A novel mitochondrial LYR protein is required for complex I assembly in Arabidopsis

Ivanova A1, Gille-Hill M1, Branca R2, Kmiec B3, Teixeira P3 and Murcha MW1

  1. School of Chemistry and Biochemistry & The ARC Centre of Excellence in Plant Energy Biology, The University of Western Australia, 35 Stirling Highway, Crawley, Perth 6009, Australia.
  2. Clinical Proteomics Mass Spectrometry, Department of Oncology-Pathology, Science for Life Laboratory and Karolinska Institutet, Stockholm, Sweden.
  3. Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, Stockholm, Sweden.

Mitochondrial Complex I, a proton pumping NADH;ubiquinone oxidoreductase is the first and most complicated enzyme involved in the generation of ATP via oxidative phosphorylation. Located in the mitochondrial inner membrane it is composed of at least 44 subunits and requires the co-ordination of both nuclear and mitochondrial gene expression, protein import, co-factor biosynthesis and the assembly of each individual subunit into a 1000 kDa complexome. So far, only two bona fide Complex I assembly factors (GLDH and INDH) have been identified for plants. Here we functionally characterise a novel Complex I assembly factor that is located in the mitochondrial matrix and contains the conserved Complex I LYR Fe/S domain. Knock-out mutants lack the monomeric Complex I and the supercomplex I + III and exhibit the phenotypic characteristics typical of Complex I defective lines. BN-PAGE analysis shows the stalling and accumulation of the 650 kDa and 850 kDa Complex I assembly intermediates, with protein-protein interaction assays displaying specificity for subunits. Consequently, there is a general upregulation of mitochondrial biogenesis with regards to protein import ability and mitochondrial translation rates. Our data suggest that this novel LYR protein facilitates the biogenesis and assembly of particular subunits that are essential for the formation of a functional Complex I.