Conditional Mutagenesis of a Novel Choline Kinase Demonstrates Plasticity of Phosphatidylcholine Biogenesis and Gene Expression in Toxoplasma gondii

Abstract

Background: Choline phosphorylation is the first step of phosphatidylcholine synthesis. Results: Toxoplasma gondii expresses a novel choline kinase forming cytosolic clusters. Its conditional mutagenesis identifies a cryptic exon-promoter. Besides, the parasite mutant displays a normal growth despite a substantial depletion of PtdCho. Conclusion: Plasticity of gene expression and membrane biogenesis are revealed. Significance: Adaptation of an intracellular pathogen to metabolic perturbations and disparate host cells can thus be ensured.

Lipid synthesis in protozoan parasites: A comparison between kinetoplastids and apicomplexans

“…In contrast, Toxoplasma parasites lack candidate genes, and enzymatic activities, for phosphoethanolamine N -methyltransferase and PE N -methyltransferase [180, 208, 233] and, thus, depend on the CDP-choline pathway for PC synthesis (Fig. 5).…”

“…5). In a recent report, T. gondii was shown to express a novel choline kinase harboring a unique hydrophobic N-terminus that is dispensable for enzyme activity but required for protein oligomerization [233]. Interestingly, expression of two additional choline kinase isoforms through a cryptic promoter compensated for the loss of choline kinase activity after conditional mutagenesis of the unusual choline kinase gene [233].…”

“…5). A cytosolically located ethanolamine kinase in T. gondii phosphorylates ethanolamine only, whereas a choline kinase showing punctate intracellular distribution mediates phosphorylation of both choline and ethanolamine [233]. Similar to the situation in Plasmodium , the T. gondii choline kinase gene cannot be disrupted, unless using a conditional knock-out approach, indicating that the enzyme is essential for parasite viability [233].…”

Phosphatidylethanolamine Synthesis in the Parasite Mitochondrion Is Required for Efficient Growth but Dispensable for Survival of Toxoplasma gondii

“…Similar to other eukaryotes, phospholipids account for a major fraction of parasite membranes, which include phosphatidylcholine (PtdCho), 2 PtdEtn, phosphatidylinositol, and PtdSer (4). T. gondii has the potential to synthesize its major phospholipids (4 -6) and harbors a relatively complete set of enzymes for de novo synthesis (4,5). Unlike PtdCho and PtdSer, for which the parasite harbors only one route, PtdEtn is made by decarboxylation of PtdSer and by the CDP-ethanolamine pathway (4).…”

Microbial Modulation of Host Immunity with the Small Molecule Phosphorylcholine

“…Parasites, in contrast, use the Kennedy pathway for phosphatidylcholine synthesis, similar to most eukaryotes (21)(22)(23). Some bacterial species can also synthesize phosphatidylcholine, either through the Kennedy pathway or by methylation of phosphatidylethanolamine, which is an alternative method for phosphatidylcholine synthesis also used by eukaryotes (24)(25)(26).…”