Mutations in the gene encoding C8orf38 block complex I assembly by inhibiting production of the mitochondria-encoded subunit ND1.
The assembly of complex I (NADH-ubiquinone oxidoreductase) is a complicated process, requiring the integration of 45 subunits encoded by both nuclear and mitochondrial DNAs into a structure of approximately 1 MDa. A number of "assembly factors" that aid complex I biogenesis have recently been described, including C8orf38. This protein was identified as an assembly factor by its evolutionary conservation in organisms containing complex I and by a C8orf38 mutation in a patient presenting with Leigh syndrome and isolated complex I deficiency. In this report, we have undertaken the characterization of C8orf38 and its role in complex I assembly. Analysis of mitochondria from fibroblasts of a patient harboring a C8orf38 mutation showed almost undetectable levels of steady-state complex I and defective biogenesis of the mtDNA-encoded subunit ND1. Complementation with wild-type C8orf38 restored the levels of both ND1 and complex I, confirming the C8orf38 mutation as the cause of the complex I defect in the patient. In the absence of ND1 in patient cells, early- and mid-stage intermediate complexes were still formed; however, assembly of late-stage intermediates was impaired, indicating a convergence point in the assembly process. While C8orf38 appears to behave at a step in complex I biogenesis similar to that of the assembly factor C20orf7, complementation studies showed that both proteins are required for ND1 synthesis/stabilization. We conclude that C8orf38 is a crucial factor required for the translation and/or integration of ND1 into an early-stage assembly intermediate and that mutation of C8orf38 disrupts the initial stages of complex I biogenesis.
Centre for Reproduction and Development, Monash Institute of Medical Research, Clayton 3168, Australia.
Matthew
M
McKenzie
Elena J
EJ
Tucker
Alison G
AG
Compton
Michael
M
Lazarou
Christa
C
George
David R
DR
Thorburn
Michael T
MT
Ryan
D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D004272:DNA, Mitochondrial / Q000235:genetics*; D005347:Fibroblasts / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D007888:Leigh Disease / Q000235:genetics; D016086:Lentivirus / Q000235:genetics; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000737:chemistry*; D009154:Mutation; D014176:Protein Biosynthesis; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary
D004272:DNA, Mitochondrial; D024101:Mitochondrial Proteins; C530233:NDUFAF6 protein, human; D020033:Protein Isoforms