Identification and functional characterisation of putative mitochondrial nucleotide transporters from the human pathogen Trypanosome brucei

Trypanosoma brucei is a medically important protozoan parasite that causes African sleeping sickness in humans. Although disease treatment is possible, it is hindered by the limited availability of effective drugs and the rapid emergence of drug resistance. It is, therefore, important to identify novel drug targets for the development of new, more effective drugs. Mitochondrial carrier family (MCF) proteins transport a wide range of key metabolites across the mitochondrial inner membrane. They are important for the maintenance of key metabolic pathways in all eukaryotic cells. In particular, the MCF proteins that have been implicated in mitochondrial adenosine triphosphate (ATP) import appear to be essential for cell function and survival due to their roles in defence against oxidative stress and in the provision of the ATP required for mitochondrial electron transport and associated ATP production. Based on their important physiological roles, mitochondrial nucleotide transporters are potential novel drug targets. The main aim of this thesis was to identify and functionally characterise the putative mitochondrial nucleotide transporters in T. brucei. Sequence analysis revealed that the T. brucei genome contains 5 MCF proteins: TbMCP1, TbMCP15, TbMCP16, TbMCP20 and TbMCP23. The proteins were predicted to have roles in mitochondrial nucleotide transport based on their homology to functionally characterised MCF proteins that transport nucleotides. Of these TbMCPs, TbMCP1 has the highest sequence similarity to functionally characterised mitochondrial flavin carriers and peroxisomal ATP/adenosine monophosphate carriers in other eukaryotes, such as Flx1 in Saccharomyces cerevisiae. Sequence analysis further predicted that TbMCP15 and TbMCP16 were closely related to mitochondrial adenosine diphosphate (ADP/ATP) transporters, such as AAC2 in S. cerevisiae, whereas TbMCP20 appeared to be closely related to mitochondrial S-adenosylmethionine transporters, such as SAM5 in S. cerevisiae, and TbMCP23 appeared to be closely related to mitochondrial pyrimidine transporters, such as S. cerevisiae RIM2.