GMD

GMD (PF3D7_0813800) is a cytoplasmic GDP-mannose 4,6-dehydratase that catalyzes the first committed step of de novo GDP-fucose biosynthesis in Plasmodium falciparum, converting GDP-mannose toward GDP-fucose as demonstrated by in vitro assay of the recombinant enzyme (PMID:23615908). Epitope-tagged GMD localizes to the parasite cytoplasm during the intraerythrocytic developmental cycle (PMID:23615908). Genetic disruption of GMD completely abolishes labeling by the fucose-binding lectin UEA-I, establishing that GMD is required for production of fucose-containing glycoconjugates; however, GDP-fucose remains detectable in the null mutant, indicating an alternative, non-GMD route sustains residual GDP-fucose pools (PMID:27849032). GMD is dispensable for asexual blood-stage development, as the null mutant shows normal growth and invasion in culture (PMID:27849032). Beyond these findings, no further mechanistic detail — including structural basis, regulation, or downstream fucosylation targets — has been characterized in the available corpus.

1. 2013 Medium

   Establishing whether P. falciparum encodes a functional entry enzyme for de novo GDP-fucose synthesis, this work showed the recombinant protein is catalytically active on GDP-mannose.

   Evidence In vitro enzymatic assay of recombinant P. falciparum GMD

   PMID:23615908

   Open questions at the time

   • Kinetic parameters and structural basis of catalysis not determined
   • Activity shown in vitro only, not linked to in vivo flux at this stage
   • Single lab, single method
2. 2013 Medium

   To place the enzyme in a subcellular context, tagging showed GMD resides in the parasite cytoplasm during intraerythrocytic development.

   Evidence Fluorescence microscopy of epitope-tagged GMD in transgenic 3D7 parasites

   PMID:23615908

   Open questions at the time

   • Localization from a single tagging approach without orthogonal validation
   • Does not address whether localization changes across stages or is complexed with partners
3. 2016 High

   To test GMD's cellular role, knockout demonstrated it is required for fucosylated glycoconjugates yet revealed a GMD-independent source of residual GDP-fucose.

   Evidence PfGMD null mutant with UEA-I lectin labeling and LC-MS/MS quantification of GDP-fucose

   PMID:27849032

   Open questions at the time

   • Identity of the alternative GDP-fucose-generating mechanism not defined
   • Fucosylated substrate glycoconjugates not molecularly identified
4. 2016 Medium

   To assess essentiality, the null mutant showed normal asexual growth and invasion, establishing the de novo GDP-fucose pathway is dispensable for blood-stage development in culture.

   Evidence Growth and invasion assays of the PfGMD null mutant in culture

   PMID:27849032

   Open questions at the time

   • Does not address requirement in sexual/mosquito or liver stages
   • In vitro culture only; in vivo relevance untested

• The molecular identity of the alternative GDP-fucose source and the biological function of GMD-dependent fucosylation in the parasite remain unknown.
• Salvage or alternative enzymatic route sustaining residual GDP-fucose unidentified
• Downstream fucosylated targets and their functional consequences uncharacterized
• Role, if any, in non-blood life-cycle stages untested