POFUT2-mediated O-glycosylation of MIC2 is dispensable for Toxoplasma gondii tachyzoites

Abstract

Toxoplasma gondii is a ubiquitous obligate intracellular eukaryotic parasite that causes congenital birth defects, disease of the immunocompromised and blindness. Protein glycosylation plays an important role in the infectivity and evasion of immune response of many eukaryotic parasites and is also of great relevance to vaccine design. Here, we demonstrate that MIC2, the motility-associated adhesin of T. gondii, has highly glycosylated thrombospondin repeat domains (TSR). At least seven C-linked and three O-linked glycosylation sites exist within MIC2, with >95% occupancy at O-glycosylation sites. We demonstrate that the addition of O-glycans to MIC2 is mediated by a protein O-fucosyltransferase 2 homologue (TgPOFUT2) encoded by TGGT1_273550. While POFUT2 homologues are important for stabilizing motility associated adhesins and host infection in other apicomplexan parasites, in T. gondii loss of TgPOFUT2 has only a modest impact on MIC2 levels and the wider proteome. Consistent with this, both plaque formation and tachyzoite infectivity are broadly similar in the presence or absence of TgPOFUT2. These findings demonstrate that TgPOFUT2 O-glycosylates MIC2 and that this glycan is dispensable in T. gondii tachyzoites.