Toxoplasma ceramide synthases: Gene duplication, functional divergence, and roles in parasite fitness

Authors:
Zisis Koutsogiannis, John G. Mina, Christin A. Albus, Matthijs A. Kol, Joost C. M. Holthuis, Ehmke Pohl, Paul W. Denny
In:
Source: FASEB J
Publication Date: (2023)
Issue: 37: 11
Research Area:
Parasitology
Cells used in publication:
Toxoplasma gondii
Species: unicellular
Tissue Origin:
Platform:
4D-Nucleofector® X-Unit
Experiment

Transient transfections were carried out using a 4D Nucleofector (Lonza), protocol FI 158. Briefly, parasites freshly lysed from HFFs monolayer were homogenized by passage through a 25-gauge needle and isolated by centrifugation at 1500?×?g for 10?min at 4°C. The pellet was resuspended in P3 buffer with added supplementary buffer P1 (Lonza). 20?µL of the parasite suspension (107?mL-1) were added to a dried pellet of ethanol-precipitated pTXP_TgCerS1-FLAG or pTXP_TgCerS2-FLAG plasmid and electroporated.

Abstract

Toxoplasma gondii is an obligate, intracellular apicomplexan protozoan parasite of both humans and animals that can cause fetal damage and abortion and severe disease in the immunosuppressed. Sphingolipids have indispensable functions as signaling molecules and are essential and ubiquitous components of eukaryotic membranes that are both synthesized and scavenged by the Apicomplexa. Ceramide is the precursor for all sphingolipids, and here we report the identification, localization and analyses of the Toxoplasma ceramide synthases TgCerS1 and TgCerS2. Interestingly, we observed that while TgCerS1 was a fully functional orthologue of the yeast ceramide synthase (Lag1p) capable of catalyzing the conversion of sphinganine to ceramide, in contrast TgCerS2 was catalytically inactive. Furthermore, genomic deletion of TgCerS1 using CRISPR/Cas-9 led to viable but slow-growing parasites indicating its importance but not indispensability. In contrast, genomic knock out of TgCerS2 was only accessible utilizing the rapamycin-inducible Cre recombinase system. Surprisingly, the results demonstrated that this “pseudo” ceramide synthase, TgCerS2, has a considerably greater role in parasite fitness than its catalytically active orthologue (TgCerS1). Phylogenetic analyses indicated that, as in humans and plants, the ceramide synthase isoforms found in Toxoplasma and other Apicomplexa may have arisen through gene duplication. However, in the Apicomplexa the duplicated copy is hypothesized to have subsequently evolved into a non-functional “pseudo” ceramide synthase. This arrangement is unique to the Apicomplexa and further illustrates the unusual biology that characterize these protozoan parasites.