J Biol Chem. 2012 Mar 26. [Epub ahead of print]
Conditional mutagenesis of a novel choline kinase demonstrates the plasticity of phosphatidylcholine biogenesis and gene expression in Toxoplasma gondii.
Sampels V, Hartmann A, Dietrich I, Coppens I, Sheiner L, Striepen B, Herrmann A, Lucius R, Gupta N.
SourceHumboldt University, Germany;
The obligate intracellular and promiscuous protozoan parasite Toxoplasma gondii needs an extensive membrane biogenesis that must be satisfied irrespective of its host-cell milieu. We show that the synthesis of the major lipid in T. gondii, phosphatidylcholine (PtdCho), is initiated by a choline kinase (TgCK, ~70-kDa). Full-length TgCK displayed a low affinity for choline (Km ~0.77 mM), and harbors a unique N-terminal hydrophobic peptide that is required for the formation of enzyme oligomers in the parasite cytosol but not for activity. Conditional mutagenesis of the TgCK gene in T. gondii attenuated the protein level by ~60%, which was abolished in the off state of the mutant (Δtgcki). Unexpectedly, the mutant was not impaired in its growth, and also exhibited a normal PtdCho biogenesis. The parasite circumvented the loss of full-length TgCK by a cryptic promoter identified within exon 1 sequence, which can express two putative 53-kDa and 44-kDa isoforms. TgCK-Exon1 alone was also sufficient in driving the expression of GFP in E. coli. The presence of a cryptic promoter correlated with the persistent enzyme activity, PtdCho synthesis and susceptibility of T. gondii to a choline analog, dimethylethanolamine. Quite notably, the mutant displayed a regular growth in the off state despite a 35% decline in PtdCho content and lipid synthesis suggesting a compositional flexibility in the parasite membranes. The observed plasticity of gene expression and membrane biogenesis can ensure a faithful replication and adaptation of T. gondii in disparate host or nutrient environments.
PMID: 22451671 [PubMed - as supplied by publisher]