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.

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

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Sources and fates of metabolites

Examples of adenosylmethionine-dependent methyltransferases in Cryptosporidium muris genome