bims-cytox1 Biomed news
on Cytochrome oxidase subunit 1
Issue of 2018‒08‒05
two papers selected by
Gavin McStay
Staffordshire University

  1. Trends Cell Biol. 2018 Jul 25. pii: S0962-8924(18)30107-7. [Epub ahead of print]
    Fiedorczuk K, Sazanov LA.
      Complex I has an essential role in ATP production by coupling electron transfer from NADH to quinone with translocation of protons across the inner mitochondrial membrane. Isolated complex I deficiency is a frequent cause of mitochondrial inherited diseases. Complex I has also been implicated in cancer, ageing, and neurodegenerative conditions. Until recently, the understanding of complex I deficiency on the molecular level was limited due to the lack of high-resolution structures of the enzyme. However, due to developments in single particle cryo-electron microscopy (cryo-EM), recent studies have reported nearly atomic resolution maps and models of mitochondrial complex I. These structures significantly add to our understanding of complex I mechanism and assembly. The disease-causing mutations are discussed here in their structural context.
    Keywords:  NADH–ubiquinone oxidoreductase; cryo-electron microscopy; mitochondrial disease; mitochondrial respiratory chain; respiratory complex I
  2. Biochim Biophys Acta. 2018 Jul 25. pii: S0925-4439(18)30271-0. [Epub ahead of print]
    Cole LK, Kim JH, Amoscato AA, Tyurina YY, Bayır H, Karimi B, Siddiqui TJ, Kagan VE, Hatch GM, Kauppinen TM.
      Cardiolipin (CL) is a key mitochondrial phospholipid essential for mitochondrial energy production. CL is remodeled from monolysocardiolipin (MLCL) by the enzyme tafazzin (TAZ). Loss-of-function mutations in the gene which encodes TAZ results in a rare X-linked disorder called Barth Syndrome (BTHS). The mutated TAZ is unable to maintain the physiological CL:MLCL ratio, thus reducing CL levels and affecting mitochondrial function. BTHS is best known as a cardiac disease, but has been acknowledged as a multi-syndrome disorder, including cognitive deficits. Since reduced CL levels has also been reported in numerous neurodegenerative disorders, we examined how TAZ-deficiency impacts cognitive abilities, brain mitochondrial respiration and the function of hippocampal neurons and glia in TAZ knockdown (TAZ kd) mice. We have identified for the first time the profile of changes that occur in brain phospholipid content and composition of TAZ kd mice. The brain of TAZ kd mice exhibited reduced TAZ protein expression, reduced total CL levels and a 19-fold accumulation of MLCL compared to wild-type littermate controls. TAZ kd brain exhibited a markedly distinct profile of CL and MLCL molecular species. In mitochondria, the activity of complex I was significantly elevated in the monomeric and supercomplex forms with TAZ-deficiency. This corresponded with elevated mitochondrial state I respiration and attenuated spare capacity. Furthermore, the production of reactive oxygen species was significantly elevated in TAZ kd brain mitochondria. While motor function remained normal in TAZ kd mice, they showed significant memory deficiency based on novel object recognition test. These results correlated with reduced synaptophysin protein levels and derangement of the neuronal CA1 layer in hippocampus. Finally, TAZ kd mice had elevated activation of brain immune cells, microglia compared to littermate controls. Collectively, our findings demonstrate that TAZ-mediated remodeling of CL contributes significantly to the expansive distribution of CL molecular species in the brain, plays a key role in mitochondria respiratory activity, maintains normal cognitive function, and identifies the hippocampus as a potential therapeutic target for BTHS.
    Keywords:  Barth syndrome; Brain; Cardiolipin; Cognition; Hippocampus; Monolysocardiolipin; Tafazzin