RESUMO
KEY MESSAGE: The functional absence of the electron-transfer flavoprotein: ubiquinone oxidoreductase (ETFQO) directly impacts electrons donation to the mitochondrial electron transport chain under carbohydrate-limiting conditions without major impacts on the respiration of cell cultures. Alternative substrates (e.g., amino acids) can directly feed electrons into the mitochondrial electron transport chain (mETC) via the electron transfer flavoprotein/electron-transfer flavoprotein: ubiquinone oxidoreductase (ETF/ETFQO) complex, which supports plant respiration during stress situations. By using a cell culture system, here we investigated the responses of Arabidopsis thaliana mutants deficient in the expression of ETFQO (etfqo-1) following carbon limitation and supplied with amino acids. Our results demonstrate that isovaleryl-CoA dehydrogenase (IVDH) activity was induced during carbon limitation only in wild-type and that these changes occurred concomit with enhanced protein content. By contrast, neither the activity nor the total amount of IVDH was altered in etfqo-1 mutants. We also demonstrate that the activities of mitochondrial complexes in etfqo-1 mutants, display a similar pattern as in wild-type cells. Our findings suggest that the defect of ETFQO protein culminates with an impaired functioning of the IVDH, since no induction of IVDH activity was observed. However, the functional absence of the ETFQO seems not to cause major impacts on plant respiration under carbon limiting conditions, most likely due to other alternative electron entry pathways.
Assuntos
Proteínas de Arabidopsis , Arabidopsis , Flavoproteínas Transferidoras de Elétrons , Aminoácidos de Cadeia Ramificada/farmacologia , Arabidopsis/citologia , Arabidopsis/efeitos dos fármacos , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Metabolismo dos Carboidratos , Técnicas de Cultura de Células , Complexo IV da Cadeia de Transporte de Elétrons/genética , Complexo IV da Cadeia de Transporte de Elétrons/metabolismo , Flavoproteínas Transferidoras de Elétrons/genética , Flavoproteínas Transferidoras de Elétrons/metabolismo , Regulação da Expressão Gênica de Plantas , Isovaleril-CoA Desidrogenase/genética , Isovaleril-CoA Desidrogenase/metabolismo , Mitocôndrias/genética , Mitocôndrias/metabolismo , MutaçãoRESUMO
Isovaleric acidemia (IVA) is an inborn error of metabolism caused by deficiency of isovaleryl-CoA dehydrogenase. IVA clinical picture includes gastroenterological and progressive neurological symptoms which can lead to permanent disability and death. Early detection by newborn screening (NBS) and treatment promotes normal development. In this study, clinical summaries, biochemical measurements and targeted next generation sequencing (tNGS) data from the IVD gene were compared in 13 Mexican patients. The main symptoms were vomiting, feeding refusal, abdominal pain, impaired alertness, lethargy, stupor, coma; hypotonia, ataxia, hallucinations, seizures; anemia, neutropenia and pancytopenia. Mean blood concentration of isovalerylcarnintine was above the reference value (0.5⯵M) in symptomatic patients (8.78⯵M), as well as in the screen positive newborns (2.23⯵M). The molecular spectrum of this cohort was heterogeneous, with 14 different variants identified, seven were previously-described, and seven were novel. The most frequent variant was c.158Gâ¯>â¯C (p.R53P). In this study, we found a long diagnostic delay (average of 44â¯months). Thus, it is essential to increase physician awareness of this treatable condition. Biochemical IVA NBS accompanied by molecular studies (e.g. tNGS) will permit identification of potentially asymptomatic forms of the disease, and improve genotype-phenotype relationship, management decisions and follow-up.