Phosphoproteomic Analysis of GAP50-Deficient Parasites Reveals the Inner Membrane Complex Is Involved in Ion Regulation in Toxoplasma gondii.

The Alveolata group of organisms is characterized by a vesicular structure located beneath the plasma membrane. In apicomplexa, this structure is known as the inner membrane complex (IMC). The IMC acts as a scaffold during the budding of the daughter parasite and is utilized as a rigid base for the glideosome. In this study, we discovered that the phosphatase activity of GAP50 is crucial for its function in the biogenesis of the IMC. Through further phosphoproteomic analysis of parasites lacking GAP50, we identified that an NIPA family transporter is localized in the IMC. Knocking out TgNIPA1 significantly impairs the robust growth of the parasites. Additionally, expressing TgNIPA1 in a Salmonella strain lacking magnesium transporters could rescue the growth phenotype of bacteria under low magnesium conditions, indicating that it functions as an active magnesium transporter. Our results strongly suggest that the flattened vesicles of the IMC may play important roles in ion regulation in T. gondii.