title: The cytochrome b p.278Y>C mutation causative of a multisystem disorder enhances superoxide production and alters supramolecular interactions of respiratory chain complexes.
abstract: Cytochrome b is the only mtDNA-encoded subunit of the mitochondrial complex III (CIII), the functional bottleneck of the respiratory chain. Previously, the human cytochrome b missense mutation m.15579A>G, which substitutes the Tyr 278 with Cys (p.278Y>C), was identified in a patient with severe exercise intolerance and multisystem manifestations. In this study, we characterized the biochemical properties of cybrids carrying this mutation and report that the homoplasmic p.278Y>C mutation caused a dramatic reduction in the CIII activity and in CIII-driven mitochondrial ATP synthesis. However, the CI, CI + CIII and CII + CIII activities and the rate of ATP synthesis driven by the CI or CII substrate were only partially reduced or unaffected. Consistent with these findings, mutated cybrids maintained the mitochondrial membrane potential in the presence of oligomycin, indicating that it originated from the respiratory electron transport chain. The p.278Y>C mutation enhanced superoxide production, as indicated by direct measurements in mitochondria and by the imbalance of glutathione homeostasis in intact cybrids. Remarkably, although the assembly of CI or CIII was not affected, the examination of respiratory supercomplexes revealed that the amounts of CIII dimer and III2IV1 were reduced, whereas those of I1III2IVn slightly increased. We therefore suggest that the deleterious effects of p.278Y>C mutation on cytochrome b are palliated when CIII is assembled into the supercomplexes I1III2IVn, in contrast to when it is found alone. These findings underline the importance of supramolecular interactions between complexes for maintaining a basal respiratory chain activity and shed light to the molecular basis of disease manifestations associated with this mutation.
authors: Dipartimento di Farmacia e Biotecnologie, Universita` di Bologna, Via Irnerio 42, Bologna 40126, Italy.
authors: Anna
authors: A
authors: Ghelli
authors: Concetta V
authors: CV
authors: Tropeano
authors: Maria Antonietta
authors: MA
authors: Calvaruso
authors: Alessandra
authors: A
authors: Marchesini
authors: Luisa
authors: L
authors: Iommarini
authors: Anna Maria
authors: AM
authors: Porcelli
authors: Claudia
authors: C
authors: Zanna
authors: Vera
authors: V
authors: De Nardo
authors: Andrea
authors: A
authors: Martinuzzi
authors: Flemming
authors: F
authors: Wibrand
authors: John
authors: J
authors: Vissing
authors: Ivana
authors: I
authors: Kurelac
authors: Giuseppe
authors: G
authors: Gasparre
authors: Nur
authors: N
authors: Selamoglu
authors: Fevzi
authors: F
authors: Daldal
authors: Michela
authors: M
authors: Rugolo
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis; D002460:Cell Line; D045303:Cytochromes b / Q000235:genetics*; D004272:DNA, Mitochondrial / Q000235:genetics; D004579:Electron Transport / Q000235:genetics; D042967:Electron Transport Complex I / Q000235:genetics / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000235:genetics / Q000378:metabolism*; D004734:Energy Metabolism; D004789:Enzyme Activation; D005978:Glutathione / Q000378:metabolism; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D013481:Superoxides / Q000378:metabolism*
chemical_list: D004272:DNA, Mitochondrial; D013481:Superoxides; D000255:Adenosine Triphosphate; D045303:Cytochromes b; D003576:Electron Transport Complex IV; D042967:Electron Transport Complex I; D005978:Glutathione