Foto-Cewek Seminar Series: Mitochondrial metabolism of the Apicomplexa

News article 6 Feb 2014

Foto-Cewek’s seminar series continued this week with a presentation by Dr James MacRae, Head of Metabolomics at the (NIMR) in London. His seminar, “Mitochondrial metabolism of the Apicomplexa”, was introduced by Foto-Cewek’s .

Dr MacRae started by looking at the question “What is a Metabolome?” and looking at metabolomics as a discipline and its importance in understanding the metabolism of the parasites causing malaria and toxoplasmosis. He started by explaining how his group exploits gas chromatography-mass spectrometry (GC-MS), liquid chromatography-MS, and stable isotope labelling to carry out quantitative analysis on low molecular weight metabolites and biosynthetic pathway activity in any biological sample.

He described apicomplexan organisms, a large group of unicellular parasites, including Plasmodium spp. and Toxoplasma gondii, and then discussed how the application of these techniques could provide an understanding of the mitochondrial metabolism of these parasites. He illustrated the TCA (or citric acid cycle) ofI. and talked about how recent dogma claimed that there was no TCA cycle in P. falciparum because the gateway enzyme linking glycolysis to the TCA, pyruvate dehydrogenase, was not present in the mitochondrion of these cells. Work carried out by Dr MacRae and his collaborators has proved that P. falciparum does, in fact, have canonical TCA activity.

He explained the difference in the TCA cycle between different developmental stages of the parasite and showed how glucose and glutamine were incorporated in these stages, demonstrating that there is a preference for different carbon sources at different life cycle stages. When a TCA inhibitor (sodium fluoroacetate) was added, the team saw an arrest in the gametocyte maturation, although some cells survive (those cells surviving being morphologically altered).  The analysis carried out has shown that the function of PDH, which is lacking in the parasite mitochondrion, was being carried out by another enzyme, Branched chain keto-acid dehydrogenase (BCKDH), providing the missing link between glycolysis and the TCA cycle in P. falciparum.

Dr MacRae then concluded by looking at T. gondii, explaining its life cycle and illustrating its method of host-infection. Biochemical and genetic work carried out to look at the TCA cycle of T. gondii proved again that BCKDH, the enzyme carrying out the function of PDH, was important for parasite viability and virulence.

He took a number of different questions from the audience about his work and talked about potential future applications for the analysis.