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O‐GlcNAc occurs in the protozoan parasite Toxoplasma gondii and is part of the histone code (790.4)

O‐GlcNAcylation, the addition of N‐acetylglucosamine to Serine or Threonine residues, is an abundant, dynamic posttranslational modification that occurs in many eukaryotes; very little is known about its role in early eukaryotes including protozoa. Here, we describe O‐GlcNAcylation in the protozoan parasite Toxoplasma gondii, which causes one of the most common parasitic infections in humans and warm‐blooded animals, Toxoplasmosis. T. gondii is an obligate intracellular parasite, which has the unique ability of being able to switch between two developmental stages, a phenomenon that is crucial for pathogenesis and is thought to be regulated by sensing of nutrient availability and metabolism. How parasites sense changes in the host cell environment is unclear; since O‐GlcNAc is important for metabolic sensing in other eukaryotes, this led us to hypothesise that O‐GlcNAc is a metabolic sensor in T. gondii, regulating developmental programming. Here, we demonstrate that both the T. gondii homologue of O‐GlcNAc transferase (TgOGT) and O‐GlcNAc are present in nuclear and cytoplasmic compartments in T. gondii parasites. As O‐GlcNAc is an important epigenetic regulator, we focussed on its role on T. gondii histones, on which we show by mass spectrometry and immunoprecipitation that it is also present, indicating that it is a dynamic modification in T. gondii. To identify more O‐GlcNAcylated proteins associated with chromatin, we performed immunoprecipitations and mass spectrometry. Surprisingly, native ChIP‐chip experiments localised O‐GlcNAc to centromeric and telomeric regions of the T. gondii genome, where it colocalises with other epigenetic modifiers, suggesting that it plays a role in mitotic chromatin dynamics. Current efforts include overexpression of dominant negative mutants and conditional knockdown to investigate the function of TgOGT in T. gondii.