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    

 

Open in a new window

 

 

Sources and fates of metabolites

 

Substrate Source pathways Product Fate pathways
L-Aspartate Asparagine and aspartate metabolism, Host O-acetyl-L-homoserine ?