Center for Tropical and Emerging Global Diseases, University of Georgia, Georgia, GA, USA.
Department of Cellular Biology, University of Georgia, Athens, GA, USA.
Mol Microbiol. 2021 May;115(5):1054-1068. doi: 10.1111/mmi.14722. Epub 2021 Apr 19.
Ca is a universal intracellular signal that regulates many cellular functions. In Toxoplasma gondii, the controlled influx of extracellular and intracellular Ca into the cytosol initiates a signaling cascade that promotes pathogenic processes like tissue destruction and dissemination. In this work, we studied the role of proton transport in cytosolic Ca homeostasis and the initiation of Ca signaling. We used a T. gondii mutant of the V-H -ATPase, a pump previously shown to transport protons to the extracellular medium, and to control intracellular pH and membrane potential and we show that proton gradients are important for maintaining resting cytosolic Ca at physiological levels and for Ca influx. Proton transport was also important for Ca storage by acidic stores and, unexpectedly, the endoplasmic reticulum. Proton transport impacted the amount of polyphosphate (polyP), a phosphate polymer that binds Ca and concentrates in acidocalcisomes. This was supported by the co-localization of the vacuolar transporter chaperone 4 (VTC4), the catalytic subunit of the VTC complex that synthesizes polyP, with the V-ATPase in acidocalcisomes. Our work shows that proton transport regulates plasma membrane Ca transport and control acidocalcisome polyP and Ca content, impacting Ca signaling and downstream stimulation of motility and egress in T. gondii.
钙是一种普遍存在于细胞内的信号分子，调节着许多细胞功能。在刚地弓形虫中，细胞外和细胞内钙的受控流入细胞质会引发信号级联反应，促进组织破坏和传播等致病过程。在这项工作中，我们研究了质子运输在细胞质钙稳态和钙信号起始中的作用。我们使用了一种 V-H+-ATPase 的刚地弓形虫突变体，该泵先前被证明可以将质子运送到细胞外介质中，并控制细胞内 pH 值和膜电位，我们发现质子梯度对于维持生理水平的静息细胞质钙和钙内流非常重要。质子运输对于酸性储存器（包括内质网）中的钙储存也很重要。出乎意料的是，质子运输还影响多磷酸盐（polyP）的含量，多磷酸盐是一种结合钙并在酸性液泡中浓缩的磷酸聚合物。这一点得到了证实，因为液泡转运伴侣 4（VTC4）与 V-ATPase 在酸性液泡中共定位，VTC4 是合成 polyP 的 VTC 复合物的催化亚基。我们的工作表明，质子运输调节质膜钙转运，并控制酸性液泡内的 polyP 和钙含量，从而影响钙信号和刚地弓形虫下游运动和出芽的刺激。
