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A non-technical overview of this article for general readers

Posted by almanzo on 27 Mar 2009 at 14:31 GMT

Higher organisms with a complete nervous system and requirement for catecholamine neurotransmitter signaling molecules have developed three distinct types of aromatic amino acid hydroxylase: Phenylalanine hydroxylase, which converts phenylalanine to tyrosine; Tyrosine hydroxylase, which converts tyrosine to L-DOPA and Tryptophan hydroxylase, which converts tryptophan to 5-hydroxytryptophan (5-HT). L-DOPA and 5-HT are the precursors for the neurotransmitters dopamine and serotonin, respectively. Toxoplasma gondii is a protozoan parasite of all warm blooded vertebrates including humans detectable by seroprevalence in 10-30% of the human population. We have cloned two nearly identical, aromatic amino acid hydroxylase genes that can utilise both phenylalanine and tyrosine, seemingly encoding a hybrid of multi-cellular organism’s phenylalanine and tyrosine hydroxylases, with some preference for tyrosine conversion to L-DOPA. Therefore the T. gondii enzymes can synthesize tyrosine and convert tyrosine into L-DOPA. We have found that one copy of the gene encoding this enzyme is constitutively expressed across the parasite lifecycle and one is upregulated during the brain and muscle cyst forming stage. Therefore it is possible that the two genes may fill different roles in the different stages of the parasite lifecycle. We discuss here the implications of this finding on our view of the interactions between the parasite and it’s host. We also discuss how the discovery of a third paralogous set of enzymes that are developmentally regulated across the parasite lifecycle, impacts on our view of how the parasite transitions from the fast dividing blood borne stage to the slow dividing cyst forming stage.

No competing interests declared.