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 CMU_028430
S-adenosylmethionine-dependent methyltransferase 2.1.1.- CMU_014260
S-adenosylmethionine-dependent methyltransferase 2.1.1.- CMU_029480
Homocysteine S-methyltransferase 2.1.1.10 Missing in annotation
Methionine adenosyl transferase 2.5.1.6 CMU_034740
Adenosylhomocysteinase 3.3.1.1 CMU_037660
Met-tRNA ligase 6.1.1.10 CMU_006170
tRNA binding protein none CMU_018940

 

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

 

CMU_015150 CMU_032300

 

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Sources and fates of metabolites

 

Substrate Source pathways Product Fate pathways
Methionine Host Adenosine Purine metabolism


 

Examples of adenosylmethionine-dependent methyltransferases in Cryptosporidium muris genome

 

Enzyme EC Number Gene id
DNA (cytosine-5-)-methyltransferase 2.1.1.37 CMU_018810
DNA (cytosine-5-)-methyltransferase 2.1.1.37 CMU_039710