Trypanosomal TAC40 constitutes a novel subclass of mitochondrial β-barrel proteins specialized in mitochondrial genome inheritance

Abstract

Mitochondria cannot form de novo but require mechanisms allowing their inheritance to daughter cells. In contrast to most other eukaryotes Trypanosoma brucei has a single mitochondrion whose single-unit genome is physically connected to the flagellum. Here we identify a β-barrel mitochondrial outer membrane protein, termed tripartite attachment complex 40 (TAC40), that localizes to this connection. TAC40 is essential for mitochondrial DNA inheritance and belongs to the mitochondrial porin protein family. However, it is not specifically related to any of the three subclasses of mitochondrial porins represented by the metabolite transporter voltage-dependent anion channel (VDAC), the protein translocator of the outer membrane 40 (TOM40), or the fungi-specific MDM10, a component of the endoplasmic reticulum-mitochondria encounter structure (ERMES). MDM10 and TAC40 mediate cellular architecture and participate in transmembrane complexes that are essential for mitochondrial DNA inheritance. In yeast MDM10, in the context of the ERMES, is postulated to connect the mitochondrial genomes to actin filaments, whereas in trypanosomes TAC40 mediates the linkage of the mitochondrial DNA to the basal body of the flagellum. However, TAC40 does not colocalize with trypanosomal orthologs of ERMES components and, unlike MDM10, it regulates neither mitochondrial morphology nor the assembly of the protein translocase. TAC40 therefore defines a novel subclass of mitochondrial porins that is distinct from VDAC, TOM40, and MDM10. However, whereas the architecture of the TAC40-containing complex in trypanosomes and the MDM10-containing ERMES in yeast is very different, both are organized around a β-barrel protein of the mitochondrial porin family that mediates a DNA-cytoskeleton linkage that is essential for mitochondrial DNA inheritance.organelle | parasitic protozoa

Outer membrane protein functions as integrator of protein import and DNA inheritance in mitochondria

“…These features are hallmarks of TAC components (21,22). If pATOM36 indeed is essential for formation of the TAC, its ablation should cause similar phenotypes.…”

“…Relative quantification of the size of kDNA networks is described in ref. 22. Isolation of flagella was done according to ref.…”

Integrity of the core mitochondrial RNA-binding complex 1 is vital for trypanosome RNA editing

“…Given this complication, we opted to take advantage of a BS cell line bearing a L262P site mutation in the ATP synthase γ-subunit, which allows T. brucei at this life-cycle stage to be viable despite blocked kDNA inheritance or expression (Dean et al 2013;Schnarwiler et al 2014). We predicted that the knockout of both MRB8620 alleles would be achievable as RNA editing is rendered redundant in this genetic background.…”

U-insertion/deletion RNA editing multiprotein complexes and mitochondrial ribosomes in Leishmania tarentolae are located in antipodal nodes adjacent to the kinetoplast DNA

“…These filaments position the kDNA disk to a region of the matrix and also possibly mediate segregation of daughter kDNA networks in the cell cycle. Several TAC proteins have been so far identified (Bonhivers et al, 2008; Lacomble et al, 2012; Schnarwiler et al, 2014; Zhao et al, 2008). See Fig.…”