title: Alteration of structure and function of ATP synthase and cytochrome c oxidase by lack of Fo-a and Cox3 subunits caused by mitochondrial DNA 9205delTA mutation.
abstract: Mutations in the MT-ATP6 gene are frequent causes of severe mitochondrial disorders. Typically, these are missense mutations, but another type is represented by the 9205delTA microdeletion, which removes the stop codon of the MT-ATP6 gene and affects the cleavage site in the MT-ATP8/MT-ATP6/MT-CO3 polycistronic transcript. This interferes with the processing of mRNAs for the Atp6 (Fo-a) subunit of ATP synthase and the Cox3 subunit of cytochrome c oxidase (COX). Two cases described so far presented with strikingly different clinical phenotypes-mild transient lactic acidosis or fatal encephalopathy. To gain more insight into the pathogenic mechanism, we prepared 9205delTA cybrids with mutation load ranging between 52 and 99% and investigated changes in the structure and function of ATP synthase and the COX. We found that 9205delTA mutation strongly reduces the levels of both Fo-a and Cox3 proteins. Lack of Fo-a alters the structure but not the content of ATP synthase, which assembles into a labile, ∼60 kDa smaller, complex retaining ATP hydrolytic activity but which is unable to synthesize ATP. In contrast, lack of Cox3 limits the biosynthesis of COX but does not alter the structure of the enzyme. Consequently, the diminished mitochondrial content of COX and non-functional ATP synthase prevent most mitochondrial ATP production. The biochemical effects caused by the 9205delTA microdeletion displayed a pronounced threshold effect above ∼90% mutation heteroplasmy. We observed a linear relationship between the decrease in subunit Fo-a or Cox3 content and the functional presentation of the defect. Therefore we conclude that the threshold effect originated from a gene-protein level.
authors.affiliation: *Institute of Physiology Academy of Sciences of the Czech Republic v.v.i., Vídeňská 1083, 14220 Prague 4, Czech Republic.
authors.forename: Kateřina
authors.initials: K
authors.lastname: Hejzlarová
authors.affiliation: *Institute of Physiology Academy of Sciences of the Czech Republic v.v.i., Vídeňská 1083, 14220 Prague 4, Czech Republic.
authors.forename: Vilma
authors.initials: V
authors.lastname: Kaplanová
authors.affiliation: *Institute of Physiology Academy of Sciences of the Czech Republic v.v.i., Vídeňská 1083, 14220 Prague 4, Czech Republic.
authors.forename: Hana
authors.initials: H
authors.lastname: Nůsková
authors.affiliation: *Institute of Physiology Academy of Sciences of the Czech Republic v.v.i., Vídeňská 1083, 14220 Prague 4, Czech Republic.
authors.forename: Nikola
authors.initials: N
authors.lastname: Kovářová
authors.affiliation: *Institute of Physiology Academy of Sciences of the Czech Republic v.v.i., Vídeňská 1083, 14220 Prague 4, Czech Republic.
authors.forename: Pavel
authors.initials: P
authors.lastname: Ješina
authors.affiliation: *Institute of Physiology Academy of Sciences of the Czech Republic v.v.i., Vídeňská 1083, 14220 Prague 4, Czech Republic.
authors.forename: Zdeněk
authors.initials: Z
authors.lastname: Drahota
authors.affiliation: *Institute of Physiology Academy of Sciences of the Czech Republic v.v.i., Vídeňská 1083, 14220 Prague 4, Czech Republic.
authors.forename: Tomáš
authors.initials: T
authors.lastname: Mráček
authors.affiliation: †Center for Medical Genetics, UZ Brussel, Vrije Universiteit Brussel, Laarbeeklaan 101, 1090 Brussels, Belgium.
authors.forename: Sara
authors.initials: S
authors.lastname: Seneca
authors.affiliation: *Institute of Physiology Academy of Sciences of the Czech Republic v.v.i., Vídeňská 1083, 14220 Prague 4, Czech Republic.
authors.forename: Josef
authors.initials: J
authors.lastname: Houštěk
mesh_terms: D002460:Cell Line; D004272:DNA, Mitochondrial / Q000235:genetics*; D003576:Electron Transport Complex IV / Q000235:genetics* / Q000378:metabolism; D017353:Gene Deletion; D006801:Humans; D025261:Mitochondrial Proton-Translocating ATPases / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D009154:Mutation / Q000235:genetics*; D021122:Protein Subunits / Q000172:deficiency / Q000235:genetics / Q000378:metabolism
chemical_list: D004272:DNA, Mitochondrial; C501005:MT-ATP6 protein, human; D021122:Protein Subunits; D003576:Electron Transport Complex IV; D025261:Mitochondrial Proton-Translocating ATPases