Abstract

Cardiolipin (CL) is a mitochondrial inner membrane glycerophospholipid that associates with mitochondrial proteins to promote their activities and to facilitate protein complex and super-complex formation. Loss of CL leads to destabilized respiratory complexes and mitochondrial dysfunction. The role of CL in an organism lacking a conventional electron transport chain (ETC) has not been elucidated so far. We now report that in Trypanosoma brucei bloodstream forms, in which the ETC is truncated and composed of alternative oxidase and glycerol-3-phosphate dehydrogenase, and the mitochondrial membrane potential is generated by the hydrolytic action of the FoF1-ATP synthase, the inducible depletion of cardiolipin synthase (TbCls) is essential for parasite survival. Loss of TbCls and CL caused a rapid drop in ATP levels and a decline in the mitochondrial membrane potential. Unbiased proteomic analyses revealed a reduction in the levels of many mitochondrial proteins, most notably of FoF1-ATP synthase subunits and of the alternative oxidase, resulting in a strong decline of glycerol-3-phosphate-stimulated oxygen consumption. Interestingly, the changes in cellular respiration preceded the observed decrease in FoF1-ATPase stability, suggesting that the truncated ETC is the first pathway responding to the decline in CL. In addition, proteomic and metabolomic analyses revealed that select proteins and pathways involved in glucose and amino acid transport and metabolism are up-regulated during CL depletion, possibly as a stress response to restore cellular ATP levels.