TGME49_267730

The putative GDP-fucose transporter NST2 in Toxoplasma gondii supplies the sugar-nucleotide donor required for O-fucosylation of thrombospondin type I repeats (TSRs) within the secretory pathway (PMID:30538131). Disruption of NST2 abolishes O-fucosylation on the TSRs of the micronemal adhesin MIC2, markedly reduces cellular MIC2 levels, and mislocalizes MIC2 to earlier secretory compartments, identifying NST2 as the Golgi GDP-fucose transporter that feeds POFUT2-dependent O-fucosylation of TSR-containing proteins (PMID:30538131). Loss of NST2 impairs host cell attachment and invasion to an extent comparable to the Δmic2 phenotype, linking this glycosylation pathway to parasite infectivity (PMID:30538131). Beyond (PMID:30538131), no further mechanistic detail has been characterized in the available corpus.

1. 2018 High

   Whether a dedicated Golgi GDP-fucose transporter supports TSR O-fucosylation in T. gondii was unknown; knockout of NST2 established that this transporter is required to deliver GDP-fucose for POFUT2-dependent modification of MIC2, coupling glycosylation to adhesin stability and invasion.

   Evidence Gene knockout (Δnst2) with mass spectrometry glycan analysis, anti-GlcFuc antibody detection, immunofluorescence, and host cell invasion/attachment assays in human foreskin fibroblasts

   PMID:30538131

   Open questions at the time

   • Direct biochemical demonstration of GDP-fucose transport activity by NST2 (e.g. reconstituted transport assay) is not shown
   • The full set of TSR-containing substrates beyond MIC2 dependent on NST2 is not defined
   • Structural basis of substrate recognition and Golgi targeting of NST2 is uncharacterized

• Whether NST2 directly transports GDP-fucose across the Golgi membrane and the complete substrate repertoire and structural mechanism remain to be established.
• No in vitro transport reconstitution establishing direct GDP-fucose transport
• No structural model of the transporter
• Substrate scope beyond MIC2 undefined