OXA 1L mutations cause mitochondrial encephalopathy and a combined oxidative phosphorylation defect

Abstract

OXA1, the mitochondrial member of the YidC/Alb3/Oxa1 membrane protein insertase family, is required for the assembly of oxidative phosphorylation complexes IV and V in yeast. However, depletion of human OXA1 (OXA1L) was previously reported to impair assembly of complexes I and V only. We report a patient presenting with severe encephalopathy, hypotonia and developmental delay who died at 5 years showing complex IV deficiency in skeletal muscle. Whole exome sequencing identified biallelic OXA1L variants (c.500_507dup, p.(Ser170Glnfs*18) and c.620G>T, p.(Cys207Phe)) that segregated with disease. Patient muscle and fibroblasts showed decreased OXA1L and subunits of complexes IV and V. Crucially, expression of wild‐type human OXA1L in patient fibroblasts rescued the complex IV and V defects. Targeted depletion of OXA1L in human cells or Drosophila melanogaster caused defects in the assembly of complexes I, IV and V, consistent with patient data. Immunoprecipitation of OXA1L revealed the enrichment of mtDNA‐encoded subunits of complexes I, IV and V. Our data verify the pathogenicity of these OXA1L variants and demonstrate that OXA1L is required for the assembly of multiple respiratory chain complexes.

Kinetic analysis of ATP hydrolysis by complex V in four murine tissues: Towards an assay suitable for clinical diagnosis

“…They are among the most frequent inherited metabolic diseases, with an incidence evaluated around 1/6000 [4]. Identified genetic alterations causing human ATP synthase defects affected nine different genes: the two mitochondrial DNA genes encoding F 0 structural subunits ( MT-ATP6 and MT-ATP8 [5]) and seven nuclear genes encoding either assembly factors ( ATP12 , TMEM70 [6, 7]), structural subunits of the F 1 domain ( ATP5F1E , ATP5F1A , ATP5F1D [8–11]) or OXA1L , a mitochondrial insertase, whose alteration causes a combined OXPHOS defect including complex V [12].…”

“…Spectrophotometric assays of the reverse ATP hydrolysis reaction, coupled to NADH oxidation by an enzymatic ATP-regenerating system, have the great advantage to be possible on frozen samples and to measure the activity at its maximal rate. In the literature, these different approaches have been applied but rarely compared [8, 10–12]. In few instances, they have brought divergent results [14, 15].…”

Mitochondrial OXPHOS Biogenesis: Co-Regulation of Protein Synthesis, Import, and Assembly Pathways

“…TIM21 does not strongly interact with MITRAC7, which is a COXI-specific chaperone that is present in later-stage MITRAC complexes and acts downstream of TIM21, incorporating early nuclear-encoded subunits into assembly intermediates of CIV [74]. FLAG immunoisolation in both MITRAC15 FLAG and C12orf62 FLAG expressing cell lines also identified mitochondrial ribosomal proteins and OXA1L as interacting partners [73], while affinity purification MS analysis of proteins interacting with OXA1L FLAG identified MITRAC12, ACAD9, and TIM21 among the proteins with a greater than three-fold enrichment in OXA1L FLAG expressing HEK293 cells compared to controls, as well as most mtDNA-encoded proteins and many nuclear-encoded CI and CIV subunits and assembly factors [65]. These data demonstrate close spatial proximity of the mitochondrial import machinery, mitoribosomes, and insertase machinery to early respiratory CI intermediates as being important for the coordination of assembly of both the mtDNA-and nuclear-encoded OXPHOS subunits.…”

“…Oxa1p is known to have a direct role in the insertion of several nuclear-encoded IMM proteins [59] including Oxa1p itself [60], and it has an indirect effect on many more IMM proteins, including several metabolite transporters [61], since it is crucial for the biogenesis of the Tim18-Sdh3 module of the TIM22 carrier translocase in yeast [62]. Oxa1p and its human homolog OXA1L are also required for the co-translational insertion of most mtDNA-encoded proteins including Atp6p, Atp9p, Cox1p, Cox2p, Cox3p, and Cytb in yeast [59,60,63,64], and OXA1L interacts with at least nine mtDNA-encoded subunits in humans (COX1, COX2, COX3, ND1, ND2, ND3, ND4, ND5 and ATP6) [65]. Expression of OXA1L partially rescued the phenotype of impaired cytochrome c oxidase (COX) assembly in an Oxa1p null strain of Saccharomyces cerevisiae, suggesting that OXA1L likely performs similar roles to the yeast Oxa1p in human cells [66].…”

Muscle Involvement in a Large Cohort of Pediatric Patients with Genetic Diagnosis of Mitochondrial Disease

“…mtDNA depletions were detected in tissues, mainly in muscle. In brackets, we quoted the references where some of our patients were previously published [30,31,32,33,34,35,36,37,38,39].…”