Mebratu Bitew

Thank you so much Francesca🙏. Looking forward to hearing your thoughts on the final version of the paper.

Big thanks to the whole team for the hard work on this one. This work wouldn't have been possible without the incredible support and guidance from my PI @saeijlab.bsky.social and the amazing contributions from all co-authors: @wanglab-toxo.bsky.social @apicolipid.bsky.social

A genome-wide CRISPR screen identifies GRA38 as a key regulator of lipid homeostasis during Toxoplasma gondii adaptation to lipid-rich conditions - Nature Communications Here, using a genome-wide CRISPR screen, Bitew et al. identify GRA38, a phosphatidic acid phosphatase, as a key factor in Toxoplasma gondii adaptation to lipid-rich conditions via keeping lipid balanc...

Thrilled to share some great news—my new paper is published in @natcomms.nature.com and out today!
We conducted a genome-wide CRISPR screen in Toxoplasma gondii and identified GRA38, a dense granule protein, as a key regulator of lipid homeostasis www.nature.com/articles/s41...

Huge thanks to all collaborators and colleagues! @saeijlab.bsky.social @apicolipid.bsky.social

11/ In summary:
GRA38 helps Toxoplasma adapt to lipid-rich environments by maintaining PA/DAG balance.
Without it, the parasite accumulates lipids, grows poorly, exits early, and loses virulence.
We highlight a new node in the host-parasite lipid interface.

10/ In mouse infection studies, Δgra38 and catalytic mutants were significantly less virulent than WT.
This shows that GRA38 isn't just a metabolic player—it’s important for Toxoplasma pathogenesis in vivo.

9/ We purified recombinant GRA38 and showed that it has PAP activity in vitro.
Mutation of the DxDxT/V motif reduced activity, and known PAP inhibitors (like propranolol) blocked it.
GRA38 is a phosphatidic acid phosphatase!

8/ Lipidomic profiling revealed major metabolic disruptions in Δgra38 parasites:

↑ PA species

Altered DAG species

Broad changes in phospholipids and fatty acids
This confirms GRA38 regulates lipid metabolism and balance.

7/ Δgra38 parasites accumulate more lipid droplets (LDs), especially under lipid-rich conditions.
They also take up more fluorescently labeled PA, showing GRA38 helps regulate PA levels in the PV.
The catalytic mutant behaves just like the knockout.

6/ We mutated the DxDxT/V motif (→ AxAxT/V) and found that this catalytic site is essential.
Δgra38 and GRA38D72/74A mutants showed impaired growth in 10% FBS but not in 1% FBS.
They also triggered premature host cell death—suggesting early egress.

5/ GRA38 is a dense granule protein that localizes to the parasitophorous vacuole (PV).
It’s highly conserved and contains a DxDxT/V motif—typical of phosphatidic acid phosphatases (PAPs).
Structural modeling supports its similarity to known PAPs.

4/ Our CRISPR screen revealed condition-specific essential genes.
Some genes mattered more in lipid-poor settings, others (like GRA38) were critical in lipid-rich conditions.
Growth competition assays confirmed that Δgra38 parasites struggle in 10% FBS.

3/ First, we established a baseline differences in
host lipid composition in 1% vs. 10% FBS conditions.
Cells in 10% FBS had a massive increase in lipid abundance—especially phosphatidic acid (PA), DAG, TAG, and cholesterol.
So, host lipid composition really shifts with serum level.

2/
Why lipids?
Toxoplasma scavenges host lipids to grow—but how it senses and responds to different lipid environments was unclear.
We used a genome-wide CRISPR screen to uncover molecular mechanisms underlying the Toxoplasma's ability to sense lipid availability and mediate metabolic adaptation.

Excited to share our new preprint:

We uncover how Toxoplasma senses host lipid levels and adapts metabolically to survive in different nutrient environments. www.researchsquare.com/article/rs-6...