Methionine metabolism

Methionine, an essential amino acid in humans is also essential to all apicomplexans and need to be salvaged from the host. The methionine metabolism pathway in Cryptosporidia is essential for providing S-adenosylmethionine, the methyl group donor in various reactions. A metabolic capability which is present in Plasmodium falciparum and absent in Coccidia including Cryptosporidia is the synthesis of polyamines such as spermine and spermidine. This has been incorporated with methionine metabolism in MPMP (methionine and polyamine metabolism). The genes coding for the enzymes ornithine decarboxylase, arginine decarboxylase and spermine/spermidine synthase are absent in the genomes of Cryptosporidia. Polyamine oxidase and spermine/spermidine N-acetyltransferase (SSAT) enzymes are present in Cryptosporidia genomes as in other Coccidia. The activities of arginine decarboxylase, spermine N-acetyltransferase and spermidine N-acetyltransferase were detected in Cryptosporidium parvum extracts although ornithine decarboxylase was not experimentally detected [1, 2]. This suggests the occurance of back conversion of putrescine from spermine salvaged from host.

 

Enzyme EC Number Gene id
[methionine synthase] reductase 1.16.1.8 Missing in annotation
S-adenosylmethionine-dependent methyltransferase 2.1.1.- Chro.10303
Homocysteine S-methyltransferase 2.1.1.10 Missing in annotation
Methionine adenosyl transferase 2.5.1.6 Chro.70301
Adenosylhomocysteinase 3.3.1.1 Chro.30017
Met-tRNA ligase 6.1.1.10 Chro.80398
tRNA binding protein none Chro.40444

 

List of genes annotated as tRNA-Met in C. hominis genome

 

Chro.trn020 Chro.trn021

 

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Sources and fates of metabolic pathways

 

Substrate Source pathways Product Fate pathways
Methionine Host Adenosine Purine metabolism

 

Examples of adenosylmethionine-dependent methyltransferases in Cryptosporidium hominis genome

 

Enzyme EC Number Gene id
DNA (cytosine-5-)-methyltransferase 2.1.1.37 Chro.40428
DNA (cytosine-5-)-methyltransferase 2.1.1.37 Chro.50169