title: Disparate phenotypic effects from the knockdown of various Trypanosoma brucei cytochrome c oxidase subunits.
abstract: The Trypanosoma brucei cytochrome c oxidase (respiratory complex IV) is a very divergent complex containing a surprisingly high number of trypanosomatid-specific subunits with unknown function. To gain insight into the functional organization of this large protein complex, the expression of three novel subunits (TbCOX VII, TbCOX X and TbCOX 6080) were down-regulated by RNA interference. We demonstrate that all three subunits are important for the proper function of complex IV and the growth of the procyclic stage of T. brucei. These phenotypes were manifested by the structural instability of the complex when these indispensible subunits were repressed. Furthermore, the impairment of cytochrome c oxidase resulted in other severe mitochondrial phenotypes, such as a decreased mitochondrial membrane potential, reduced ATP production via oxidative phoshorylation and redirection of oxygen consumption to the trypanosome-specific alternative oxidase, TAO. Interestingly, the inspected subunits revealed some disparate phenotypes, particularly regarding the activity of cytochrome c reductase (respiratory complex III). While the activity of complex III was down-regulated in RNAi induced cells for TbCOX X and TbCOX 6080, the TbCOX VII silenced cell line actually exhibited higher levels of complex III activity and elevated levels of ROS formation. This result suggests that the examined subunits may have different functional roles within complex IV of T. brucei, perhaps involving the ability to communicate between sequential enzymes in the respiratory chain. In summary, by characterizing the function of three hypothetical components of complex IV, we are able to assign these proteins as genuine and indispensable subunits of the procyclic T. brucei cytochrome c oxidase, an essential component of the respiratory chain in these evolutionary ancestral and medically important parasites.
authors.affiliation: Institute of Parasitology, Biology Centre, České Budějovice, Czech Republic.
authors.forename: Anna
authors.initials: A
authors.lastname: Gnipová
authors.forename: Brian
authors.initials: B
authors.lastname: Panicucci
authors.forename: Zdeněk
authors.initials: Z
authors.lastname: Paris
authors.forename: Zdeněk
authors.initials: Z
authors.lastname: Verner
authors.forename: Anton
authors.initials: A
authors.lastname: Horváth
authors.forename: Julius
authors.initials: J
authors.lastname: Lukeš
authors.forename: Alena
authors.initials: A
authors.lastname: Zíková
mesh_terms: D014450:Electron Transport Complex III / Q000235:genetics / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000235:genetics* / Q000378:metabolism; D004736:Energy-Generating Resources; D004795:Enzyme Stability; D055785:Gene Knockdown Techniques; D008928:Mitochondria / Q000201:enzymology; D025261:Mitochondrial Proton-Translocating ATPases / Q000378:metabolism; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D010641:Phenotype; D020836:Protein Structure, Quaternary; D021122:Protein Subunits / Q000235:genetics* / Q000378:metabolism; D015800:Protozoan Proteins / Q000235:genetics* / Q000378:metabolism; D034622:RNA Interference; D014346:Trypanosoma brucei brucei / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development
chemical_list: D021122:Protein Subunits; D015800:Protozoan Proteins; D003576:Electron Transport Complex IV; D025261:Mitochondrial Proton-Translocating ATPases; D014450:Electron Transport Complex III