Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, GA, 30602, USA.
Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Heath, Baltimore, MD, 21205, USA.
Nat Commun. 2021 Oct 4;12(1):5802. doi: 10.1038/s41467-021-25987-5.
Two-pore channels (TPCs) are a ubiquitous family of cation channels that localize to acidic organelles in animals and plants to regulate numerous Ca-dependent events. Little is known about TPCs in unicellular organisms despite their ancient origins. Here, we characterize a TPC from Toxoplasma gondii, the causative agent of toxoplasmosis. TgTPC is a member of a novel clad of TPCs in Apicomplexa, distinct from previously identified TPCs and only present in coccidians. We show that TgTPC localizes not to acidic organelles but to the apicoplast, a non-photosynthetic plastid found in most apicomplexan parasites. Conditional silencing of TgTPC resulted in progressive loss of apicoplast integrity, severely affecting growth and the lytic cycle. Isolation of TPC null mutants revealed a selective role for TPCs in replication independent of apicoplast loss that required conserved residues within the pore-lining region. Using a genetically-encoded Ca indicator targeted to the apicoplast, we show that Ca signals deriving from the ER but not from the extracellular space are selectively transmitted to the lumen. Deletion of the TgTPC gene caused reduced apicoplast Ca uptake and membrane contact site formation between the apicoplast and the ER. Fundamental roles for TPCs in maintaining organelle integrity, inter-organelle communication and growth emerge.
双孔通道（TPCs）是广泛存在于动物和植物中的一类阳离子通道，定位于酸性细胞器，调节许多依赖 Ca 的事件。尽管单细胞生物的 TPCs 起源古老，但对其了解甚少。在这里，我们描述了刚地弓形虫（导致弓形体病的病原体）中的一种 TPC。TgTPC 是 Apicomplexa 中新的 TPC 家族的成员，与先前鉴定的 TPC 不同，仅存在于球虫中。我们表明，TgTPC 不定位在酸性细胞器中，而是定位在顶质体中，这是一种在大多数 Apicomplexa 寄生虫中发现的非光合质体。TgTPC 的条件沉默导致顶质体完整性逐渐丧失，严重影响生长和裂解周期。TPC 缺失突变体的分离揭示了 TPC 在复制中的选择性作用，与质体丧失无关，这需要孔衬区域内的保守残基。使用靶向顶质体的遗传编码 Ca 指示剂，我们表明源自 ER 的 Ca 信号而不是来自细胞外空间的 Ca 信号被选择性地传递到腔中。TgTPC 基因的缺失导致顶质体 Ca 摄取减少和顶质体与 ER 之间的膜接触位点形成减少。TPCs 在维持细胞器完整性、细胞器间通讯和生长方面的基本作用凸显出来。
