A Spinster-like Transporter at the Inner Membrane Complex is critical for Toxoplasma gondii cytokinesis, motility and invasion.

The Major Facilitator Superfamily (MFS) comprises a large and diverse group of membrane transport proteins involved in the translocation of metabolites across cellular membranes. The genome of Toxoplasma gondii encodes approximately 60 putative MFS transporters, yet the functions of most remain poorly characterized. Conserved across the superphylum Alveolata, the inner membrane complex (IMC) is a specialized peripheral membrane system essential for parasite replication, structural integrity, motility, and host cell invasion. Here, we identify Toxoplasma gondii Daughter Cell Transporter 1 (TgDCT1), a previously uncharacterized MFS transporter, as a critical regulator of daughter cell formation. TgDCT1 localizes predominantly to the daughter cell IMC and contains a predicted spinster-like MFS domain. Phylogenetic and structural analyses reveal that TgDCT1 is conserved across Alveolata, shares a canonical MFS fold with its Plasmodium falciparum orthologue, and exhibits striking structural similarity to the human sphingosine-1-phosphate (S1P) transporter SPNS2, suggesting an evolutionarily conserved role in lipid transport. Conditional depletion of TgDCT1 results in severe defects in cytokinesis, including disrupted IMC architecture, aberrant daughter cell morphology, and failure of plasma membrane abscission. Although TgDCT1-depleted parasites retain the capacity for microneme secretion and egress, they display profoundly impaired motility and host cell invasion, ultimately leading to arrest of the lytic cycle. Notably, pharmacological inhibition of the S1P transporter SPNS2 using the compounds 11i and 33p phenocopies TgDCT1 depletion, impairing parasite morphogenesis, intracellular replication, and division synchrony. Furthermore, transgenic complementation demonstrates that the spinster-like domain of the P. falciparum DCT1 orthologue can functionally substitute for TgDCT1, indicating that these transporters likely recognize the same substrate. Together, these findings establish TgDCT1 as a central regulator of lipid homeostasis required for IMC maturation, endodyogeny, and parasite propagation in Toxoplasma gondii and likely other Apicomplexa.