Mitochondrial Outer Membrane Proteome of Trypanosoma brucei Reveals Novel Factors Required to Maintain Mitochondrial Morphology

Abstract

Trypanosoma brucei is a unicellular parasite that causes devastating diseases in humans and animals. It diverged from most other eukaryotes very early in evolution and, as a consequence, has an unusual mitochondrial biology. Moreover, mitochondrial functions and morphology are highly regulated throughout the life cycle of the parasite. The outer mitochondrial membrane defines the boundary of the organelle. Its properties are therefore key for understanding how the cytosol and mitochondria communicate and how the organelle is integrated into the metabolism of the whole cell. We have purified the mitochondrial outer membrane of T. brucei and characterized its proteome using label-free quantitative mass spectrometry for protein abundance profiling in combination with statistical analysis. Our results show that the trypanosomal outer membrane proteome consists of 82 proteins, twothirds of which have never been associated with mitochondria before.

A component of the mitochondrial outer membrane proteome of T. brucei probably contains covalent bound fatty acids

“…The protein POMP39 was found as component of the MOM proteome in PCF trypanosomes that combined biochemical fractionation with quantitative mass spectrometry (Niemann et al, 2013). It is encoded by four nearly identical ORFs (Tb927.8.2070, Tb927.8.2260, Tb927.8.2270, Tb927.8.2280, which differ by 2-7 amino acids among each other (see SupFig.…”

“…This unique position in the eukaryotic evolutionary tree results in many special features in their biology, many of which concern mitochondrial biogenesis. As a consequence, African trypanosomes have recently been subjected to sub-cellular and suborganellar proteomics approaches scrutinizing the protein inventory of mitochondria and their membranes Niemann et al, 2013;Panigrahi et al, 2009), the mitochondrial ribosomes (Zikova et al, 2009) and the respiratory chain . Moreover, the composition of the flagellum has also been analyzed in detail (Broadhead et al, 2006;Oberholzer et al, 2011).…”

“…However, it is often unclear whether this reflects crosscontamination that is inherent in many biochemical purifications or whether these proteins are genuinely dually localized and moonlight in an alternative sub-cellular context (Collingridge et al, 2010). In a recent study we have raised the protein inventory of the mitochondrial outer membrane (MOM) of T. brucei by combining sub-organellar fractionation with correlated protein abundance profiles and statistical analysis (Niemann et al, 2013). Out of the 82 MOM proteins identified, only 30 have predicted transmembrane helices and five belong to the ß-barrel protein family (Niemann et al, 2013).…”

“…In a recent study we have raised the protein inventory of the mitochondrial outer membrane (MOM) of T. brucei by combining sub-organellar fractionation with correlated protein abundance profiles and statistical analysis (Niemann et al, 2013). Out of the 82 MOM proteins identified, only 30 have predicted transmembrane helices and five belong to the ß-barrel protein family (Niemann et al, 2013). Thus, 47 MOM proteins have no canonical membrane-spanning domain, leading to the question as to how these proteins associate with the MOM.…”

“…Here we present evidence for the acylation of a protein that is dually localized to both, the MOM and the flagellum of T. brucei. The membrane-association of the polypeptide termed POMP39 (present on the mitochondrial outer membrane proteome #39; Niemann et al, 2013) likely depends on the dual acylation at the N-terminus of the protein. In summary our result suggest that protein acylation represents a versatile mechanism to allow association with different membranes within the same cell.…”