RESUMO
Mitochondria cannot form de novo but require mechanisms that mediate their inheritance to daughter cells. The parasitic protozoan Trypanosoma brucei has a single mitochondrion with a single-unit genome that is physically connected across the two mitochondrial membranes with the basal body of the flagellum. This connection, termed the tripartite attachment complex (TAC), is essential for the segregation of the replicated mitochondrial genomes prior to cytokinesis. Here we identify a protein complex consisting of three integral mitochondrial outer membrane proteins-TAC60, TAC42 and TAC40-which are essential subunits of the TAC. TAC60 contains separable mitochondrial import and TAC-sorting signals and its biogenesis depends on the main outer membrane protein translocase. TAC40 is a member of the mitochondrial porin family, whereas TAC42 represents a novel class of mitochondrial outer membrane ß-barrel proteins. Consequently TAC40 and TAC42 contain C-terminal ß-signals. Thus in trypanosomes the highly conserved ß-barrel protein assembly machinery plays a major role in the biogenesis of its unique mitochondrial genome segregation system.
Assuntos
DNA de Cinetoplasto/biossíntese , DNA de Cinetoplasto/genética , DNA Mitocondrial/biossíntese , DNA Mitocondrial/genética , Trypanosoma brucei brucei/genética , Trypanosoma brucei brucei/metabolismo , Animais , Genoma Mitocondrial , Genoma de Protozoário , Humanos , Dinâmica Mitocondrial , Membranas Mitocondriais/metabolismo , Complexos Multiproteicos/química , Complexos Multiproteicos/genética , Complexos Multiproteicos/metabolismo , Sinais Direcionadores de Proteínas/genética , Proteínas de Protozoários/química , Proteínas de Protozoários/genética , Proteínas de Protozoários/metabolismo , Trypanosoma brucei brucei/patogenicidadeRESUMO
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 ß-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 ß-barrel protein of the mitochondrial porin family that mediates a DNA-cytoskeleton linkage that is essential for mitochondrial DNA inheritance.
Assuntos
Genes Mitocondriais/genética , Membranas Mitocondriais/metabolismo , Proteínas Mitocondriais/genética , Modelos Biológicos , Porinas/genética , Proteínas de Protozoários/genética , Trypanosoma brucei brucei/genética , Sequência de Bases , Linhagem Celular , Análise por Conglomerados , Citoesqueleto/metabolismo , DNA Mitocondrial/metabolismo , Imunofluorescência , Espectrometria de Massas , Microscopia Eletrônica de Transmissão , Dados de Sequência Molecular , Organismos Geneticamente Modificados , Filogenia , Análise de Sequência de DNA , Homologia de SequênciaRESUMO
The mitochondrial outer membrane protein Tom40 is the general entry gate for imported proteins in essentially all eukaryotes. Trypanosomatids lack Tom40, however, and use instead a protein termed the archaic translocase of the outer mitochondrial membrane (ATOM). Here we report the discovery of pATOM36, a novel essential component of the trypanosomal outer membrane protein import system that interacts with ATOM. pATOM36 is not related to known Tom proteins from other organisms and mediates the import of matrix proteins. However, there is a group of precursor proteins whose import is independent of pATOM36. Domain-swapping experiments indicate that the N-terminal presequence-containing domain of the substrate proteins at least in part determines the dependence on pATOM36. Secondary structure profiling suggests that pATOM36 is composed largely of α-helices and its assembly into the outer membrane is independent of the sorting and assembly machinery complex. Taken together, these results show that pATOM36 is a novel component associated with the ATOM complex that promotes the import of a subpopulation of proteins into the mitochondrial matrix.