Amino acid transporters in Trypanosoma brucei brucei
Two approaches have been used to investigate the nature of amino acid transport in T. brucei. The first approach involved studying the uptake of radiolabelled amino acids by the parasite, the second approach involved the identification, cloning and expression in a heterologous system of a gene encoding for a putative amino acid transporter. The biochemical approach revealed that methionine uptake was of relatively high affinity in procyclic and bloodstream forms and dependent on a proton motive force. The recognition motif of this transporter encompasses the amino acid core as well as the two carbon atoms of the side chain. The anionic amino acids, aspartate and glutamate, were shown to be taken up poorly or not at all by specific transport mechanisms in the two forms of the parasite. The aromatic amino acids, phenylalanine, tyrosine and tryptophan, are taken up via several different routes indicating the importance of these amino acids for the parasite. The cloning and expression of TbAATP1 in Xenopus oocytes revealed that this gene encodes for an amino acid transporter that is able to transport tyrosine, glutamine and glutamate. TbAATP1 is the first member of what was subsequently shown to be a family of genes, encompassing at least twelve members present on three different chromosomes (IV, VI, VIII). On chromosome IV six of these genes appeared to form a cluster.