Threonine metabolism
Threonine is one of the ten essential amino acids in human, which needs to be obtained from the diet. Toxoplasma gondii and Neospora caninum possess the genes for four of the five enzymes involved in threonine biosynthesis from aspartate. The missing enzyme in the pathway is homoserine dehydrogenase. Lysine and threonine are the only amino acids which can be synthesised by cyst forming Coccidia, but absent in other Apicomplexa. The first two enzymes are common to the threonine biosynthesis and lysine biosynthesis pathways as the precursor substrate for these amino acids is aspartate. Of the 4 enzymes of threonine biosynthesis identified in the genome, homoserine kinase is the only enzyme identified by MS-based proteomics studies at least in the oocyst stage of T. gondii [1].
Enzyme | EC Number | Gene id | Protein localisation | Localisation data source |
---|---|---|---|---|
Homoserine dehydrogenase | 1.1.1.3 | Missing in annotation | ||
Aspartate semialdehyde dehydrogenase | 1.2.1.11 | TGME49_205420 | Cytosol | GO annotation |
Homoserine O-acetyltransferase | 2.3.1.31 | TGME49_320730 | ||
Homoserine kinase | 2.7.1.39 | TGME49_216640 | ||
Aspartate kinase | 2.7.2.4 | TGME49_227090 | ||
Threonine synthase | 4.2.3.1 | TGME49_220840 | ||
Threonine-tRNA ligase | 6.1.1.3 | TGME49_219430 | ||
Threonine-tRNA ligase | 6.1.1.3 | TGME49_300260 | Apicoplast | Previous publication |
List of genes annotated as tRNA-Thr in T. gondii genome
TGME49_015110 | TGME49_015120 | TGME49_024120 | TGME49_043320 |
TGME49_051720 | TGME49_053840 | TGME49_076950 | TGME49_092180 |
TGME49_100641 | TGME49_100652 |
Sources and fates of metabolites
Substrate | Source pathways | Product | Fate pathways |
---|---|---|---|
L-Aspartate | Asparagine and aspartate metabolism, Host | O-acetyl-L-homoserine | ? |
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