Novel antibodies detect nucleocytoplasmic O-fucose in protist pathogens, cellular slime molds, and plants

Cellular adaptations to change often involve post-translational modifications of nuclear and cytoplasmic proteins. An example found in protists and plants is the modification of serine and threonine residues of dozens to hundreds of nucleocytoplasmic proteins with a single fucose (O-fucose). A nucleocytoplasmic O-fucosyltransferase occurs in the pathogen <i>Toxoplasma gondii</i>, the social amoeba <i>Dictyostelium</i>, and higher plants, where it is called Spy because mutants have a spindly appearance. O-fucosylation, which is required for optimal proliferation of <i>Toxoplasma</i> and <i>Dictyostelium</i>, is paralogous to the O-GlcNAcylation of nucleocytoplasmic proteins of plants and animals that are involved in stress and nutritional responses. O-fucose was first discovered in <i>Toxoplasma</i> using <i>Aleuria aurantia</i> lectin, but its broad specificity for terminal fucose residues on N- and O-linked glycans in the secretory pathway limits its use. Here we present affinity-purified rabbit antisera that are selective for the detection and enrichment of proteins bearing fucose-O-Ser or fucose-O-Thr. These antibodies detect numerous nucleocytoplasmic proteins in <i>Toxoplasma, Dictyostelium</i>, and <i>Arabidopsis</i>, as well as O-fucose occurring on secretory proteins of <i>Dictyostelium</i> and mammalian cells except when blocked by further glycosylation. The antibodies label <i>Toxoplasma</i>, <i>Acanthamoeba</i>, and <i>Dictyostelium</i> in a pattern reminiscent of O-GlcNAc in animal cells including nuclear pores. The O-fucome of <i>Dictyostelium</i> is partially conserved with that of <i>Toxoplasma</i> and is highly induced during starvation-induced development. These antisera demonstrate the unique antigenicity of O-fucose, document the conservation of the O-fucome among unrelated protists, and enable the study of the O-fucomes of other organisms possessing O-fucosyltransferase-like genes.IMPORTANCEO-fucose (O-Fuc), a form of mono-glycosylation on serine and threonine residues of nuclear and cytoplasmic proteins of some parasites, other unicellular eukaryotes, and plants, is understudied because it is difficult to detect owing to its neutral charge and lability during mass spectrometry. Yet, the O-fucosyltransferase enzyme (OFT) is required for optimal growth of the agent for toxoplasmosis, <i>Toxoplasma gondii</i>, and an unrelated protist, the social amoeba <i>Dictyostelium discoideum</i>. Furthermore, O-fucosylation is closely related to the analogous process of O-GlcNAcylation of thousands of proteins of animal cells, where it plays a central role in stress and nutritional responses. O-Fuc is currently best detected using <i>Aleuria aurantia</i> lectin (AAL), but in most organisms, AAL also recognizes a multitude of proteins in the secretory pathway that are modified with fucose in different ways. By establishing the potential to induce highly specific rabbit antisera that discriminate O-Fuc from all other forms of protein fucosylation, this study expands knowledge about the protist O-fucome and opens a gateway to explore the potential occurrence and roles of this intriguing posttranslational modification in bacteria and other protist pathogens such as <i>Acanthamoeba castellanii</i>.