less virulent type II strain results in a dramatic loss of infectivity and complete failure to form a chronic infection. We then use deletion analyses to dissect functional regions of the protein which reveals a key subregion of the alveolin domain that is sufficient for IMC targeting and also required for function. We then show that IMC1 interacts directly with IMC4 and the loss of IMC1 results in mislocalization of IMC4 specifically in forming daughter buds. This study thus reveals the critical role that IMC1 plays in forming and maintaining the architecture of the filamentous network of the IMC.
Parasites in the phylum Apicomplexa maintain their intracellular lifestyle using specialized organelles that mediate the lytic cycle of host cell invasion, intracellular replication, and egress. One of these organelles is the inner membrane complex (IMC), which consists of membrane vesicles supported by a cytoskeletal meshwork formed from proteins called alveolins. This study focuses on the first identified alveolin IMC1 and determines its precise function via expression timing, gene knockout, deletion and mutagenesis, partner identification, and in vivo infection studies. We show that this protein is critical to the ultrastructure of the parasite which is important for every stage of its lytic cycle. We also identify key regions of the protein that are important for localization, function, and interaction with another key alveolin, IMC4.
疟原虫及相关顶复门寄生虫利用一种独特的膜和细胞骨架细胞器——内膜复合体（IMC）来维持细胞形态、运动性、宿主细胞入侵及复制。该细胞器的细胞骨架部分是由称为alveolins的蛋白质组成的丝状网络，其精确功能和组织方式尚不清楚。在此，我们描述了alveolins的创始成员IMC1的功能，我们发现它与IMC4一起表达并加载到正在形成的子芽上，但比其他关键的alveolins（IMC3、IMC6和IMC10）要晚。IMC1的破坏会导致严重的形态缺陷，影响寄生虫细胞骨架的完整性，并破坏入侵、复制和逸出过程。在毒性较小的II型菌株中缺失IMC1会导致感染力急剧丧失，并完全无法形成慢性感染。然后，我们使用缺失分析来剖析该蛋白质的功能区域，揭示了alveolin结构域的一个关键子区域，该区域足以实现IMC靶向，也是功能所必需的。然后，我们表明IMC1直接与IMC4相互作用，IMC1的缺失会导致IMC4在正在形成的子芽中特异性地错误定位。因此，这项研究揭示了IMC1在形成和维持IMC丝状网络结构中所起的关键作用。
顶复门的寄生虫利用专门的细胞器维持其细胞内生活方式，这些细胞器介导宿主细胞入侵、细胞内复制和逸出的裂解周期。其中一个细胞器是内膜复合体（IMC），它由膜囊泡组成，由称为alveolins的蛋白质形成的细胞骨架网络支撑。这项研究聚焦于首个被鉴定的alveolin IMC1，并通过表达时间、基因敲除、缺失和诱变、伙伴鉴定以及体内感染研究来确定其精确功能。我们表明，这种蛋白质对寄生虫的超微结构至关重要，而超微结构对其裂解周期的每个阶段都很重要。我们还确定了该蛋白质的关键区域，这些区域对定位、功能以及与另一个关键alveolin IMC4的相互作用都很重要。
