Discussion

Many proteinogenic amino acids are essential for cell viability in the kinetoplastid Trypanosoma brucei. These amino acids are not only required for protein synthesis, but are also substrates in metabolic pathways such as lipid synthesis or used for energy production. Here we characterized two members of the amino acid transporter (AAT) family. Both belong to the AAT7 locus that comprises nine close homologs in a tandem array. The characterized AAT7 members showed high affinity for transport of threonine (apparent K_m 298.96 and 74.41 µM), besides transporting other small and uncharged amino acids like serine and alanine. Depletion of these proteins by RNAi in bloodstream form T. brucei did not result in a growth defect in culture, showing that alternative import pathways (e.g. by other members of the AAT7 family) and/or de novo synthesis of threonine and serine are sufficient to sustain cell viability.