Toxoplasma gondii VIP1 mediates parasitophorous vacuole-host endoplasmic reticulum interactions to facilitate parasite development.

Membrane contact sites (MCS) are areas of close apposition between organelles without membrane fusion, allowing for exchange of biomolecules. The endoplasmic reticulum (ER) forms many MCS via two proteins, vesicle-associated membrane protein-associated proteins A and B (VAPA and VAPB). The obligate intracellular parasite Toxoplasma gondii resides within mammalian cells in a parasitophorous vacuole (PV), which closely contacts the host ER at distances compatible with MCS. However, the proteins mediating this interaction remain largely unknown. Here, using molecular and microscopy approaches, we show that VAPA and VAPB localize at the PV membrane and, with motile sperm domain-containing protein 2 (MOSPD2), mediate ER-PV interactions. Cells deficient in VAPA, VAPB and MOSPD2 do not recruit host ER at the PV, and parasites show growth defects. We identify a parasite protein that localizes at the PV membrane, called TgVIP1, which harbours an FFAT-like motif that binds VAPA and VAPB. These findings lay the basis for understanding how and why Toxoplasma exploits ER-PV interactions and may uncover new drug targets.