Mannose and fructose metabolism

The mannose and fructose metabolism pathway presented here is different from the pathway for Toxoplasma gondii in two aspects. This pathway utilises fructose, a hexose (may be from host) and fructose-6-phosphate, a glycolysis intermediate for the production of important nucleotide sugar GDP-D-mannose in Cryptosporidium species. This is an essential substrate for glycosylphosphatidylinositol (GPI) anchor biosynthesis and synthesis of the anchors for N-glycans (N-glycans biosynthesis). GDP-L-fucose is also synthesised in T. gondii and Plasmodium falciparum, which is missing in Cryptosporidium species. The enzyme mannitol dehydrogenase was identified in all three Cryptosporidium genomes, which is absent in T. gondii gene models. No other enzymes involved in mannitol metabolism were identified so far in these genomes.

 

Enzyme EC Number Gene id
Mannitol dehydrogenase 1.1.1.255 cgd5_2670
Hexokinase 2.7.1.1 cgd6_3800
Mannose-1-phosphate guanylyltransferase 2.7.7.13 cgd2_1770
Mannose-6-phosphate isomerase 5.3.1.8 cgd8_1920
Phosphomannomutase 5.4.2.8 cgd4_960

 

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Sources and fates of metabolites

 

Substrate Source pathways Product Fate pathways
beta-D-Fructose-6P Glycolysis GDP-D-Mannose N-glycan biosynthesis
beta-D-Fructose Starch metabolism, Host    
D-Mannose Host D-Mannitol ?