An essential bacterial-type cardiolipin synthase mediates cardiolipin formation in a eukaryote

Abstract

Cardiolipin is important for bacterial and mitochondrial stability and function. The final step in cardiolipin biosynthesis is catalyzed by cardiolipin synthase and differs mechanistically between prokaryotes and eukaryotes. To study the importance of cardiolipin synthesis for mitochondrial integrity, membrane protein complex formation, and cell proliferation in the human and animal pathogenic protozoan parasite, Trypanosoma brucei , we generated conditional cardiolipin synthase-knockout parasites. We found that cardiolipin formation in T. brucei procyclic forms is catalyzed by a bacterial-type cardiolipin synthase, providing experimental evidence for a prokaryotic-type cardiolipin synthase in a eukaryotic organism. Ablation of enzyme expression resulted in inhibition of de novo cardiolipin synthesis, reduction in cellular cardiolipin levels, alterations in mitochondrial morphology and function, and parasite death in culture. By using immunofluorescence microscopy and blue-native gel electrophoresis, cardiolipin synthase was shown to colocalize with inner mitochondrial membrane proteins and to be part of a large protein complex. During depletion of cardiolipin synthase, the levels of cytochrome oxidase subunit IV and cytochrome c1, reflecting mitochondrial respiratory complexes IV and III, respectively, decreased progressively.

Biosynthesis, remodeling and turnover of mitochondrial cardiolipin

“…A bacterial-type CL synthase is also present in some unicellular eukaryotes [22]. Not surprisingly, the CL pathway is regulated by PGC-1, the transcription factor that controls the biogenesis of mitochondria [23].…”

Lipid synthesis in protozoan parasites: A comparison between kinetoplastids and apicomplexans

“…Low levels of PG and CL have been demonstrated in T. brucei procyclic and bloodstream forms [137, 149] and Leishmania [151, 158, 229]. Very recently, a protein homologous to PGP synthase from mammalian cells and yeast has been identified and experimentally characterized in T. brucei [266].…”

“…Surprisingly, CL synthase in T. brucei was found to contain the characteristic prokaryotic-type, rather than eukaryotic-type, CL synthase motif consisting of two phospholipase D domains [149, 180]. Conditional gene knock-out of T. brucei CL synthase in procyclic forms demonstrated that it is essential for parasite survival in culture [149].…”

“…Conditional gene knock-out of T. brucei CL synthase in procyclic forms demonstrated that it is essential for parasite survival in culture [149]. Ablation of CL synthase activity inhibited CL formation and resulted in impaired mitochondrial function [149].…”

The chimeric origin of the cardiolipin biosynthetic pathway in the Eukarya domain

“…Afterward, a similar mechanism during secondary and, probably, tertiary endosymbiotic events within Archaeplastida gave rise to a third pathway where both enzymes were replaced by PLD-enzymes. Experimental evidence has shown the presence of CL in several members of the Alveolata (Apicomplexa) and Excavate (Kinetoplastid) groups [34,35]. In these organisms CL is present at low levels, which could be due to the presence of a pure PLD pathway.…”