RESUMEN
The human genome comprises large chromosomes in the nucleus and mitochondrial DNA (mtDNA) housed in the dynamic mitochondrial network. Human cells contain up to thousands of copies of the double-stranded, circular mtDNA molecule that encodes essential subunits of the oxidative phosphorylation complexes and the rRNAs and tRNAs needed to translate these in the organelle matrix. Transcription of human mtDNA is directed by a single-subunit RNA polymerase, POLRMT, which requires two primary transcription factors, TFB2M (transcription factor B2, mitochondrial) and TFAM (transcription factor A, mitochondrial), to achieve basal regulation of the system. Here, we review recent advances in understanding the structure and function of the primary human transcription machinery and the other factors that facilitate steps in transcription beyond initiation and provide more intricate control over the system.
Asunto(s)
ADN Mitocondrial/genética , Transcripción Genética , HumanosRESUMEN
Impaired oxidative phosphorylation (OXPHOS) is implicated in several metabolic disorders. Even though mitochondrial DNA encodes several subunits critical for OXPHOS, the metabolic consequence of activating mitochondrial transcription remains unclear. We show here that LRP130, a protein involved in Leigh syndrome, increases hepatic ß-fatty acid oxidation. Using convergent genetic and biochemical approaches, we demonstrate LRP130 complexes with the mitochondrial RNA polymerase to activate mitochondrial transcription. Activation of mitochondrial transcription is associated with increased OXPHOS activity, increased supercomplexes, and denser cristae, independent of mitochondrial biogenesis. Consistent with increased oxidative phosphorylation, ATP levels are increased in both cells and mouse liver, whereas coupled respiration is increased in cells. We propose activation of mitochondrial transcription remodels mitochondria and enhances oxidative metabolism.
Asunto(s)
Ácidos Grasos/metabolismo , Mitocondrias Hepáticas/metabolismo , Proteínas Mitocondriales/metabolismo , Proteínas de Neoplasias/metabolismo , Fosforilación Oxidativa , Animales , ARN Polimerasas Dirigidas por ADN/genética , ARN Polimerasas Dirigidas por ADN/metabolismo , Ácidos Grasos/genética , Células Hep G2 , Humanos , Enfermedad de Leigh/genética , Enfermedad de Leigh/metabolismo , Ratones , Mitocondrias Hepáticas/genética , Proteínas Mitocondriales/genética , Complejos Multiproteicos/genética , Complejos Multiproteicos/metabolismo , Proteínas de Neoplasias/genética , Oxidación-Reducción , Consumo de Oxígeno/fisiología , Transcripción Genética/fisiologíaRESUMEN
The assembly of cytochrome c oxidase (CcO) in yeast mitochondria is shown to be dependent on a new assembly factor designated Coa1 that associates with the mitochondrial inner membrane. Translation of the mitochondrial-encoded subunits of CcO occurs normally in coa1Delta cells, but these subunits fail to accumulate. The respiratory defect in coa1Delta cells is suppressed by high-copy MSS51, MDJ1 and COX10. Mss51 functions in Cox1 translation and elongation, whereas Cox10 participates in the biosynthesis of heme a, a key cofactor of CcO. Respiration in coa1Delta and shy1Delta cells is enhanced when Mss51 and Cox10 are coexpressed. Shy1 has been implicated in formation of the heme a3-Cu(B) site in Cox1. The interaction between Coa1 and Cox1, and the physical and genetic interactions between Coa1 and Mss51, Shy1 and Cox14 suggest that Coa1 coordinates the transition of newly synthesized Cox1 from the Mss51:Cox14 complex to the heme a cofactor insertion involving Shy1. coa1Delta cells also display a mitochondrial copper defect suggesting that Coa1 may have a direct link to copper metallation of CcO.
Asunto(s)
Complejo IV de Transporte de Electrones/fisiología , Proteínas Fúngicas/fisiología , Regulación Fúngica de la Expresión Génica , Procesamiento Proteico-Postraduccional , Proteínas de Saccharomyces cerevisiae/fisiología , Factores de Transcripción/fisiología , Cobre/química , Complejo IV de Transporte de Electrones/química , Hemo/química , Proteínas de la Membrana/fisiología , Mitocondrias/metabolismo , Proteínas Mitocondriales , Modelos Biológicos , Proteínas Nucleares/fisiología , Consumo de Oxígeno , Unión Proteica , Biosíntesis de ProteínasRESUMEN
A mitochondrial matrix copper ligand (CuL) complex, conserved in mammalian cells, is the likely source of copper for assembly of cytochrome c oxidase (CcO) and superoxide dismutase 1 (Sod1) within the intermembrane space (IMS) in yeast. Targeting the copper-binding proteins human Sod1 and Crs5 to the mitochondrial matrix results in growth impairment on non-fermentable medium caused by decreased levels of CcO. This effect is reversed by copper supplementation. Matrix-targeted Crs5 diminished Sod1 protein within the IMS and impaired activity of an inner membrane tethered human Sod1. Copper binding by the matrix-targeted proteins attenuates levels of the CuL complex without affecting total mitochondrial copper. These data suggest that attenuation of the matrix CuL complex via heterologous competitors limits available copper for metallation of CcO and Sod1 within the IMS. The ligand also exists in the cytoplasm in an apparent metal-free state.